[Electrical Communication Systems Engineering]
[From the U.S. Government Publishing Office, www.gpo.gov]
W 1.35'. u-4^
Document - j py / pj p r~ <]i pie is simple. The sum of the losses of two
—■' -----■' —■’ —■’ loops alone, or two loops plus the maximum
" trunk losses, should not exceed about 30 db.
Uldb iTdb jTdb In laYing out trunk losses i1; is generally wise
6 6 to allow 6 db for the loss of each loop, though
- in particular cases the loop loss may be less.
3ooR24db____________ This leaves 18 db for the sum of the trunk
— ^odb __________________„ losses. This 18 db would be used up by three
•----------------------------------- 6 db via trunks in tandem,
g
f. Figure 2-2 shows a few simple applications. In figure 2-2-A, the 30-db requirement p___ xxxx xxx xx is met for all connections shown except the
<;— <--- <7^ one from theater headquarters to division
.bd_b i _ .bdb j _bdb_j . t>db__| headquarters. When there is sufficient traffic
h"bdVLi1 LI l__^T^b^l_| over such a channel, an improved circuit jedb |«dt jBdb j6db j/dt* should be provided, for example, as shown in legend: c figure 2-2-B, where one or more via trunks
tl 53212-s are provided directly between theater and
Figure 2-2. Simple telephone transmission plans. Army headquarters. It may be possible to
7
PAR.
204 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
provide the improved circuit by adding repeaters.
g. The number and type of trunks provided depends, among other things, on traffic requirements. For example, in addition to the via trunks, one or more terminal trunks might be provided between division and corps, as indicated in figure 2-2-C.
h. Variations of the plans illustrated above can be used, if they comply with the general principle. For example, in a situation where not over two via trunks must be connected in tandem, the permissible loss of each via trunk
is 9 db. Likewise, loops which are never switched to trunks may have a loss of 15 db.
i. Figure 2-3 gives illustrative values of the maximum length of various types of wire and radio circuits which should provide satisfactory voice transmission for various kinds of switched circuits and point-to-point circuits. Chapters 5 and 6 give additional information.
j. The grade of transmission which it is practicable to provide will be greatly affected by the tactical situation. Near an active front, speed of installation is essential, and circuits are more liable to damage; hence transmis-
Switched Circuit
Type of Circuit Transmission loss (db) Type of wire Approximate maximum length (miles')
Loops 8 6 W-130-A (assault wire) 1
W-110-B (field wire) 2
W-143 (long range tactical wire) 5
Terminal trunks b 18 W-110-B 6
W-143 nonloaded 15
CC-358-( ) (spiral-four cable) voice frequency 24
W-143 loaded 56
Open wire 080 C-S (40%) 72
104 C-S (40%) 100
Lead-covered cable, repeatered Greater distance
Via trunks 6 W-143 nonloaded 5b
W-143 loaded 19b
CC-358-( ) with CF-1 carrier 150
Open wire carrier Greater distance
Lead-covered cable, repeatered Greater distance
Radio 6 Radio Sets AN/TRC-3 and AN/TRC-4 or AN/TRC-11 and AN/TRC-12 with 4-channel carrier 100°
a Maximum loop lengths are for local battery telephones. With usual common battery telephones, distance for Wire W-130-A or Wire W-110-B would be less. Sound-powered instruments not suitable except in special situations.
b These lengths can be increased by using telephone re
peaters on cable or open wire or by loading on cables where not already applied (ch. 5).
0 Can be increased by discarding the top one of the four channels. Distance is nominal and depends on terrain, repeater spacing, and other factors.
Figure 2-3. Maximum lengths of various types of circuit. (continued on opposite page)
8
PARS.
CHAPTER 2. TELEPHONE SYSTEMS 204-205
Point-to-point Wire Circuit
Type of tcireb Approximate maximum length, miles') »
Local battery telephones b Sound-powered telephones
W-130-A 5 3
W-110-B 11 5
W-143 25 12
Open wire: 080 C-S (40%) 120 60
104 C-S (40%) 165 85
Point-to-point Radio Circuit
Transmission frequency Approximate maximum lengths
25-250 megacycles, nonrepeatered 1 to 50 miles multichannel and 1 to 100 miles single channel, depending on type of sets and terrain.
25-250 megacycles, repeatered Up to fairly long distances depending on type of sets and terrain.
2-25 megacycles 1 mile to very long distances depending on type of sets, terrain, and ionospheric conditions.
a These lengths can be increased by using telephone repeaters on cable or open wire or by loading on cables where not already applied (ch. 5).
b Allowable transmission loss of wire is 30 db with local battery telephones; 15 db with sound-powered telephones.
Figure 2-3. Maximum lengths of various types of circuit (continued).
sion may have to suffer. On this account it is all the more important to provide good transmission on trunks farther to the rear, so that the transmission loss between telephones on built-up connections will be reasonably sat
isfactory. On long circuits well to the rear, where opportunity permits, the grade of construction and transmission approaches or equals that of good commercial telephone practice.
Section III. TELEPHONE STATION EQUIPMENT
205. GENERAL.
a. A telephone system consists of a network of interconnecting wires, wire transmission equipment, and radio equipment which provide means for the transmission of electrical energy between any two terminals of the system. In order to use this network for speech communication a telephone handset, head and chest set, or some other arrangement of microphone and telephone receiver must be connected to each of its terminals. The characteristics of microphones and telephone receivers must conform to the communication system with which they are used. For example, the transmitting effi
ciency of sound-powered telephones makes them unsuitable for use in extensive switched telephone systems (par. 209); also only certain types of microphones are suitable for use where ambient (acoustic) noise is high (par. 212b). As another example, a telephone receiver may have a peaked response-frequency characteristic which makes it ideal for the reception of Morse telegraph yet inferior for use in a speech communication system. The principal features of the telephones most commonly used in communication systems are discussed in paragraphs 206 to 210, inclusive, and the characteristics of microphones and
9
PARS.
205-206
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
telephone receivers are discussed in paragraph 212.
b. Telephones and head and chest sets include a microphone (telephone transmitter) which converts sound waves to electrical waves and a telephone receiver which converts electrical waves to sound waves. The effectiveness of microphones and receivers as converters of energy greatly affects the performance of a telephone system. Other factors which affect transmission of speech and are of particular importance in the design of microphones, telephone receivers, and telephones include:
(I) High ambient noise (engine, gunfire, etc.) at the talker or listener stations.
(2) Operation at extreme temperatures and humidities.
(3) Operation with oxygen masks or gas masks.
(4) Operation at high altitudes.
c. A telephone usually includes signaling apparatus consisting of a switchhook or hand generator to signal the telephone central or other telephones; also a bell or buzzer and, in some cases, a lamp, by which the operator may be signaled. Some telephones are also equipped with a push-to-talk switch whereby the microphone is connected to the circuit only when this switch is closed.
d. A battery-powered telephone has a carbon microphone which requires an external source of d-c power for converting sound waves into electrical waves. It acts not only as a converter of energy but also as an amplifier. An antisidetone type of coil is utilized through which the microphone and receiver are connected to the line. This type of coil is used to reduce masking of received speech by noise picked up by the microphone, thereby improving transmission. It also reduces the volume of the user’s own voice in his receiver thereby tending to cause him to talk louder, thus further improving transmission.
e. The sound-powered microphone is similar in construction to the telephone receiver, and since no amplification is provided, such as that inherent in the carbon microphone, its efficiency is comparatively low. The carbon microphone, such as that used in Handset TS-9, is about 25 db more sensitive than the most efficient sound-powered type, such as that used in Handset TS-10. Because of this low efficiency an antisidetone coil normally is
not used in sound-powered telephones. Specific information regarding microphones, telephone receivers, telephones, head sets, chest sets, and head and chest sets may be obtained from TM 11-487.
206. LOCAL BATTERY TELEPHONES.
a. Local battery antisidetone telephones such as the EE-8-( ) are used on point-to-point circuits and on loops to magneto switchboards. They are also used on long loops to common battery switchboards where, because of the high resistance of the line, an adequate amount of direct current does not reach the microphone. They also may be used on short loops to common battery switchboards if common battery telephones are not available.
b. With good batteries, the direct current through the microphone in Telephone EE—8—( ) will be from 0.06 to 0.07 ampere.
Figure 2-4. Telephone EE-8-B.
A satisfactory grade of transmission will be obtained between two such telephones connected by lines having transmission losses up to 30 db. Average talking into a local battery telephone will deliver to the loop a volume in the neighborhood of —5 vu, and for the loud talkers the output from the telephone may be +3 vu (ch. 12).
c. Handset TS-9-( ) which is furnished as part of Telephone EE-8-( ) contains a compensated magnetic-type receiver in which the diaphragm is damped and free to move at the edge. This type of receiver reproduces about equally well all the frequencies in the
10
rBATTERY
! COMPARTMENT
tNTER(ORTl 53083
CHAPTER 2. TELEPHONE SYSTEMS
PARS.
206-208
speech transmission band which are important from the standpoint of intelligibility (200 to 3,000 cycles).
d.- The speech transmission loss caused by bridging a Telephone EE-8-( ) across a 600-ohm line is about 3 db. However, because of resonance between the capacitance and inductance elements in the telephone, the impedance of Telephone EE-8-( ) is very low at 500 cycles and the bridging loss at this frequency may under some conditions be as much as 15 db. It is therefore important to avoid bridging of Telephones EE-8-( ) on circuits using 500-cycle ringing.
e. Figure 2-4 is a photograph of a typical Telephone EE-8-( ) and figures 2-15 and 2-20 show the response-frequency characteristics of the microphone and receiver of Handset TS-9-( ).
207. TELEPHONE TP-9.
a. This telephone combines the functions of Telephone EE-8-( ) and transmitting and receiving amplifiers located at the same point. It is equipped with a transmitting amplifier which gives a fixed gain of 17 db compared to Telephone EE-8-( ) and is capable of providing a maximum power output of 15 db above one milliwatt. Because of this limitation on power output, the maximum gain of 17 db will be available only with talkers whose speech volume is not above average. The receiving amplifier provides a variable gain up to a maximum of about 55 db. The direction of transmission is controlled by the push-to-talk switch in the handset handle. During talking the receiver circuit is open and the talker neither hears sidetone nor can he hear the distant party if he attempts to interrupt. This telephone cannot be used on common battery loops since no coil is provided to complete the d-c signaling path.
b. This telephone is intended for use where line losses are so great that transmission with Telephone EE-8-( ) is unsatisfactory. Since it has a power output which is approximately 15 db greater than that of the EE-8-( ), the probability of introducing crosstalk into other telephone circuits and overloading telephone repeaters is materially increased.
c. The large gains in receiving efficiency which are available will be effective in improving transmission on loops which have high attenuation losses and are not subject to inter-
ference from power circuits or other extraneous sources, and in locations where ambient (acoustic) noise is high.
d. The high receiving gain of this telephone points to the possibility of using it for listening in on enemy circuits either through a direct high impedance bridge or through crosstalk into a coupled path.
e. Figure 2-5 is a photograph of a typical Telephone TP-9. Additional information is given in TM 11-2059.
Figure 2-5. Telephone TP—9 (model).
208. COMMON BATTERY TELEPHONES.
a. Common battery antisidetone telephones such as Telephone TP-6 are used on loops to common battery switchboards, and the direct current for the microphone is obtained over the loop. The transmitting efficiency of these telephones is therefore poorer when connected to a long loop than when connected to a short loop. On very short loops the transmitting efficiency is about the same as that of a local battery telephone.
b. The microphone and receiver used in the handset which is a part of the TP-6 are similar in their performance to the microphone and receiver in Handset TS-9-( ).
c. The transmitting loss of the common battery antisidetone telephone for different loops,
11
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PARS.
208-209
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
compared to that of the local battery telephone, is given by the empirical formula,
R
L = ----4 db, where L is the amount, in
4J&
db, by which the transmitting loss of the common battery set exceeds the transmitting loss of the local battery set, R is the total circuit resistance, and E is the voltage of the common battery supply.
d. The various elements of a typical loop circuit which contribute to the total circuit resistance and consequently to the amount of direct current which flows through the microphone are shown in figure 2-6.
dTHIS IS THE AVERAGE RESISTANCE OF THE SET WHILE TALKING INTO THE TRANSMITTER. IN DETERMINING LOOP SIGNALING RANGES A HIGHER FIGURE IS ASSUMED.
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Figure 2-6. Typical common battery loop connection.
e. Figure 2-7 shows approximate transmitting losses of common battery Telephone TP-6 compared to local battery Telephone EE-8-( ) for different loop resistances.
Conductor loop resistance — (ohms') Transmission loss (db)
24 volts 50 ohms in central office 48 volts 400 ohms in central office
0- 200 a a
200- 400 0 0
400- 600 2 1
600- 800 4 2
800-1,000 7 3
a For these short loops the common battery telephone is slightly better than the local battery telephone.
Figure 2-7. Approximate transmitting losses of common battery Telephone TP-6 compared to local battery Telephone EE-8-( ).
f. The receiving efficiencies of antisidetone telephones such as common battery Telephone TP-6 and local battery Telephone EE-8-( ) are about the same.
g. Figure 2-8 is a photograph of a typical Telephone TP-6.
Figure 2-8. Telephone TP-6.
209. SOUND-POWERED TELEPHONES.
a. Sound-powered telephones are used for point-to-point connections where the line loss is relatively low. They can also be used on switchboard connections where the performance of dry batteries in local battery telephones is unsatisfactory. However, substandard transmisE.on will be obtained on switchboard connections unless the loop and trunk losses are very low (subpar, d below).
b. Compared to the local battery Telephone EE-8-( ), the sound-powered Telephone TP-3 which employs Handset TS-10, is about 25 db poorer in transmitting efficiency.
c. Handset TS-10 contains a resonant magnetic receiver in which the diaphragm is undamped and clamped at the edge and the armature drives the diaphragm through a mechanical coupling. In this type of receiver greater efficiency is obtained over the conventional type of magnetic receiver, where there is no mechanical coupling between the diaphragm and the pole pieces, without introducing an excessive amount of frequency distortion. The receiving efficiency of Telephone TP-3 is about 10 db better than that of Telephone EE-8-( ). This 10-db improvement in receiving efficiency is ineffective where the line noise is high. The response-frequency characteristics of the microphone and the receiver of Handset TS-10 are shown in figures 2-15 and 2-20.
d. The sound-powered telephone is suitable for use on point-to-point lines which have a maximum loss of about 15 db. If the line noise is excessive, this limit may drop to 5 db. If it is used in the transmission plan referred to in paragraph 204, transmission will be
12
CHAPTER 2. TELEPHONE SYSTEMS
PARS.
209-212
below standard, even where the loops are very-short, since the trunks alone may exceed 15 db.
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Figure 2-9. Reel Equipment CE-11.
e. Because of the relatively high impedance of the sound-powered handset, the maximum efficiency is obtained when no induction coil is employed and it is connected directly to the telephone line. On some short point-to-point circuits where signaling is not required the sound-powered Handset TS-10 may be used without other parts of the telephone. Such an arrangement is provided in Reel Equipment CE-11 (TM 11-2250), as shown in figure 2-9.
210. SUMMARY OF TELEPHONE STATION FEATURES.
The essential features of the above telephones are summarized in figure 2-10.
211. STATION WIRING PLANS.
a. A station wiring plan consists of one or more telephone stations with associated keys to permit switching to different loops without the assistance of a switchboard operator. Wiring plans may also include arrangements for intercommunication between nearby telephones without going through the switchboard. Buzzers, controlled from push buttons, are sometimes provided for signaling in connection with wiring plans.
Item EE-8- ( ) TP-9 TP-6- { ) TP-3
Type of case Leather or canvas Metal None (desk set) Leather or canvas
Type® LB LB CB SP
Battery supply Dry batteries Dry batteries CB None
Ringer Yes Yes Yes Yes
Generator ‘Yes Yes No Yes
Push-to-talk switch Yes Yes No No
Dial No No Optional No
Induction coil AST 0 AST None
Handset TS-9-( ) TS-9-( ) d TS-10-( )
Switchboard® Mag or CBb Mag CB Mag
Technical Manual TM 11-457 TM 11-333 TM 11-2059 TM 11-458 TM 11-2043
“ LB = local battery; CB = common battery; SP—sound-powered; AST = antisidetone; Mag = magneto.
b Telephone EE-8-( ) uses dry batteries for transmitter supply when connected to CB switchboard.
0 Telephone TP-9-( ) includes amplifiers in microphone and receiver circuits.
d Part of telephone, no separate nomenclature.
Figure 2-10. Summary of telephone station features.
b. The simplest wiring plan is a 2-position key such as Switchbox BE-54-A which enables a telephone to be connected to either one of two loops. A group of six mechanically interlocked push buttons such as the Western Electric Company key No. 6021K can be provided to pick up any one of six loops. A key can be provided at one telephone to cut off another telephone from a loop. Arrangements for holding supervision on loops are sometimes provided so that a call on a loop can be held while the telephone is connected to another loop or local intercommunicating line. Various wiring plans are described further in TM 11-474.
212. MICROPHONES AND TELEPHONE RECEIVERS.
a. General. In addition to the microphones and receivers used in telephones, a variety of
656935 O—45----
13
^-HANDSET TS-IO
Hr—AEEL OR-8
PAR.
212____________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
other microphones and receivers are available for use in head and chest sets, chest sets, headsets, and hand-held microphones. The physical and electrical characteristics of these instruments and photographs of many of them are given in TM 11-487. They are used in the operation of a telephone system for telephone switchboards, AWS operations centers (sec. V), radio sets, and other services where continuous operation or other special features require their use. The characteristics of these telephone instruments are such that maximum intelligibility of speech will be obtained when they are used as a part of the particular system for which they were designed.
b. Microphones.
(1) The hand-held microphone such as Microphone T-17-( ) (fig. 2-11) is suitable for use in high ambient noise fields without acoustic shielding. It is designed to discriminate against ambient noise which is predominantly high or low in frequency. It does not discriminate against ambient noise which is of the same frequency as the more important speech sounds.
Figure 241. Micrcophone T-17.
(2) Microphones such as Microphone T-45-( ) are of the differential type, having both sides of the diaphragm open to the sound field. This type is worn suspended over the lip and when used in an ambient sound field originating from a source at some distance, the ambient noise is partially cancelled out, thereby giving an improvement in speech-signal to ambient noise ratio over that obtained with the conventional type of microphone. For intense ambient noise this improvement in signal-to-noise ratio is about 15 db. The satisfactory performance of this transmitter in high ambient noise fields is therefore dependent on wearing it in the proper position. Figure 2-12 is a photograph of Microphone T-45 in use.
Figure 2-12. Microphone T-45.
(3) The amphibious forces require microphones and telephone receivers which must be capable of withstanding submersion in water. Headset Assembly CW-49507A (Navy nomenclature) which is suitable for this purpose consists of lip Microphone M-6 ( ) /UR and two very thin watch case type receivers CW-49505 (Navy nomenclature). A photograph of Headset Assembly CW-49507A is shown in figure 2-13.
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Figure 2-13. Headset Assembly CW-49507A (Navy nomenclature).
14
|g TL 54905 ■
1 MICROPHONE M-6 V )/UR-
RECEIVERS
CW-49505—*s~ (NAW) x
CHAPTER 2. TELEPHONE SYSTEMS
PAR.
212
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Q-ro >5 1-
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(4) Microphone T-30-( ), which is worn at the throat, is also used where ambient noise is extremely high. The intelligibility of speech transmitted by this microphone is appreciably poorer than speech transmitted by Microphones T-17- ( ) or T-45- ( ), because it picks up only the low-frequency throat sounds and does not pick up the higher frequencies developed in the head cavities, which are necessary for good intelligibility.
(5) Microphones of the ANB-M-C1 and T-44-( ) types (fig. 2-14) which are for use in oxygen masks are designed for greater effi-
Figure 2-14. Microphone ANB-M-C1 (Cover M-369 removed).
ciency at high than at low voice frequencies. This complements the response of the enclosure, wherein the low frequencies of speech are reinforced, so that the response characteristic of such a mask-microphone combination is essentially flat.
(6) Figure 2-15 shows the response-frequency characteristics of representative microphones. They indicate the relative efficiencies of these microphones at different frequencies in the speech transmission band. These efficiencies are shown in db relative to a reference condition, which is arbitrarily located in the general neighborhood of the curve for the microphone in Telephone EE-8- ( ).
c. Telephone Receivers.
(1) Compensated magnetic receivers such as those used in Head and Chest Sets HS-17-( ) and HS-19- ( ) and in Headset HS-30-( ) (TM 11-487) are suitable for the reception of speech as they reproduce about equally well all the more important frequencies in the speech transmission band. They are about equal in performance to the receiver in Handset TS-9-( ). The performance of the compensated
+ IO -----------------—T-
♦ 5------------—
3 3 ___------------' m \f V
£ 6 -|0 -/----------------------\--
□ o / \
i y -|5 ---------------/A-------V—
"20-------------—\7--------------
-25-----------7—V--------A-------
z > / I
y 5 - 30--------/■__________1______
b tn ” 35 7s *—*--------------—--
< \ /' \ \ /Y
z-40 ----——\ (4—
-45----------
-50------- —--------------VJ----—
-55 -----------------------------
200 300 400 500 600 600 1000 2000 3000 4000
FREQUENCY IN CYCLES PER SECOND
LEGEND:
I T-17 (CARBON)
H UNIT OF TS-9-C XAl^SO T-26, T-28-C ), T - 35, T-36-1 ). T-38-C ), (CARBON)
HI T-45 (CARBON, LIP)
II ANB-M-Cl (CARBON, OXYGEN MASK J
V T-34-A AND T-44-( ) (MAGNETIC, OXYGEN MASK)
H T —50 (MOVING COIL)
XU UNIT OF TS-10 (SOUND POWERED)
TL 5306T
Figure 2-15. Response-frequency characteristics of microphones.
magnetic watch-case type receiver under conditions of high ambient noise has been im-proved with the development of new types of ear cushions. The large volume of enclosed air in over-the-ear Cushion MC-114 used with Headset HS-17—( ) results in an appreciable loss in receiving efficiency. In the development of the ANB-H type receiver the use of a smaller Cushion MC-162-( ) (Headset HS-33- ( )) gives a better seal against interfering noise and a wider response-frequency range is also obtained. This type of
Figure 2-16. Head and Chest Set HS-17.
15
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Tt 53078
PAR.
212
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Figure 2-17. Headset HS-33.
Figure 2-18. Headset HS-30.
receiver is particularly effective when listening to a microphone such as the T-17-( ) which discriminates against low-frequency ambient noses. Headset HS-30- ( ) uses hearingaid type receivers with Inserts M-300, which provide a good seal against interfering noise. It can be worn under the battle helmet. This headset replaces the headset used in the above head and chest sets and in many other headsets. Photographs of typical Head and Chest Sets HS-17- ( ), Headset HS-33- ( ), and Headset HS-30-( ) are shown in figures 2-16, 2-17, and 2-18, respectively and cording ar-
16
TL 53076
530 74
HS-30 —HS-30- A. /A HS-30 HS-30 -
— A *— Z\ rJUNCT,ON I— /\
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™ FORMER CORD- CORD-
rmn cd-604 '5001 co-933
F6 INCHES , I K INCHES
LONG H LONG
r 0 r 0 cco°??4
CORD- CORD -
CD-3O7-A CD-307-A
tf S ! u
HIGH IMPEDANCE HIGH IMPEDANCE LOW IMPEDANCE LOW IMPEDANCE
SINGLE CORD WITH BAIL-OUT WITH BAIL-OUT SINGLE CORD
TL 53075
Figure 2-19. Headset HS~30-( ), cording arrangements.
PARS.
CHAPTER 2. TELEPHONE SYSTEMS 212-214
rangements which are available for use with Headset HS-30-( ) are shown in figure 2-19.
(2) The resonant magnetic receiver such as that used in Headset P-16 is most suitable for the reception of tone signals if the resonant peak of the receiver matches the frequency of the tone. Its use should be confined to the reception of tone telegraph signals.
(____________ \ \/ I
< rz — —_____ \___' XA II P
u a -io---------—---------------V--FhAS
b b X J n
ct -15-----------————---------- Is -—kl
< 200 300 400 500 600 800 1000 2000 3000 4000
FREQUENCY IN CYCLES PER SECOND
LEGEND:
I R-13, ALSO R-2, R-2-A, R-3, R-14,AND R-15 (RESONANT MAGNETIC)
II UNIT OF TS-9, ALSO R-21, AND R-22 (COMPENSATED MAGNETIC)
HI R-30-( HCOMPENSATED MAGNETIC) IZANB-H-I (COMPENSATED MAGNETIC) X UNIT OF TS-IO (SOUND POWERED)
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Figure 2-20. Response-frequency characteristics of telephone receivers.
Section IV. TELEPHONE CENTRALS
213. INTRODUCTION.
The principal equipment in a telephone central is a switchboard for interconnecting loops and trunks. The central may include power equipment, distributing frames, and protectors; testing, monitoring, observing, and recording equipments; repeaters, carrier equipment, telegraph equipment, and various accessories. This section describes the principal features of switchboards and closely associated equipments. Telegraph equipments are described in chapter 3, repeaters and carrier equipments in chapter 5, power equipment in chapter 7, and protectors in chapter 10. Data and brief descriptions covering these equipments are contained in TM 11-487.
214. TYPICAL CENTRALS.
a. General. A telephone central is generally located near the center of the area which it serves and is connected by loops to the telephones in the area, and by trunks to centrals in other areas. The size of the area served by a switchboard is determined by a combination of many factors including the number of telephones in the area, the distribution of traffic between the telephones, the availability of certain types of wires and switchboards, the permissible transmission losses, and the signaling ranges. The objective in planning the size of an area is to keep at a minimum the quantity of materials for loops, trunks, and switch
boards and to produce maximum efficiency in the operation and maintenance of the communication system. In general, one large central is preferable to several smaller centrals in the same area because the larger central will provide the better telephone service as a result of fewer trunked calls and a larger and more efficient team of maintenance and operating personnel; this is discussed further in chapter 11.
b. Typical Centrals for Small and Large Areas. Typical centrals for small and large areas are illustrated in figure 2-21. In a small area, such as Area A in this figure, only a single central may be provided, while in a larger area, such as Area B, several centrals may be provided. A central which serves loops and has all of its trunks terminated in the same area is called a local central. One which handles only long distance traffic is called a long distance (LD) central. Army centrals commonly handle both local and long distance traffic and such a central is called a combined local and long distance central.
c. Switchboards for Telephone Centrals. The switchboards used in Army centrals are of various types and these are broadly classified as tactical switchboards which are designed for use principally in forward areas, and fixed plant switchboards which are like those designed for civil telephone central offices. The
17
PAR.
214 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
_ J* B £ A - A__ _________________AREA JB___________________________
niwu^-riCOMBINED LOCAL ANcil ^COMBINED LOCAL AND
TRKS TO LONG DISTANCE | | LONG DISTANCE Itrks TO
1 CENTRAL------ ] -----CENTRAL----- ^STAnS
centrals! _ . .......n-—__________________________________________________
T U U iLONG DISTANCE, U U
I 1 TRKS. |
, ----। (VIA GRADE), --------------fl.---------o--------------------------------- I
nr ! : > I
1 U I 1 U •—LONG DISTANCE SWITCHING—* >
SWBD । | SWBD TRKS. 2-WAY RINGDOWN I
______CORD______I' ,L______CORD_____ (VIA GRADE) |
1 loops 1 . Iloops
1_°_______________I I ° I
] LOCAL CENTRAL I LOCAL CENTRAL2 .
I L_a[] [] J------- 0 JI I
I
D*—*-----------------*—A 0 |
LOCAL TRUNKS „
(TERMINAL GRADE)
SWBD SWBD
CORD I______GQRD______ .
1 |loops Sloops
I__________________________________________________I
Figure 2-21. Typical centrals for small and large areas.
TL 54983
principal features of the switchboards which can be regularly procured for Army centrals are described in the following paragraphs of this section. Foreign civil central office switchboards which can be interconnected with these Army switchboards are described in chapter 8.
d. Typical Trunks. The trunks between centrals in different areas are called long distance trunks. Trunks between centrals in the same area are called local trunks if they are not used on connections to long distance trunks. If they are used for long distance calls, they are called long distance switching trunks. Trunks of this type are provided between a local central and a combined local and long distance central or a local central and a separate long distance central. However, a separate group of local trunks may be provided between local centrals and combined local and long distance centrals if the traffic is heavy. A via grade of transmission is generally provided on long distance trunks while the terminal grade of transmission is provided on local trunks (par. 204). The trunks between telephone centrals are classified as ringdown or automatic, according to the type of signaling. Trunks which use ac for signaling are known as ringdown trunks, and those which use de for signaling are known as automatic trunks. Two-way ringdown trunks are commonly used between
Army switchboards. These- are also used between these switchboards and civil magneto central offices. Trunks which are automatic in one direction and ringdown in the other direction (called common battery trunks) are generally provided between Army switchboards and civil common battery central offices.
e. Typical Loops. The loops which connect telephones to centrals are classified as magneto or common battery according to the types of telephones and signaling. The telephones on magneto loops are equipped with hand generators (sometimes called magnetos) for signaling, and the microphones are energized by local dry batteries. Telephones EE-8-( ) are commonly used on magneto loops. The telephones on common battery loops are equipped with switchhooks for signaling and the microphones are generally energized by currents which flow over the loops from a common battery in the central. Telephones TP-6 are generally used on common battery loops. A local battery Telephone EE-8-( ) can be used on a common battery loop when the screw switch in the telephone is in the position for common battery signaling with the switchhook; in this case however, microphone current is obtained from the batteries in the telephone. The telephones on both types of loops are equipped with bells which ring
18
PAR.
CHAPTER 2. TELEPHONE SYSTEMS 214
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Figure 2-22. Typical applications of telephone centrals in a communications zone illustrating types of switchboards, trunks, and loops.
19
PARS.
214-217________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
when 20-cycle ringing voltage is applied to the loops at the switchboards. All common battery switchboards can be connected to at least a few magneto loops in addition to the common battery loops. Magneto switchboards have no provision for common battery loops.
f. Typical Centrals for a Communications Zone. Figure 2-22 illustrates the types of switchboards which may be used in centrals which make up a communications zone. In this illustration the communications zone is divided into three areas, each large enough for several local centrals. The First and Second Army Headquarters in the combat zone each have only a single central. In the areas, trunks are provided to the switchboards of civil telephone systems over fixed plant equipment. Connections to the combat zones are established over tactical equipment through switchboards such as those of the First and Second Army Headquarters. Connections from combat zone switchboards to the areas further to the rear may be established over direct trunks or over trunks connected in tandem through intermediate switchboards. The trunks between areas are terminated on long distance or on combined local and long distance switchboards.
g. Mobile Centrals. Mobile centrals can be assembled by mounting tactical switchboards and associated equipment such as carrier terminals in mobile shelters or semitrailers. Arrangements for such centrals are described in chapter 11.
215. TACTICAL SWITCHBOARDS.
a. Tactical switchboards are ruggedly constructed to withstand frequent moving and are designed for quick installing and dismantling, as may be required in forward areas. These switchboards are available .in various sizes from one position with a capacity of six loops up to six positions with a capacity of 540 loops. Each of the switchboards having a capacity of 40 loops or less is an individual position containing all of the equipment required for operation, including protectors and binding posts for the line wires. The larger tactical switchboards are components of telephone central office sets. These have separate components for the power equipment, test equipment, and distributing frames with protectors. Cabling arrangements include rubber-covered cables which are attached to binding posts or screw terminals without soldering.
b. The small tactical switchboards which have capacities of 12 loops or less are of the magneto monocord type such as the Switchboard BD-72 (par. 219). The functions of a small tactical magneto switchboard can also be performed by Emergency Switchboard SB-18/GT or by a group of Adapter Plugs U-4/GT (par. 218) with Telephone EE-8-( ). The next larger tactical switchboard is the magneto cordless Switchboard BD-95 (par. 220) which has a capacity of 20 loops or trunks. The larger tactical switchboards are of the manual cord type (par. 221) and may be either magneto or common battery. The largest tactical switchboards are of the multiple common battery type (par. 223) with universal cord circuits (par. 231) which can be connected to magneto and common battery loops.
216. FIXED PLANT SWITCHBOARDS.
a. Switchboards of the fixed plant type are less rugged than the tactical switchboards and are practically the same as those used in commercial telephone systems. They are more suitable than tactical switchboards for stable situations particularly for very large installations, and over a long period of time they will have less maintenance and will give better service than tactical switchboards. Most of the cables to these switchboards are textile insulated arid the wires are soldered to terminals. They require various amounts of auxiliary equipment depending on their size and application, including distributing frames, protectors, power plants, test equipment, and relay racks; and they should generally be engineered and installed by experienced men. These switchboards are furnished through the Army Communications Service on specific order.
b. The sizes of these switchboards are from one position with 12 loops up to about 60 positions with about 3,000 loops. The smallest of these is the common battery cordless switchboard described in paragraph 220. The next larger switchboards are of the single position nonmultiple cord type (par. 222), with capacities from 60 to 100 loops per position. The largest switchboards are of the multiple common battery type described in paragraph 223.
217. DIAL SWITCHBOARDS.
a. Step-by-step and all-relay types of dial switchboards are available for certain fixed
20
CHAPTER 2. TELEPHONE SYSTEMS
PARS.
217-218
plant conditions. The capacity of the step-by-step switchboards in Signal Corps stock is 2,000 loops; however, larger switchboards have been supplied to the theaters. The capacity of each all-relay switchboard in stock is 600 loops. Connections originated at telephones connected to loops from these switchboards are automatically established by switches or relays which are controlled from the dials at the telephones. However, a manual switchboard is provided with each dial switchboard so that operators can complete incoming and outgoing calls over trunks to manual centrals and render assistance to dial telephone users, principally on long distance calls.
b. The. number of operators required in connection with a dial switchboard is less than that for a manual switchboard serving the same number of loops. The speed of establishing connections through a dial switchboard is generally a little faster than that through a manual switchboard. However, over-all advantages from a dial switchboard cannot be realized unless the conditions where it is installed are stable and the telephone directory information is kept up to date. Without reliable directory information, a large proportion of the telephone traffic would probably require assistance from the operators, and this would tend to nullify the advantages of dial service.
c. Greater skill is required to maintain dial equipment than to maintain manual equipment. The floor space and power requirements for a dial switchboard are greater than those for a manual switchboard of equivalent size. The use of dial switchboards by the Signal Corps has been extensive in the zone of the interior, and considerable use has been made of these switchboards in the theaters of operation However, further discussion of these switchboards is not included in this chapter.
218. ADAPTER PLUGS FOR INTERCONNECTING MAGNETO LOOPS AND TRUNKS.
The simplest equipment for interconnecting a few loops and trunks consists of a group of 2-pronged Adapter Plugs U-4/GT and a Telephone EE-8-( ). These plugs can be connected to magneto loops and 2-way ringdown trunks and serve as a lightweight substitute for a small magneto switchboard. Emergency Switchboard SB-18/GT (fig. 2-23) consists of seven Adapter Plugs U-4/GT, one Plug Holder MT-313/GT, and one Case
CY-229/GT. Each plug weighs only about 1.5 ounces. It consists of a neon glow lamp, two binding posts, two pins, and two sockets, all molded together in translucent plastic. The pins serve as the thumbscrews of binding posts to which wires are connected. They are
Figure 2-23. Emergency Switchboard SB-18/GT (with Telephone EE-8-B).
also the plugs which are inserted in the sockets of another adapter plug to establish a connection between two lines. Several plugs can be connected in tandem for conference connections, or so that an operator’s telephone can
21
TL 54973
TL 53035
PARS.
218-220 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
be connected to a loop while it is also connected to another loop or trunk. Ringing on a loop to which a plug is connected lights the neon glow lamp in the plug. An audible signal is not obtained when the neon lamp lights, except that the ringer of the Telephone EE-8-( ) will sound if it is connected to a loop while ringing occurs. A luminous dot is provided on each side of the plug to facilitate locating and handling in darkness. The number of the line to which a plug is connected can be written in pencil or ink on a luminescent backed designation strip which is embedded in the surface of the plug. Such numbers are visible in silhouette against the luminescent background under black-out conditions. The uses of these plugs are described in TB SIG 61 (to be superseded by TB SIG 147 when published).
219. MONOCORD MAGNETO SWITCHBOARDS.
The smallest switchboards are of the magneto monocord type. These switchboards are available in capacities from four loops as provided by Switchboard BD-9 up to 12 loops as provided by Switchboard BD-72. The latter switchboard is shown in figure 2-24. The equipment for each loop or trunk is principally a cord, a jack, a drop, and a 2-way lever-type key. Ringing from the distant end of the loop operates the drop. The operator’s telephone is connected to the loop by the op-
Figure 2-24. Switchboard BD-72.
eration of the key in one direction. Operation of the key in the other direction connects the hand generator to the loop. A connection between two loops is established by connecting the cord of one loop to the jack of the other loop.
Figure 2-25. Stvitchboard BD-95.
220. MANUAL CORDLESS SWITCHBOARDS.
Two types of manual cordless switchboards are used in Army communication systems. One is switchboard BD-95 (fig. 2-25) which has capacity for 20 magneto loops or trunks. The other is the Western Electric Company No. 506B switchboard which has a capacity for 12 common battery loops and five common battery trunks. Each of these has five connecting paths which permit five simultaneous calls. However, Switchboard BD-95 has means for readily/splitting the connecting paths in the middle of the switchboard by changing cross-connections in the back of the switchboard, thus providing two groups of 10 loops with five connecting paths for each group. A common battery Telephone EE-91 with a Handset TS-12-( ) is normally used with
this switchboard. This equipment, however, is not a component of Switchboard BD-95. Under the split condition, the operator’s telephone is patched to the last group of 10 loops or trunks, by connecting a patching cord between the operator’s test jack and the line test jack of any one of the 10 loops or trunks. A vertical row of three 2-way locking, lever-type keys is provided for each loop or trunk and a similar row of keys is provided for the operator’s telephone. EacK key can be operated up or down from normal; thus
22
TL 53095 »
PARS.
220-222
CHAPTER 2. TELEPHONE SYSTEMS
ion the being ler
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there are six operated key positions for each loop or trunk. Five of these positions are associated with the five connecting paths, respectively. The sixth position on the keys for loops and ringdown trunks is used for ringing. This sixth position on the keys for common battery trunks is used for holding connections to other switchboards. A connection from one loop or trunk to another loop or trunk is established by operating the associated keys to the same connecting path. Ringing signals are indicated on lamps in Switchboard BD-95; it is equipped with one lamp for each loop and one lamp for each trunk. Ringing on common battery trunks in the Western Electric Company No. 506B switchboard operates drops. Switchhook supervisory signals from common battery telephones are indicated in this switchboard on magnetic signals, one of which is provided on each loop and on each connecting path.
221. CORD SWITCHBOARDS.
a. The manual switchboards larger than those of the monocord and cordless types are of the cord type. Connections through these switchboards are established by cord circuits terminated in pairs of cords. To establish a connection, one cord of a pair is connected to the jack of a calling loop or trunk and the other cord of the pair is connected to the jack of the called loop or trunk. Supervisory signals during connections over the cord circuits are indicated on drops or lamps associated with the cords. Signals on loops and trunks, while the cords are disconnected, are indicated on drops or lamps associated with the jacks. Connections to the operator’s telephone are established through cord circuit keys. Similar keys are provided in the cord circuits for ringing on the loops and trunks. Further information on cord-type switchboards is given in paragraphs 222 and 223.
b. The smallest cord switchboard is the tactical magneto Switchboard BD-91-( ) with 20 magneto loops, 4 manual and dial common battery trunks, and 8 cord circuits. A similar switchboard with 40 loops and 12 cord circuits is Switchboard BD-96 shown in figure 2-26. The smallest common battery cord switchboard is Switchboard BD-89-( ) (part of Telephone Central Office Set TC-2) with 20 magneto loops, 37 common battery loops, 1 dial trunk, 2 common battery manual trunks, and 13 cord circuits. A substitute for the TC-2 is Telephone Central Office Set AN/
TTC-1 (TM 11-2002) which includes switchboard SB-27/TTC-1 (Western Electric Company No. 551B PBX, X-66070A) with 20 magneto loops, 40 common battery loops, 3 manual and dial common battery trunks, and 10 cord circuits. The latter switchboard is also used in fixed plant service. Most of the other switchboards have 15 cord circuits per position. The largest multiple switchboards have 17 cord circuits per position.
Figure 2-26. Switchboard BD-96.
c. The cord circuits are of various types, but all in a particular switchboard are the same. The principal distinguishing features among cord circuits in different switchboards are related to the signaling and battery supply conditions. Magneto cord circuits provide signaling by ringing only and do not include battery supply circuits (par. 224). Common battery cord circuits include battery supply circuits (par. 227) and provide signaling in response to the flow of the battery supply currents. These cord circuits are classified as local cords (par. 230), universal cords (par. 231), and PBX cords (par 232). Cords may be connected to outside conductors through the jacks of various line and trunk circuits. Some of the line circuits are described in paragraph 223. Some of the trunk circuits are described in paragraphs 233, 234, and 235.
222. NONMULTIPLE SWITCHBOARDS.
a. Positions. A switchboard having not more than one or two positions is of the nonmultiple type in which each loop and each trunk appears on only one jack. A single-position nonmultiple fixed plant switchboard is shown
23
PAR.
222___________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
in figure 2-27. A 2-position nonmultiple tactical switchboard is shown in figure 2-28. All of the jacks are located in the face of the switchboard within the reach of the operators. The maximum practical reach for an operator is a little less than 3 feet. The width of each position is about 2 feet. Consequently, the size of a nonmultiple switchboard is practically limited to two adjacent positions. If three nonmultiple switchboard positions were installed in a line-up, the loops and trunks appearing at one end of the line-up could not be reached by the cords at the other end of the line-up, and even if longer cords were provided, the operators could not efficiently reach so far. In installations with only two nonmultiple positions, the length of the switchboard cords is greater than that in installations of only a single position and with these longer cords the positions are raised on platforms so that the cord weights will not hit the floor.
b. Cut-off Jacks. The jacks connected to loops in nonmultiple switchboards are of the cutoff type shown in figure 2-29. Each of these jacks has two cut-off springs in addition to the tip, ring, and sleeve springs. Each cut-off spring is in contact with its associated tip or ring spring when a plug is not in the jack; but the circuit through each of these contacts is opened when a plug is in the jack. The loop
Figure 2-27. K100 switchboard (Kellogg Switchboard & Supply Company).
from the telephone is connected to the tip and ring springs. The line lamp, line relay, or drop is connected to the cut-off springs so that it is cut off from the loop while a plug is in the jack.
Figure 2-28. Two Switchboards BD-89 and Cabinets BE-79, assembled.
24
BD-S9 BO-89
* ---T~ BE-79 BE-79
PAR.
223
CHAPTER 2. TELEPHONE SYSTEMS
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Figure 2-29. Plug in cut-off jack.
223. MULTIPLE SWITCHBOARDS.
a. Multiple Jack Appearances. Switchboards having three or more positions are of the multiple type with some or all .of the loops and trunks connected to two or more jacks. A tactical multiple switchboard is shown in figure 2-30. A large fixed plant multiple switchboard with a typical floor plan is shown in figure 2-31. The multiple jack appearances of each loop and trunk are located in different positions with a distance between successive appearances equal to the width of approximately two positions, which is about 4 feet. In the smaller multiple switchboards, two jack panels are provided at each position and multiple appearances of the loops and trunks are in every fourth panel. In the large multiple switchboards with relatively small jacks, three jack panels are provided at each position and the
loops and trunks are multipled to appear in every sixth or seventh panel. The relatively large jacks which are provided in most of the multiple switchboards are of the cut-off type (fig. 2-29) similar to those in nonmultiple switchboards. The smaller jacks provided in the larger switchboards have only two plug springs and a sleeve and are not equipped with cut-off springs. A relay connected to the sleeves of the jacks is required for the cut-off function with these smaller jacks (subpar, c).
b. Series Multiple. The multiple switchboards with cut-off jacks are known as series multiple switchboards because the circuit between each loop and its associated lamp or line relay is connected in series with the cut-off springs of all the jacks on the loop (fig. 2-32). The lamp or relay is cut off from the loop when a plug is inserted in any one of the jacks. Switchboard BD-110-( ) (fig. 2-30) is an example of the series multiple type. The contacts between springs in the cut-off jacks may become dirty and cause open circuits. However, series multiples are generally satisfactory with less than about 10 jacks on each loop. In the larger switchboards having a greater number of multiple jacks per loop, the bridged multiple arrangement is generally provided.
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Figure 2-30. Telephone Central Office Set TC-1Q, assembled.
25
PAR.
223
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
11 ...........
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all DIMENSIONS SHOWN ARE IN FEET AND INCHES FOR EXAMPLE 4-6 FOR 4 FEET 6 INCHES.
DIMENSIONS IN BRACKETS ARE THOSE MOST COMMONLY USED, ALL OTHERS ARE FIXED.
TL 53127
Figure 2-31. No. 11 szvitchboard and floor plan (Western Electric Company).
26
PAR.
223
CHAPTER 2. TELEPHONE SYSTEMS
------------------- THROUGH CONTACTS OF OTHER MULTIPLE JACKS
FIRST INTERMEDIATE LAST
MULTIPLE MULTIPLE MULTIPLE
JACK JACK JACK
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Figure 2-32. Series multiple line circuit.
c. Bridged Multiple. The large multiple switchboards which are equipped with the smaller jacks without cut-off springs are known as bridged multiple switchboards because all of the jacks on each loop are bridged in parallel (fig. 2-33). A line relay is connected to each loop through normally closed contacts of a cut-off relay. This relay is operated when a plug of a cord is connected to any one of the associated jacks. The operating circuit for the cut-off relay is from battery over the sleeve
of the cord to the sleeve of the jack, and then through the winding of the cut-off relay to ground. A typical example of a bridged multiple switchboard is the Western Electric Company No. 11 switchboard illustrated in figure 2-31. The advantages of a bridged multiple in comparison with a series multiple are in the elimination of the cut-off springs in the jacks. This simplifies installing, reduces contact maintenance, and permits conference service between three or more telephones by
FIRST INTERMEDIATE LAST
MULTIPLE MULTIPLE MULTIPLE CUTOFF line
JACK AND LAMP JACK AND LAMP JACK AND LAMP RELAY RELAY
d T J .1
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Figure 2-33. Bridged multiple line circuit.
27
PARS.
223-226 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
means of two or more cord circuits connected to multiple jacks on the same loop.
d. Lamp Sockets. Lamp sockets are provided with all multiple jacks in some common battery switchboards but lamps are placed in these sockets only at positions where it is desired to have the incoming calls answered. The maximum number of line lamps permissible on each loop is generally not more than two without a line relay (series multiple) nor more than five with a line relay (series or bridged multiple) ; three are most generally provided.
e. Multiple Wiring. The wiring between multiple jacks and between lamp sockets is in fabric-covered cables which are laid on long pins or a shelf. The individual wires (called skinners) which extend from the cables to the terminals of the jacks and sockets are flexible enough to permit removal of the jacks to the rear of the switchboard for maintenance, replacements, or cable extensions.
224. MAGNETO SWITCHBOARDS.
a. Magneto switchboards are the simplest types of switchboards, principally because they are arranged for local battery telephones and for signaling by means of hand generators and drops. The smallest magneto switchboards are of the monocord type described in paragraph 219. These are available with capacities of 4, 6, or 12 loops or trunks. Emergency Switchboard SB-18/GT consisting of Adapter Plugs U-4/GT can be used instead of small magneto switchboards (par. 218). A cordless magneto Switchboard BD-95 (par. 220) has a capacity of 20 loops or trunks. Tactical cordtype magneto switchboards are available in capacities of 20 or 40 loops or trunks. Similar fixed plant switchboards are available with a capacity of 100 loops or trunks. All magneto switchboards supplied for Army communication systems are of the nonmultiple type.
b. All signaling to and from magneto switchboards is by means of ringing. Thus a telephone user must exert conscious effort at the beginning and end of each call to signal the switchboard operator. When one loop is connected through a magneto switchboard to another loop, the ringing from one telephone will ring the bell at the other telephone unless the switchboard cord circuits are of the nonring through type.
c. Dry batteries are required at magneto switchboards for the operators’ telephones and for audible signals associated with the drops.
225. COMMON BATTERY SWITCHBOARDS; GENERAL.
A common battery switchboard is distinguished, principally, by its storage battery which is common to all of the battery supply and automatic signaling circuits in the switchboard. Battery supply for telephones on the loops is obtained from the cord circuits except in the cordless switchboard where it is obtained from the switchboard connecting paths. Other battery supply circuits are provided for the operators’ telephones. Automatic signaling circuits are associated with the line and cord lamp signals which are controlled from the switchhooks of the telephones on the loops. Similar signals are controlled from ringing on the trunks. These features contribute to high operating efficiency and are particularly desirable in large centrals.
226. COMPARISON OF COMMON BATTERY SWITCHBOARDS WITH MAGNETO
SWITCHBOARDS.
a. The advantages of common battery switchboards in comparison with magneto switchboards are principally as follows:
(I) Automatic signaling in response to the movements of the switchhooks at the telephones provides fast and reliable signals with almost no conscious effort by the telephone users. This reduces the work of the switchboard operators by eliminating, to a great extent, the need for monitoring and challenging to avoid excessive holding of trunks after conversations are finished.
(2) A single storage battery for the switchboard and associated telephones is more desirable than dry batteries.
(3) A common battery telephone is lighter than a magneto telephone because it does not contain a hand generator or dry batteries.
b. The disadvantages of common battery switchboards are in the working limits for signaling on the common battery loops. These limits are based on the operating capabilities of the switchboard and require that the insulation resistances of these loops be maintained at more than 10,000 ohms. The insulation resistances on magneto loops can be as low as 1,000 ohms. The higher insulation resistances require greater
28
CHAPTER 2. TELEPHONE SYSTEMS
PARS.
226-228
care in the construction and more labor in the maintenance of the outside plant. The permissible conductor resistances of common battery-loops are from 50 ohms to 1,000 ohms depending on the particular switchboard, whereas magneto loops can generally have 2,000 or 3,000 ohms, provided that voice transmission considerations permit. Working limits are discussed further in paragraph 237 and in TM 11-487. On long loops, transmission is poorer with common battery telephones than with local battery telephones (par. 208e).
227. BATTERY SUPPLY CIRCUITS.
a. Repeating Coil Type. The battery supply circuits in the cord circuits of some switchboards such as the Western Electric Company No. 11 switchboard are of the repeating coil type with a 24-volt battery, as illustrated in figure 2-34. In this circuit, the battery is connected in series with the windings of the repeating coil and the voice currents follow the same path as the battery supply currents through the battery. Although the voice currents from many different circuits pass through the same battery, these currents do not produce crosstalk because the impedance of the battery is very low (less than 0.1 ohm), provided that the leads to the battery are arranged properly.
/REPEAT IN G COIL x
to r to
LOOP_ 24 _T | LOOP
OR !♦- VOLTS “T -i- “►! OR
trunk I ■ r-L) 11 TRUNK
_ bl J
TL 525O8-S
Figure 2-34. Repeating coil 24-volt battery supply circuit.
b. Bridged Impedance Types. Battery supply circuits of the bridged impedance types are arranged with the battery connected in series with retardation coils or relays which are bridged across the voice channels in the cord circuits. A battery supply circuit with a single bridged impedance is illustrated in figure 2-35-A. A similar circuit with two bridged impedances is illustrated in figure 2-35-B. The d-c resistance of each of the inductors is small enough to permit the flow of an adequate amount of battery supply current for the telephone. However, their impedance to voice-fre-
551 switchboard, a single bridged impedance circuit is provided. In cord circuits such as those of Switchboard BD-110-( ), two bridged impedances are provided, one for the front cord and the other for the back cord, and capacitors are connected in series with the voice channels between the bridged impedances (fig. 2-35). In the double bridged impedance type of battery supply circuit, each loop connects to a separate relay while in the single bridged impedance circuit both loops connect to a single retardation coil. The single bridged impedance type of circuit is suitable only where most of the loops are relatively short because the shunting effect of a short loop reduces the battery supply to a longer loop on the same cord circuit.
228. SIGNALING ON COMMON BATTERY LOOPS.
When a call to a cord switchboard is originated at a common battery telephone, direct current flows from the switchboard line circuit such as that shown in figure 2-32 or figure 2-33. This causes the lighting of all line lamps connected to that line. When the call is answered by an operator, the flow of current from the line circuit is cut off by the connec-
656935 O—45
4
29
quency currents is high enough to avoid excessive transmission loss. In cord circuits such as those of the Western Electric Company No.
LOOP RETARDATION C~ . , I LJgp
OR “ coil -lQr
TRUNK ( VOLTS -L TRUNK
I—P,-------------1—-nJ
SINGLE BRIDGED IMPEDANCE A
'-----------------II------------------
TO r it TO
LOOP SUPERVISORY^------ --------^SUPERVISORY LooP
or~ RELAY ( -h|i|i|iH f=wF-) relay -Lg£P
TRUNK --------- ) _L (______TRUNK
48 - - 48 LJ
VOLTS VOLTS
I------------------1|----------------J
DOUBLE BRIDGED IMPEDANCE B
' TL 54984
Figure 2-35. Single and double bridged impedance battery supply circuits.
PARS.
228-231 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
tion of a cord to a jack, but then the battery supply current flows over the loop from the cord circuit. Battery supply currents flow through the windings of relays, the contacts of which control the supervisory lamps or signals. Telephones are signaled from the switchboard with ringing current applied to the loop by the operation of a ringing key in the cord circuit.
229. COMMON BATTERY CORD CIRCUITS.
The cord circuits in common battery switchboards contain the battery Supply circuits de-' scribed in paragraph 227; they also contain relays and lamps for producing supervisory signals; and they include keys for ringing on loops and trunks, and for connecting the circuits to the operator’s telephones. The different types of common battery cord circuits are broadly classified local cords, universal cords, and PBX cords. All cords in a single type of switchboard are of the same type.
230. LOCAL CORD CIRCUITS.
The battery supply circuits in the local cords are of the 24-volt repeating coil type (fig. 2-34) or 48-volt double-bridged impedance type (fig. 2-35-B). These battery supply circuits are always connected to the plugs of the cord circuit. Local cord circuits are the same on connections to magneto loops as on connections to common battery loops. The magneto loops and ringdown trunks associated with these cord circuits are terminated in relays which convert the incoming ringing signals into common battery signals before they are transmitted to the cord circuits. An example of a switchboard with this type of cord circuit is the Western Electric Company No. 11 switchboard.
231. UNIVERSAL CORD CIRCUITS.
a. Principal Features. Universal cord circuits are provided in switchboards which are designed for use with a considerable number of magneto loops in addition to the common battery loops. A universal cord circuit has its battery supply circuit in use only when the cord is connected to a common battery loop. At other times, such as when the cord circuit is connected to a ringdown trunk or to a magneto loop, a ringing bridge, instead of the battery supply circuit, is provided in the cord circuit. The transfer from the ringing bridge
to the battery supply circuit is accomplished by a relay which is operated over the sleeve of the cord in combination with the sleeves of the jacks. In a typical switchboard with universal cords such as Switchboard BD-110-( ), the circuits from the sleeves of the jacks on magneto lines are open and the circuits from the sleeves of jacks on common battery loops are closed to the battery. When a cord is connected to one of these closed circuits, the sleeve relay in the cord circuit operates and connects the battery supply circuit. When a cord is connected to a ringdown trunk or a magneto line with an open sleeve, this sleeve relay does not operate, thus providing the circuit arrangement for receiving ringing signals without the battery supply circuit. The ringing signals are indicated on cord circuit recall supervisory lamps. In Switchboard BD-110—( ), a recall ringing signal is provided in addition to two common battery supervisory lamps for each cord circuit. In some other switchboards, only two lamps are provided for each cord circuit and these are arranged for recall ringing signals in addition to common battery signals.
b. Nonlocked-in versus Locked-in Recall Signals. The recall ringing signals on the universal cord circuits in some switchboards such as Switchboard BD-110-( ) are nonlocked-in, that is, the recall supervisory lamps are lighted only for the duration of ringing. The recall ringing signals in other switchboards are locked-in; that is, the lamps remain lighted after ringing ceases until the associated operator’s talking key is operated. The nonlocked-in signals may be somewhat undesirable under conditions where it may be necessary to ring several times to attract the attention of an operator. The locked-in signals avoid the necessity for ringing more than once to produce a steady signal. At switchboards in which the same cord lamps are used for recall ringing signals and for common battery signals, the locked-in recall signals may tend to delay the operators in disconnecting cords from common battery loops because they will have to challenge and be sure that each call is finished before the cords are disconnected; or they will have to trace the cords to the jacks and ascertain whether it is connected to a magneto loop or common battery loop. This situation could be avoided in such switchboards by handling the magneto lines at positions which are different from those where the com-
30
mon battery lines are handled. In switchboards such as the BD-110-( ), having separate lamps or drops for recall ringing signals, the locked-in feature would be satisfactory from an operating standpoint.
c. Conversion from Nonlocked-in to Locked-in Signals. The nonlocked-in ringing signals on Switchboards BD-80-( ) and BD-110-( ) can be converted to locked-in signals by adding one relay and associated wiring to each cord circuit as shown in figure 2-36. Any relay having at least one pair of make contacts and a winding suitable for operation on 48 volts is usually satisfactory for this addition. The resistance of this winding should not be less than about 1,000 ohms to avoid overheating while operating. The winding of this relay is connected in parallel with the lamp and its contacts are connected in series with a normally closed pair of contacts on the associated talk key. The circuit through these two pairs of contacts is connected to ground so that when the added relay operates it will lock operated until the talk key is operated. This, relay operates from the same voltage that lights the lamp when ringing is received. It remains operated until the operator answers the ringing signal by operating the talk key. The extra contacts on the talking key have been provided in all Switchboards BD-80-( ) and BD-110-( ) but are not used with nonlocked-in signals. The details of these modifications are described in MWO SIG 28 (when published).
232. PBX CORD CIRCUITS.
a. The designation PBX is derived from the words Private Branch Exchange which is used to describe a civil telephone switchboard lo-
cated on a subscribers premises and arranged to connect the loops on the same premises to each other and to trunks extending to a telephone central. A PBX may also be connected to tie trunks extending directly to other PBX’s and to off-premise extensions to distant telephones. The operating features of a PBX are designed for maximum efficiency on the most common types of connections occurring on subscriber premises, namely: those from one short loop to another short loop and those between such a loop and a trunk to a central (called PBX trunk) which terminates at the central in a common battery station line circuit. These line circuits are designed primarily for connections to common battery telephones. Therefore the signaling arrangements utilize ringing outgoing from the central to signal the PBX operator and direct current, also from the central, for supervision between the PBX or telephone and the central. The trunk circuits from Army PBX’s which use these signaling arrangements are called common battery trunks and are described in paragraph 234.
b. Switchboards such as the Western Electric Company No. 551 switchboard which were originally designed for PBX’s in commercial telephone systems are equipped with cord circuits similar to universal cord circuits. Each cord circuit has two different transmission conditions. One is the battery supply condition like that shown in figure 2-34 which is used on loop-to-loop connections. The other condition is a bridged impedance without connections to the battery and with a ringing bridge like that shown in figure 2-37. This is used on connections from loops to common bat-
31
PARS.
____________________________ CHAPTER 2. TELEPHONE SYSTEMS 231-232
A BS FS c
________________________________
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fit3 i _ ;'T
U !! । R I {j talk R,NC
U u?- lJ I I
V * O— — — — M
O .. . .
' --X—CL RESISTANCE OF WINDING ______________c
matf. 1 SHOULD NOT BE LESS THAN ' fl ♦
r’u 1 t. 7 ABOUT IOOO“*TO AVOID —o-.JI I
EXISTI NG EQUIPMENT AND WIRING I LI OVERHE ATI NG. THE NUMBER ~ ♦
SHOWN BY DOTTED LINES. I OF TURNS OF WIRE IN THE
ADDITIONAL RELAY AND WIRING I WINDING SHOULD BE ADEQUATE
SHOWN BY SOLID LINES. J. FOR RELIABLE OPERATION ON
1-?: ABOUT 45 VOLTS.
•T
-A TL 5 3210-S
Figure 2-36. Part of universal cord circuit in Switchboards BD—80—( ) and BD—110—( ) showing additional relay and wiring for locked-in recall ringing signals.
PARS.
232-234
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
tery trunks. The bridged inductor has a relatively low d-c resistance but its impedance to voice currents is high enough to avoid excessive transmission loss. When this d-c bridge is connected to a common battery trunk, current flows from the distant switchboard, over the trunk and through this bridge. This current controls the supervisory signals in the distant switchboard. A ringing bridge which consists of a relay in series with a capacitor is connected in parallel with the d-c bridge. It indicates ringing signals which are sent from the distant switchboard. The supervisory relay adjacent to the d-c bridge controls the supervisory signals from the switchhook of the telephone on the loop.
RINGING RELAY
THROUGH CONTACTS OF OTHER RELAYS
LOOP
_ COMMON BATTERY TRUNK
RETARDATION COIL
SUPERVISORY RELAY
Figure 2-37. PBX cord circuit, cut-through condition.
TL 54985
c. A cord circuit of the type shown in figure 2-37 is known as a cut-through cord because battery supply currents from the common battery trunk flow through the cord circuit to the telephone on the loop. With such circuits, in combination with common battery trunks which are similarly cut-through, the battery supply currents through the telephones on the loops depend on the battery supply circuits in the central. This battery supply condition may be troublesome on trunks to some foreign civil centrals having high resistances in their battery supply circuits as described in chapter 8. Cut-through cords are generally advantageous on trunks to American civil centrals because they provide practically the same battery supply for PBX telephones as is obtained by other common battery telephones connected to the central. The cut-through cords also minimize the current drain from the PBX battery. Some common battery trunks are equipped with repeating coils and associated arrangements which include battery supply circuits so that the battery supply currents to the telephones on the PBX loops are derived from the PBX battery even though the cord circuits are of the cut-through type.
d. Switchboards having cords of the noncut-through type may be used as PBX’s when equipped with suitable common battery trunk circuits (par. 234).
e. Each PBX cord also has a night and through-dial key which is not supplied with other types of cord circuits. The operation of this key permits incoming and outgoing, manual or dial calls to pass directly to and from the station and the central, through the cord circuit, without the assistance of the PBX operator. This key is used in Army telephone systems only on night calls and through-dial calls to civil centrals. The operation of this key converts the cord circuit practically into a patching cord. Only the winding of the supervisory relay remains connected in series with the cord, and in most PBX’s the ringing bridge also remains connected across the cord but without the d-c retardation coil bridge shown in figure 2-37.
233. TWO-WAY RINGDOWN TRUNK CIRCUITS.
The switchboard circuits for 2-way ringdown trunks are the same as those for magneto loops. In magneto switchboards, each of these circuits contains a drop for indicating the ringing signals. In common battery switchboards equipped with universal cord circuits, each of these trunk circuits contains either a drop like that of a magneto switchboard, or a relay which operates and locks when ringing is received and lights the lamps connected to it, In common battery switchboards equipped with local cord circuits, each ringdown trunk circuit contains several relays; some are used for converting incoming ringing signals into common battery signals to the cord circuit and others are used for transmitting ringing signals from the cord circuit through the trunk circuit to the outside conductors. These trunks are arranged to respond to 20-cycle ringing.
234. COMMON BATTERY TRUNK CIRCUITS— OUTGOING AUTOMATIC AND INCOMING RINGDOWN.
Common battery trunk circuits are provided in common battery switchboards on trunks to civil common battery central offices. These circuits are designed to be connected to common battery station line circuits in the civil central. Each trunk circuit includes a relay which responds to ringing on an incoming call from the civil central and lights the associated lamps in the switchboard. When the call is answered
32
PARS.
CHAPTER 2. TELEPHONE SYSTEMS 234^235
by connecting a cord to the trunk, a d-c bridge is connected across the trunk to cause the flow of direct current over the conductors to control the supervisory signals. The simplest common battery trunk circuit is that provided in PBX switchboards such as the Western Electric Company No. 551 switchboard. When such a switchboard is connected to a dial central, the dial provided in the operators telephone circuit connects through the cord circuit to the trunk circuit on outgoing calls. The common battery trunks in switchboards having local or universal cord circuits are equipped with dial jacks whereby calls may be completed through dial centrals. With such a trunk circuit the operator connects a dial cord to a dial jack, dials the desired number, and removes the dial cord immediately.
235. TWO-WAY AUTOMATIC TRUNK CIRCUITS.
The supervisory signals on 2-way automatic trunk circuits are controlled by the flow of direct currents over the outside plant conductors without ringing. These trunks are not used extensively in Army communication systems. The simplest circuits for a 2-way automatic trunk consist of a regular common battery line circuit at one switchboard connected to a similar line circuit at the other switch-
board. However, a reversal is made in the tip and ring conductors between the two line circuits and each circuit is modified by disconnecting the path from the tip side of the line through the cut-off jack or relay to ground (figs. 2-32 and 2-33). With this arrangement the line relay at one switchboard is operated from the connection of ground to the tip side of the trunk through the cord circuit at the other switchboard. When the call is answered, the supervisory signals in the cord circuits are controlled from the flow of the battery supply currents from both the cord circuits in series. These currents flow because the two batteries in the different switchboards are connected in series aiding as a result of the reversal in the trunk conductors. At the end of the call, when a cord is disconnected at one switchboard, the cord supervisory lamp lights at the other switchboard. The line lamp at the switchboard where the cord is disconnected lights and remains lighted until the cord at the other switchboard is disconnected. This relighting of the line lamp is somewhat undesirable on trunk circuits of this type. It is avoided in more complicated types of trunk circuits. This simple type of automatic trunk circuit may also be undesirable because of noise induction in areas where the trunk conductors are adjacent to power circuits.
-------INSTRUCTION BOOK [------TUBE COMPARTMENT COVER
SHOCK MOUNTING-! r—INSTRUCTION CARO
GASKET-------®
case— - ------y -----TERM STRiP COVER
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JanW Ik "THir........................■W'1...........................il F
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BATTERY---if Mfr Ml
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" I-- l—SPARE TUBES COVER vibhhivk
"* TL 53197
Figure 2-38. Ringing Equipment EE-101-A.
33
PARS.
236-237________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
236. VOICE-FREQUENCY RINGERS.
Voice-frequency ringing must be used on trunks operating over carrier channels and on trunks equipped with composite sets or voicefrequency repeaters which are not arranged for 20-cycle operation. Twenty-cycle ringing may be used on nonrepeatered, noncomposited voice-frequency trunks and on repeatered voice-frequency trunks arranged to relay or bypass the 20-cycle ringing at the repeaters. On 2-way ringdown trunks requiring voicefrequency ringing, 20-cycle ringing is used between each of the trunk circuits and the nearest voice-frequency ringer. The ringing between two voice-frequency ringers at opposite ends of the same trunk is by means of either 500 cycles or 1,000 cycles, interrupted
----TWO 2-ClRCUIT RECEIVER- .Z'i OSCILLATOR UNITS
• ’ ■■ ; »Paaat;
fclrtMr
Is s"**® ■ flEBWIHl' I’ |D
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Brea w—b i>.i imciiiawigju" •a
®HIB j iggg 18
Ol®h©j S
fi '■ . J
E' >1 B
-- STATIC .RINGING ’ ft GENERATOR AND 4 H
POWER RECEPTACLES
TL 53205
Figure 2-39. Ringer package; voice frequency; 4 circuit X-6L820A.
or noninterrupted. One-thousand cycle ringing interrupted at a rate of 20 cycles per second is standard for Army use. Five-hundred cycle ringing, either interrupted or noninterrupted, may be used on interconnections with foreign systems. The allowable loss between voicefrequency ringers is about 30 db. This, in general, permits satisfactory ringing over any Army long distance trunk which is satisfactory for speech transmission. The ringers at opposite ends of a circuit must use the same frequency interrupted at the same rate. Fig
ure 2-38 shows Ringing Equipment EE-101-A which consists of two 1,000/20-cycle ringers. This is a part of Ringer Set TC-24 and is designed for use with tactical equipment such as Telephone Terminal Set TC-21. Figure 2-39 shows the packaged voice-frequency ringer which consists of four 1,000/20-cycle ringers arranged for fixed plant applications. The individual ringers in this package are electrically the same as Ringing Equipment EE-101-( ). These and other available ringers are described in TM 11-487.
237. WORKING LIMITS.
a. General. The lengths and gauges of the wires in the loops and trunks are limited by transmission and signaling conditions. The transmission limits are established by the transmission plan discussed in section II of this chapter and are expressed in terms of the maximum loss in db which can be tolerated. The signaling limits are controlled by the type of signaling and the type of switchboard. Signaling limits are expressed in terms of the ohms resistance permissible in the conductors of the loops and trunks. The signaling limits of the various switchboards are specified in TM 11-487. The actual working limit of a loop or trunk is determined by the signaling limit or the transmission limit, whichever is the smaller. The conductor loop resistances and transmission losses of various lengths and gauges of conductors are enumerated in figure 2-40. For example, consider the problem of determining the proper kind of wire for a loop from a Telephone Central Office Set TC-1 to a Telephone EE—8—( ) over a distance of 10,000 feet with common battery signaling and local battery talking. Assume that the transmission plan permits a maximum loss of 6 db in the loop. Reference to the table of working limits for this central office set in TM 11-487 indicates that the resistance of the conductors in the loop should not exceed 500 ohms. Reference to figure 2-40 indicates that Wire W—110-B will be satisfactory for this loop because the length of this wire producing 6-db loss is between 11,300 and 12,800 feet and its resistance is between 400 and 450 ohms. Of course, wire having less transmission loss and less resistance per unit length such as Wire W-143 would also be satisfactory. Wire W-130-A would not be satisfactory because 10,000 feet of this wire would
34
PAR.
237
CHAPTER 2. TELEPHONE SYSTEMS
)1-
1g- nd , Switchboard !Ill working limits, • resistance of 1g- loop- (ohms) cy cle Thousands of feet
Nonloaded wires (wet) Nonloaded cables
083 GI 109 GS 080 40% c-s 104 40% C-S W—130—A WD-3/T1 W-110-B W-143 CC-345 CC—355—A Paper insulated
16 ga. 19 ga. 22 ga.
IS. 50 2.0 3.5 6.2 10.0 0.4 1.4 7.4 2.9 6.3 3.1 1.5
re 75 3.2 5.2 9.7 15.6 0.7 2.1 11.3 4.4 10.0 4.6 2.3
nt 1QQ 4.1 7.0 12.3 20.8 0.9 2.8 15.3 5.9 13.3 6.1 3.1
g- 125 5.1 10.5 15.4 26.0 1.1 3.5 18.9 7.3 16.7 7.7 3.8
150 6.1 10.5 18.5 31.2 1.3 4.2 22.7 8.8 20.4 9.2 4.6
175 7.1 12.3 21.6 36.4 1.6 5.0 26.5 10.3 23.3 10.7 5.3 "2-db limit
200 8.1 14.0 24.7 41.6 1.8 5.7 30.3 11.8 26.7 12.3 6.2
225 IP 9.1 15.8 27.7 46.8 2.0 6.4 34.1 13.2 30.0 13.8 6.9
250 10.2 17.6 30.9 52.0 2.2 7.1 37.9 14.7 33.4 15.3 7.7
™ 275 11.2 19.4 34.0 54.2 2.4 7.8 41.7 16.2 36.7 16.9 8.5
le 300 12.2 21.1 37.2 62.5 2.7 8.5 45.5 17.6 40.1 18.4 9.2
ie 325 13.2 22.9 40.2 . 67.7 2.9 9.2 49.3 19.1 43.4 19.9 10.0
350 14.2 24.6 43.8 72.8 3.1 9.9 53.1 20.6 46.7 21.5 10.8
ie 375 15.3 26.4 46.4 78.1 3.3 10.6 56.9 22.1 50.1 23.0 11.6 4-db limit
1. _ 400 16.3 28.2 49.4 83.2 3.6 11.3 60.7 23.5 53.4 24.5 12.4
>e 450 18.3 31.7 55.6 93.6 4.0 12.8 68.2 26.5 60.1 27.6 13.9
L 500 20.3 35.2, 61.7 104.1 4.5 14.2 29.4 66.7 30.7 15.5
e 550 22.4 38.7 67.8 114.4 4.9 15.6 32.4 73.4 33.7 17 0 6-db limit
S 600 24.4 42.2 74.1 125.8 5.3 17.0 35.3 80.1 36.8 18.5
s 650 26.4 45.8 80.2 135.3 5.8 18.4 38.3 86.7 39.8 20.1
n - ™ 27.4 49.3 86.4 145.7 6.2 19.9 41.2 93.5 42.8 21.7
a 750 30.5 52.8 92.6 156.2 6.7 21.3 44.1 100.0 45.9 23.6
. 32.5 56.3 98.7 166.4 7.1 22.7 47.1 106.6 49.1 24.7
850 34.5 59.8 104.9 176.9 7.6 24.1 50.0 113.4 52.2 26 3
900 36.6 63.3 111.1 187.5 8.0 25.5 55.2 27.8
, 950 38.6 66.8 117.3 197.5 8.5 26.9 58.2 29.4
1 1,000 40.6 70.4 123.5 208.0 8.9 27.4 61.3 30.9
3 1,100 p 44.7 77.5 135.9 239.0 9.8 31.2 67.6 34.0
1,200 48.8 84.5 148.4 249.5 10.7 74.0 37.1
_ MOO 52.8 91.5 160.6 270.6 11.6 40.2
1,400 56.8 98.6 173.0 291.4 12.5 43.3 "15-db limit
1.500 60.9 105.0 185.4 312.5 46.5
2,000 81.3. 141.0 247.0 416.5
2,500 102.0 176.0 309.0 522.0
3,000 122.0 211.0 371.0
The data given in this table are based on the following wire characteristics:
Item Nonloaded wires (wet) Nonloaded cables
083 GI 109 GS 080 40% C-S 104 40% C-S W-130-A WD-3/TT W-110-B w-143 cc-345 CC-355-A Paper insulated
16 ga. 19 ga. 22 ga.
ohms/mile 130.0 75.0 42.8 25.3 590.0 186.0 35.0 90.0 42.0 86.0 171.0
ohms/M ft 24.6 14.2 8.1 4.8 112.0 35.2 6.6 17.0 8.0 16.2 32.3
db/mile (wet) 0.37 0.31 0.25 0.18 6.50 2.80 1.20 1.70
db/M ft (wet) 0.07 0.06 0.05 0 03 1.23 0.53 0 23 0.32
db/mile 0.73 1.08 1.79
db/M ft 0.14 0.20 0.34
Figure 2-40. Lengths of station line wire and cable for various switchboard transmission and working limits.
35
PARS.
237-242 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
have a loss of more than 12 db and a resistance of more than 1,100 ohms.
b. Limits for Ringdown Loops and Trunks. The working limit for 20-cycle signaling on ringdown loops and trunks without repeating coils or other intermediate line equipment is generally about 3,000 ohms. This is established by the ringing voltage and the sensitivity of the ringers, drops, or relays which respond to the 20-cycle ringing voltage. On similar trunks equipped with a ring-through repeating coil at each end, the working limit is reduced to about 2,000 ohms. Insulation resistances down to about 1,000 ohms can generally be tolerated on these trunks. On trunks equipped with telephone repeaters or carrier terminals, the signaling is by means of 500 cycles or 1,000 cycles between ringers and is by means of 20 'cycles between the ringers and the terminals (par. 236).
c. Limits for Common Battery Loops. The working limits for common battery loops are established principally by the transmission losses, including the battery supply losses (par. 208), and the supervisory relays in the cord circuits. On loops connected to line circuits without line relays, the brilliancy of the line lamps may also be controlling. The insulation resistance of the loops is sometimes a limiting factor because the supervisory relays must release while current is flowing through the insulation resistance. In general, the insulation resistance of common battery loops should be greater than 10,000 ohms. To obtain such insulation resistance, a high grade of maintenance on the outside wires, cables, and terminals is required.
238. DISTRIBUTING FRAMES.
The connections from outside wires to a switchboard having a capacity for 40 loops or more, are completed through a separate distributing frame such as Frame FM-19 shown in figure 2-30. This frame consists of terminals, some for the outside wires and others for the inside wires. Cross-connecting wire is used to connect the outside terminals to the inside terminals. This wire can be readily transferred between terminals, thereby providing flexibility in the assignments of the outside wires to various switchboard circuits.
239. PROTECTORS.
Protectors are provided in telephone centrals on the wires coming in from outside for
the purpose of protecting the switchboards and associated equipment from damage which might otherwise result from lightning or accidental contacts between communication circuits and high-voltage power lines. Protectors are frequently located on distributing frames. Protection is discussed in chapter 10 and various kinds of protective equipment are described in TM 11-487.
240. POWER EQUIPMENT.
The storage batteries in telephone centrals are charged by rectifiers connected to 50- or 60-cycle engine-driven generators or commercial power sources. The 20-cycle ringing voltage is obtained from ringing vibrators, static ringing machines, or rotating ringing generators. Power equipments are described in chapter 7 and in TM 11-487.
241. MONITORING, OBSERVING, AND RECORDING EQUIPMENT.
Equipments which may be installed in centrals for use in monitoring, observing, and recording on local and long distance telephone connections are described in TM 11-487. One of the observing cabinets is designed for connection to a long distance trunk and includes arrangements to prevent the completion of each call until cleared by the observer. A group of these cabinets can be associated with a group of long distance trunks by means of a patching cabinet having a capacity of 10 trunks. Another cabinet is arranged for monitoring on any one of 30 loops or trunks. This cabinet includes lamps which respond to common battery or ringdown signaling to indicate when calls are in progress. Another cabinet is designed for observing on any one of five common battery loops. A film-type recorder, which embosses the sound track on cellulose acetate tape, may be used for recording conversations in connection with the monitoring and observing cabinets.
242. TESTING AND MAINTENANCE.
a. When outside wire's develop faults such as contacts with ground, short circuits, crosses with other wires, or open circuits, the service on these wires can be restored by using testing equipment to locate the troubles. This equipment includes voltmeters or Wheatstone bridges or both, in combinations with tones, ringing voltages, and d-c voltages.
36
PARS.
242-243
CHAPTER 2. TELEPHONE SYSTEMS
Types of such testing equipment which may be used in centrals are Test Set EE-65- ( ),
Test Set TS-27/TSM, Test Board BD-101, Cabinet BE-70, Test Set AN/FCM-4 (mobile test unit X-63699A), and Test Set AN/FCM-5 (test and control board X-66034A). This equipment js also used to locate faults on wires and equipment inside the centrals. After troubles have been located, they can be cleared by the use of various types of maintenance equipment. The features of these test sets, test equipments, and maintenance equipments are described in TM 11-487. Information on testing and maintenance procedures is given in chapter 11.
b. The tests which can be performed with test equipment installed in telephone centrals are briefly as follows:
(1) Test calls can be originated and answered on magneto and common battery loops.
(2) Tests can be made with a voltmeter or voltohmmeter to check the continuity of a circuit and detect accidental grounds, short circuits, crosses, and opens.
(3) Ringing voltage can be applied to a circuit as a step in detecting grounds, short circuits, or opens.
(4) The capacitance from a line to ground or to another line can be indicated by the swing of a voltmeter needle in combination with the initial application of a potential through the voltmeter to the line.
(5) Voltages can be measured.
(<5) Conductor loop resistance and insulation resistance can be measured with a voltohmmeter or Wheatstone bridge.
(7) Approximate locations of open circuits on open wire lines can be estimated from capacitance tests with a voltmeter.
c. A small central with a fixed plant switchboard will ordinarily be equipped with a portable Wheatstone bridge such as Test Set 1-49
for use in locating faults on outside lines and for miscellaneous measurements of resistance. A central at a terminal of a main cable route will generally contain a Test Set AN/FCM-4 (mobile test unit X-63699A) for use in locating and analyzing faults on the wires. In large centrals a Test Set AN/FCM-5 (test and control board X-66034A) will generally be provided.
d. When a loop or trunk goes out of order, the following procedures may be adopted to clear the trouble. The trouble is analyzed by making over-all ringing and talking tests. Then specific tests are made to trace the trouble step by step. In the smaller centrals, these tests may be made with a voltmeter at the switchboard. In the larger centrals, they may be made with the test unit or test board. The line is sectionalized and analysis tests are made on each section. When the section with the trouble is determined, the test board or testing equipment nearest to the trouble is used for locating it more closely. Finally the trouble is found by physical inspection.
e. Test and control board equipment provides jacks and paching cords for removing circuits from service such as (may be required for trouble tests, routine tests, or transmission measurements. It also provides arrangements for monitoring and talking on the lines. The monitoring jacks may be arranged in some test boards to make the circuits test busy at the associated switchboards so as to avoid interference between the regular traffic and test calls and give full control of the circuits to the testers. In centrals where these automatic make-busy features are not provided, it will be necessary for the tester to ask an operator to make the circuit busy at the switchboard. The latter procedure is followed in centrals with Switchboards BD-80-( ), BD-110-( ), or smaller switchboards.
Section V. AIRCRAFT
243. INFORMATION AND OPERATIONS CENTERS.
Information and operations centers are used in aircraft warning systems to receive information on activities of enemy and friendly forces in different areas, to plot this information so that it can be readily visualized and analyzed, and to transmit it and operational
WARNING SYSTEMS
orders to the organizations concerned for their information and action. This equipment consists of telephones, relays, jacks, lamps, power plants, and furniture arranged to be quickly unpacked and installed and subsequently packed and transported in motor vehices. Several different types of equipment which are
37
PARS.
243-245
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Figure 241. Operations Center AN/TTQ-1, mobile use.
used for these centers are described in TM 11-487. A typical arrangement is shown in figure 2-41. This is an Operations Center AN/TTQ-1 assembled for mobile use with the plotting tables on the ground and the other equipment in two trucks on opposite sides of the plotting tables. A tent to protect the equipment is shown in this figure. However, it can also be installed in a shelter or building separate from the trucks. The telephone equipment can be connected to wire lines and radio channels. Facilities are provided for automatic remote control
of various types of radio sets. The furniture consists of tables, benches, and platforms. The communication channels are terminated on jacks or keys at the operating positions so that an officer or plotter can directly select the particular line to which he connects his telephone. Most of the communication channels provide point-to-point service. A small tactical switchboard however, is included for a few interconnections over trunks to centrals in Army communication systems.
Section VI. RAILWAY TRAIN DISPATCHING TELEPHONE SYSTEM
244. GENERAL.
a. A train dispatcher controls the movement of trains on a definite length (division) of each railway and transmits train orders by telephone to the way-station operators for control of trains. The length of railway controlled by one train dispatcher varies with the traffic density and geography of the railway. It may be any length up to 200 miles or more. A telephone circuit with connections to every way station along the railway division is provided for transmission of the train orders. Two telegraph wires, also with connections at every way station, are provided, which can be used for transmitting train orders in case of failure of the telephone circuit.
b. The railway communication system is provided and installed by the Signal Corps and, after installation, it is operated and maintained by the Military Railway Service. This communication system, with some of the principal features and limitations, is described in this section.
245. REFERENCES.
Technical manuals to be prepared by the Transportation Corps will describe the components, operation, and maintenance of railway communication systems. Technical manuals prepared by the Signal Corps on the principal items of dispatching equipment are available for such specific apparatus as: amplifiers, rec
38
PARS.
245-248
CHAPTER 2. TELEPHONE SYSTEMS
tifiers, etc. A booklet entitled Maintenance of Way Manual; Military Railway Service; Supplement A; Telephone, Telegraph, and Signals is available from The Director General, Military Railway Service, Washington 25, D. C. In the past, commercial literature such as Western Electric Company’s Bulletin No. 672A has been furnished with some of this equipment. T/O and E 55-227 lists the communication personnel and equipment of the Maintenance of Way Company of a Railway Operating Battalion. The following field and technical manuals also contain pertinent information:
FM 55-50, Military Railroads and Military Railway Service
FM 55-55, Railway Operating Battalion (superseding TM 5-405)
TM 11-2256, Amplifier No. 3BLH
TM 11-2257, Rectifier Power Units No. 1152 and No. 1161
246. TELEPHONE SYSTEM.
a. A railway train dispatching telephone system is a special form of long distance telephone party line with selective ringing, which enables a train dispatcher to call individually any one of the way stations on the line. The lines usually are open wire, and the Military Railway Service has purchased No. 9 B&S gauge (114-mil) copper wire such as that used in commercial train dispatching installations. If it is planned to use cable for any part of the line, it may be necessary to obtain cable which is specially designed to withstand the high signaling voltages which may be used, as the normal telephone cables are not designed to withstand these voltages. The operating limits of the equipment provided are such that a 114-mil copper open wire line may be as long as about 500 miles and have as many as 60 way stations; if any substantial amount of cable is used, the range will be less.
b. The dispatcher listens continuously on the line by loudspeaker or head receivers, and he talks to way stations through a chest microphone. He rings the bell at the individual way station by means of selector calling keys which control the application of 200- to 500-volt 3^-cycle alternating current to the line. This 3H-cycle alternating current operates the waystation selectors.
c. The way-station operators do not listen constantly because they have various duties
to perform. When they have occasion to talk to the dispatcher, as for example, to report the passing of a train, they listen on the line and if it is idle they talk to the dispatcher. The telephones at the way stations are of a special push-to-talk type which cause relatively small transmission loss to other way stations when in the listening condition. Low loss under this condition is important because a large number of stations may listen on a line simultaneously.
247. EMERGENCY SERVICE.
Emergency communication service is required when the telephone train dispatching circuit is out of service because of trouble. The Military Railway Service plan provides two separate wires for single Morse manual telegraph operation. At each station each wire is equipped with suitable station equipment. These telegraph wires parallel the train dispatching telephone wires and are used for both regular telegraph service and emergency train dispatching.
248. DISPATCHERS’ EQUIPMENT.
a. Dispatchers’ Telephone Equipment. Telephone equipment with a head receiver which is provided for each dispatcher is shown in figure 2-42. During periods when the dispatcher does
Figure 242, Dispatcher’s station telephone equipment.
39
PAR.
248
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
not wish to wear the head receiver, a loudspeaker instead of the head receiver can be connected to the line. A contact on the foot switch provides means for reducing the loudspeaker volume so that the transmission path through the loudspeaker and microphone will not howl when the dispatcher is speaking.
b. Selector Keys. Two different types of keys are provided to enable a dispatcher to call individual way stations: the individual type and the master type. One of the individual type selector keys is used to call each of the way stations. A group of these keys is installed in a selector key case which is mounted on the
Figure 2-43. Individual type selector key and case (Western Electric Company No. 60A key).
Figure 2-44. Master type selector key (Western Electric Company No. 61A key).
dispatcher’s table. The selector key and a case which has a capacity for 24 keys is shown in figure 2-43. The master type selector calling key (fig. 2-44) is provided for emergency use. When this key is used, the three levers are placed opposite the numbers that make up the code of the way station to be called. Then the fourth lever, which is equipped with a handle, is pulled down and is allowed to return to nor-
Figure 245, Selector apparatus case (Western Electric Company No, 62B).
n a
i: c
1 1
< <
<
40
TL 54859
TL 53209-S
RELAY
Tl 54345
PARS.
248-249
CHAPTER 2. TELEPHONE SYSTEMS
mal. Thus, this one key can be used for calling any of the way stations.
c. Selector Apparatus Case. The selector calling keys are connected to a selector apparatus case shown in figure 2-45, which contains the apparatus by which the d-c impulses from the keys control the 3Mz-cycle alternating current for transmission to the line.
d. Power Supply. The 3i/2-cyde alternating current is derived from direct current by means of a reversing relay in the selector apparatus case. The d-c voltage is obtained from a power supply unit that can be set to produce various potentials between 200 and 500 volts de. The voltage is adjusted for proper operation of the way station selectors and is governed by the length of line and number of selectors on the line as explained in paragraph 251.
249. WAY-STATION EQUIPMENT.
a. Telephone Equipment. The telephone provided in each way station is shown in figure 2-46. It uses a microphone and head receiver which are similar in their electrical character
istics to the microphone and receiver of Telephone TP-6. A push-to-talk button is provided in the associated desk set box.
b. Selector Set.
(7) A selector set is provided at each way station. The selector and the selector set of which it is a part are shown in figures 2-47 and 2-48 respectively.
Figure 2-47. Selector (Western Electric Company No. 60AP).
Figure 2-46. Way-station telephone.
(2) The selector has a toothed code wheel and when this wheel has advanced to the 17th step it closes a local battery circuit which rings the way-station bell. Each station has assigned to it a 3-digit code, and the sum of the three digits of each station code is 17. The dispatcher’s calling keys introduce short pauses between the three digits.
(5) The selector code wheel at each way station is advanced by the 3 V-)-cycle impulses which are sent by the calling key at the dispatcher’s station. Only those code wheels stay in the advanced position, during the pause,
TL 54 644
Figure 2-48. Selector set (Western Electric Company No. 162C).
41
DISPATCHER'S OFFICE
OTHER WAY STATIONS q ----OTHER WAY STATIONS-
| LINE EAST _______ A______________ LINE WEST 1 , n
STATION STATION —/I ct^tTom WAY WAY <1
EQUIP EQUIP --tT-- r-n ?° STATION STATION STATION
- W r*l| r EQUIP. J EQUIP. EQUIP. P
DISPATCHER'S ’SIMPI Fit
LTO EQUIP. TELEPHONE TELEGRAPH ,.________ SIMPLEX*-1
DISPATCHER'S EQUIPMENT CONNECTION TELEGRAPH
APPARATUS --- "-------------------------------------- CONNECTION
CASE — DISPATCHERS
r~j<_7 CALLING KEYS
• II WAY
PffTiriro BRANCH * ■ * > STATION
RECTIFIER • LINE EQUIP.
! 60 CYCLE AC I
| I *---OTHER WAY STATIONS
L------------------------------J j+
notes: nU—
I. THE SIMPLEX TELEGRAPH CIRCUIT CAN BE APPLIED ^Qu'p/^
AT ANY TWO PQINTS A AND B ALONG THE LINE. -----—
2 WAY STATION EQUIPMENT INCLUDES SELECTOR SET
AMD TELEPHONE EQUIPMENT.
TL 54855
Figure 2-49. Principles of standard method for operating train dispatching telephone system.
42
DISPATCHER’S OFFICE 1
I '
I TRANSMISSION BY-PASS
! __________Il_________ |
ei-AV-. | ---- OTHER WAY STATIONS-
[4—| Lj r-iA | I-?8/1”!
e | | |line west ! \ _ | B B |_* c
I th p ffr Mkil
g STATION STATION | --------- ----------- STATION ~~~_ E 4_____4 STATION b
F EQUIP. EQUIP. I SIMPLEX DISP EQUIP rTJTOi ' EQUIP F
UJ ----- ------- I Urf TELEGRAPH 1EL ------- H I H INT STA ------ I—J
I I-♦ CONNECTION rnillD SIMPLEX-*---• TE LEG. CONN,
SIMPLEX I SIMPLEX [_ EQUIP. TELEGRAPH SIMPLEX
TELEGRAPH I TELEGRAPH 1 ___ CONNECTION ————------------- TELEGRAPH
CONNECTION CONNECTION ^RA^U S ~ DISPATCHER’S ---1 CONNECTION
I CASE — CALLING KEYS -- *-
। _ ____ ___ BRANCH____________ WAY
{ | | , LINE * STATION
J | | RECT IFIE R I—EQUIR_
♦ ♦ M-OTHER WAY STATIONS
60 CYCLE AC ________ ________________
NOTES r —
WAY
I. SIMPLEX TELEGRAPH CIRCUITS CAN BE APPLIED IN VARIOUS WAYS, STATION
FOR EXAMPLE. A TO B, B TOC, E TO D AND F TO G, EQUIP
2. IF VOICE TRANSMISSION IS REQUIRED BETWEEN LINE EAST AND LINE WEST, A REPEATING COIL TRANSMI SSION BY-PASS IS CL. ,.71G
REQUIRED AS INDIC ATED 3. WAY. STATION EQUPMENT INCLUDES SELECTOR SET AND ’
TELEPHONE EQUIPMENT. -rn'erowu
ILLLUnArn
CONNECTION TL 54856
Figure 2-50. Principles of transformer method for operating train dispatching telephone system.
43
PARS.
249-252
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
which have a code pin inserted in the code wheel at the step which corresponds to the number of impulses sent from the dispatcher’s key. The code wheels of selectors at all other stations return to the zero position during the pause.
(4) The impulses of the second and third digits sent from the dispatcher’s key again advance the code wheels, some from the advanced position and others from zero. However, only the selector which has code pins to hold the code wheel during the pauses between the first and second and between the second and third digits will advance to step 17 and ring the bell.
(5) For example, a way station with a ringing code 8-5-4 has code pins set at steps 8, 13, and 17 on the code wheel.
(6) After a ringing interval of about two seconds, the dispatcher’s key sends a release impulse which restores the way station selector to normal.
(7) As the bell is rung, a tone is also sent onto the line which is called the answer-back. This indicates to the dispatcher that the bell is ringing.
(8) The code pins can be set for 78 different combinations.
250. SPECIAL ADJUNCTS.
Train dispatching telephone circuits can be arranged to provide for the following features :
a. A simplex telegraph circuit can be obtained between two or more places along a line without interfering with telephone service. This circuit can be operated single or duplex, manual, or teletypewriter.
LOOP RESISTANCE OF LINE IN OHMS
4OQ.2 684996 1326 l&.fe0, l992 2324 2656 2988 3320 3652
W360 ------------------------
o ' <4/
>320-------------------------
z $' / Sz,'''
I- 280-------— ----------—
C ---------------------------
a 240 -. - >/4Xz--— —------
O _____Z/.X s ________—
<200 ———^-=4—--------——------
I — --------
g 160 — — — ______-= = _
120* .1 1. O————————————L_
40 80 120 160 200 240 280 320 360 400 440
LENGTH OF LINE IN LOOP MILES OF 114 MIL COPPER WIRE
TL54826
Figure 2-51. Range of No. 160 type selectors for various line voltages and numbers of bridged selectors (no transformer).
b. Branch or spur lines can be connected.
c. Way-side telephones in pole boxes or portable telephones with a line pole for making connections to line wires can be used at points along a line for telephoning the dispatcher.
LOOP RESISTANCE OF LINE IN OHMS
332 664 996 1328 ,1660 1992 2324 2656 2988 3320 3652
4 40 —-------------;X--------—
co -----------------------------------
J 400 -----------—--------------------
-----------------
O 360 -fPX-----------------------_____
g. ------___________________
a 320 —-------------------------------
£ —----------------—__________________
° 280 — — —-3(1^^- —------------— ==»-«= — * * * * * * * * * * * * 251 252
cc 240 --------2<——- —----------------
0 —--=-T—'
Z —==———------------------------------
200 ------------H----------------_ —
10 —ZZ UZZ___
I 60 *■—1 I I 1 I I I—I— ————————|_
40 80 120 160 200 240 280 320 360 400 440
LENGTH OF LINE IN LOOP MILES OF 114 MIL COPPER WIRE
TL54827
Figure 2-52. Range of No. 160 type selectors for various
line voltages and numbers of selectors (one No.
341A transformer).
251. OPTIONAL METHODS OF SELECTOR OPERATION.
a. Two arrangements are available for connecting selectors at the dispatcher’s station and way stations to the telephone line, namely: the standard arrangement and the transformer arrangement. The standard arrangement provides a greater range and more stations for a given line voltage. However, with the transformer arrangement other desirable features such as additional telegraph circuits between way stations can be obtained.
b. The circuit operating principles of these two arrangements are illustrated in figures 2-49 and 2-50. Signaling range data corresponding to these two circuit arrangements are shown in figures 2-51 and 2-52 respectively. In the latter range chart, one No. 341A transformer is assumed to be in the circuit. If the circuit includes more than one transformer, the ranges will be less than those indicated.
252. PROTECTION.
Because of the high voltages present, protector blocks with higher than normal breakdown voltage must be used at the dispatcher’s station and at all way stations. Normal fuses (7-amp.) are used at all stations
44
CHAPTER 3
TELEGRAPH SYSTEMS
Section I. WIRE AND RADIO TELEGRAPH SYSTEMS
301. MAJOR COMPONENTS OF TELEGRAPH SYSTEMS AND NETWORKS.
Telegraph, systems serving areas of moderate extent include central office and station equipment operating in conjunction with wire or radio transmission circuits or a combination of wire and radio. Comparatively simple facilities which would be characterized as telegraph circuits rather than systems are shown by figures 3-1 and 3-2, the connecting circuits be-
REPEATER — - REPEATER
0R OR LINE UNIT WIRE LINE LINE UNIT
TT TT aTELETYPEWRITER TT
circuits or over built-up circuits involving one or more switchboards. Messages may also be relayed semiautomatically or manually from one circuit to another, that is, received at an. intermediate point and retransmitted to one or more other points. Teletypewriter operation with semiautomatic relaying is used to handle practically all of the traffic in the Army Command and Administrative Network which is discussed in chapter 11. Teletypewriter equipment should be manned by personnel having some degree of skill. Messages sent by all forms of telegraph usually are writton out before transmittal and before delivery; this written record is a very valuable feature. Telegraph circuits, particularly those using teletypewriters, may be used also for interchanging infor-
TL 54979
Figure 3-1. Direct (point-to-point) d-c wire teletypewriter circuit.
tween the teletypewriter stations being direct (point-to-point) wire and radio connections, respectively. A system is made up of numerous components, including stations with their individual extensions (local lines), main transmission circuits, terminal and repeating equipment, retransmitting equipment, switchboards, and branch circuits extending to outlying localities. A relatively simple system involving such components is shown in figure 3-3. Furthermore, systems utilizing wire and radio facilities are combined to form a rather extensive network to provide communication throughout a theater of operations as illustrated in figure 3-4,
302. MESSAGE HANDLING METHODS.
Messages may be sent directly from a station to one or more distant stations over fixed
---------— I RADIO ________________ ________
J .rvro 1—1 BAdTo I RADIO _________ RADIO
KLYEK TRANSMITTER I RECEIVER TELE~
~ ■ —'I ------------ TYPE
TERM-
1-1=--------------------1 LlNALh
I RADIO I
I TELE’ I
I TYPE ________________ RADIO | --------------~|
I TERM- I RADTO ||_ -^Jl RADIO I |
j I INAL |~| RECEIVER |j । TRANSMITTER|~[ ||
t i T i
STATION AND I STATION AND
TELETYPE- TELETYPEWRITER WRITER
EQUIPMENT EQUIPMENT
SIGNAL CENTER A SIGNAL CENTER B
TL 53218-S
Figure 3-2. Direct (point-to-point) radio teletypewriter circuit.
mation in a conversational manner. Automatic switching to a very limited extent and on a specially engineered basis is used whereby a connection is established by switches actuated by certain teletypewriter characters.
656935 0-45------5
45
PAR.
3°3 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
RADIO
Y . y
r- RADIO RADIO ______
terminal) terminal
EXTENSION
^WIRE_LINE J T.CKTS. ] WIRE LINE ’'
CARRIER CARRIER “ “ “ “ *
EXTENSION Y ------- Y
I--1 CIRCUITS ----1---- TELEGRAPH _____________TELEGRAPH | EXTENSION ___
Uj“ -----CARR|ER TERMINAL TERMINAL rioo.ro ---— -U-- — LINE O
-> _ CARRIER UN|T r|
----------- TELEGRAPH ________________________ TELEGRAPH________________ —~~
-----terminal TFnMiwA. r-------------
TERMINAL --------- REPEATER
---- REGENERATIVE--------------------------------------- ------- REPEATER [tt]
------] STATION -—TELEGRAPH
|~—1 LINE LINES ”“
|TTr~" UNIT — — - - —1 SWBD. REPEATER REPEATER----— REPEATER
--------- । । ' s । branch L_J
REPEATER —— — — REPEATER ■CIRCUIT
TL 53230-S
Figure 3-3. Teletypewriter system with wire (d-c and carrier) and radio transmission circuits.
303. INTERNATIONAL MORSE-CODE VERSUS TELETYPEWRITER OPERATION.
a. International Morse-code Methods and Speeds.
(I) In manual telegraphy the signals are formed as dots and dashes by the operation of a telegraph key by a trained operator. They are received as audible tone signals and recorded by hand or on a typewriter. The signals shown in figure 3-5-A illustrate the formation of typical characters. As indicated, a dot signal followed by a space of equal length is called a dot-cycle or sometimes simply a cycle. Certain administrations use a unit of speed called the baud, which is a rate of 14 cycle per second. Thus a speed of 23 dot-cycles per second may be expressed as 46 bauds. Since the baud is a unit of speed, it is incorrect to speak of a character or word as consisting of so many bauds. With average operators, a speed of 10 to 15 words per minute may be expected and perhaps twice as much with skilled operators.
(2) The International Morse Code is also used with automatic sending equipment, particularly where speeds up to about 400 words per minute or more are desired, such as on certain long-haul radio circuits. In this case, a
punched tape is prepared by operating a keyboard; this tape is fed into a keying head capable of sending at a readily adjustable speed which is in accordance with circuit capabilities and traffic requirements. It is customary to assume that the average word consists of six characters, including one for a* space at the end of the word. Use is being made of the test word CODEZ as a standard-length word in determining military speeds; on this basis a speed of 100 words per minute corresponds to 50 dot-cycles per second.1 At comparatively low speeds, the signals may be received by ear. Generally, at speeds over about 25 words per minute, the signals are received by means of an ink recorder and transcribed by one or more operators at an average speed of about 35 words per minute for each operator. Sent and received tapes are illustrated in figure 3-6. Automatic equipment used for International Morse-code operation is described in paragraph 330.
1 The transmission of the word CODEZ and the following space utilizes a transmission time equivalent to that of 30 dot-cycles. Therefore, a speed of 100 words per minute is 3,000 dot-cycles per minute or 50 dotcycles per second.
46
PAR.
CHAPTER 3. TELEGRAPH SYSTEMS 303
V R A D IO / \. R A D । o J
V, _x_ m corps ncorps V . ■,
Y, Y T f
UJ Lu ill LlI
2ND ARMY HQ 1ST ARMY HQ — £ CORPS
WIRE LINES [SC [ - II CORPS
WIRE LINES WiRE LINES WIRE LINES
\^RADIO^/ \\RADIO
H XX
AAFHQ WRE LINES
------------------------U LEGEND:
|s Q I ~ I 'xt7
1 1 IsCI I RADIO RECEIVERS
WIRE LINES |~R~|
WIRE LINES
■ - Y
| RADIO TRANSMITTERS
\aRADIO // | T |
Y Xt7 i—। teletypewriter signal
CIVIL IxEJ CENTER
"TrI [Y] rehabilitated
1 1 1—1 TELEPHONE cable
BASE SECTION
HQ ________WIRE LINES
[sc |
TL 54929
Figure 3-4. Typical theater teletypewriter network.
b. Teletypewriter Methods and Speeds. that of a typewriter, and the corresponding
CO The form of teletypewriter signals is characters are typed in page form or on tape shown in figure 3-5-B ; these signals are dis- by machines at both sending and receiving sta-cussed in more detail in chapter 12. The letters tions. Signals may also be sent from a punched and the space between words are all of equal tape prepared locally by a perforator which length and the code is slightly more efficient in the use of line time than the International o o o □ JTo o oo ooo ?
Morse code. Signals are produced by the opera- 1? o o o i o o o o o o i o o o o o o o o o o i o o o o o 3
tion of a teletypewriter keyboard similar to j{oo Io o o d o p 6q 6 p q
I i i i i i I i I i i i । Pi । tiii 11 ! 111 m iiii 111111! A 111! । m 1111! I i । sent
■m ■ 11 BHi ■■ ■■■ i । ■ aaa ■■■ llllll■■ll■■■>l>
111111111111111111111 • 11111111111 ri 111111111111111111 I । i
i INTERNATIONAL MORSE CODE "*L„b I N ! O I W, I | I S
"DOT । I I I
CVCLC"
A 4-----------:___________;___________I I i
J।r«j:।iwj"*urriciw।w।ijwu।J jrvLinnn hn/x Im !aaa I .l!un 1111111 । " 111 111 ■ I ■ ! I " r" I " J________________ _____________________ I
TELETYPEWRITER CODE WITH START AND B
STOP PULSES. Tl . RECEIVED
TL 53219 S TL 53220-S
Figure 3-5. Telegraph codes, typical characters. Figure 3-6. International Morse-code tapes.
47
PAR.
303 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
has a keyboard similar to that of the teletypewriter. A sample of this tape is shown in figure 3-7. Teletypewriter signals may be received over a line by a typing reperforator, which records the message as partial perforations and as typed characters on the same tape. Some typing reperforators have keyboards from which
io ooo o oooo oo o oooo 66 \
o oo oooo ooo ooo o OO O / ooooooooooooooooooooooooooooooooX . O OO OOO OOO O OOO O ? I OOOOOO o o o o o>
O oo OOO O o_________OOP OO OO I
TL 54910
Figure 3-7. Perforated teletypewriter tape.
tape may be prepared locally. The typing reperforator may also be used as a teletypewriter in sending messages. The form of tape, illustrated in figure 3-8, is called chadless and may be used for retransmitting the message. As a general rule, American Army teletypewriter equipment operates at a nominal speed of 60 words per minute, that is, 368 operations2 per minute (opm). This speed may be increased to a nominal speed of 66 words per minute (404 operations per minute) to work with British teleprinters. However, for interoperation, other factors are important (par. 350).' When sending directly to a circuit from a keyboard, the average operator will type at a nominal rate of 25 to 30 words per minute; because of the transmission of headings, nontyping selections, etc., the corresponding net message (text) speed is about 23 words per minute. When sending from tape at normal machine speed of 60 words per minute the average message (text) speed is about 50 words per minute.
Figure 3-8. Chadless (partially perforated) teletypewriter tape ivith typing.
(2) A few teletypewriter circuits, wire and radio, are being operated on a provisional basis at 100 words per minute. Operation at this speed requires modifications of teletypewriter equipment and associated testing ar
2 An operation is considered to be a typing character or a nontyping selection. Examples of nontyping selections are carriage return and line feed.
rangements. The modifications consist of introducing certain new parts and changes in adjustments. Also, new requirements, are imposed on transmission facilities because the signaling speed is about 37 cycles per second as compared with about 23 cycles per second for 60 word-per-minute service.
c. Relative Advantages.
(I) The advantages of teletypewriter operation as compared to manual telegraph operation are: high average speed, automatic reception of multiple copies in typed form at one or more points, use of operators with a lower degree of skill, possibility of regenerating signals automatically, and relaying of messages from circuit to circuit by means of tapes. The main disadvantages as compared to manual .telegraphy are: size and weight of the equipment, complexity requiring skilled maintenance forces, need for high grade circuits, and need for about 100 to 300 watts of power per station.
(2) In the manual Morse method, the operators may reduce speed to meet the capabilities of the circuit. The use of manual Morse generally permits operation under more adverse circuit conditions than either teletypewriter or voice. Its main disadvantages are relatively slow speed and the need for more skillful operators. For operation on wire lines, manual telegraph uses simple sets which are readily portable and operable from batteries. These sets are relatively inexpensive, small in size, and light in weight (seven pounds without typewriter). The weight is roughly 1/50 that of teletypewriter station equipment.
(3) Automatic Morse operation is particularly advantageous in the case of a circuit which is operable for only a small part of the time, for example, on certain h-f radio circuits operating over paths near a magnetic pole a large amount of traffic can sometimes be moved in a few hours, using a speed of several hundred words per minute. The speed of automatic Morse operation may be regulated to suit the capabilities of the circuit. However, this equipment is complicated, requires about 500 to 600 watts of power, is heavier and larger than comparable teletypewriter equipment, and trained personnel is required to transcribe the signals from the received tape.
48
PAR.
304
CHAPTER 3. TELEGRAPH SYSTEMS
Section II. WIRE AND RADIO TELEGRAPH TRANSMISSION
304. TRANSMISSION.
a. Dotting Speeds. Telegraph signals are sent at different rates, depending on the method of working and on circuit conditions. In manual International Morse the rate of sending dot-cycles is from about 6 to 15 cycles per second, the average being about 8 cycles per second. In teletypewriter operation, the line speed in dot cycles per second is set by the machine independently of the rate at which the keyboard is operated. The speeds are approximately 23 and 25 cycles per second for nominal word speeds of 60 and 66 per minute (368 and 404 operations per minute), respectively. In automatic Morse-code operation, the speed of signaling may reach 100 dot-cycles or more.
b. Frequency Band Widths. Although telegraph signals are made up of pulses during which the operating current substantially reaches a steady value, they also contain alternating-current components of different frequencies; the range of essential frequencies from the lowest to the highest is called the signal frequency band. It is necessary to provide a circuit having the proper characteristics to transmit this band. In the case of a d-c telegraph circuit, this band ordinarily extends from zero cycles, per second, that is, direct current, up to about three times the maximum speed in dot-cycles per second. Thus, in manual telegraphy a band of about 50 cycles in width would ordinarily be adequate. In teletypewriter operation (60 word-per-minute speed) a band about 75 cycles wide is desirable; in highspeed automatic Morse-code operation, a band several hundred cycles in width may be required for the highest speeds. In carrier and radio telegraph, when current of a single tone or frequency is keyed on and off, the required band is twice as wide, extending in each direction from the carrier frequency by the amount required for the d-c case. When two frequencies (one for marking and another for spacing3) and two channels are used, the band width is again doubled. With tone modulated radio telegraph, the whole voice band is generally used.
, A signaling interval during which current flows through the teletypewriter receiving magnet is called a mark, and the circuit is said to be marking. When no current flows through the magnet, the signal is called a space, and the circuit is said to be spacing.
c. Wire Transmission. The two general types of wire telegraph circuits are de and carrier. Carrier telegraph facilities operating in the voice range between 300 and 2,400 cycles per second generally form the main transmission circuits for long and medium distance communication on land lines. D-c circuits are used especially for the shorter facilities, including extensions to stations and branch circuits to outlying offices. Wire telegraph circuits will, in general, furnish dependable and accurate service if reasonable standards of circuit layout and maintenance are adhered to.
d. Radio Transmission. Although radio transmission provides a high degree of flexibility for point-to-point communication from a station to any one of a large number of stations and for broadcasting to a plurality of stations, transmission is, on the whole, less dependable than that over wires. This is because of variable conditions in the transmission medium and the possibility of accidental or intentional jamming. The transmission impairment is not only in the form of displacements of transitions between marks and spaces (time distortion) but also in variations in strength of received signals and the occasional obliteration of the received signals by interference. Singlechannel and multichannel teletypewriter circuits are operated satisfactorily over radio links within limits of distances from a few thousand yards to many thousands of miles. International Morse-code operation is being replaced in some cases by teletypewriter operation. Most of these applications make use of radio facilities operating within either the h-f or v-h-f range, but in polar latitudes radio frequencies in the order of 50 to 200 kilocycles are used. For operation in the h-f range over radio circuits using sky-wave transmission, it is generally desirable to use diversity operation. Thus signals may be received simultaneously at two or more locations separated by several wavelengths (space diversity), or each, signal may be sent simultaneously at two or more frequencies to be combined at the receiving station (frequency diversity). Where space is limited, two different adjacent antennas, such as vertical and horizontal, or differently-oriented horizontals, may give some improvement by providing polarization-diversity reception. Further information regarding tele
49
PARS.
304-305
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
typewriter operation over radio will be found in section VII. Refer to chapter 6 for general information on radio transmission, including antennas.
e. Repeaters. The limiting length of a telegraph circuit, either wire or radio, is generally reached when a signal becomes so weak as to be incapable of actuating the receiving apparatus properly, when the waveshape is modified so that the time distortion of the telegraph impulses is excessive, or when the received signal strength is too low to override the interference. Usually the circuit can be extended by inserting a repeater before the limiting length is reached. In d-c telegraphy, such a repeater involves reception of the signals by means of a relay and automatic retransmission using a local source of energy, such as a set of batteries or rectifiers. In carrier or radio telegraphy, the signals may .be converted to d-c form before retransmission, or the repeater may be a vacuum-tube device merely to amplify them. In teletypewriter operation, a regenerative repeater may be used at an intermediate point. This repeater will automatically retransmit the received signals in practically perfect form if they have not suffered an amount of distortion which would cause errors in the copy in a teletypewriter at that point. The punching of a tape by a reperforator and retransmission from a transmitter-distributor is also a means of regenerating signals. This method is applicable to both wire and radio circuits.
f. Single and Duplex Methods of Operation.
(I) Over wire circuits, telegraph operation which is limited to one direction at a time is known as single- or half-duplex operation; a break feature is provided to enable the receiver to stop the sender. In radio operation, such to-and-fro service using only one radio frequency assignment is called either simplex or one-way reversible; in teletypewriter service, no break feature is provided but in manual circuits there may be a break-in feature. The term half-duplex as applied to radio is used to describe to-and-fro teletypewriter service using two radio-frequency assignments with a break feature. As noted in paragraph 305d, the term simplex also applies to a method of using wires to obtain d-c telegraph simultaneously with telephone.
(2) In any telegraph circuit (wire or radio) in which independent transmission
paths are provided for the two directions of transmission, it is possible to transmit messages in both directions simultaneously. This is known as duplex operation, and is also called full-duplex operation. This method involves certain inconveniences from an operating standpoint, but allows moving approximately twice as much traffic as the single method. Carrier telegraph is particularly suited to the duplex method. With radio circuits, the duplex method requires different frequency assignments for the two directions of transmission.
305. D-C WIRE TELEGRAPHY.
a. Neutral. D-c neutral circuits operate on the basis of current for marking and no current for spacing. A metallic pair or a wire with ground return may be used between the sending and receiving points. Figure 3-9 shows schematically a manual neutral circuit. Simple open-and-close operation is sometimes used between teletypewriters connected directly to the line without line relays; in such cases, operation between teletypewriters is limited to distances in the order of a mile when field wire is used. This limitation is imposed primarily
> TO
•------- r —— INTERRUPTER
F AND
?__headset
m n tJ line Lin m
’IMf ft—
J.+ RELAY J.+
TL 5322 3*5
Figure 3-9. Neutral telegraph circuit (manual operation).
by signal distortion resulting from varying weather conditions. This distortion cannot be readily compensated for in the adjustment of the teletypewriter mechanism. However, this form of signal distortion can be overcome to a certain extent by interposing an adjustable receiving relay between the line and the teletypewriter, as shown in figure 3-10. At A the relay is biased mechanically; at B the bias is electrical.
b. Polar. In d-c polar circuits, approximately equal values of positive and negative voltage are applied alternately to the line at the transmitting end. At the receiving end, a polar relay responds to the direction of the current rather than to its magnitude. A one-way polar telegraph circuit (fig. 3-11) generally uses one line conductor with ground return,
50
PAR.
CHAPTER 3. TELEGRAPH SYSTEMS 305
A-neutral line relay B- polar Line relay
TT REC. MAGNET TT REC J AAA m
"A“ET tCT? —I—-IC VA
x-fi — -----------UNE------------CvTwd—---------'r-------
TT SEND RELAY* BIAS |J JVW-| TT SENQ
CONTACTS RELAY SPACING \ LINE . 1 CONTACTS
1 RELAY I
* LOCATED IN LINE UNIT.
b LOCATED IN TT. TL 53243-S
Figure 3-10. Neutral telegraph circuit (teletypewriter operation).
but two conductors may be used on a metallic- referred to as the polar-sending end, applies return basis. A 2-path polar circuit consists of equal voltages of opposite polarities for mark-two one-way polar circuits and is suitable for ing and spacing and the other end, referred to duplex operation provided the local circuits are as the differential-sending end, applies ground so arranged. The British have a reversible for marking and positive polarity for spacing, one-way polar arrangement which uses one The operating ranges of polar and polarential wire and reverses the direction of transmission circuits are substantially the same, and exceed by switching, which is automatic in the case
of teletypewriter operation. This reversible
arrangement does not lend itself to duplexing POLARTsENniNr differential
or multisection connections, and it is also sub- _75v REC
ject to false operation when idle. American ^■I^SEND -gf
sewo RECe,VE
Lj +H SV. ~
♦ o- TL 53225 5
~ LINE 40 Figure 3-12. Polarential telegraph circuit.
Slip] --
,ZL polar -X that of a neutral circuit provided with an ad-
21 relay ' justable receiving relay. No adjustment is re-
tl 53224-s quired in equipment operating on a polar or
Figure 3-11. One-way polar telegraph circuit. polarential basis to compensate for varying
weather conditions. In the case of distributed teletypewriters are not arranged for reversible leakage, there is little difference between the one-way polar operation. See paragraph 350 transmission capabilities of a polar and polar-for interoperation of British and American ential circuit. However, a polar circuit will teletypewriters. tolerate somewhat more leakage concentrated
c. Polarential. A polarential circuit (fig. 3- a^ one Part of the line, and somewhat more 12) provides practically the equivalent of a difference of ground potential between the ter-half-duplex 2-path polar circuit and uses only minal points, than a polarential circuit.
one line conductor instead of two. In a polar- d. Simplexed Circuits. D-c telegraph circuits ential circuit,, the transmission in one direction are generally obtained from conductors which is polar, and in the other direction it is equiva- are used simultaneously for telephone purposes lent to polar as far as the receiving relay is rather than by the use of conductors exclusively concerned. This polar equivalent is attained for telegraph purposes. One method of doing by providing the receiving relay at the polar- this is by simplexing (fig. 3-13), wherein one sending end with a local bias current which in winding of a repeating coil or transformer is magnitude is midway between the marking line connected across the line pair and a point current and the spacing current. The trans- midway between the coil terminals of this line mittmg arrangments at the two terminals winding is connected to the telegraph equip-of a polarential circuit are dissimilar; one end> ment. With reasonably good impedance bal-
51
PARS.
305-306___________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
™^bTreen ?e tWn 'v'.res,of the Pa!r> tele- less on composited telegraph circuits than g aph cunents will divide approximately it is on simplexed circuits, equally between the two wires and hence will < t i u E «. _. ..
not interfere with telephone transmission A n. Jele3,aPh C.reuifs. Circuits of
noise killer is often included in the transmit T*’ .sorae‘lmes referred to either as lo-
^“'teUg “nh°dUCe V01‘-
transmitted on a metaHiTbasis’y teletypewriter equipments located
tLainc oasis. ln stations or signal centers. Furthermore,
repeating repeating this tyPe of circuit is used to interconnect the
3c0’|z-----------coil local sides of line equipment, that is, carrier
g J g terminals and d-c repeaters, at an intermedi-
H line rt j telephone a^e P°int with or without teletypewriter equip-
R Id e ment. Extensions may be operated neutral
1__________J _______ half-duplex, neutral full-duplex, 2-path polar,
or polarential. Neutral full-duplex and 2-path polar extension circuits require two indepen--------- ------------ dent transmission paths to the teletypewriter telegraph telegraph--station. Extensions operating on a neutral
----j--- —_--------- basis may use either a metallic or a ground-
I TL53226S return circuit. To minimize interference, me-i 1 • ■ * tallic return is preferable, when conductors
F.gure 3-13. Soupl^d ma. are available. When interference is not the con-
e. Composited Circuits. The compositing trollin£ factor> ground return would be used in method for deriving d-c telegraph circuits s0!ne cases because of the lower total line cir-from wires used for telephone circuits is CUlt resistance-based on frequency discrimination that fil
tering, which is a method of selecting*t'e de- ^RR^^niE^R^HT^^^^ sired electrical frequencies and rejecting ARR,ER W,RE TELEGRAPHY.
others. A composite set (fig. 3-14) consists of a’ General-
a retardation coil and capacitors, and pro- (1) In general, carrier telegraphy uses vides a low-pass filter (0 to about 80 cycles) an alternating current of fixed frequency for for the telegraph currents and a high-pass each channel, which is switched on and off at filter for the telephone currents. The composit- ^he sending end by a sending relay actuated ing method has the advantage of providing d’c signals. Frequencies in the voice-fre- II____________ quency band which are used for carrier tele-ro____________________________________________f_graph systems (roughly 300 to 2,400 cycles)
equipment CAPAC|IT0RS line are given in the frequency allocation chart
-----------1|------------_________ in chapter 5. The carrier currents are trans-|----------------------------------mitted through their respective channel filters,
and at the receiving end are separated by filternanded-c r^T' ' filters and then rectified in detectors to re-
eouepment l£~1- । '' produce the original d-c signals. Circuits suit-
- — -----XL-ropJ_ able for telephone transmission are used, and
retardation only a small part of the total voice band width
capacitors C0 L tl54993 available is required for each telegraph chan-
Figure 3-14. Composite set. neh Simultaneous operation of several (2 to
, . . n . 12) telegraph circuits may be obtained in the
two telegraph channels from a pair of wires, voice range, each circuit being capable of A composited circuit can be phantomed but not duplex operation.
simplexed. Compositing is usually applied to (2) Carrier telegraph systems are oper*-open wires in order to derive as many d-c facili- ated sometimes on 2-wire circuits and some-ties as possible. Generally the effect of leakage times on 4-wire circuits or the equivalent in
52
PAR.
CHAPTER 3. TELEGRAPH SYSTEMS 306
which the transmission in the two directions is independent. In 2-wire carrier telegraph operation, different frequencies are used for the two directions of transmission. In the 4-wire case, the same frequencies may be used for both directions. When using the same frequencies in this manner the requirements as regards crosstalk between the two sides of the circuit are more severe for full-duplex telegraph operation than they are for telephone operation. Excessive crosstalk- coupling between the two sides of the circuit will cause serious impairment of telegraph signals transmitted in one direction because of the telegraph currents sent in the opposite direction on the other side of the circuit.
(3) The power levels used in carrier telegraph systems must be properly coordinated with the telephone transmission levels. If the net loss from the originating long distance telephone switchboard to a point in the circuit is 0 db, this point is said to be at O-db transmission level. The power in dbm (db referred to one milliwatt) per carrier telegraph channel, at a point of O-db transmission level, is known as the specific telegraph level. Typical specific telegraph levels for various types of circuits are given in the following table for general information purposes. Various particular adjustments of telephone and telegraph equipment gains or losses are made in order to realize such telegraph levels. For specific information, see the manuals on particular telegraph and telephone equipments.
Type of Specific telegraph
telephone system {ch. 5) level {dbm)
Telephone Terminal CF-l-( ) (carrier) 4-channel v-f telegraph........................—10
6-channel v-f telegraph........................—10
12-channel v-f telegraph........................—18
Type C or H carrier telephone 6-channel v-f telegraph........................—12
12-channel v-f telegraph, on type C............—15
11-channel v-f telegraph, on type H............—15
Voice-frequency loaded cable (4-wire) 6-channel v-f telegraph........................—18
12-channel v-f telegraph........................—21
b. Carrier Telegraph on Spiral-four Cable. Carrier telegraph systems are available for operation on one or more of the four telephone channels of a spiral-four cable system using Telephone Terminal CF-1- ( ). This equipment can also be used on other wire telephone circuits, and on radio circuits as covered by paragraph
342. A schematic of a 4-channel carrier telegraph terminal (Telegraph Terminal CF-2-( )) is shown in figure 3-15. Telegraph Ter-
OSCILLATOR CHANNEL
OSCILLATOR SEND FILTERS
A RELAY____________________ L445-I CHAN-»
Is 4- l445~ —
IlJ ............. 11615 ** I ■
I—___I SEND
-----------------|l78&~|--
e4
TO ~ 2-WIRE
TEt^APH- REcei v e -3 i^Rcyit
EQPT RELAY __ CHANNEL 9 £
CHAN. I n |s+ DETECTOR FILTERS
------1 [------[|IO5~|P-HAN 1
------|g35-.|----S ,
------pq—3 ------|595'v|-----
L—____I TL53227-S
Figure 3-15. Elementary Schematic of Telegraph Terminal CF-2-( ).
minal CF-2- ( ) with or without the addition of Telegraph Terminal CF-6 may be operated on either a 2-wire or a 4-wire basis and are normally associated with Telephone Terminal CF-l-( ). In this case the method of operation is designated 2-wire or 4-wire, depending upon whether the connection between Telephone Terminal CF-l-( ) and Telegraph Terminal CF-2-( ) uses 2 wires or 4 wires. If a 2-wire connection is used, four telegraph circuits can be obtained, using four frequencies for one direction of transmission and four for the opposite direction. The addition of Telegraph Terminal CF-6 to Telegraph Terminal CF-2-( ), connected 2-wire, provides two additional 2-way circuits making a total of six 2-way circuits. If a 4-wire connection is used between the CF-l-( ) and two CF-2-( ) terminals, the eight available telegraph transmission frequencies can be used in each direction of transmission, thereby providing eight 2-way telegraph circuits. In this case, the addition of two Telegraph Terminals CF-6 will increase the number of 2-way telegraph circuits to 12. Telegraph Terminal CF-2-( ) may be operated on channels of the British Apparatus Terminal Carrier Telephone (1 +4), on types C or H carrier telephone systems, or in general over any good telephone channel.
c. Carrier Telegraph on Type C or H Carrier Telephone System. Another telegraph system (packaged equipment), providing 6 or 12 channels on a 4-wire basis, is also available for
53
PARS.
306-307
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
operation on type C or H carrier telephone circuits or on 4-wire cable circuits with suitable loading. The same frequencies are used in both directions of transmission. Channel 2 of a type C system is normally used for telegraph when only one telegraph system is required; two or all three channels of a type C system may, however, be used for telegraph if desired. In a type C system carrying telegraph, the channels used for telephone service must be equipped with volume limiters to prevent interference with the telegraph. In the case of type H, the number of telegraph channels or the quality of transmission for a given number of channels is somewhat restricted, depending principally on the stability of the system from a level standpoint. Telegraph channel 1 is generally not usable. Channels 2 to 12 can be operated simultaneously provided line variations are very small. Best results are obtained by using channels 2 to 6 inclusive, or 7 to 12 inclusive.
307. SPEECH-PLUS-SIMPLEX AND SPEECHPLUS-DUPLEX SYSTEMS.
a. General. These systems are designed to derive carrier telegraph from a portion of the frequency band used by a telephone channel while retaining the use of the channel for speech transmission. The speech-plus-simplex (S + SX) system, which is British, provides service in both directions on a circuit but in
only one direction at a time. The speech-plus-duplex (S 4- DX) system is used by the British and the American Army, and provides full-duplex service but may be operated half-duplex if required.
b. S + SX. The British speech-plus-simplex equipment is furnished in three types: S-|- SX Nos. 1, 2, and 3. Nos. 1 and 2 are arranged to use carrier frequencies of 300, 900, and 2,300 cycles per second. The No. 3 equipment uses frequencies of 300, 1,740, and 2,300 cycles per second. With any one of these three types of equipment, two telegraph circuits, together with a speech channel, may be obtained by using the 300-cycle and the 2,300-cycle channels for telegraph and the intervening band of frequencies for the telephone channel. One S + SX system normally uses either the 300-cycle or the 2,300-cycle frequency and uses the same frequency in both directions of transmission. Two such systems are therefore required to obtain two telegraph circuits from one speech channel. When adverse line conditions interfere with transmission, the telephone can be abandoned and the telegraph worked at one of the emergency frequencies of 900 cycles or 1,740 cycles. In the S + SX equipment, the carrier is transmitted for spacing and interrupted for marking.
c. S + DX. In the speech-plus-duplex system (British and American), a band from about 1,500 to 2,000 cycles is eliminated from the
BAND STOP J_______I_ V-F RINGER
L|NE FILTER VOLUME I000/20~ TELEPHONE
1500*' LIMITER OR EQUIPMENT
____ ________ 20 00~ —।----------------1— 50 0/20*'
__ BAND PASS _________,_nv
f'LTER ____
____ OSCILLATOR - fs~°~ l3°V'
OR MODULATOR --------+ I30V.
I860** “
I<-> SEND LOOP
-±- J> RECEIVE
-------- ’ " < RELAY
HYBRID ____ ] TELEGRAPH
COIL ~j Jr EQUIPMENT
♦ 130V. — -— — os । RECEIVE LOOP
- |30V.---—Ipl SEND
-------- ——J______r\______________________- RELAY
BAND PASS __
---- AMPLIFIER?^--. ----„___906r° rectifierJ> —J----- 1680
I I TL 53242-S
Figure 3-16. Speech-plus-duplex system.
54
PARS.
307-308
CHAPTER 3. TELEGRAPH SYSTEMS
speech transmission circuit and used for telegraph purposes. The carrier midband frequencies employed are 1,680 cycles for one direction of transmission and 1,860 cycles for the other direction. Carrier is transmitted for marking and interrupted for spacing. The British equipment is known as British Apparatus, V.F. Telegraph, S -]-DX. The American equipment, Telegraph Terminal TH-l/TCC-1, is shown schematically in figure 3-16. Further information on Telegraph Terminal TH-1/ TCC-1 and its use will be found in paragraph 333. Interoperation of the British and American speech-plus-duplex equipment is described in paragraph 351. The British S + SX equipment is not operable with S 4-DX equipments since the two use different frequencies.
d. Use of S + SX and S 4- DX Systems. These systems have the advantage that the telegraph circuit can be set up quickly without arranging for simplexing or compositing, or setting up intermediate telegraph repeaters. The removal of the 1,500- to 2,000-cycle band from the speech circuit and the losses at other frequencies caused by the S + DX apparatus often produce impairment in speech transmission as discussed in paragraph 333h. It is generally desirable to confine the use of speech-plus-duplex equipment to cases where facilities and time are insufficient to provide a telegraph circuit by other means. When these systems are used, telegraph levels must be coordinated with the telephone layout, and telephone net losses for the S + DX system are restricted, as discussed in paragraph 333.
308. METHODS OF OPERATING RADIO TELETYPEWRITER CIRCUITS.
a. Single Channel.
(1) General. Single-channel teletypewriter operation over h-f or v-h-f radio may be accomplished by modulating or keying the radio transmitter in a number of ways, depending upon the type of radio transmitter, radio receiver, and teletypewriter terminating equipment used, and upon the distance of transmission. The more common methods are described in subparagraphs (2) to (6) below, and transmission comparisons relative to these methods of operation are given in paragraph 309. C-w and single-tone modulation are applicable to manual and automatic Morse operation as well as to teletypewriter operation. Two-tone modulation and frequency-shift
methods are used especially for teletypewriter operation.
(2) Cw {Keyed Carrier). This is a method in which the radio transmitter emits a radio-frequency wave during closure of the teletypewriter contacts (marking signal) and emits nothing during spacing signals. For reception of this type of signal, the radio receiver includes a beat-frequency oscillator to provide the audible tone from the output of the receiver to the teletypewriter receiving circuit whenever a marking signal is received. There is no tone during a spacing signal. A teletypewriter receiving circuit, capable of amplifying and rectifying the tone signals obtained from the output of the receiver and of operating the receiving teletypewriter in response to these tones is required for operation with the radio receiver.
(3) Single-tone Modulation. In this method, the radio-frequency carrier emitted by a radio telephone transmitter is generally modulated with an audible tone during teletypewriter marking signals and unmodulated during spacing signals. In some cases, however, the carrier wave may be modulated for the spacing signal instead of for the marking signal. The term tone-modulation is applied to this method of modulation.4 It is applicable to either an amplitude-modulation or frequencymodulation radio system suitable for speech transmission. A teletypewriter sending circuit that furnishes, for example, an audible tone for marking and no tone for spacing is required for operation with the transmitter. A teletypewriter receiving circuit that amplifies and rectifies the tone signals and operates the receiving teletypewriter in response to these tone signals is required.
(4) Two-tone Modulation. With this method the radio-frequency carrier emitted by a radio telephone transmitter is modulated with one audible tone during marking signals and by another audible tone during spacing signals. It is applicable to either an amplitudemodulation (a-m) or a frequency-modulation (f-m) radio system suitable for speech. A teletypewriter sending circuit that furnishes one audible tone for marking and another for spac
4 The term mew is not used in this chapter since in radio parlance its use is rather indefinite and is related to a number of different methods of keying. It is sometimes used to mean single-tone modulation. For further discussion of tone-modulation and mew, see chapter 6.
55
PARS.
308-309 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
ing is required for operation with the transmitter. A teletypewriter receiving circuit, equipped with band filters, a fast-acting wide-range current limiter, an amplifier-detector for receiving marking signals, an amplifier-detector for receiving spacing signals, and a receiving relay, is used with the radio receiver to provide the operating currents to the teletypewriter in response to the tones obtained from the output of the receiver.
(5) Frequency Shift. This is a method in which a radio wave having a particular frequency is emitted by the radio transmitter during teletypewriter marking signals and another radio wave of the same amplitude but slightly different frequency is emitted during spacing signals. This method, is sometimes called carrier shift. Radio transmitters capable of c-w emission operating in the h-f range may be arranged for use with this method. A suitable transmitter keying arrangement must be provided to shift the radio frequency. A conventional h-f receiver can be used provided that suitable radio teletype terminal equipment is available. The radio receiver is equipped with a beat-frequency oscillator to provide the two tones, one for marking and the other for spacing, from which the marking and spacing teletypewriter pulses are derived. A teletypewriter receiving circuit, equipped with band filters, a fast-acting current limiter, an amplifier-detector for marking signals, an amplifier-detector for spacing signals, and a receiving relay, is used with the radio receiver to supply the operating currents to the receiving teletypewriter in response to the tones obtained from the output of the receiver.
(6) Diversity Operation. If reception is on a space-diversity basis, two receiving antennas spaced a few wavelengths apart, two radio receivers, and two teletypewriter receiving circuits with one polar relay for operating the receiving teletypewriter equipment are used. If reception is on a frequency-diversity basis, the transmitter is modulated with two audible tones during marking signals and by two other audible tones during spacing signals. In this latter case, both the teletypewriter sending and receiving circuits become more complicated than for space-diversity reception, but only one receiving antenna and one radio receiver are required. Two-tone modulation operation may use space diversity with or without frequency diversity. Fre
quency-shift operation is commonly on a space-diversity basis.
b. Multichannel.
(1) General. Where multichannel teletypewriter operation is required over radio, the single-tone modulation method may be used where the transmission is by ground wave, as is ordinarily the case with v-h-f radio circuits. The 2-tone modulation method is used primarily to aid in overcoming the effects of fading which is experienced on h-f radio circuits using sky-wave transmission (ch. 6). Transmission comparisons of the single-tone modulation and the 2-tone modulation method for multichannel teletypewriter operation will be found in paragraph 310.
(2) Single-tone Modulation. In multichannel radio teletypewriter operation using the single-tone modulation method, the carrier omitted by the radio telephone transmitter may be modulated simultaneously by a number of audible tones, one for each teletypewriter channel. In each channel, the tone is usually sent when the teletypewriter sends a marking signal and in this case no tone is sent for spacing. The teletypewriter connecting circuits are fundamentally the same as for singlechannel single-tone modulation operation.
(3) Two-tone Modulation. In the case of 2-tone modulation multichannel operation, each channel is arranged fundamentally in the same manner as for 2-tone modulation singlechannel operation. The teletypewriter connecting circuits are basically of the same design as for single-channel 2-tone modulation operation.
309. TRANSMISSION COMPARISON OF SINGLECHANNEL TELETYPEWRITER METHODS OF OPERATION.
a. Relative Transmitter Power Required for Morse, Teletypewriter, and Voice. Various types of radio transmitters and receivers and methods of operation have different effectiveness in overcoming electrical interference or noise.
Relative transmitter
Method of operation carr ier power required
Manual Morse, c-w................................. 1
Automatic Morse, c-w..............................io
Teletypewriter, c-w...............................20
Teletypewriter, single-tone, a-m..................40
Teletypewriter, 2-tone, a-m.......................io
Teletypewriter, frequency-shift....................5
Voice, full transmitter modulation, a-m...........25
56
PAR.
309
CHAPTER 3. TELEGRAPH SYSTEMS
Therefore, different amounts of transmitter power are required for overcoming a given strength of interference. Some order-of-mag-nitude comparisons of relative power required per channel, based largely on experience, are given in the above table in which it has been assumed that the receiver band-width is roughly the same throughout and that the transmitter is approaching full modulation. In this table manual Morse, automatic Morse, and voice are listed for reference purposes only. Furthermore, the table applies more particularly to ground-wave than to sky-wave transmission ; that is, little or no fading is assumed. These figures are to be considered as general guides only, and do not necessarily apply exactly to any particular case, since much, depends on the design of the transmitter and receiver, the radio frequency used, the band width of the receiver, and the skill of the operating personnel, as well as the nature of the
interference. With c-w manual telegraphy, results depend, to a large extent, on the skill and experience of the receiving operator in copying signals through interference and in adjusting the radio receiver; for example, a particularly good operator may receive signals successfully through 5 to 15 times as much interference as an ordinary operator. The above estimates assume that the operator has fair or moderate skill. It is assumed that in teletypewriter service comparatively few errors are permissible and that in automatic Morse-code operation an easily legible tape record is required.
b. Relative Transmitter Power Required, Further Comparisons for Teletypewriter Operation. Figure 3-17 gives some data for various methods of operating single-channel teletypewriter circuits over radio. These are intended to indicate, as a first approximation, the relative transmitter power required for representative
Method of operation H-f or v-h-f radio equipment* Assumed pass band of receiving teletypewriter circuit (cycles) Estimated relative amounts of transmitter power required for satisfactory teletypewriter operation (db)
Ground-wave h-f or v-h-f transmission nondiversity reception b Sky-wave h-f transmission space-diversity reception b
Cw Tg or a-m tp type, with c-w keying of transmitter, and c-w (beat-frequency) oscillator in receiver 1,0008 0° 0°
Single-tone modulation A-m tp type transmitter and receiver 100 + 10 to 0d Do not compare these columns horizontally b not recommended
2,000 + 16 to +6d
F-m tp type transmitter and receiver 100 + 2 to —2 e not recommended
2,000 + 4 to 0e
Two-tone modulation A-m tp type transmitter and receiver 200 < + 6 to —4d — 5 to —15
F-m tp type transmitter and receiver 200 t 0 to —4 o — No data
Frequency shift Tg or a-m h-f tp type, with c-w (beat-frequency) oscillator in receiver 2,0008 —4 -17
0 A-m — amplitude modulation; f-m = frequency modulation; tp = telephone; tg = telegraph; c-w = continuous wave.
b Figures in ground-wave column should not be compared with those in sky-wave column as the data do not indicate the relative efficiencies of ground-wave and sky-wave transmission.
0 The O-db figure is chosen arbitrarily as a reference for comparison with the other methods.
d First figure assumes 30 percent modulation of transmitter; second figure assumes 100 percent.
8First figure assumes 30 percent of full degree of modulation for which transmitter was designed; second figure assumes full modulation.
f Assumes marking and spacing filters each having a pass band of 100 cycles.
8 By closely regulating the oscillator frequency in the radio transmitter and receiver these pass-band widths may be reduced with an attendant reduction in transmitter power.
Figure 3-17. Comparison of various methods of operating single-channel teletypewriter circuits over radio.
57
PAR.
309 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
receiver pass bands under average conditions. It will be noted that the differences are not large with ground-wave transmission, whereas with sky-wave transmission the frequency-shift and 2-tone a-m methods offer a great advantage.
c. Audio Pass-band Widths. As regards the width of audio pass bands of receiving circuits, the single-tone and 2-tone modulation methods have the practical advantage over the other methods in that frequencies of audio signals delivered to the teletypewriter connecting circuits do not vqry appreciably, and narrow band filters may, therefore, be inserted in the receiving teletypewriter circuits to eliminate some of the noise that would otherwise interfere with reception. For 60-word-per-minute teletypewriter service, a filter having a pass band of 100 cycles (6-db point5) may be used with the single-tone modulation method; and for 2-tone modulation two 100-cycle filters will permit satisfactory operation. With the c-w and frequency-shift methods, where frequency drift of transmitter and receiver oscillators becomes a factor, such narrow filters cannot ordinarily be used. The width of the pass band of the receiving circuit with the c-w method may be as narrow as about 1,000 cycles, and with the frequencyshift method it may be about 2,000 cycles, with the average types of radio sets. A greater degree of protection against noise can be obtained by further narrowing these pass-band widths, if stable oscillators are used in the radio sets or if proper compensation is provided for the frequency drifts of transmitter and receiver oscillators; this may require automatic frequency control or frequent monitoring by skilled operators.
d. Degree of Modulation. In comparing the various methods from the standpoint of their ability to overcome the effects of noise, with the single-tone and 2-tone modulation methods, best results are obtained if the transmitter is fully modulated. Under this condition a larger portion of the total power transmitted is contained in the intelligence-bearing sidebands than when the transmitter is only partially modulated. For example, with only 30 percent amplitude modulation 10 times as much power
5 This a rough measure of the boundaries of a bandpass filter. The 6-db points are the two frequencies at which the loss in the filter is 6 db greater than the minimum loss in the pass band.
is required to maintain the same signal-to-noise ratio as with full modulation. With the c-w and frequency-shift methods, this problem is not present because both are essentially 100-percent modulation schemes.
e. Radio Relay Operation. Where it is desired to transmit beyond the limit of a single radio section with ground-wave transmission, v-h-f radio equipments suitable for speech transmission, such as Radio Sets AN/TRC-1, -3, or -4, may be used to provide operation over several radio sections in tandem. In this case the single-tone modulation method is used. Multisection operation is, of course, more complicated than single-section operation, as radio relay equipment is introduced. The length of each section may also have to be reduced below that for single-section operation, because the noise present in each section contributes to over-all degradation of transmission. H-f radio equipment is not recommended for multisection ground-wave transmission because of the relatively large amount of interference from noise in the h-f range.
f. Ground-wave Transmission. Any of the methods described in paragraph 308a may be used to provide a single-channel teletypewriter circuit over a radio link where groundwave transmission is used. With ground-wave transmission the permissible distance for satisfactory teletypewriter operation with any of the methods will depend on the power transmitted, the radio frequency used, the antennas used, the terrain, and the amount of noise in the radio path. The distance ranges can be estimated from the information in chapter 6, together with the table in paragraph 309a and figure 3-17. Since transmission is on a groundwave basis there should be little or no trouble from fading.
g. Sky-wave Transmission.
(1) General. For distances beyond the ground-wave transmission range, sky-wave transmission may be used with radio sets operating in the h-f range. The permissible distance of transmission will depend on the power transmitted, the radio frequency used, the types and directivity of antennas used, and the amount of noise in the radio paths. In addition, the distance will depend largely upon the severity of fading encountered in the sky-wave paths. The frequency-shift, 2-tone modulation, or c-w methods may be used in that order of preference from a transmission standpoint.
58
PARS.
309-310
CHAPTER 3. TELEGRAPH SYSTEMS
The single-tone modulation method is not recommended.
(2) Overcoming the Effects of Fading. Various methods may be used to cope with fading. To overcome the effects of rapid fading prevalent in sky-wave transmission, and particularly of flat fading (uniform over the frequency range of the receiver pass band) of the telegraph channel, a preferred method is to use either frequency-shift or 2-tone modulation transmission in combination with a compensating arrangement such as a wide-range fastacting constant-output current limiter in the receiving circuit. The limiter attenuates high currents and amplifies weak currents so as to practically eliminate amplitude variations and thereby furnish the detectors with signals of a constant amplitude. In either the frequencyshift or 2-tone modulation cases, the limiter may be used effectively because a radio wave is emitted at all times. In the c-w system, it would cause considerable trouble by amplifying the noise energy received during the no-signal or spacing intervals. Either the frequency-shift or 2-tone method of working with a limiter reduces the effects of flat fading and is of some advantage for selective fading (nonuniform over frequency range of the receiver pass band). Furthermore, noise components superimposed on the received signals will cause little interference as long as they are materially less in amplitude than the signals. The- effects of fading (either flat or selective) may be substantially reduced by using space diversity, in which the receiving arrangement consists of two or more antennas spaced a few wavelengths apart, with individual radio receivers and receiving circuits connected to a common receiving relay.
310. TRANSMISSION COMPARISON OF MULTICHANNEL TELETYPEWRITER METHODS OF OPERATION.
a. General.
(1) In multichannel operation, it is expedient to use the tone modulation methods of operation. In the case of ground-wave transmission systems, single-tone modulation is preferable because of its simplicity; for sky-wave transmission, the 2-tone modulation method should be used to combat fading. In the v-h-f range, single-tone can be used on multisection radio circuits.
(2) As regards relative transmitter power required, receiver band width, etc., the
transmission comparisons given in paragraph 309 and figure 3-17 for single-channel operation are generally applicable. However, there is an additional limitation that may materially reduce the ability of a multichannel system to operate satisfactorily. Since several different audio-frequency currents are applied simultaneously to the radio transmitter, it is necessary in a multichannel system to reduce the input level of current delivered by each channel to the transmitter sufficiently to prevent the composite current, made up of currents from all channels, from having peaks that will overload the transmitter. This reduction is a function of the number of channels and the type of equipment used; for example, with four channels it is 6 to 12 db. The resulting signal-to-noise ratio in this case is correspondingly less per channel than it would be with the same system lined up and operated on a singlechannel basis.
(5) In the single-tone modulation case, when all teletypewriter channels are marking, the radio-frequency carrier is modulated by all the channel tones; when all channels are spacing the carrier is unmodulated. Therefore, the degree of modulation varies with signaling on the various channels. This is not true with 2-tone modulation operation. In the case of 2-tone modulation multichannel operation, each channel is arranged fundamentally in the same manner as for 2-tone modulation singlechannel operation.
b. Twin-channel Single-sideband System. A suitable though elaborate arrangement for obtaining multichannel radio teletypewriter operation over long distances makes use of twin-channel single-sideband radio telephone equipment operating in the h-f range. Two radio telephone circuits are normally obtained over such a radio link, one telephone circuit using the spectrum of the lower sideband and the other using the spectrum of the upper sideband. Each sideband, therefore, carries intelligence independently of the other. In addition, a large portion of the radio-frequency carrier is suppressed, which further increases the efficiency of the transmitter from a radio transmission standpoint. Such a telephone channel may be used for multichannel teletypewriter operation. When a telephone channel of a twin-channel single-sideband system is used for multichannel telegraph service, the other telephone channel can be used for
59
PARS.
310-313
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
telephone, multichannel telegraph, or other service; however, some sacrifice in the power per channel will be required. The system is many db better than the single-tone modulation method described in paragraph 308b from the standpoint of transmitter power required for satisfactory teletypewriter operation over long distances. To care for the fading problems prevalent in long distance sky-wave transmission, limiters are provided in the receiving teletypewriter circuits and frequency diversity is used. Frequency diversity rather than space diversity was chosen for this particular system mainly because sufficient radio receivers were not available initially to provide space-diversity reception. From a transmission standpoint, there is apparently little difference between the two schemes as regards their effectiveness in overcoming selective fading.
311. RADIO TELETYPEWRITER ARRANGEMENTS; FIXED PLANT AND TACTICAL.
a. Radio teletypewriter arrangements available for fixed plant installations include:
(1) A single-channel system using spacediversity with frequency-shift transmission and using' Radio Teletype Terminal Equipment AN/FGC-1 at the receiving point. This equipment may be used on circuits up to several thousand miles in length.
(2) A multichannel system using 42B1 carrier telegraph equipment which provides six single-tone modulation wide-band telegraph channels. This equipment, described in paragraph 341b, is generally used with short-haul v-h-f radio circuits.
(
Figure 3-27. Reperforator Transmitter TG-26-A.
eral, they consist of a page-type teletypewriter or reperforator transmitter, a line unit, a rectifier, ground rods, and in some cases, a gasoline-engine-operated generator as a power source. Teletypewriter Set EE-97-A which includes a page-type teletypewriter and Reperforator Teletypewriter Set TC-16, which includes a transmitter-distributor and typing reperforator, are shown in figures 3-28 and 3-29.
(2) Station arrangements using 2-path polar or polarential operation are available as
TELETYPEWRITER TG-7-B——-------------, [— -----CHEST CH-158
CHFRTCM so f______________. ----iSk ------RECTIFIER RA-8?
CHEST CH - DO - F LINE UNIT BE - 77-A
CHEST CH -62-F----------’ , ■ -
CHEST CH-53-A raKB /fyA'SE? POWER UNIT
4|Ja PE-77-1 )
LT^jaKgr' Sr .■ .mt , ■kmbk WHWbjmMf
■ ■ > dr
flflfl^H^H^^^
TL 54869
Figure 3-28. Teletypewriter Set EE-97-A.
71
PARS.
324-325
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
QI
REPERFORATOR /DlHKlKl iMSOOiBi''
TRANSMITTER TG-26-O <-*■ iGBaUnaSSfiKH ~ QrrT,c,_
.i " " QhiMliMtiifcjM Ih I-RECTIFIER RA--8?
j F'LINE UNIT BE - 7 7 - A
CHEST CH-53-A-] fix ■■■
ataffi IPEmM iflta
o?QMBLZzZ?>
V ~ lO ' H--------------33"----*i p^r'// W
WHHHHBv <0^ -
CHEST CH-I5B - / "'jjifflr
TL 54 916
Figure 3-29. Reperforator Teletypewriter Set TC-16.
repeater sets. Repeater Sets TC-18 (terminal, 2-path polar or polarential) and TC-19 (intermediate, polarential) each consist of a repeater with built-in rectifier and ground rods; they do not include a teletypewriter or a power unit.
325. FIXED PLANT TELETYPEWRITER STATION AND SIGNAL CENTER EQUIPMENTS.
a. Model 15 Teletypewriter Set. Teletypewriters used in fixed plant installations are commercial equipment procured to meet Signal Corps requirements. Model 15 teletypewriter when supplied with a metal table and rectifier is known as a model 15 teletypewriter set (fig. 3-30). This is a sending and receiving page-type teletypewriter equipped with a line relay and a governed series motor. Either communications or weather keyboard teletypewriters may be obtained. The table is equipped with a combination terminal and jack box for making external connections and for connecting the teletypewriter cords. Rectifiers may be obtained for various voltages and frequencies. Since the teletypewriter is supplied with a line relay, it may be connected to a neutral loop or extension circuit without the use of a line unit or a telegraph repeater. The tactical Teletypewriter TG-7-A or -B, in combination with a line unit, may be used in extension circuits in place of a model 15 teletypewriter equipped with a line relay.
b. Model 19 Teletypewriter Set. Where tape transmission is required, a model 19 teletype-
f—MODEL 15 TELETYPEWRITER
IB 1
i send pec
■■ REC 1 HER
T SrEEt- TABLE
TL 53237
Figure 3-30. Model 15 teletypewriter set.
72
PAR.
325
CHAPTER 3. TELEGRAPH SYSTEMS
writer set (fig. 3-31) is often used. The set consists of a page teletypewriter, the keyboard of which may be used to send to the line or to perforate the tape, a transmitter-distributor for tape sending, and a rectifier for furnishing
y—SENDING AND
/ RECEIVING
/ teletypewriter
PERFORATOR-, --------T~
TRANSMITTER ■ /Wt .. +
DISTRIBUTOR- JP’* ' "! - “ ,T?
TABLE • <. 'Si -I-
Wr'
TL53238
Figure 3-31. Model 19 teletypewriter set.
de for local circuits. The teletypewriter supplied with a model 19 teletypewriter set is equipped with a line relay. The motor in the teletypewriter and the motor in the transmitter-distributor is a governed series motor. The teletypewriter is supplied with either a communication or a weather keyboard.
c. Signal Corps Nomenclature for Model 15 and Model 19 Teletypewriter Sets. Joint Army-Navy nomenclatures for models 15 and 19 teletypewriter sets which have been assigned recently are given in the following table. Sets
Joint Army-Navy Commercial description,
nomenclature Teletype Corporation
Teletypewriter TT-5/FG Code 2.18A-1
(communications keyboard)....... (model 15 printer set)
Teletypewriter TT-6/FG Code 2.16A-1
(weather keyboard)................ (model 15 printer set)
Teletypewriter TT-7/FG Code 4.15A-1
(communications keyboard)....... (model 19 printer set)
Teletypewriter TT-8/FG Code 4.13A-1
(weather keyboard)................ (model 19 printer set)
furnished according to these nomenclatures include tables and rectifiers in addition to the teletypewriter equipments.
d. 132A2 Teletypewriter Set.
(1) This equipment, for use especially on radio teletype circuits, includes a typing reperforator (without keyboard) and a transmitter-distributor, mounted on the top of a cabinet-type table. The exterior appearance of this equipment is similar to that of the 133A2 set shown in figure 3-32. A synchronizing circuit, a power supply rectifier, miscellaneous control apparatus, and a tape storage bin are located inside of this cabinet. The typing reperforator records the incoming message on a tape in the form of perforations and printed characters. The outgoing message, in the form of perforated tape, is sent from the transmitter-distributor.
f—TRANSMITTER-DISTRIBUTOR ---------------------TAPE splicer
—NUMBER TAB
si TAPING
Mtox- SR v '
■siEih i Hl
. V j .
26 Wr TL 54934
Figure 3-32. 133A2 teletypewriter set.
(2) The synchronizing circuit keeps the typing reperforator in synchronism with automatic signals received from the distant sending station in case a start or stop pulse,
73
PAR.
325
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
133 A2 SET
MON. —o']
LOCK-UP <_r——oj————————
TYPING REPEATER
REPER- ______________
FORATOR •<— -4--POLAR
TRANS. REPEATER
DI ST. -------------------------------------
—► POLAR----►
^>>1
SEND SEND & REC MON
RADIO RECEIVER MONITOR CONTROL
RADIO RECEIVER CONTROL
(USED ONLY WHEN ARRANGED FOR MONITOR SIMPLEX)
LINE FROM RADIO RECEIVER
LINE TO RADIO TRANSMITTER
RADIO TRANSMITTER CONTROL
TL 53248-S
ON
Figure 3-33. 133A2 teletypewriter set connected to a radio circuit, simplex or duplex operation.
or even several characters are lost because of interference or fading on the radio channel. A key is provided for cutting out the synchronizing circuit when radio transmission conditions do not require its use, or when the set is used on wire circuits.
(3) A tape splicer may be mounted on top of the typing reperforator and a numbertab dispenser may be located on the side of the typing reperforator beneath the tape splicer. These are designated in figure 3-32. The tape splicer is used to join message tapes so that continuous transmission of a number of teletypewriter messages may take place. The splicer is also used to splice message-identifying numbers in the message tapes. The numbertab dispenser contains these message-identifying numbers in the form of a roll of perforated tape with consecutive numbers preceded by and followed by a number of “letters” characters. The letters characters provide space on the tape for tearing and splicing.
e. 133A2 Teletypewriter Set.
(I) This set, used on radio or wire circuits, includes a typing reperforator (without keyboard) and a transmitter-distributor, mounted on a cabinet-type table as shown in figure 3-32. These units perform the same functions as the typing reperforator and transmitter-distributor of the 132A2 set described in subparagraph d above. The 133A2 set contains two polar-relay repeaters, a power supply rectifier, and two control keys. These control
keys are used with the single-channel radio teletype system using Radio Teletype Terminal Equipment AN/FGC-1 as the receiving teletype terminal. The synchronizing circuit supplied in the 132A2 set is not furnished in the 133A2 set and therefore greater stability of the radio circuit is required. The tape splicer and number-tab dispenser may be used in the same manner as described for the 132A2 set.
(2) A diagram of the 133A2 set connected to a radio circuit is shown in figure 3-33. The repeaters provide polar transmission to and from the radio transmitter and radio receiver, respectively. The control features permit turning the radio transmitter on and off, monitoring when transmission is taking place on a simplex basis, and arranging the Radio Teletype Terminal AN/FGC-1 sc that noise and interference will not cause extraneous operations of the typing reperforator when the distant radio transmitter is off-the-air.
(3) A diagram of two 133A2 sets operating over a wire circuit is shown in figure 3-34. One of the 133A2 sets might be replaced by a 133A1 set (subpar, f below) or a Teletypewriter Set AN/TGC-1 (subpar, h below) or similar equipment, with or without intervening line transmission equipment.
f. 133A1 Teletypewriter Set. Like the 132A2 and the 133A2 sets, the 133A1 set includes a typing reperforator and transmitter-distributor for receiving and sending messages in perforated tape form and has the same general appearance as the 133A2 set shown in figure 3-32.
74
PAR.
325
CHAPTER 3. TELEGRAPH SYSTEMS
_________SET__________________
TLP'N° RtPEATE* REPEATER
REFER- _____ * ___ _________________ TRANS.
FORATOR ------- ------------------ * ---- DI ST.
TRANS. REPEATER REPEATER TYPING
DI ST. —— * —------------------------------ ----------------- # ----- REPER-
--------► —► FORATOR
__________ * IF NEUTRAL TRANSMISSION IS --------- USED, REPEATERS MAY BE -
- OMITTED. TL53249-S
Figure 3-34. 133A2 teletypewriter sets connected to a wire line, duplex operation.
The set contains one repeater unit, for sending or receiving polar signals. By the use of a second repeater unit, it may be arranged both to send and to receive on a polar basis. A common use of the 133A1 set is in local circuits (called room circuits), but it may be used with certain limitations in connection with wire or radio circuits. The radio receiver and transmitter control features of the 133A2 set are not provided. A tape splicer and numbertab dispenser may be used if required.
g. XD91 Transmitter-distributor (Two-channel Start-stop).
(1) The traffic capacity of circuits operating either simplex or duplex may be doubled under favorable conditions by the use of a 2-
DlSTRlBuTOR face
transmitter A-k
transmitter a SEND-STOP LEVER-x.
transmitter
motor switch
tl 5324b
Figure 3-35. XD91 transmitter-distributor.
transmitter b 5END-STOP LEVER -
transfer RELAY
BEHIND COVER
Single-double, channel transfer lever
channel XD91 transmitter-distributor (fig. 3-35) to send to the radio channel. This requires that the channel be capable of transmitting 46-cycle signals, which may be done on systems having sufficient band width, such as those using Radio Teletype Terminal Equip
ment AN/FGC—1. Any d-c or extension circuits which may be involved must also be capable of transmitting 46-cycle signals. This method of operation is called diplex. In diplex operation the normal start and stop pulses are transmitted, but each of the five selecting pulses is divided in half. The first half of each of the five normal pulses carries the intelligence of one channel (Transmitter B, fig. 3-35), while the second half carries the intelligence of the other channel (Transmitter A, fig. 3-35). A second typing reperforator, connected in series with the typing reperforator of the 132A2 set or the 133A2 set, is used to receive the second channel. The two typing reperforators are kept in synchronism by the start and stop pulses. One typing reperforator is oriented to receive the first half-pulses while the other is oriented to receive the second half-pulses. The traffic capacity in doubled, for example, from a nominal 60 words per minute to 120 words per minute for simplex operation. The capacity is 120 words per minute in each direction or 240 words per minute in the two directions combined on a duplex basis.
(2) The 2-channel transmitter-distributor is substituted for a single-channel transmitter-distributor on the 132A2 set, the 133A1 set, or the 133A2 set. Two tapes may be sent from the unit simultaneously, and either tape may be started and stopped independently of the other. Since the same start and stop pulses are used, the synchronizing unit of the 132A2 set is effective on each channel. When the traffic is light, or if the radio channel temporarily deteriorates so that it will not transmit 120 words per minute, the transmitter-distributor may be switched to single-channel opera
75
PAR.
325
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
tion, in which case it sends 60-word-per-minute signals. The second typing reperforator is then shut down.
h. Teletypewriter Set AN/TGC—1.
(1) This equipment, known as a semiautomatic packaged unit, is for use in signal centers where a number of teletypewriter lines terminate. It provides a means for receiving messages from any line on perforated tape with typing, and permits tearing the tape into message tapes for manual insertion in transmitter-distributors for sending to other lines, as may be required. Teletypewriter Set AN/TGC-1 is supplied in a console-type cabinet 65 inches high and 24 inches wide, and includes a multiple transmitter-distributor (two message transmitters and one number transmitter, subparagraph (2) below) driven by a common motor and two typing reperforators without keyboards. It also includes a motor-driven tape winder, a rectifier, and tape feed-out arrangement, together with the necessary controls and alarms. This unit (fig. 3-36) may be used to terminate two separate circuits which may be operated either single or duplex. Duplex operation may be either neutral or polar. Typical line circuit connections for Teletypewriter Set AN/TGC-1 are shown at A and B in figure 3-37. At A the set is shown operating duplex on one line, and at B operating on two lines, one single and one duplex.
BGTAPE holder
■number sheet
-CONSOLE
"B” TRANSMITTER
Multiple transmitter Distributor
Figure 3-36. Teletypewriter Set AN/TGC-1.
(2) When the unit is used for terminating one circuit, one typing reperforator is used for recording the received message and the other for monitoring on the sending side of the circuit to provide a copy of the transmitted message. With this circuit arrangement both message transmitters are used and the message numbers are inserted automatically and trans-
DUPLEX
SINGLE DUPLEX
LINE I
tt
A
,____________, TYPING
REPERFORATOR WINDER
(MONITOR) z
TYPING /
REPERFORATOR ---------1--)
.__| I MULTIPLE
"N0’ A" "B" *-----------TRANS-DIST
TAPE TRANS TRANS TRANS COMMON MOTOR
DRIVE
NUMBER TAPE------' •---MESSAGE TAPES
LINE LINE
o >
< u g d
o y u 8
I,./ B
REy SEND --------------
------- li TYPING REPERFORATOR
TYPING
REPERFORATOR U—- 1— MESSAGE TAPE
s/
MESSAGE-/ "NO" "A" "B" ___TRANS*-DIST
TAPE TRANS TRANS TRANS COMMON MOTOR
p. DRIVE
REEL ( TAB NUMBERS
NUMBER TAPE—L—MESSAGE TAPES
TL 54954
Figure 3-37. Teletypewriter Set AN/TGC-1, typical line circuit connections.
76
PARS.
325-327
CHAPTER 3. TELEGRAPH SYSTEMS
RADIO RECEIVING • STATION 1 • orr „„ , SIGNAL CENTER
CHAN CHAN DIVER5ITY i
A B RECEIVER ’ I32A2 SET I33AI SET
|af |af i t7o7m7 1 model is
1 I I TYPING _ . TRANSMITTER . _ _ _ tfi ftvpfu/ditfr
I 'REPERFORATOR^- ’*■*’ DISTRIBUTOR f r TELETYPEWRITER
CHAN CHAN --------------D~c I » . CARRIED ----------------
A B I a BY
d.Lth ctLc *rro.. ’ ! _ ["TRANSMITTER-! , -T TYPING 1_________________________- MODEL 15 OR 19
RADIOTELETYPE TERMINAL I DISTRIBUTOR ?“ X REPERFORATOR * TELETYPEWRITER
AN/FGC-1 | ।-------------1 I-------------1 SET
___________________________l n X-b6IObA RER AND CONTROL _D’C UNIT ________________
RADIO < \ TRANSMITTING \ / STATION
1—1 r~rv7.-r.ro 1 * MAY BE S INGLE - CH ANN E L OR TWO-CHANNEL
TOAMc.T-rro UMIT । TRANSMITTER DISTRIBUTOR(>D9I). IN LATTER
lHANSMiTTtH - UNII ------j-J CASE SECOND TYPING REPERFORATOR MOUNTED
______________ —— I ON SEPARATE TABLE IS CONNECTED IN SERIES | WITH TYPING REPERFORATOR OF I32A2 SET.
I TL53249
Figure 3-38. Elements of a single-channel radio teletype terminal and signal center.
mitted by the number transmitter. When both message transmitters are used on one circuit, they are arranged for tandem operation whereby a tape inserted in the idle transmitter will be automatically numbered and sent when the working transmitter becomes idle. The numbers sent from the number transmitter are prepared as perforations in a tape and stored on a number-tape reel, the capacity of which is about 750 numbers.
(3) When used for terminating two circuits, a typing reperforator is assigned to each circuit. The number transmitter may be associated with one of the message transmitters, and short lengths of perforated tape with tab numbers are sent from the other message transmitter. These numbers are stored on the tab-number reel.
(4) The transmitter-distributor and reperforators operate at 60 words per minute.
326. SIGNAL CENTER TELETYPEWRITER EQUIPMENT USED WITH RADIO TELETYPE TERMINAL EQUIPMENT AN/FGC-L
a. Teletypewriter Equipment. Reception at the signal center may take place on the typing reperforator of a 132A2 teletypewriter set (par. 325d) or on the typing reperforator of a 133A2 teletypewriter set (par. 325e). Transmission may be from a single-channel transmitter-distributor normally supplied with these sets or from an XD91 transmitter-distributor (2-channel start-stop) described in par. 325g. The elements of a single-channel
radio teletype terminal (AN/FGC-4) and associated signal center are shown in figure 3-38. TM 11-2207 covers a radio teletype signal center.
b. Circuits between Radio Stations and Signal Center. The circuits from the radio receiving and radio transmitting stations to the signal center operate on a d-c basis. Normally a metallic circuit is used between the radio receiving station and the signal center, although a metallic or ground return circuit may be used between the signal center and the radio transmitting station. The allowable length of circuit varies greatly, depending on the type of line facility used. Reasonable maximum distances for single-channel (23-cycle signals) ground return operation are 15 miles of cable or 100 miles of open wire with average groundpotential and ground-resistance conditions. For single-channel metallic operation, these distances might be doubled providing the line resistances do not exceed 4,150 ohms (sending) or 3,700 ohms (receiving). In the case of diplex operation (par. 325g), these distances will have to be reduced in most cases for satisfactory operation because of the use of 46-cycle signals.
327. TELETYPEWRITER LINE UNITS AND D-C TELEGRAPH REPEATERS.
a. General Comparison.
(1) In tactical teletypewriter systems, either a line unit or a d-c telegraph repeater (terminal or intermediate) should be used be-
656935 O—45------7
PAR.
327
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
tween the line and the teletypewriter sending and receiving equipment. Jacks are provided on line units and d-c repeaters for the send and receive cords of the teletypewriter equipment which is generally placed close by. The personnel in the station or signal center maintain the service adjustments, required for line circuit operation by means of the external controls on the line unit or d-c telegraph repeaters. Line units provide neutral line transmission and d-c telegraph repeaters provide polarential or two-path polar line transmission.
(2) In fixed plant teletypewriter systems the station teletypewriter equipment usually contains a receiving relay in the teletypewriter, in which case no line unit or d-c repeater is required at the station. Transmission to and from the station is usually on a neutral basis. The station personnel make no line circuit or extension circuit adjustments, since they are made by the maintenance personnel at the repeater equipment located at the central office (sec. V).
(3) A line unit contains a line relay which receives signals from the line and operates the receiving selector magnet of the teletypewriter in a local circuit. The sending contacts of the teletypewriter, when connected to a line unit, open and close the line circuit directly for sending. The line relay in the line unit responds to these outgoing signals and operates the receiving magnet to provide a local copy in the same manner as it operates the receiving magnet on incoming line signals.
(4) In the tactical d-c telegraph repeater the receiving relay operates the receiving selector magnet on incoming signals but it does not respond to outgoing signals. The sending contacts of the teletypewriter operate sending relays in the repeater, and the contacts of these relays send signals to the line circuit. Arrangements are made to provide a local copy of the sent signals.
b. Line Units BE-77, BE-77-A, and BE-77-B. Line units are used generally to connect Teletypewriter TG-7-A or -B or the typing reperforator of Reperforator Transmitter TG-26-A to a neutral line transmission circuit or a neutral extension circuit. All line units contain, in addition to the line relay, a rheostat for adjusting and a meter for measuring the line current. Line Unit BE-77-A (fig. 3-39) and Line Unit BE-77-B contain, in addition
to these features, a bias measuring circuit for use in adjusting the line relay and a means for measuring the voltage of the power supply. Line Unit BE-77-B is the same as Line Unit BE-77-A except for minor apparatus differences. Line Unit BE-77 does not contain the
r-LINE BINDING POST VOLTS-MA-BIAS KEY-,
TELETYPEWRITER SEW I | FINDING POST
AND REC. JACKS-------1 m »
aMgn —BLOWN FUSE hfg INDICATOR
fuse M ETER
X —LINE
RHEOSTAT
rPOWER
CORD
c r £ I t 1 ( 1 ( (
TL S32I6
Figure 3-39. Line Unit BE-77-A.
bias measuring feature or a means for measuring the voltage of the power supply, these features being obtained by using Bias Meter I-97-A and Voltmeter IS—170 in combination with the line unit. Line units are equipped with jacks for connecting the teletypewriter send cord and receive cord and binding posts for making line and ground connections.
c. Repeater TG—30 (Terminal). This repeater, shown in figure 3-40, is used for making connections from a polarential or 2-path polar line circuit to Teletypewriter TG-7-A or -B, or to a neutral type local circuit, such as that used in Switchboard BD-100, Line Unit BE—77, BE—77—A, or BE—77—B, Telegraph Terminal CF-2-A or -B, Telegraph Terminal CF-6, and Telegraph Terminal TH-l/TCC-1. The polarential or 2-path polar line side may extend to another Repeater TG-30 or similar polarential or 2-path polar termination such as furnished in the carrier telegraph terminals. Repeater TG-30 is commonly used for point-to-point teletypewriter circuits on long field wire lines with or without a Repeater TG-31 (Intermediate) described in subparagraph d below. The 2-path polar line operating feature is intended primarily for operating to British terminal units referred to in section IX. The local sides Of two Repeaters TG-30 may be connected for intermediate
78
PARS.
CHAPTER 3. TELEGRAPH SYSTEMS 327-328
operation and, if required, a teletypewriter may be used in the local circuit for sending and receiving, but the connection between the repeater and teletypewriter should be limited to the length of the teletypewriter cords. The repeater operates on 115- or 230-volts, 50-60-cycle ac, or on a nongrounded source of 115-volts de, such as supplied by a gasoline-engine-driven power unit. A-c power is converted to de by a built-in rectifier. Repeater TG-30 pro-
OPERATING
INSTRUCTIONS—, POCKET FOR
.j, TECHNICAL
MANUALS---
SPARC LAMPS Kit !: '■
AND FUSES---SMI W, W
HANDLES
FOR REMOVING > HK. ■ 3F
EQUIPMENT ' CWmW'?
from carrying xiET ''
CASE —.... .* ' ‘jfffS
'"RC
FA: :; F ; ' 7 \? '
TL 53217
Figure 3-40. Repeater TG-30 (terminal).
vides half-duplex service only. A manual telegraph set utilizing an oscillating circuit with an adjustable tone is built into the equipment, and a telephone headset is supplied. The repeater is supplied complete in a wooden carrying case.
d. Repeater TG—31 (Intermediate). This equipment repeats directly from one line circuit to another and provides a means for connecting a teletypewriter to send simultaneously to both lines and to receive from either line, one at a time. The repeater is arranged for polarential line operation only and it is always a differential sending repeater. It may be used to extend the operating range of certain circuits on which the terminal equipment is arranged for polarential (polar sending) operation. This repeater may be used on an unattended basis with power supplied by dry batteries or storage batteries or other stable power sources.
The battery voltages should be checked every 2 or 3 days. The power source may be 115- or 230-volts, 50-60-cycle ac, 12-volt storage batteries, 115-volt dry-battery, or 115-volt de from a gas-engine power unit. If some other d-c source is used the positive side must not be grounded. The a-c or a 12-volt storage-battery source is converted to the required d-c voltage by a built-in rectifier and a vibrator is included for use when the power source is 12-volts de. This is the only d-c telegraph repeater available for storage-battery and dry-battery operation. A teletypewriter cannot be used with the repeater when the power source is dry batteries or storage batteries. Like Repeater TG-30, Repeater TG-31 is supplied in a wooden carrying case and includes a manual telegraph set.
e. X-63638 Telegraph Repeater. This repeater, which is no longer in production, is arranged for 2-path polar line operation. The local side may be connected to teletypewriter equipment located nearby. One local pair of wires is required for the sending circuit and another pair for the receiving circuit. This equipment was produced in small quantities pending the development of Repeater TG-30. The X-63638 telegraph repeater is arranged for operation only on 115-volt, 50-60-cycle ac. A built-in rectifier converts ac to de. The receiving relay 209FG per D-l63120 may be adjusted without using a polar relay test set, as covered in Western Electric Company instruction book X-63639.
328. TELETYPEWRITER POWEP. AUXILIARIES AND TELETYPEWRITER SUPPLIES.
a. Rectifiers. Selenium dry-disc rectifiers, such as Rectifier RA-37 and Rectifier RA-87, are used as one means of supplying the direct current required for line and local circuits when the primary power supply is alternating current. These rectifiers are components of tactical teletypewriter sets. They are portable and supplied in wooden chests from which they are removed for service. Fixed plant teletypewriter sets also use selenium-disc rectifiers which are electrically similar to the tactical rectifiers but mechanically designed for mounting on teletypewriter tables. The d-c voltage output of the rectifiers may be adjusted to compensate for normal a-c voltage variations; automatic regulation to compensate for short period a-c voltage variations
79
PARS.
328-329
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
is not provided. The rectifiers are available for frequencies of 25 and 50-60 cycles and for a-c input voltages of 115 volts or of 230 volts with provision for a 115-volt, a-c source for teletypewriter motors.
b. Power Units. When no other power source is available, gasoline-engine-driven generator sets may be used at outlying teletypewriter stations and, in some cases, in signal centers to supply power for line and local circuits and for teletypewriter motors. At a station consisting of a line unit or repeater and one teletypewriter, Power Unit PE-77 with a rated output of 250 watts may be used. Power units of a higher rating are available for larger groups of teletypewriters and for use in signal centers. For example, Power Unit PE-75 with a rating of 2,500 watts is a typical unit.
c. Teletypewriter Supplies. All teletypewriter equipments require lubricating oil and lubricating grease for proper operation. The one type of oil and one type of grease which are available (TM 11-487) are obtained through normal supply channels. Page teletypewriters require rolls of paper and inking ribbon. Typing reperforators require rolls of tape and inking ribbon. Keyboard perforators require tape. The chest for Line Unit BE-77, BE-77-A, or BE-77-B may be obtained with a supply of paper and ribbon for use with a teletypewriter. The chest for Line Unit BE-77-A or -B, when furnished with Reperforator Transmitter TG-26-A or TG-27-A, may be obtained with a supply of tape and ribbon. Teletypewriter rolls of paper may be procured for single copies, or with carbon paper for duplicate or triplicate copies.
329. MANUAL TELEGRAPH SETS.
a. Telegraph Sets TG-5-A and TG-5-B are tone telegraph sets of the open-circuit d-c type used for telegraph communication. A few intermediate stations may be used between terminal stations. These sets consist essentially of an electromechanical oscillator also known as an interrupter or howler, a line relay, a telegraph key, and a headset. The oscillator is used only to convert the d-c line signals to an audible tone in the headset. Telegraph Set TG-5-B is shown in figure 3-41. The line relay in Telegraph Set TG-5-A is a 600-ohm relay and about 1.0 to 1.5 milliamperes minimum operating current is required. It has airgap and spring tension adjustments. The line
'1 jA * ■
? J
BATTERY-----------------------------CIRCUIT
B / DIAGRAM
R£LAY~ ----HEADSET
receptacle
BELL —-—BlNDING POSTS ------------------------------* 1N TERR UPT ER
HEADSET PLUG
headset /
RECEIVER—' feBWWF f
’"C g fi'ilBiHlflKi
TL 53220
Figure 3-41. Telegraph Set TG-5-B.
relay in Telegraph Set TG-5-B is a 4,400-ohm relay and requires about 0.2 milliampere minimum operating current. It has spring tension adjustment only. The linfe battery is normally a 22.5-volt dry battery and the local battery for operating the interrupter is normally a 3-volt battery. Two batteries may be used to provide a 45-volt line battery when required. The sets are equipped with a calling-in bell which is disconnected when the headset is plugged in.
b. By the use of an adapter cord, a manual telegraph set may be used as a tone keyer for the transmitter of certain radio sets designed for voice operation. This adapter cord may be used with Radio Sets SCR-508, SCR-510,
[keying I I HEAD | '
i drive i \xxxx
MARK[______! g SPRING -------------
BAT r 1 -A-g-------------- RADIO
rHn ? ! ry^T~RAL— TRANSMITTER
4= { I I «—| RELAY ------------------
1 KEYING ! i
1 HEAD I I I
1-1 NEUTRAL KEYING CIRCUIT
T KEYING 1 XI/
! HEAD I
I DRIVE । |
MARK I J A ____
, f j I A---------------TRANSMITTER
'' ! I . !__________B POLAR ___________________
l A 4+—i RELAY
-4 i——* । □ 1
SPACE KEY'NG |
1 BAT. ] hEAD i
’--------1 POLAR KEYING CIRCUIT
TL 54962
Figure 3-42. Neutral and polar keying circuits, automatic keying head.
80
PARS.
329-330
CHAPTER 3. TELEGRAPH SYSTEMS
Q .. i
I'm' "VKEYING HEAD /
------------PERFORATED—x / r I II-------- \ TAPE Lr- ZZ1--LU
KEYnnivrEAD \ Vk HAND TELEG.-x / ITTTTTTTTTT r-WHEATSTONE
DRIVE \ KEY T Pt'T PT'! T'Pt'T ' PERFORATOR
Figure 3-43. Transmitting table equipment.
SCR-608, SCR-610, or SCR-619. It is furnished with a Plug PL-55 containing a 400-ohm resistor for connecting to the telegraph set and a Plug PL-68 for connecting to the radio set.
330. AUTOMATIC KEYING AND RECORDING EQUIPMENT.
a. Boehme equipment is generally used to automatically transmit and receive International Morse-code telegraph signals primarily on radio. The operating speed is adjustable and it may be operated up to about 400 words per minute. The equipments are arranged on tables at the transmitting and receiving points.
b. At the transmitting point the equivalent of dots and dashes are perforated in tape (fig. 3-6) by the use of a Wheatstone perforator which has a typewriter keyboard. The tape is then run through a keying head mounted on a keying head drive. The keying head, controlled by the perforated tape, sends mark and space signal conditions to the external circuit to the radio transmitter. The basic principles of a neutral keying circuit and a polar keying circuit are illustrated in figure 3-42. Figure 3-43 is a diagram of the principal units used on a transmitting table. Figure 3-44 is a photograph of a Boehme keying head, type 4-E with keying head drive, type 4-D.
TL 53240
Figure 3-44. Boehme keying head, type 4-E with keying head drive, type 4-D.
c. At the receiving point, the principal equipments are a Boehme ink recorder and recorder driving unit, a tape puller with magnetic release attachment, a tape puller with rewind reel attachment, and a tape bridge. Recorder BC-1016, instead of Boehme recording .equipment, is sometimes used for receiving signals. The Boehme recorder driving unit
Y
Z RECORDER
TAPE__________
--------------------------- WITH REWINDER —^"1X1X1—TtfL- ,NK-RECORDER-RADIO
REEL ATTACHMENT RECORDER DRIVING UNIT®’ RECEIVER
aNOT USED FOR WIRE LINE RECEPTION
Figure 3-45. Block diagram of equipment elements at a receiving terminal.
TL-54963
31
PARS.
330-331
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
TA P E - R E E L--Vz+?X\
RECORDER 7/ H \\
DRIVING UNIT—xH-------------n //^
r PULLER WITH ‘ ® ® -7
JER ATTACHMENT \ \ @ ®//
O O O O vz—X
y—TAPE BRIDGE I TAPE PULLER WITH | \ \
/ TYPEWRITER^ MAGNETIC RELEASE
/ .--------------- ATTACHMENT^ \RECORDER
/ Lr----------'ll
fl | | A Vhano H 1
________j Ji h-—' Jilflt/LM JI f~______- -. । i
Figure 3-46. Receiving table equipment. TL 53244-S
FAUCET CONE AND HANDLE—
INK POT—<
r—PEN ARM DUST \
\ AND PEN COVER-j |
\ v~PEN ADJUSTING O
\ \ assembly S'
' ■■f IP
L-'N* hose
SHHBl '■
«r—nELD coiL
'Ik P0T
” 3r Jr 1
*—
OVERFLOW INK ti 5324)
^-RECEPTACLE ilpjc^i
Figure 3-47. Boehme ink recorder, type 4-G.
receives keyed-tone dot and dash signals from a radio receiver or similar source and converts the signals to direct current to operate the ink
recorder. The coil in the ink recorder actuates a fountain-type pen which makes a record on the tape symbolic of dot and dash signals. The elements of a typical arrangement at a receiving terminal are shown in figure 3-45. Receiving table equipment is illustrated in figure 3-46. A photograph of a Boehme ink recorder, type 4-G is shown in figure 3-47.
d. Boehme operating equipment is employed in Radio Set AN/MRC—1 which provides facilities for high-speed automatic International Morse-code c-w transmission and reception in addition to the normal functions of Radio Set SCR-399 (component of AN/MRC-1). Radio Set AN/MRC-1 is housed in two shelters, a transmitting Shelter HO-17 and an operating Shelter HO-17 or HO-27. The transmitting shelter includes the radio transmitter, amplifier, and one receiver. The operating shelter includes three radio receivers and the Boehme equipment. The Boehme equipment consists of a keying head and a hand keying circuit, a Wheatstone tape perforator, a recorder driving unit, an ink recorder and associated tape puller, two tape bridges, and two tape pullers with winding reels. Running spares for each major component of Radio Set AN/MRC-1 are supplied in their respective shelters.
Section V. TELEGRAPH LINE
331. GENERAL.
a. This section pertains to equipments which are generally located at an office at the
TRANSMISSION EQUIPMENT
termination of a line transmission section, such as an open wire line, spiral-four cable, or field wire. Extension circuits may extend
82
PARS.
331-332
CHAPTER 3. TELEGRAPH SYSTEMS
from the offices to signal centers and stations. As explained in paragraph 321, office equipments, like station and signal center equipments, may be used by either tactical or fixed plant organizations. Equipment information on carrier telegraph terminals, d-c telegraph repeaters, telegraph switchboards, and test sets will be found in TM 11-487.
b. Newly assigned joint Army-Navy nomenclature for packaged telegraph line transmission equipment is as follows:
Commercial nomenclature Joint Army-Navy nomenclature
V-f carrier telegraph terminal Carrier Terminal (1-6) X-61822A...................... OA-4/FC
V-f carrier telegraph terminal Carrier Terminal (7-12) X-61822B...................... OA-5/FC
D-c telegraph repeater X-61824A.. . Telegraph Repeater
OA-6/FC
D-c regenerative telegraph Regenerative Repeater
repeater X-66031A................ O A-3 /FC
332. CARRIER TELEGRAPH EQUIPMENT.
a. Telegraph Terminal CF-2-A (Carrier).
(7) Telegraph Terminal CF-2-A is tactical equipment and is contained in two carrying cases which are referred to as bays. Each bay provides channel terminals for two telegraph circuits, and two different bays are required at each terminal for four telegraph circuits. This equipment is supplied by the manufacturer for 2-wire operation only but may be modified in the field for 4-wire operation as covered in TM 11-2001. Telegraph Terminal CF-2-A is used in conjunction with Telephone Terminal CF-l-( ) as discussed in paragraph 306b.
(2) The telephone channel must be reasonably free from interference and rapid changes in net loss. Generally, any channels suitable for telephone may be used, but the telegraph system is usually operated over the No. 3 telephone channel of the spiral-four carrier system (Telephone Terminal CF-1-( )). The No. 2 telephone channel of the spiral-four system provides transmission which is nearly as satisfactory as the No. 3 channel and may be used.
{3) Each extension from a telegraph channel can be used for half- or full-duplex neutral operation, or for 2-path polar or polarential operation. Regulated tube rectifiers operable on 115-volts, or 230-volts, 50-60 cycles
ac and a polar relay test circuit are built into the equipment.
b. Telegraph Terminal CF-2-B (Carrier). Telegraph Terminal CF-2-B, shown in figure 3-48, is practically the electrical equivalent of Telegraph Terminal CF-2-A but the equipment has been reduced in size and weight so that the 4-channel terminal occupies one bay of the same size and about the same weight as one
2-channel bay of Telegraph Terminal CF-2-A and no modification for 4-wire operation is required. Figure 3-49 shows a typical spiral-four terminal with telegraph and telephone equipments including Telegraph Terminal CF-2-B.
SPARE POLAR RELAYS
2 7/.
BINDING posts
POLAR RELAY
TEST TOOLS
SPARE FUSES
LOOP CONTROL panel
SPARE VACUUM TUBES
FILTER AND TEST PANEL
RECEIVER PANEL
Channel frequency
OSCILLATOR PANEL
REGULATED TUBE
RECTIFIER U30V
FUSE PANEL
REGULATED TUBE RECTIFIER - 130V
Figure 3-48. Telegraph Terminal CF-2-B (Carrier).
POLAR RELAY TEST INSTRUCTIONS
SUMMARY OF INSTRUCTIONS
SCREWDRIVER
Tl 53222
c. Telegraph Terminal CF—6 (Carrier). Telegraph Terminal CF-6 contains two circuit terminations and is for use primarily in combination with Telegraph Terminal CF-2-( ) to increase the number of telegraph circuits from 4 to 6 (2-wire operation) or from 8 to 12 (4-wire operation). These extra telegraph circuits are generally called channel 5 and channel 6. Extension circuits are equivalent to those used in Telegraph Terminal CF-2-( ). When Telegraph Terminal CF-6 is used with Telegraph Terminal CF-2-( ), the sending and receiving frequencies range from 425 to
83
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
PAR.
332
84
Z"[ to other repeaters tg-30.
I OR TO LINE UNITS JW
[ BE-77 OR BE-7T-A Kg Kwf
_TO_LINE_£ Ji
TO CABLE ASSEMBLY CC-358-C > — Ab—__ CABLE STUB CC-35B ~ ~ AH ~ :
DISTANT — ..... .—<1 WBBw M'i'i'i’il " ~ ~ ...... mBSs.. JwB OR VIA REPEATERS
■*fj| HHHBS&3* ; * ■ flS9 J * : * : * ; • ■ £ I ro GROUND-', \TG‘3O
.~b ESa
’( JUDmI ojpJi k il
r— storage batteries —, i*« I 1 HViMiMK Mm&He
\I llwt isl Bill IBB.
ViH^pijywiT|i&,_________________________________________________________________________________________
I I W 0 rMib«Mi. Ismwai ■ B ■______■ ff
I /I Krtqll I c_■ h.““ « Y" II I
To CS0WD J r„. ’ '...
SUPPLY jy--—^"SUPPLY T° *-C SUPPLY ---7
SWITCHBOARD ln-0, PINGING EQUIPMENTS TELEPHONE TERMINAL TELEGRAPH TERMINAL MONITOR OPERATORS SWITCHBOARD RECTIFIER
SWITCHBOARD bo-9. ee-,0,-a c F-I - A (CARRl ER) CF-3-B (CARRIER) T ELE TYPEWRITER TG-7-B TELETYPE WR>T ER TG-7-B JShOT r2-«
TL 54S87
Figure 3-49. Typical spiral-four terminal.
CHAPTER 3. TELEGRAPH SYSTEMS
332
FUSE ALM LAMP
LINE COILS
CHANNEL TERM. PANEL
OSCILLATOR
MON TTY PANEL
METER PANEL
JACK FIELD
CHANNEL TERM. PANEL
OSCILLATOR PANEL
CHANNEL TERM
PANEL
OSCILLATOR PANEL
SPARE VAC TUBES 4 REIS ALM REL 4. SPARE FUSES RES SHIELD
FUSE PANEL
REG. TUBE RECT
A-C. POWER DISTRIBUTION OUTLET BOX
ALM. LAMP
CHANNEL TERM PANEL
OSCILLATOR PANEL
CHANNEL TERM. PANEL
CHANNEL TERM PANEL
. TUBE RECT.
OSCILLATOR PANEL
MON TTY PANEL
METER CONN PANEL JACK. FIELD
OSCILLATOR PANEL ALM REL A SPARE FUSES RES SHIELD
FUSE PANEL
TUBE RECT.
TL 53235
Figure 3-50. X-61822A or X-61822B v-f carrier telegraph repeater package.
2,295 cycles and the spacing is 170 cycles. The volume of the equipment is slightly more than one-half that of Telegraph Terminal CF-2-B. Like the Telegraph Terminals CF-2-( ), this equipment is supplied with rectifiers and a relay test circuit.
d. X—61822 Carrier Telegraph Equipment. This equipment was designed as part of the packaged system for fixed plant installations. It provides a maximum of 12 2-way telegraph circuits. The equipment is arranged in 7-foot metal cabinets, and one cabinet contains three telegraph circuit terminals. Six channel terminals, that is, two cabinets, shown in figure 3-50, are the minimum number operable as a unit. Four cabinets are required for a 12-chan-nel telegraph system. This system operates on a 4-wire basis over a type C or type H carrier
telephone system or over small gauge cable circuits with suitable loading. This carrier telegraph terminal is normally connected to channel 2 of the X-61819 type C carrier telephone terminal package. Telegraph equipment may, however, be connected to all three channels of the carrier telephone terminal and thereby provide a total of 36 telegraph circuits by sacrificing all carrier telephone channels. Volume limiters are provided on telephone channels but are not used when the channel is used for telegraph. The same v-f telegraph frequencies are used for both directions of transmission. Rectifiers operating from 115-volts, 50- to 60-cycle power are mounted in the cabinets to furnish direct current. The d-c extensions are arranged for neutral half-duplex and neutral full-duplex, and for 2-path polar and
85
—A-C POWER DISTRIBUTION OUTLET BOX
PARS.
332-333 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
polarential operation. Channels 1 to 6 are furnished in the X—61822A package and channels 7 to 12 in the X-61822B package6.
333. SPEECH-PLUS-DUPLEX SYSTEM USING TELEGRAPH TERMINAL TH-l/TCC-1.
a. A general description of this system including a schematic diagram is in paragraph 307. Figure 3-51 is a photograph of the equipment
BINDING
POSTS—; METER-] r-SEND (-RECEIVE ______________LfiELAY I RELAY
/W
/ - MONITORING
/ .job®1®®*™
/ A "■ MODEM
/ UN,T
k"" ” TL 53240-S
Figure 3-51. Telegraph Terminal TH-l/TCC-1.
b. The telegraph and speech channels derived from the common telephone circuit are entirely independent on the office side of the terminal. The d-c telegraph loop options are neutral half-duplex, neutral full-duplex, polarential, and 2-path polar. Carrier is on for mark and off for space.
c. The telegraph terminal may be stacked with telephone and telegraph packaged equipments. The equipment contains a power supply unit using a selenium-disc rectifier. Running spares are included.
d. The telephone branch of the terminal includes a 1,000- or 500-cycle voice-frequency ringer for ringing over the common circuit. The telephone branch also includes a neon tube limiter circuit designed to prevent interference into the telegraph, caused by peaks of signaling or speech voltages originating in the telephone branch of the system and acting on nonlinear elements, such as amplifiers, in the common branch. The limiter should be included, and voice-frequency ringing used, when the common circuit includes a repeater or other
0 The freauencies used are shown in the telegraph frequency allocation chart in chapter 5.
amplifier or a modulator. In other cases, 20-cycle or d-c signaling may be employed as an option without the limiter.
e. Telegraph Terminal TH-l/TCC-1 is designed to transmit either one of two values of telegraph power: —3 dbm and 4-4 dbm (ch. 12). The values of —3 dbm will always be used except on telephone lines containing no repeater, amplifier, or modulator or where a long connection, equivalent to approximately 7-db attenuation, is used between Telegraph Terminal TH-l/TCC-1 and the telephone or radio terminal.
f. The 1,800-cycle loss between two Tele-* graph Terminals TH-l/TCC-1 ordinarily should not exceed about 25 db. The telegraph receiving terminal has sufficient gain to permit reception of powers as low as —53 dbm at 1,800 cycles (that is, over a loss of 50 to 57 db), but powers as small as this will be usable only if circuit noise and interference from telephone into telegraph are very low.
9- A separate filter, Filter F-2/GG, can be used to bypass the telegraph circuit from one telephone circuit to another without any other telegraph equipment. If this filter is located near a 2-wire intermediate telephone repeater, the impedance irregularity introduced by the filter will tend to restrict the repeater gain obtainable without repeater singing.
h. When Telegraph Terminal TH-l/TCC-1 is applied to a telephone circuit, allowance should be made in the circuit layout for resulting impairment to speech transmission. The suppression of the band of frequencies between 1,500 and 2,000 cycles in the speech branch, impairs intelligibility because of the distortion and loss in volume. Tests have indicated that on circuits of good quality, this suppression is equivalent to increasing the net loss of the telephone branch by about 5 db. Qualitative observations on a long wet Wire W-110-B circuit indicated that the transmission impairment is less for such a circuit. The 1,000-cycle attenuation through each terminal, including the limiter, is about 1.5 db. Hence, the total transmission impairment in ordinary cases is about 1.5 4- 1.5 4- 5 = 8 db for a pair of terminals. When telephone circuits equipped with this apparatus are connected together, the transmission impairment, as compared to that without apparatus, is about 8 db for the first link, plus 3 db for each additional pair of terminals or of Filters F-2/GG.
86
PARS.
333-334
CHAPTER 3. TELEGRAPH SYSTEMS
i. Telegraph Terminal TH-l/TCC-1 can be applied to multichannel radio relay systems using carrier telephone terminals. It cannot be used on radio circuits operating on a push-to-talk basis since it requires that the circuit be capable of simultaneous transmission in both directions. Modification of radio circuits normally push-to-talk, in order to use this terminal, is not recommended. It would involve the use of two radio-frequency assignments, one for each direction of transmission, equipment changes, and new operating procedures to prevent singing, since Telegraph Terminal TH-l/TCC-1 is on a 2-wire basis.
334. D-C TELEGRAPH REPEATERS.
a. General. D-c telegraph repeaters are classified broadly as terminal repeaters, intermediate repeaters, and regenerative repeaters. Terminal repeaters are arranged for connections to a line on one side and to an extension, including teletypewriter equipment, on the other side. Intermediate repeaters are arranged for direct repetition between two line sections, and their use on certain kinds of wire increases the allowable over-all circuit length between terminals. Since regenerative repeaters reform and retime the signals, they extend the over-all allowable circuit lengths of teletypewriter networks by increasing substantially the number of sections operable in tandem. Regenerative repeaters (par. 335) do not increase the length of a line section.
b. Tactical D-c Repeaters. Repeater TG-30 (Terminal) and Repeater TG-31 (Intermediate) are suitable for office installations as well as for stations and signal centers. If desired, these repeaters may be removed from their wood carrying cases and mounted on 19-inch relay racks or the equivalent. Office installations of Repeater TG-30 will generally consist of connecting the local side to a carrier telegraph terminal or to Switchboard BD-100, in order to provide longer circuits than can be obtained with the polarential circuit termination integral in the carrier terminal or the neutral circuit termination in Switchboard BD-100. Such applications require use of Repeater TG-30 at the outlying end of the circuit. Repeaters TG-30 and TG-31 are described in paragraph 327.
c. X-61824 D-c Telegraph Repeater. This repeater is packaged equipment for use in fixed and semifixed plant and lacks the portable fea
tures of tactical d-c repeaters. A photograph of this packaged equipment is shown in figure 3-52. The line side is electrically equivalent to the line side of Repeater TG-30 and hence provides polarential or 2-path polar operation. This equipment is operable over a line circuit to a Repeater TG-30. The extension side is arranged for neutral half-duplex, neutral full-duplex, and 2-path polar operation. The neutral half-duplex and neutral full-duplex terminations are suitable for interconnection with other packaged telegraph equipment, such as the X-61822 v-f carrier telegraph terminal and the X-66031 d-c regenerative telegraph
REP 2
■+ ISO VOLT RECTIFIER
' ALARM LAMP
JACK FIELD
METER AND MONITORING KEY PANEL
REP I
-130 VOLT RECTIFIER
CONVENIENCE OUTLET
FUSES ANO SPARES
MONITORING RELAY SPARE 10 AMP FUSE SPARE RECTIFIER TUBE SPARE POLAR RELAY
PATCH CORD
FUSES
AC DISTRIBUTION OUTLET BOX
TL S3232
Figure 3-52. X-61824A d-c telegraph repeater package.
repeater. Two d-c repeaters are supplied in a 3-foot 6-inch metal cabinet which also contains positive and negative 130-volt d-c regulated rectifiers for operation on 115-volts 50-60-cycles ac. Two repeaters in the metal cabinet comprise the X-61824A d-c telegraph repeater package. The two repeaters in one cabinet, or two repeaters in different cabinets, may be interconnected locally to provide the equivalent of an intermediate repeater, and a teletypewriter, regenerative repeater, or both may be inserted in series in the extension circuits. The line operating range of the X-61824 d-c telegraph repeater is the same as Repeater TG-30, and they may be operated on the same types of conductors.
87
PARS.
335-336
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
335. D-C REGENERATIVE TELEGRAPH REPEATER.
a. X—66031 D-c Regenerative Telegraph Repeater. This equipment is arranged especially for fixed plant use in combination with packaged d-c telegraph repeaters and packaged carrier telegraph terminals. The extension circuits operate neutral, half-duplex, or full-duplex. Two repeaters are supplied in a 3-foot 6-inch metal cabinet which also contains an orientation indicator circuit required for adjusting the regenerator units. The complete cabinet arrangement with the two repeaters is the X-66031A d-c regenerative telegraph re-
FUSE ALARM LAMP—
REPEATER PANEL
REGENERATOR
PANEL------
POWER DISTRIBUTION OUTLET
BOX------------
FUSE PANEL WITH SPARES SPARE POLAR RELAY AND INDICATOR LA
JACK FIELD
Tt B48ID Figure 3-53. X-66031 A. d-c regenerative telegraph repeater package.
peater package. Each repeater in the package contains two regenerator units, and the four regenerator units in a cabinet are driven by a common a-c series-governed motor requiring 115-volts 50- to 60-cycle a-c power. D-c power for the transmission circuits is required; this is generally obtained from the rectifiers in the d-c repeater package. The rectifiers in Repeaters TG-30 and TG-31 are not suitable as
a source of d-c power for the regenerative repeater. Figure 3-53 is a photograph of the equipment package with the front door removed and the cover of the regenerator panel removed in order to show the four regenerator units.
b. Application.
(1) The X-66031 d-c regenerative telegraph repeater is used basically for two different reasons. One is to provide regeneration of teletypewriter signals to increase the number of line sections operable in tandem, and the other is to provide 3-way operation. A 3-way connection involves a branch circuit from a main line circuit, generally at an intermediate office. The branch circuit may be extended to a line-relay-equipped teletypewriter at an outlying office, or a telegraph repeater located in the intermediate office may be connected to the regenerative repeater and the circuit then extended over one or more line sections as required. Two regenerative repeaters are required at a 3-way point to provide regeneration with the branch circuit and the main line circuit. Some typical uses for regenerative repeaters with fixed plant equipment are shown in figure 3-54.
(2) The proper location for regenerative repeaters in different kinds of circuits can be determined by the combined use of telegraph coefficients and line operating ranges.
(5 ) This repeater will operate at 368 opm or 404 opm. At 404 opm the motor speed is increased about 10 percent by adjusting its speed with a No. 104984 tuning fork (marked BRITISH SPEED—404 OPM) (Stock No. 4T104984). The repeater is oriented by use of biased signals obtained from Test Set TS-2/TG which is the major component of the X-66031B d-c regenerative telegraph repeater testing package.
336. USE OF D-C REGENERATIVE TELEGRAPH REPEATERS WITH TACTICAL EQUIPMENT.
a. General. Occasions may arise where it is desirable to interconnect the X-66031 d-c regenerative telegraph repeater with tactical repeaters, tactical carrier equipment, and Switchboard BD-100. The following subparagraphs describe briefly some of the possible arrangements. For illustrative purposes, the west side of the regenerative repeater is shown connected to the tactical equipment (figs. 3-55 to 3-57). The east side of the regenerative
88
PAR.
CHAPTER 3. TELEGRAPH SYSTEMS 336
135 ML 368 0. P M A0 OR ---- ------- -- ------------- ---- -----
404 O.P.M T - REG - T T 1- REG - T-—— 104 MIL. 40%----------------------------------------------SAME AS (A)
COPPER STEEL--- ------- -- ------------- ---- -----
(A)
75 ML 404 O.P.M. ----100 M । 368 O P M. 1___
B .O..LL 1 SA"EA5'wj T T i T —
1 COPPER STEEL ---- ---- ----------------- ------------- ----- ---
legend: C CARRIER Y________________Y CARRIER j==|
c I EGI r T D-C TELEGRAPH
ui—p1 REPEATER
D-C POWER FROM D-C TELEGRAPH ---- REPEATER CABINET V . -Y V-F CARRIER TELEGRAPH
£ CHANNEL TERMINAL
p. CARRIER V EXTENSION EXTENSION REG D-C REGENERATIVE
U ----------- E ----<*—►>—I ----------- T-------------D-C LINE SECTIONS TELEGRAPH REPEATER
C ♦♦ WITH REGENERA- ---------------------
___ TIVE REPEATERS AS REQUIRED. TT LINE RELAY EQUIPPED
r1--h r*-------L1 TELETYPEWRITER
TT REG
---------------- ---- I-------------1 D*c-------------------------------------------------------- F D~C LINE T _„Fr_______________________________________________________CARRIER V _ __ Y CARRIER r-
WEST ^1 I। |^l I EAST LINE WEST c > C LINE EAST ‘
I rLG SEE NOTE | * REG SEE NOTE
T EXTENSION T EXTENSION
LT~J 1 *—T—' ।
I I
D-C LINE D-C LINE
] TT I TT
I I
BRANCH BRANCH
CIRCUIT CIRCUIT
NOTE THIS D-C REGENERATIVE REPEATER IS REQUIRED IF NECESSARY TO PROVIDE REGENERATION ON "LINE WEST", "LINE EAST", AND "BRANCH CIRCUIT" TL53246-S
Figure 3-54. Typical uses for regenerative repeaters. repeater may be arranged for balanced loop ljneT 3 l,LOcAL sf IeZst_ or °Pen aRd close loop operation to meet par-
~|TG-30 jj p west?x-66031 ticular service requirements. Service will be
local pl last | ' on a half-duplex basis except with carrier tele-
J 600 -i3ov +i3ovXTENSION graph terminals which may be arranged for
aXiow ’ either half- or full-duplex service. In prac-
A (___ ______ ___________ tically all cases standard operating practices
ADDITIONAL “I and line-up procedures are used throughout.
resistor [ n e g r e c t po s rect| b. Use with Repeater TG-30. The X-66031
tonReAgTbaTt° neuV i d-c regenerative telegraph repeater may be
topos bat.,or neut. “ used with Repeater TG-30 as shown in figure
3-55. A separate 1,600-ohm resistor connected
Figure 3-55. Repeater TG-30 connected to X-66031 to negative battery is required for connection d-c regenerative telegraph repeater. to the No. 2 LOCAL binding post of each Re-
89
PAR.
336_________________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
peater TG-30. The 1,600-ohm 10-watt fixed a cord circuit repeater as shown in figure 3-58 resistor (Stock No. 3Z6160-15) which is a to regenerate all signals received and retrans-replacement part for Line Units BE—77—A and mitted in a switchboard connection. A cord, -B may be used. An external source of positive for example Cord CC-68 (modified), can be and negative 130-volt battery is required as used to connect the regenerative repeater into described in subparagraph e below. the vacant lower jack of a Switchboard BD-100
_____________________ R connection. Any or all of the four regenerator '\\ Te^t a_units in an X-66031A cabinet may be modified.
HALF Dy1 topos x-66031 (x $ The 1,600-ohm resistor required for connec-fulldxJbat V Rast tion to terminal 5 may be secured as described
cf-26'° extension in subparagraph b above.
TH-l/TCC-1 -I30V+I30V
e. Power Supply for Regenerative Repeaters. ।-------- ----------1 The motor on the regenerator panel requires
4--------- -----------tL about 150 watts at 105- to 125-volts, 50- to 60-
a. L^JLECT20^ i a 0-1—o jackLinWaR
of positive and negative 130-volt telegraph U °; l6o^HI5*rcoRTc7X Snect.on battery is required for the regenerative re- , I I l0w -j- removedPLUG
peater as described in subparagraph e below. fo/VX i । ' ~
Figure 3-56 shows a block diagram of a typical i o-Hy a additional
connection. -----—-------------- resistor.
„ - _ b SWITCHBOARD
regenerator power supply
___ UNIT RECTIFIER. 1 LINE S 1 1 FAST
O---------p . TL54997
a WEST . b _
BD-IOO X-66031 , co rr ,
LEAST - figure 3-58. Ise of a regenerator unit m X-66031 d-c ------------ EAST regenerative telegraph repeater as cord circuit
-I30V +I30V EXTENSION repeater for Switchboard BD-100.
a. 1—--------F . RECTlFiE- FA A3 A
- - CHEST CH-62-F ■ POWER ’JNrT PE-75-D CASE — CS-82-A
TL 53238-S
Figure 3-60. Telegraph Central Office Set TC—3 prepared for operation.
91
PARS.
337-338 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
break signal followed by a bell signal to attract the attention of the station operator.
d. The equipment is mounted in a metal cabinet supplied with an iron framework for protection during transportation. This framework is removed from the board and used as a mounting while the board is in service. Switchboard BD-100 is the major component of Telegraph Central Office Set TC-3 shown in figure 3-60.
338. GROUP OPERATION OF SWITCHBOARDS BD-100.
a. Purpose. In large signal centers, arrangements for group operation of the 10-line Switchboards BD-100 have been used to improve operation and increase the traffic handling capacity of the switchboard. This paragraph describes briefly one of the arrangements devised in the field for a group of five switchboards. Figure 3-61 shows the over-all equipment arrangement.
b. Principal Features.
(1) It is possible to make direct connections between any two of 48 teletypewriter station line circuits. The remaining two line circuits are required to terminate two regular operators’ teletypewriters.
(2) All the circuits can be answered and connected by either of the two regular operators’ teletypewriters. A third operator’s teletypewriter is provided to handle overflow traffic, to line up circuits, and for general maintenance work. For switched connections, the operator at this auxiliary teletypewriter position uses regular patch cords and standard operating procedures.
(3) The five positions of switchboard are mounted adjacent to each other on a plank platform directly above the three operators’ teletypewriters (fig. 3-61).
(4) The patching jacks are made more accessible by interchanging panel positions and lowering the patching jacks on the face
[—16"--
BD-IOO BD-IOO BD-IOO BD-IOO BD-IOO LENGTH OF j BD-tOO
* 3 4 5 PLATFORM 94"
[
J II II II II [
L/T— TX /111 z-r r-x llh X -1 ■ IF 11 11 11~1 CORD AND ’
C 5 I 11 / °1 r 1) L W Li==Pl -I IL . KEY SHELF
1 EE ra /FT ..
1 !■*— I I Ifi"' =£| | I P ~" ^| / / CORDS SHELF
// POSITION POSITION \\ *PL ATFOR^V / / V
/ / I 2 \ \ 2,,PLATFORM II / y 40"
~7 / 1 ~ — \ \= in-ir—l/./ / /
r uptsO i
FRONT VIEW SIDE VIEW
r-----,2”---1
;t—[----------
3- DIMENSIONS ARE APPROXIMATE © © © © © @ © ANS CORDS
b- AUXILIARY TT FOR OVERFLOW OPERATION, „ © © © © @ © © CALL CORDS
MAINTENANCE AND TESTING. 13
C- JACK TERMINATIONS FOR AUXILIARY TT 3. S S S S S S S TYPING_KEYS
GRD
ENLARGED VIEW OF
CORD AND KEY SHELF TL 54941
Figure 3-61. Installation of Switchboards BD-100 arranged for group operation.
92
PAR.
338
CHAPTER 3. TELEGRAPH SYSTEMS
of the switchboard. A rearrangement of the panels is shown in figure 3-62. The local cable is long enough to permit relocating the panels, but it will be necessary to drill and tap the framework.
LINE-RHEOSTAT AND METER PANEL
METER CONTROL PANEL
®®@®®®®®®@ ooooooooooo
MONITORING KEY PANEL
® ® ® ® ® ® ® ® ® ® OQQOOQOOOQ OOOOOOOOQQ
PATCHING JACK PANEL
oj LINE SWITCH AND FUSE PANEL |q I 234 567 69 IO
OOOOOOOO oo
©©©©©©©@(g)(o)(g)© oooooooooooo
TL 54939
Figure 3-62. Front view of Switchboard BD-100, panels rearranged for group operation.
(5) A cord and key shelf is located immediately to the right of each of the two regular operators’ teletypewriters. Each key shelf contains 7 pairs of cords, so that a total of 14 simultaneous connections can be made. An enlarged view of the cord and key shelf is shown as part of figure 3-61. Additional scheduled or overflow connections may be set up with the normal patching cords.
(6) Each pair of cords has an associated 3-position typing key for answering a call, completing a connection, or monitoring a connection. A teletypewriter ground key (TT GRD) is located in each key shelf. This key is operated during the idle periods to prevent the operator’s teletypewriter running open. Figure 3-63 is a schematic of one key of the
cord circuit. Other keys are wired in the same manner. This figure also shows a connection between two station line circuits.
(7) A permanent patch is made from each group of cords to the station line circuit selected as the operator station. This patch is shown in figure 3-63. When the typing key is operated, the operator’s station line is connected electrically as a member of a conference connection.
c. Method of Operation.
(1) To Answer an Incoming Call.
(a) Release TT GRD key.
(b) Operate typing key of next idle cord to ANS (back) position.
(c) Connect ANS (back) cord of the selected pair to the lower line-patching jack of calling station.
(d) Momentarily partially depress the LINE OPEN key to put out the call lamp.
(e) Acknowledge call in the regular manner.
(2) To Complete an Incoming Call.
(a) With typing key in ANS (back) position, insert calling (front) cord in upper line-patching'jack of the called station.
(b) After 2-second interval operate the typing key to the CALL or Monitor (front) position. During the 2-second interval, an open signal is sent to the station to start teletypewriter motor.
(c) Call the station operator in the prescribed manner.
(d) After calling station acknowledges call, leave the connection by restoring key to the normal (upright) position.
(e) Operate the TT GRD key to stop the operator’s teletypewriter running open.
(3) To Call a Station from Operator’s Teletypewriter.
(a) Proceed as in the first three steps of subparagraph (1) above.
(&) Operate cord circuit key to normal for 2 seconds and return it to the CALL position to start the motor of the called station.
(c) Call the station operator in the prescribed manner. Bell signals may be used for this purpose.
(4) To Monitor Connection.
(a) Only one connection can be monitored in each position at a time.
(b) To monitor connection in same position : Release TT GRD key; operate typing key to CALL, or monitor (front) position.
656935 0—45
-8
93
PARS.
338-339
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
_ SWITCHBOARD BD-JOO________________________ CORD C|RCU|T
DISTANT -----------------, H TYPING KEY
STATION r-VW-i W.- I --------
L-ljg* -easTI I ___________________ ______________________________
—.---I -JLv— ——I west
4- y— RELAY |------------
RHEOSTAT 414iL_(||l PATCHING ' f I
u U L___L=L__’ jacks —» L*ll [~* *
~° 4/ } ANS
’ . ANS CORD
--CALL
_CALMNG_STATION LI_NE______________l_—' 6 F T CORD [=(* S—n
, a r—T7~i ...____________________________ । ”*iTn nri
OPERATORS LINE j-Wr-i rWv-4--VA-- । L4-IIJ.J
! PERMANENT u LI LJ | U H. PATCH
-------------------------------------------------—
- _____________Z I OTHER
OPERATORS LINE -----T-0 U-°—HL_______________________ KEYS
L LI"E [-VA-J-VA--
—r----1 ~° aV\----o__ | clLj—“ I « GRDto
4- i—-r—] ± KEY
—gL_£p'HL
CALL CORD____
---- [ 6 FT, CORD
CALLED STAT ION LINE uZF7 i j
SMAY BE TELETYPEWRITER CONNECTED TO A LINE UNIT TL 53245-S
OR A TELETYPEWRITER WITH LINE RELAY, b. COMMON TO POSITION
Figure 3-63. Schematic of Switchboard BD-100 connection with two stations connected by means of cord circuit.
(c) To monitor connection of next position: Release TT GRD key; operate typing key of an idle cord pair to ANS (rear position) ; connect ANS cord (back) to lower line jack of called station. Do not attempt to monitor by using upper line jack of calling station.
(5) To Disconnect on a Connection.
(a) Release TT GRD key.
(6) Operate typing key to CALL or monitor (front) position.
(c) Challenge connection as specified.
(d) Grasp the plugs of both the ANS and CALL cords and pull them from their respective jacks simultaneously.
339. TELEGRAPH SWITCHBOARD SB-6/GG.
A patching board, sometimes called a loop board, differs from a switchboard used for switched service in that no supervisory features are provided and no current is supplied. Telegraph Switchboard SB-6/GG, shown in figure 3-64, is a board of this type. It is normally used for interchanging lines and equipment at signal centers or stations. When the connected equipment is operating on the nor
mally assigned line facilities, no patch cords are up at the board. Patches may be made in some cases to rearrange circuits because of equipment or circuit failures. This switch-
Figure 3-64. Three Telegraph Switchboards SB-6/GG, 12-line installation.
board has a capacity of four lines, each line containing two looping jacks and one set jack. Four miscellaneous jacks are available in each switchboard. As many as four boards may be mounted as a unit to provide up to 16 lines. This board is arranged for wall mounting and
94
PARS.
339-341
CHAPTER 3. TELEGRAPH SYSTEMS
is supplied with two 2-foot patching cords and two dummy wooden plugs. Telegraph Switchboards BD-50, -51, -52, and -53, which are now rated obsolete, are replaced by Telegraph
Switchboard SB-6/GG. In some installations Switchboard SB-6/GG has been furnished as a 63C2 telegraph loop switchboard (Western Electric Company specification).
Section VII. RADIO TELETYPEWRITER SYSTEMS AND CIRCUITS
340. GENERAL.
a. This section describes single-charnel and multichannel fixed plant and tactical radio teletypewriter arrangements. The fixed plant systems are available using standard components. At the time of writing, the tactical arrangements generally involve associating together apparatus units originally designed for other purposes.
b. On account of the growth in military usage of teletypewriters, various arrangements for transmitting teletypewriter signals over single-channel radio circuits have been devised in the field. This section contains a discussion of some factors which should be considered before attempting to devise these arrangements, and describes methods which it is be
lieved will be satisfactory if undertaken where the necessary physical facilities and qualified personnel are available.
341. FIXED PLANT EQUIPMENT USED IN RADIO TELETYPEWRITER SYSTEMS, SINGLE CHANNEL AND MULTICHANNEL.
a. Single-channel Frequency-shift System Using Radio Teletype Terminal Equipment AN/FGC—1.
(1) The AN/FGC-1 is used for singlechannel operation at the receiving end of a teletypewriter system using space-diversity reception and frequency-shift transmission. Operation may 6e over distances from a few hundred to several thousand miles. The circuit arrangement of the complete system is shown schematically in figure 3-65 and a photograph
ANTENNA CHANNEL A
--------------------------—-----------------------------------
—-______ r~ FILTER -------------------------
2I25~ RADIO____INPUT _______ . ---------
RECEIVER 1 FILTER LIMITER —< r DETECTOR
41 -------- ----------- SPACE I III
--------- L- FILTER -------------------------- ----- I LU
CHANNEL A 975 I |
-------------~] M-f ? I ’ ’
AUTOMATIC ^+4 F RADIO
FREQUENCY ----______ TRANSMITTER
ANTENNA CONTROL
CHANNEL B ONTROL —---;_> I L t
U-l RECEIVE” . ryr ___
-------- RELAY EXCITER
I MARK ----------- UNIT
FILTER ______________ 1 0-5/FR
I --------- 212 5* I ____
RADIO INPUT --------- I
RECEIVER 1“ FILTER ----- LIMITER . DETECTOR “
I --------- ----------- SPACE
--------'I *— FILTER ------------ CHANNEL B 2975*---------------------------------------------
RADIOTELETYPE TERMINAL EQUIPMENT AN/FGC-I 1___________
l5Lc2 &en_Qj STATION TELETYPEWRITER EQUIPMENT
TL 54988
Figure 3-65. Single-channel radio teletype system using Radio Teletype Terminal Equipment AN/FGC-1.
95
PAR.
341
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
of the AN/FGC-1 equipment is shown in figure 3-66. When the sending contacts of the teletypewriter at the transmitting station are in the marking position, an unmodulated carrier frequency is radiated by the transmitter;
JACKS --------
RECEIVE RELAY — PANEL
DETECTOR B
DETECTOR A
CURRENT L1MITE
CURRENT LIMITE
rectifier X-6I68O-B
outlet ano heater box
RECTIFIER ---—
K5-5844, LIST 01
ALARM ANO MI'SC EQUIPMENT
AUTOMATIC FREQUENC' CONTROL UNIT MOUN >N THIS POSITION
FUSES
SPARE FUSE MOUNTING AMD -_
TERMINAL strips
TL 53^44
84"
FREQUENCY INDICATOR PANEL
Figure 3-66. Radio Teletype Terminal Equipment AN/FGC-1.
when in the spacing position, this frequency is lowered (850 cycles usually), the amplitude remaining unchanged. Radio receivers for channels A and B provide space-diversity reception. In each channel the receiver converts the signals to two audio frequencies, 2,125 and 2,975 cycles, for marking and spacing respectively. The input filter (1,600 to 3,500 cycles at G-db points7) excludes noise frequencies outside
7 This is a rough measure of the boundaries of a bandpass filter. The 6-db points are the two frequencies at which the loss in the filter is 6 db greater than the minimum loss in the pass band.
the working band and passes both marking and spacing frequencies into a fast-operating wide-range limiter which prevents the currents from exceeding a prescribed maximum value and largely eliminates the effects of amplitude variations (fading) which are normally experienced in long distance h-f radio operation. The marking and spacing frequencies then pass through their respective filters, into a double detector which actuates the receiving relay. The marking filter passes the frequency band from about 1,700 to 2,500 cycles and the spacing filter 2,600 to 3,400 cycles. The outputs of space-diversity channels A and B are combined in the receiving relay on a d-c basis in order to avoid distortion from variable phase differences between the tones of the A and B channels. The radio teletype terminal equipment is located adjacent to the radio receivers.
(2) The two radio receivers have separate antennas located several wavelengths apart so that fading will seldom cause the loss of signals in both simultaneously. This spacediversity feature adds stability to the circuit; interconnection between the detectors for favoring the channel having the better signal-to-noise ratio effects a further increase in stability. It is generally desirable to use rhombic antennas since their directive effect gives additional improvement in signal-to-noise ratio. If it is not practicable to provide space diversity antennas, satisfactory results may be obtained in some cases by using polarization diversity (sec. V of ch. 6).
(3) Operation may be on a simplex or duplex basis. In the first case, the same radio frequency is generally used for transmission in each direction; in the latter case, different transmitting frequencies are required.
(4) Suitable transmitter power and frequency assignment are required. In other than
LOW FREQUENCY OSCILLATOR TUNING-, rTHFPMOMETER
m.xer [
resonam ifc. y• tw.y.W-WWMBS8I voltage.
INDlCATQHI jMMSBjWWr » ADJUSTOR
amplifier feO’. - --
MMEmK J*3 S' leg tor
I''!.-'. - ■ a-c rower
FILAMENT SW,TCM
SWITCH-A !£ SW|7CH
MARK-SPACE mne switch
H------------19-----------
TL 5324 7
Figure 3-67. Exciter Unit 0-5/FR.
96
PAR.
CHAPTER 3. TELEGRAPH SYSTEMS 341
polar regions, some frequency between 2 and 20 megacycles will usually be satisfactory, depending largely upon the time of day. On routes which lie near the magnetic pole, however, a low frequency (in the order of 50 to 200 kilocycles) will be preferable; in this case some modification is required in the receiving radio teletype equipment. Refer to paragraph 326 for station arrangements used with Radio Teletype Terminal Equipment AN/FGC-1.
(5) Exciter Unit 0-5/FR, shown in figure 3-67, may be used to key the radio transmitter on a frequency-shift basis. It may be applied to any h-f radio transmitter, replacing the first oscillator section of the transmitter. The crystals are not supplied as a part of Exciter Unit 0-5/FR. The method of determining the proper crystal frequency for a
8 4’
AMPLIFIER
DETECTOR PANELS
. FREQ. OSC.
CH. FREQ OSC
CH FREQ OSC
ALM. AND MISC.EQPT.
FUSE PANEL
CABLE AND T5. SUPPORT
METER PANEL
JACK STRIPS
SEND. LINE TERM. LINE AMPLIFIER
SEND. CHAN TERM.
MODULATORS
OUTLET AND HEATER BOX
CABINET
IL 54960
Figure 3-68. 42B1 carrier telegraph equipment, sending terminal cabinet No, 1.
CABLE AND T S SUPPORT
MODULATOR PANELS
RECEIVING RELAY UNIT
METER PANEL
jack strips
RECEIVING LINE TERM LINE AMPLIFIER RECEIVING CHANNEL TERM,
AMPLIFIER DETECTORS
RADIO REMOTE CONTROL OSCILLATOR 1785^ ALARM AND MISC. EQPT.
FUSE PANEL
OUTLET AND
HEATER BOX
CABINET
TL S4937
Figure 3-69. 42B1 carrier telegraph equipment, receiving terminal cabinet No. 1.
given transmitter frequency is covered in TM 11-2205.
(6) Automatic frequency control has been provided with some receivers to take care of transmitter and receiver frequency variations. Such control can be detrimental, however, when there is strong interference from an adjacent channel, because the interfering signal takes control.
b. 42B1 Carrier Telegraph Equipment Multichannel Single-tone Modulation. This multichannel carrier telegraph equipment provides six wide-band high-speed telegraph channels which may be used for teletypewriter or automatic Morse operation. The frequency spacing is 340 cycles; the lowest frequency is 425 cycles and the highest 2,125 cycles. Each tele
97
PARS.
341-342________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
graph circuit is limited to one-way service, and a separate and equivalent amount of carrier and radio equipment is therefore required for each direction of transmission. The tones are keyed on and off for teletypewriter or automatic Morse-code operation. A channel of this system may be used as a link in tandem with other facilities, such as long-haul h-f circuit. A sending-terminal cabinet containing three channels is shown in figure 3-68. A receiving-terminal cabinet containing three channels is shown in figure 3-69. A 6-channeI 2-way system requires, at each terminal, two sending-terminal cabinets and two receivingterminal cabinets.
c. Multichannel V-f Carrier Telegraph System on Single-sideband Radio Telephone System.
(1) A multichannel h-f radio telegraph system is available for application to a singlesideband radio telephone system. This telegraph and telephone equipment should be procured as a complete system through Army Communications Service. Such systems are in use for communication between various theater headquarters and continental United States. These furnish as many as six highgrade 2-way 60-word-per-minute teletypewriter circuits on either 5,000-cycle sideband of a radio system. The channels may also be used for automatic Morse-code operation at speeds up to about 75 words per minute.
(2) At the transmitting end of the circuit in this system, each teletypewriter channel is arranged to send four audio-frequency tones. Two of these are sent for marking and the other two for spacing. The two marking tones and similarly the two spacing tones are separated from each other by about 1,000 cycles, thus providing a frequency-diversity feature. Each marking tone and its corresponding spacing tone are separated by 170 cycles. The sum of the frequency bands allotted to each telegraph channel is 4 X 170 = 680 cycles. Multichannel operation is provided in the usual way for carrier telegraph by assigning different frequencies to each channel. All of the carrier telegraph channels combined modulate the radio carrier but only one sideband is transmitted, the other being suppressed. The radio carrier power is transmitted at much reduced strength compared to the sideband power.
(3) At the output of the radio receiver, each teletypewriter channel includes four
band-pass filters to separate the four tones of that channel from those of the other channels, a limiter, additional band filters to separate the marking from the spacing tones, marking and spacing detectors, and a common polar receiving relay. Two marking tones and two spacing tones, each separated from the other by about 1,000 cycles, are normally received in each channel. Because of the frequency separation, the two tones will seldom fade deeply at the same time, and thus selective fading is largely overcome. The limiter action effectively takes care of those cases where both tones are reduced simultaneously (flat fading) since the detector is supplied with a practically constant input. From the standpoint of reception, each channel of this system is equivalent to a frequency-shift system with frequency-diversity.
342. MULTICHANNEL RADIO TELETYPEWRITER ARRANGEMENTS FOR TACTICAL USE.
a. Telegraph Terminal CF-2-( ) may be applied directly (without Telephone Terminal CF-l-( )) to Radio Sets AN/TRC-1, AN/CRC-3, or similar voice-emission type radio sets operating in the v-h-f range. One to eight full-duplex telegraph channels may be obtained, using separate radio frequencies in the two directions of transmission8. The telegraph terminals are connected to the radio sets on a 4-wire basis. To provide 8-channel operation on a 4-wire basis requires at each terminal two Telegraph Terminals CF-2-A or -B. The radio transmitters should be capable of continuous emission and have reasonably flat attenuation characteristics over a range from about 100 cycles below the lowest carrier telegraph frequency used to 100 cycles above the highest. As many as 8 or 10 radio relay sections in tandem can be used with Radio Sets AN/TRC—3 and —4, the individual sections being somewhat shorter than permissible for single-section operation.
b. The input to the radio transmitter should be adjusted to give approximately full modulation with all channels marking. Figure 3-70 gives recommended input levels and approximate input impedance for certain radio trans-mitters on which tests have been made. The
8 Four additional channels may be obtained by adding two Telegraph Terminals CF-6 to Telegraph Terminal CF-2-( ). However, for some radio sets, designed for single speech channel operation, the upper and lower frequency telegraph channels may suffer some transmission impairment.
98
PARS.
342-343
CHAPTER 3. TELEGRAPH SYSTEMS
power figures apply to the operation of a 4-channel telegraph system. For a single-channel system, the power may be increased about 12 db over the recommended power per channel for a 4-channel system. For an 8-channel system the power per channel should be made about 5 db less than in the 4-channel system. Proper adjustment must be made to take account of loss in connecting wires between the telegraph and radio equipment.
Radio set or transmitter Recommended power into radio transmitter a with ^-channel operation (dbm b per telegraph channel) Approximate input impedance (ohms)
AN/TRC-1, -3, and -4 — 14d 600
AN/CRC-30 -21 50
AN/CRC-3A0 -13 50
BC-640 -27 600
TDQ (Navy) -15 600
TDG (Navy) -12 600
8 Microphone jack of-AN/CRC-3 or -3A; line terminals of other transmitters.
b dbm=db referred to one milliwatt.
'Special cooling arrangements required for continuous operation.
d Cable compensator on step 12.
Figure 3-70. Power input to radio transmitters, 4-channel telegraph.
c. For f-m operation, the minimum required carrier field strength at the receiving end for 4-channel telegraph is approximately 5 db higher than the minimum required for a single-channel point-to-point telephone circuit, assuming speech to cause practically full modulation of the radio transmitter; for eight tele^-graph channels, the corresponding value is around 8 db. For a-m operation (ground wave) the corresponding values for four and eight telegraph channels are about 4-11 db and -|-16 db, respectively.
d. Telegraph Terminals CF-2-( ) and CF-6 could be applied to suitable tactical radio sets operating in the h-f range for ground-wave use (negligible fading) and with strong enough received signals to override noise. Arrangements for doing this have not been worked out.
e. Telegraph Terminals • CF-2-( ) and
CF-6 may also be operated using one or more channels of Telephone Terminal CF-l-( ) when the telephone terminal is connected to radio sets capable of 4-channel telephone transmission (sec. II of ch, 6). In such cases, the telegraph levels are limited by Telephone Terminal CF-l-( ) and these levels are not related to the fact that a radio link is involved. The resulting telephone and telegraph circuits may be terminated independently at switchboards.
f. Multichannel systems require that radio carrier be on the air continuously in both directions.
343. SINGLE-CHANNEL RADIO TELETYPEWRITER ARRANGEMENTS FOR TACTICAL USE.
a. General. Situations may arise in the field where single-channel radio teletypewriter circuits and standard radio teletypewriter equipments which are not available could be used to advantage. In these cases, certain sending and receiving radio teletypewriter improvised arrangements may be made by qualified personnel. Ordinarily, the basic equipment for such improvising is the sending and receiving circuits of Telegraph Terminal CF-2-B, and in some cases it may be advantageous to make slight modifications in Radio Teletype Terminal Equipment AN/FGC-1 or the British Mark III 2-Tone equipment. Requirements for different forms of operation, together with a brief description of arrangements which may be made, will be found in paragraphs 344 to 347, inclusive. Arrangements may be made for one-way (simplex) or 2-way (duplex) service. Duplex operation requires a separate radio path and associated equipment, with a different radio frequency for each direction of transmission. A functional diagram of the sending and receiving circuits of one channel in the standard Telegraph Terminal CF-2-B equipment is shown in figure 3-71. Refer to TM 11-355-B for further information on Telegraph Terminal CF-2-B.
b. Impedance Matching and Use of Line Coils. A separate line coil (repeating coil) should be used for each sending and each receiving radio teletypewriter circuit because connections to the radio sets are made on a 4-wire basis. In case a portion of a CF—2—B is arranged for radio and both line coils in the bay are used, the rest of the bay may be used on wire circuits if additional line coils are obtained. This
99
PAR.
343 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
SEND
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NORM SEND
sp TL54978
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I ______|_J ' - r°“ — ’ I to
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OUT ; - f®- — * CIRCUIT
LHo ____________L...J
J2
Figure 3-71. Telegraph Terminal CF-2-B, sending and receiving circuits, functional diagram.
100
PARS.
343-344
CHAPTER 3. TELEGRAPH SYSTEMS
line coil (T4, fig. 3-71) has four balanced windings and an impedance ratio of 600 to 600 ohms. This impedance is probably satisfactory for use with many transmitter input or receiver output circuits; if not, a coil of suitable ratio may be substituted for, or placed in tandem with, the line coil in the CF-2-B.
344. ARRANGEMENTS FOR TACTICAL C-W TELETYPEWRITER OPERATION.
a. Radio Sets.
(1) Amplitude-modulation type radio sets now in use which operate in the h-f range are frequently equipped with arrangements to permit c-w operation on a manual telegraph basis with tone reception (by ear), using a beatfrequency oscillator. This feature is necessary for single-channel c-w teletypewriter operation. Amplitude-modulated type radio sets operating in the v-h-f range are generally not equipped for the c-w method of operation.
(2) The determining factor in the use of c-w transmitters for teletypewriter operation is the speed at which they may be keyed. Radio sets where the on-off carrier condition is manually keyed are generally equipped with relays which are not fast enough to follow teletypewriter operation. Teletypewriter operation at 60 words per minute requires arrangements which are reliable for a signaling speed of at least 23 cycles per second. This keying speed requirement is met by electronic keying arrangements. As a rule, the manual telegraph closed-key circuit condition is made the marking condition for teletypewriter operation.
(3) No standard arrangements are available to interconnect teletypewriter apparatus to radio transmitters and receivers equipped for c-w operation. The requirements which such apparatus must meet in case it is necessary to provide such arrangements are given in subparagraph b below.
b. Requirements.
(1) Since the keying cord may connect to the grid of the oscillator in the transmitter, a short cord similar to the cord used for manual keying is required. A d-c circuit is required between the teletypewriter equipment and the radio set, the teletypewriter circuit being arranged to produce local copy.
{2) The audio output of the receiver must be converted to de to operate the receiving teletypewriter circuit. A circuit will be required at the output of the radio receiver which in
cludes an audio gain control (if not in the radio receiver), an electronic or equivalent rectifying circuit, and a receiving relay (preferably polar) for operating the teletypewriter. It is generally necessary to provide additional audio amplification between the receiver output and rectifying circuit. If the radio receiver is not capable of delivering a fairly constant level of tone, as might be the case if it is not equipped with an automatic volume control circuit, then the teletypewriter receiving circuit should also be provided with a level compensator.
c. Improvised Transmitter Keying Circuit.
(I) A transmitter keying circuit for c-w teletypewriter operation may be provided as indicated in figure 3-72. The contacts of the polar relay duplicate electrically the manual telegraph key which is normally used. The polar relay used requires that the line current be adjusted to 60 milliamperes marking.
(2) If, for security reasons or to save transmitter power, it is required to remove carrier from the air when the circuit is idle, the line from the teletypewriter to the radio transmitter may be opened, in which case the teletypewriter motor power should be turned off. If this is done, the distant receiving teletypewriter will run open. This will result in an increase in room noise at the receiving station, and in addition the receiving teletypewriter may print extraneous characters because of noise on the radio channel, since the spacing condition increases the gain in the level compensator circuit of the CF-2-B receiving circuit.
d. Improvised Receiving Circuit The receiving circuit in each channel of Telegraph Terminal CF-2-B includes a level compensator and the other receiving requirements outlined in subparagraph b (2) above. It may be modified in the following manner to make it suitable for the reception of c-w signals for teletypewriter operation. Referring to figure 3-71, select any one of the channels. Disconnect the wires on terminals 1-2 of detector input transformer Tl and run a pair of wires to the output of the radio receiver from terminals 1-2 of Tl. The receiving circuit will now contain input transformer Tl and associated receiving circuit shown in the upper half of figure 3-71. The input impedance of the transformer Tl is 600 ohms, which is probably satisfactory for proper matching of many
101
Figure 3-72. Radio teletypewriter polar-relay keying
radio receiver output circuits. If not, a coil of suitable ratio may be placed in tandem with it. The receiving filter of the CF-2-B channel selected should in general not be used, since the received signal frequency is apt to drift out of its pass band. Operate the loop switch to a full-duplex position and arrange the d-c loop circuit the same as for reception on a wire circuit. Adjust the output tone of the radio receiver to a fairly high pitch, say, around 1,200 cycles.
345. ARRANGEMENTS FOR TACTICAL SINGLETONE MODULATION OPERATION.
a. Radio Transmitters. With the single-tone modulation method, either a-m or f-m speech transmission radio systems operating in either the h-f or v-h-f range may be used for singlechannel teletypewriter operation at groundwave distance ranges. Certain of the speechtype transmitters are equipped with an audiofrequency oscillator; if the frequency of this oscillator falls within the pass band of the receiving arrangement, it can be used to key the oscillator by the polar-relay sending circuit shown in figure 3-72. In other cases it is necessary to provide a teletypewriter sending circuit that is capable of sending an audible tone to the tone-keying jack circuit of the
TL 54964 circuit.
transmitter when a marking signal is being sent and no audible tone when a spacing signal is being sent. Such an arrangement (subpar, c below) may be obtained by using the sending circuit of one channel in Telegraph Terminal CF-2-B.
b. Radio Receivers. Speech-type radio receivers provide currents in the speech band currents to headphones or a loudspeaker. The requirements for a teletypewriter receiving circuit are the same as for c-w reception described in paragraph 344b(2).In addition, a narrowband filter, whose mid-band frequency is the same as the frequency of the radio transmitter tone oscillator is desirable between the output of the receiver and the input to the amplifier. This filter will reduce the effects of noise on teletypewriter reception. The 1,105-cycle filter (FL5) in a CF-2-B channel will serve this purpose if the transmitted tone is at or close to this frequency.
c. Improvised Single-tone Modulation Sending Circuit. The circuit of Telegraph Terminal CF-2-B, shown in figure 3-71 may be modified to obtain a single-tone modulation sending circuit. Select channel 1 and operate the sending frequency switch and the sending filter switch so as to send 1,105 cycles to the radio trans
102
PARS.
344-315_________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING_____________________
RADIO TRANSMITTER d
/ TT MAGNET
/ KEY ______ CKT. FOR LOCAL COPY
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LOCAL COPY a C-W OPERATION OR, IF EQUIPPED WITH TONE OSCILLATOR OF SUITABLE FREQUENCY, SINGLE TONE MODULATION OPERATION. b SAME TYPE AND LENGTH OF CORD AS USED WITH MANUAL TELEGRAPH KEY.
CWESTERN ELECTRIC COMPANY DESIGNATION.
PARS.
345-346
CHAPTER 3. TELEGRAPH SYSTEMS
mitter for a marking signal9. Disconnect from the channel to be modified, the receiving filter and associated receiving circuit of this channel, and the sending and receiving filters of the other channels. Connect a pair of wires from the input of the radio transmitter to the line terminals of line coil T4 (par. 343b). Arrange the d-c loop circuit for a full-duplex sending loop the same as for wire operation.
d. Improvised Single-tone Modulation Receiving Circuit. Telegraph Terminal CF-2-B (fig. 3-71) may be modified for single-tone receiving in the following manner. Disconnect from the channel to be modified, the sending filter of this channel, and the sending and receiving filters of other channels. For reception at 1,105 cycles, the position of the sending frequency switch and sending filter switch should be coordinated with positions of the equivalent switches at the sending terminal. All of the receiving circuit including transformer T4 may be used. Operate the loop switch to a full-duplex position and arrange the d-c loop circuit the same as for reception on a wire line circuit. If transmission is from a radio transmitter equipped with a tone oscillator which is close to the mid-band frequency of some other CF-2-B channel, the receiving filter used should have the same mid-band frequency. Refer to chapter 5 for the channel frequencies available in the CF-2—B. If the tone oscillator does not fall in any CF-2-B channel, the channel filter may be removed from the circuit, with a resulting signal-to-noise impairment.
346. ARRANGEMENTS FOR TACTICAL 2-TONE MODULATION OPERATION.
a. Radio Sets. The same types of a-m and f-m radio telephone transmitters and receivers used for single-tone modulation operation may be used for single-channel 2-tone modulation teletypewriter operation. In case of groundwave transmission, the added complications required to provide 2-tone modulation suggest its use only for cases where somewhat greater ability to overcome noise is important. Comparative data for single-tone modulation and 2-tone modulation are given in paragraph 309. Where transmission is by sky-waves the 2-tone modulation method may give service where the single-tone modulation method will not, be
9 If other channels in the bay are used on a wire circuit, do not operate these switches without proper coordination of frequencies with distant wire terminal.
cause of the ability of the 2-tone method to overcome the effects of flat fading. The use of either frequency- or space-diversity is highly desirable in order to effectively overcome selective fading. The arrangements described in the following subparagraphs cover the 2-tone modulation method with space-diversity.
b. Keying Transmitter for 2-tone Modulation Operation. Although certain h-f telephone type radio transmitters are equipped with an audiofrequency oscillator, which may be keyed by the equivalent of teletypewriter contacts for single-tone modulation, it is unlikely that this oscillator can be readily modified for 2-tone modulation. To key the transmitter, it will probably be more convenient to provide a teletypewriter sending circuit that is capable of sending one audible tone for marking and another audible tone for spacing. This circuit may be connected to the microphone jack or equivalent circuit of the radio transmitter. For this method, a tone of 1,785 cycles has been chosen for marking and a tone of 1,955 cycles for spacing. These frequencies are used so as to be within the band of the input filter of the Radio Teletype Terminal Equipment AN/FGC-1 used to receive 2-tone signals (subpar. d below).
c. Improvised 2-tone Modulation Sending Circuit. A teletypewriter sending circuit of this type may be provided by a modification of the sending circuit of two channels of Telegraph Terminal CF-2—B. By providing two sending circuits, one for sending a 1,785-cycle frequency and the other a 1,955-cycle frequency, and by associating these circuits with two sending relays, as shown in figure 3-73, the 1,785-cycle frequency (channel 3) will be sent to the radio transmitter for a marking signal and the 1,955-cycle frequency (channel 4) for a spacing signal. These modifications should be made in the following manner. Disconnect from transformer T4 the sending and receiving filters of other channels and the receiving filter and associated receiving circuits of channels 3 and 4. Connect the windings of the sending relay of channel 4 in series with the windings of the sending relay in channel 3 as shown in figure 3-73. This rewired relay is designated S2. The SEND CARR key in channel 4 is redesignated SP on the marking side of the key. No rewiring of the SEND CARR keys is required.
103
PAR.
346
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
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TL 54953
Figure 3-74. Space-diversity reception using two British Apparatus Telegraph Mark III Two-tone.
d. Use of Radio Teletype Terminal Equipment AN/FGC—1 for 2-tone Modulation Reception. Since the 2-tone modulation method is recommended chiefly for sky-wave use, where a limiter in the receiving circuit is needed, a Radio Teletype Terminal Equipment AN/FGC-1 is suggested for receiving, even though it is large and difficult to transport. In order to be able to receive the frequencies available in the sending equipment (subpar, c above), it is necessary to change the marking and spacing filters in the AN/FGC-1. This may be accomplished by substituting filter FL3 used in CF-2-B equipment for the marking (MCH) filter and the FL4 filter used in the CF-2-B for the spacing (SCH) filter. Two FL3 filters and two FL4 filters are required for one AN/FGC-1 equipment. The narrower filters obtained from the CF-2-B will provide improvement in suppressing noise and are practicable with the 2-tone modulation method because of its inherent frequency stability.
e. British Apparatus Telegraph Mark III 2-tone.
(7) British Apparatus Telegraph Mark III Two-tone equipment may be available. This is designed to provide service using the 2-tone modulation method. The Mark III equipment contains both sending and receiving circuits for single-channel teletypewriter operation without space-diversity. The marking fre
quency is set for 1,560-cycle tone and the spacing frequency for 840-cycle tone.
(2) The British Mark III equipment contains the necessary apparatus and circuit elements similar to those of the AN/FGC-1 arrangement (subpar, d above), with the possible exception of the-current limiter. The characteristics of the Mark III limiters are not well known at present and their performance may or may not be as good as those included in the AN/FGC-1 equipment.
(5) To provide space-diversity reception, two Mark III equipments would be required, one connected to each radio receiver; for sending, only one Mark III equipment would be used. The outputs of the two receiving circuits would be combined in a common polar receiving relay, as shown in figure 3-74, for operating the receiving teletypewriter equipment.
347. ARRANGEMENTS FOR TACTICAL FREQUENCY-SHIFT OPERATION.
a. Frequency-shift Keying Methods.
(1) High-frequency radio transmitters may be keyed on a frequency-shift basis, using various alternative schemes. The more important ones are described in this paragraph. All of the schemes of keying transmitters on a frequency-shift basis permit control of the keyer on a d-c basis over a pair of wires extending
105
PAR.
347 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
from the teletypewriter sending equipment, either directly or, through a relay.
(2) The-radio transmitter may be keyed by means of a keyer unit which in effect is substituted for the first oscillator section in the radio transmitter. This keyer unit consists of a crystal controlled oscillator with a frequency which differs from the required radio frequency by about 200 kc, and a stable 200-kc oscillator whose tuned circuit frequency can be shifted by about ±425 cycles. The radio frequency oscillator is modulated by the 200 kc + 425 cycles and 200 kc —425 cycles in response to teletypewriter marking and spacing signals respectively. All modulation products except the sum of the crystal oscillator frequency and of the 200-kc ± 425-cycle oscillator frequency are filtered out, and the remaining radio-frequency signal with minor sidebands is fed into the first amplifier stage of the radio transmitter. Exciter Unit 0-5/FR (par. 341a (5)) is an arrangement of this type.
(5) The frequency of the tuned circuit of some types of r-f crystal oscillators may be varied by adding a capacitor under control of either a diode tube or the contacts of a keying polar relay. The crystal oscillator may be the one normally used in the transmitter. Owing to difficulty in modifying an oscillator not originally designed to include this feature, it is, in most cases, simpler to provide a separate oscillator in an applique frequency-shift keyer rather than use the one in the transmitter. This is especially true if the job is to be done at a depot rather than at the point of manufacturing before the set is shipped. Many types of crystal are unsuitable for such operation; in general it may be said that AT-cut crystals will give best results, BT-cut crystals will be unsatisfactory, and other types may or may not give the desired shift. The proper value of capacitor will have to be determined by test. The amount of shift may be checked by adjusting a receiver with a beat-frequency oscillator to zero beat for the normal crystal frequency, and measuring the frequency of the beat note after shifting, by comparison with tone from a calibrated audio oscillator.
(4) A master oscillator (electronic) rather than a crystal oscillator may be used. It may be more practicable to supply an external oscillator as a part of an applique frequency-shift keyer rather than attempt to modify the one normally supplied in the set. A
frequency-shift keyer is now being developed for application to Radio Transmitter BC-610 (part of Radio Set SCR-399). This frequencyshift keyer will make use of a master oscillator (electronic) whose frequency will be shifted by a diode tube under control of a polar relay. The output of the keyer will be applied to the radio frequency amplifier in Radio Transmitter BC-610 instead of using the crystal oscillator of the set.
b. Receiving Frequency-shift Signals. For receiving frequency shift signals, a-m type radio receivers, operating in the h-f range and equipped with beat frequency oscillators to provide tone reception of telegraph signals transmitted on a c-w basis, may be used. Either one or two receivers and associated antennas and teletypewriter terminating equipments will be required to take care of reception. Where fading is not present, one receiver only with its associated antenna and terminating equipment will suffice; for longer haul reception two sets will be needed with the antennas separated, one from the other, by a few wavelengths.
c. Radio Set AN/MRC-2.
(7) This equipment, as planned for procurement, is described herein for information only.
(2) Radio Set AN/MRC-2 will provide a single-channel radio-teletype system using carrier-frequency shift keying and dual spacediversity reception with a modified Radio Set SCR-399. Service may be on a one-way reversible basis using the same radio frequency for both directions of transmission, or on a halfduplex or full-duplex basis using two radio frequencies, one for each direction of transmission. It is proposed to assemble the components of Radio Set AN/MRC-2 in three Shelters (HO-17 or HO-27). In the description which follows, these shelters will be designated as a transmitting shelter, a receiving shelter, and an operating shelter (signal center). Voice communication between shelters may be provided for by use of Telephones EE-8-( ).
(J-k- 111 II --------LINE SIGNAL CORD AND Plug
'"'’iPRs 1^3a4 dM^F' ^1'—LOCAL test D-C CORD and plug
TL 53319
dlral fL' ''“WINDINGS
4 f’'g Figure 3-78. Test Set TS-2/TG.
« PERMANENT
MAGNET
b- Distortion Test Set TS-383/GG. This set
i contm^t!^ (Teletype Corporation nomenclature DXD4)
“screws 1 i is primarily for maintenance depot use and
locmng^uts—j TL53PI4-S contains, in general, the sending features of
Test Set TS-2/TG but not the 60-milliampere Figure 3-77. Telegraph polar relay D-164816.
with a predetermined percentage of marking E^wopSTORTiON
or spacing end distortion. The percentage of /< —-
bias or end distortion can be changed but is control 4' •; ‘ .
not adjustable by external means. The test jBhfe 4 distortion
signals may be used for checking orientation ,X —-KNOBROL
ranges of teletypewriter receiving selectors or MOTOfi S B-run-stop
for sending over line circuits to distortion ' jgl ™obrol
measuring apparatus or to teletypewriters in
order to check the quality of transmission. The KNOBCTiNG
bias and end distortion is used for checking • —
tolerances of teletypewriter equipment and ~
associated line facilities. The space-bar signals TL 53330
may be used with bias meters for adjusting Figure 3-79. Distortion Test Set TS-383/GG. neutral type relays such as those in line units
and Switchboard BD-100. The test set is sup- local circuit, and in addition it contains a plied with an a-c governed series motor which means for measuring distortion of signals by may be adjusted for use at 368 or 404 opera- use of a stroboscopic device. The set (fig. 3-79) tions per minute. A 60 milliampere test circuit is arranged to use an a-c series-governed
656935 0—45--9
PARS.
349-350
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
motor and includes motor unit and gears. It is fundamentally equivalent to its predecessor, Teletype signal distortion test set DXD1 except that it supplies blank, T, 0, M, V, or letters signals in addition to the test message, R, and Y signals.
c. X-66421A Automatic Telegraph-service Monitoring Set. The automatic telegraph-service monitoring set, shown in figure 3-80 provides a means for continuous monitoring of 60, 75, and 100-word-per-minute or 60-word-per-min-ute double-channel (120 words per minute) teletypewriter circuits. The monitoring set is connected like a teletypewriter in the d-c loop or local circuit of telegraph terminals or repeaters. It observes teletypewriter signals and registers the presence of unit signal elements which have been shortened excessively. If an excessive number of these is registered in a predetermined time, an alarm is sounded, calling in the attendant. By sampling the signals in this way an indication is provided when the transmission has deteriorated to such an extent that service is unsatisfactory or is likely to become so; this is accomplished without requiring continuous monitoring by an attendant. The set is contained in a steel cabinet with full-length doors, front and rear. The dimensions of the cabinet are 2214 x 17 x 42 inches. The weight is approximately 300 pounds. It operates on a 115- or 230-volt, 50- to 60-cycle power supply.
I. I« ■ I
U----------------- 22^-------------------4
| ^-ALARM LAMP j
» • » .1
I I Hl i * .1 fc ’ B IB IS K? '
K\ jg
81 ®. sb r |
I is
• qHB »
| v U V. - * —— -------
"ar' 7 : ?
i, 9
Up.--
e- ■
...... jlw"-''TVS*®5*
POWER RECEPTACLES A-C
POWER SWITCH^ TL 52507-S
Figure 3-80. X-66421A automatic telegraph-service monitoring set.
Section IX. INTEROPERATION OF BRITISH
350. INTEROPERATION OF TELETYPEWRITERS USING 2-PATH POLAR OR CARRIER LINE FACILITIES.
a. American teletypewriters and British teleprinters may be operated on the same circuits. Typical circuits are shown in figure 3-81. The British teleprinter is usually associated with the British Teleprinter Terminal Unit Mark IV. It may operate directly over a 2-path polar line to a distant American 2-path polar terminal equipment or on a 2-path polar basis over an extension to a carrier Telegraph Terminal CF-2-( ), CF-6, X-61822, or TH-l/TCC-1 and thence over a carrier channel to the proper American carrier terminal
AND AMERICAN TELEGRAPH APPARATUS
equipment at a distant point. At this point, the extensions may be as required for the American equipment.
b. At the American carrier telegraph terminal, the line current in the extension circuit is adjusted only in the line sending to the British terminal unit. Line current must also be adjusted in the line which receives from the British equipment. In order to do this, a rheostat and meter should be provided at the British equipment.
c. Certain changes are required to permit interoperation of the teletypewriters. The most important is to speed up the American teletypewriter from its standard speed of 368
110
operations per minute to 404 operations per minute. This is accomplished by the use of a tuning fork (par. 335b (3)) which is a part of Tool Equipment TE-50-A. The standard 10-spot target is retained on the motor governor. Several adjustments, are also changed on the American teletypewriter and some differences in the keyboard exist. For information on these points, refer to TM 11-353, Changes No. 3, Appendix (Added), 27 December 1943.
d. In case it is necessary to connect any stations equipped with British teleprinters into a switching network using, for example, Switchboard BD-100, all teletypewriters must be adjusted for 404 operations per minute (subpar, c above) in order to provide interconnections with all stations in the network.
e. The British Teleprinter 7B(WD) is a portable field unit equipped with a polar receiving selecting magnet and polar sending-contacts. For single wire 2-way operation, it includes an automatic send-receive switch. This switch is in the receive position when all keyboard levers are normal and it operates to the send position when any key is depressed. The teleprinter may be arranged also for neutral operation by attaching a spring to the selector magnet armature to move it to a spacing position. The automatic send-receive switch is not required for neutral operation. The teleprinters are equipped with a timing device which stops the motors if the line remains marking and idle for about 1*4 to 3 minutes.
The motors run on 24-volt storage battery and are started by a short spacing signal.
f. American teletypewriters employ a signaling code 7.42 time units in length, each character consisting of a start and five selecting impulses each 1 unit in length, and a stop impulse 1.42 units in length (6 X 1 + 1.42 = 7.42). British teleprinters use the same length start and selecting impulses but the stop impulse is 1.50 units in length, making the signaling code 7.50 units in length. British equipment operates at 400 operations per minute and therefore the American equipment should operate at 404 operations per minute (400 X 7.50 — 404 X 7.42). The British line signaling frequency is 25 cycles per second.
351. INTEROPERATION OF TELEGRAPH TERMINALS (SPEECH-PLUS-DUPLEX).
' The British Apparatus VF Telegraph S + DX and the American Telegraph Terminal TH-l/TCC-1 use the same frequencies for transmission and may be connected on opposite ends of a line circuit as shown in figure 3-82. The filters and v-f ringer are integral in the American equipment, whereas the equivalent apparatus in the British equipment (models 1C and 1W) is in individual cabinets which are interconnected at the time of installation. A later model (S + DX No. 2) is like the American equipment in this respect. The d-c telegraph extension circuits in Telegraph Terminal TH-l/TCC-1 are identical to
111
PARS.
_______________________CHAPTER 3. TELEGRAPH SYSTEMS_____________________________________350-351
LOCAL
TWO-PATH POLAR
REPEATER: TG-30 NEUTRAL ,___, ______, TWO-PATH POLAR LINE v ®.* 1
ral=j MKiv |----------— »■ — x'*'®24 -H~g
X-6 3638 ---
EXTENSIONS___________ ____________________EXTENSIONS
CARRTER I CARRIER
T-n-T------FTTh-v |---------. TELEGRAPH TELEGRAPH
LgJ--------(MK1V TERMINAL TERMINAL ----f---fTI
CF-2-A CF-2-A 1--1
---I----------1__________ OR OR -- | MKIV p. ______ CF-2.-B —-------- CF-2-B _______iZTZd A I OR CARRIER n R____________'---------1
FB^-------------------------— CF-6* LINE CF°_R6a,
---- 1-----1 OR OR 1--1
I---1______।-----._______ X-61822* X—61822^
| B zq MKIV L— —_ OR „ OR .-------::-- A
th-i/tcc-i th-i/tcc-i ---
TVTOLARH tg extensions neutral
SYMBOLS: polar ^'TWELVE TG EXTENSIONS BA1A2rllT111
A»AMERICAN TELETYPEWRITER c*ONE TG EXTENSION POLARENTIAL
B-BRITISH TELEPRINTER TWO-PATH POi AR
MK.IV-BRITI5H TELEPRINTER TERMINAL UNIT ° ?
Figure 3-81. Interoperation of American and British teletypewriters.
PARS.
351-353
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
BRITISH
AMERICAN
|«-LINE FREQUENCY BAND ----4
TELEPHONE |TELEGRAPH| TELEPHONE
W///////AWA ~JO
1500^ 2000^
RINGER
--------------------- FILTER. ----------------------------------------------““ ~Z ~~
TELEPHONE SIGNALING TELEGRAPH.S+DX UNE TERMINAL TELEPHONE
-------L____l--------l 7^J--------------------------------------------------TH-I/TCC-J I
TELEGRAPH MID-BAND FREQUENCIES z ------- H0/220V
—-1680^ --------- 60 nj A-C
Z1 -—I860 OR |2V. STORAGE
100/240 V ----- z। APPARATUS V.F. g BATTERY
50 C/S A-C =>1 „DADU4 -------------
OR 12V STORAGE---- (X-66147)
42B1 Carrier Telegraph Equipment X-61757
Voice-frequency Carrier Telegraph X-66578
System Single-sideband High Frequency Radio Telegraph Equipment
b. D-c Telegraph Equipment.
Repeater Set TC-18 (Terminal) TM 11-2004
Repeater Set TC-19 (Intermediate) TM 11-2005
D-c Telegraph Repeater (Packaged TM 11-2034
Equipment) (X-66038)
D-c Regenerative Telegraph Repeater TM 11-2032 (Packaged Equipment)
Line Unit BE-77-A and Line Unit TM 11-359 BE-77
Reperforator Transmitters TG-26-A and TG-27-A
Printers TG-7-A, TG-7-B, and TG-37-B, Chests CH-50-A and CH-50-B, Chests CH-62-A, and CH-62-B. (Teletypewriters)
Telegraph Printer Sets (Teletypewriter) EE-97 and EE-98. Teletypewriter Sets EE-97-A, EE-98-A, and EE-102
Installation and Maintenance of Telegraph Printer Equipment
Instructions for Treatment of Teletypewriter Paper Rolls
Interoperation of American and British Teletypewriters in the Field
d. Telegraph Switchboards.
Telegraph Central Office Set TC-3 Operation of Circuits in Switchboard
BD-100
Connection and Line-up Procedure for Switchboard BD-100
Telegraph Switchboard SB-6/GG
c. Teletypewriter Equipment and Sets.
Teletypewriters TT-5/FG and TT—6—/FG (Model 15 Teletypewriter Set)
Teletypewriter TT-7/FG and TT-8/FG Model 19 Teletypewriter Set)
Teletypewriter Set AN/TGC-1
132A2 Teletypewriter set and Associated Equipment
133A1 Teletypewriter Table and Associated Printer Apparatus
133A2 Teletypewriter Set and Associated Equipment
XD91 Two-Channel Start-Stop Transmitter-Distributor
Reperforator Teletypewriter Sets TC-16 and TC-17
TM 11-2215 (Instruction Manual No. 7 or 22)
TM 11-2216 (Instruction Manual No.
10 or 26)
TM 11-2203
TM 11-2210 (X-66154)
TM 11-2211 (X-66152)
TM 11-2214
X-66355
TM 11-2201
TM 11-2220 (Inst. Man. No. 38)
TM 11-352 (Inst. Man. No. 11)
TM 11-354
TM 11-353 with changes
TB SIG 28
TM 11-353 Changes No.
3 Appendix (Added)
TM 11-358
TB 11-358-1
TB SIG 52
TM 11-2035
e. Morse-code Telegraph Sets and Equipment.
Telegraph Sets TG-5, TG-5-A, and TG-5-B
Instructions for use of Telegraph Set TG—5, TG—5—A, TG—5—B as Tone Keyer
Boehme Automatic Keying and Recording Equipment
Radio Set AN/MRC-1
Recorder BC-1016
TM 11-351 with changes TB 11-351-2
TM 11-377
TM 11-602
TM 11-441
f. Radio Teletype and Associated Equipment.
Radio Teletype Terminal Equipment TM 11-356 AN/FGC-1
Exciter Unit 0-5/FR TM 11-2205
Radio Teletype Code Room and Sig- TM 11-2207 • nal center
g. Testing and Monitoring Equipment.
Distortion Test Set (Teletype Corp. Models DXD1 and DXD4)
Test Set I-193-A
Test Set TS-2/TG
Test Set X-61809A
Automatic Telegraph-Service Monitoring Set
Bias Meter I-97-A
Inst. Man. No. 23 (TM 11-2217 when published) TM 11-2513 TM 11-2208
(Inst. Man. No. 43)
X-63631
TM 11-2053
TM 11-2200
113
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Nomenclature Dimensions and weight Power » Tubes D-c extension operation^
Dimensions in use (inches) Weight (pounds) Dimensions in case {inches) Weight in case {pounds)
Apparatus, VF Telegraph, S+SX No. 3 Terminal 8 x 18x 14^ 47 Same 24v de, 1.5 amps. 1-ARP7 3-ARP9 Spares 1-ARP7, 1-ARP9 2-line simplex
Filter composite telegraph 300 or 2,300 cycles 6 x 10 x 6 36 Same
Apparatus, VF Telegraph, S+DX Terminal 15 x 23)^2 x 11M 94 Same 100/240v ac, 30-40 watts 12-v battery, 3 amps. 5-6V6G 2-line simplex
Filter 8 x 20 x 7 34 Same
Apparatus, Terminal, VF Telegraph 3 channel Duplex, Group 1 and Group 2 • 2 boxes each 22 x 23 x 20 120 each Same 24v de, 2J4 amps. 6-VT73 or AR12 6-VT88 or AR13 50% Spares 2-line simplex on each channel
Apparatus, VF Telegraph 6 Channel Duplex 3 bays each 66 x 21 x 16 1,120 total 2,465 total 24v de, 7.5 amps. 1-VT75 or AR11 12-VT73 or AR12 6-VT88 or AR 13 20% spares 2-line simplex on each channel
a A-c power is 50 cycles.
b 2-line simplex similar to American 2-path polar.
Figure 3-83. British ( continued
114
CHAPTER 3. TELEGRAPH SYSTEMS
Max. line loss db No. channels Major components required per terminal Remarks
30 at 1,740 cycles 1 Apparatus VF Telegraph S+SX No. 3, Filter Composite Telegraph 300 cycles, Filter Composite Telegraph 2,300 cycles, Teleprinter 7B (WD), Unit Signaling VF No. 3 with Rectifier No. 7 or No. 2, for voice circuit Line operation on simplex (half-duplex) basis. Uses frequencies above or below speech band. Carrier 300 or 2,300 cycles. Carrier is transmitted for space. Also may use 1,740 cycle carrier by eliminating voice circuit. 2 separate filters supplied for 300 cycle or 2,300 cycle operation. Voice circuit must use 500/20 cycle ringing. Must provide 24v batteries or Rectifier No. 6; plate supply from rotary transformer in S + SX set. Relay 299AN required to permit remote working to Teleprinter Terminal Unit 80 + 80 Volt connected to a teleprinter.
50 at 1,900 cycles 1 Apparatus, VF Telegraph, S+DX, Filter, Composite, Telegraph, S + DX, Teleprinter 7B (WD), Unit Signaling VF No. 3, Supply Unit Rectifier No. 7 or 12 batteries Dry Refill 8 cell No. 2 Line operation on duplex basis. Uses 1,500 to 2,000 cycles band from speech circuit, equivalent 4-wire carrier frequencies 1,680 cycles and 1,860 cycles. Carrier is transmitted for mark. Consists of oscillators, detectors, power unit, spare tubes. Output +7 db, +2 db, —3 db. Voice circuit must use 500/20 cycle signaling. Portable in metal case. Includes vibrator No. 4. 1 working —1 spare. Requires 24v for tt. Includes neon voltage limiter to keep down voice peaks on associated voice circuit. Models 1C and 1W have filter and signaling unit in separate boxes. Model No. 2 will have them combined with the telegraph apparatus and supplied in a single box similar to the American Telegraph Terminal TH-l/TCC-1.
40 at 1,980 cycles 3 or 6 For 3 channels group 2 should be used. Either terminal may be A or B. Group 2 Ch 1 1,980 cycles A-B; Group 1 Ch 4 1,620 cycles A-B; 420 cycles B-A 780 cycles B-A Ch 2 1,860 cycles A-B; Ch 5 1,500 cycles A-B; 540 cycles B-A 900 cycles B-A Ch 3 1,740 cycles A-B; Ch 6 1,380 cycles A-B; 660 cycles B-A 1,020 cycles B-A 2 wire or 4 wire line operation. Includes test transmitter which generates unbiased reversals to line up channels. 4 vibrators No. 2 used plus 4 spare. Must have external power supply for 24v. Built in unit supplies 80 + 80 volts for local extension. Electrically similar to 6 channel systems and will work with it. TT station must be equipped with Teleprinter Terminal Unit 80 + 80 volts. Uses Rectifier No. 6 for A-C operation.
40 at 1,980 cycles 6 Apparatus VF Telegraph Six Channel Duplex, Bays No. 1 and No. 2, Apparatus VF Telegraph Six Channel Duplex, Spare parts case, Apparatus Terminal Carrier Telephone (1+4), Bay No. 3 (Power and Test Bay), Transformer Rotary HT 50 watt No. 1 or No. 2, Teleprinters 7B (WD) Standard commercial equipment. Electrically similar to VF Telegraph 3 Channel Duplex. May use 2 six channel systems 4 wire to get 12 channels. Max. Receiving Gain 26 db. A and B terminal separate. Filament and plate supply from power and test bay served by 24v office supply. Filament 20.5 volts. Plate 150 volts. One power and test bay may serve 2 VF Telegraph or 2 (1 + 4) Carrier Telephone Terminals.
Army telegraph equipment, on following page)
115
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Nomenclature Dimensions and weight Power 8 Tubes D-c extension operation'0
Dimensions in use (inches') Weight (pounds) Dimensions in case (inches) Weight in case (pounds)
Repeater VF Telegraph No. 1 15 x 20 x 73 90 20 x 25 x 15 135 100/240v ac, 12 watts 12-v battery, 1 amp. 2-ARP34 200% spares
Teleprinter Terminal Unit Mark IV 8)4 x 12)4 x 5)4 15 — — 24v de, • 3 amps. — Switched0 simplex, half duplex, or 2-line simplex all with or without local record
Teleprinter Terminal Unit 80 +80 volt 6)4 x 8 x 6)4 8)4 80 +80 volts de, 15 to 20 ma 2-line simplex with or without local record
Supply Unit Rectifier No. 6 16 x 19 x 7 90 — —• 100/240v ac in steps of 10 volts — —
Supply Unit Rectifier No. 7 7)4 x 7)4 x 9)4 12 — — 100/240v ac in 10-volt steps or 12-volt battery — —
Teleprinter 7B (WD) Floor space—-48x30 Over-all height 38 210 including 20 for terminal unit 24x29 x 14 191 24 volts, 2.5 amps. Switched simplex 2-line simplex
a A-c power is 50 cycles.
b 2-line simplex similar to American 2-path polar.
0 American terminology is reversible one-way polar. Teleprinter 7B (WD) has automatic send-receive switching feature.
d Electrically equivalent to Western Electric Company 209 type polar relay.
Figure 3-83. British ( continued
116
CHAPTER 3. TELEGRAPH SYSTEMS
Max. line loss db .Vo. channels Major components required per terminal Tiemarks
Used with 3 or 6-channel systems. Consists of 2 directional filters and 2 amplifiers. Consists of terminal panel, miscellaneous panel, spare parts panel. Rack mounted. Max. gain 26 db from 300 to 2,400 cycles Directional filters separate bands at 1,200 cycles. Equalization for 7% or 15 mi. PCQT cable 40 change by U linkstraps. Output +12 dbm. Max. gain 20 db at 2,400 cycles with full equalization. Uses Vibrator No. 4.
— Simplification of previous units MK III and uses U links instead of keys to set up connections. Uses 299 AN relay d for relayed operation. Teleprinter may operate direct. Requires center tapped 24 volt, 3 ampere d-c supply for telegraph line voltage 12+12 volts. May use higher voltage of suitable battery supplied.
Part of proposed teleprinter network where 80 +80 telegraph voltage supplies are available. Relay operates on 15-20 ma. Contacts supply battery to printer magnet. If direct operation of printer magnet is used one Terminal Unit 80+80 volts used. If relayed operation necessary, then it is arranged that 2 Terminal Units 80+80 volts can be used together. Call key included to call Teleprinter switchboard. Must use Rectifier No. 7 for a-c operation.
— — — Provides 22 to 26 volts for operation of equipment requiring 24 volt battery. Furnishes currents up to 6 amps. Intermittent load of 7.5 amps. Full wave metal rectifier.
— — — Provides 80-0-80 volts at 30 ma.; 12 volts d-c 30 ma. filtered; 40 volts, 17 cycle a-c 30 ma. Westinghouse rectifier with vibrator Mallory type G-65.
Teleprinter 7B (WD), terminal Unit Mark IV or Terminal Unit 80 +80 Volts, 24-Volt Storage Battery This is a Creed machine arranged for portable field use by the Army, It is equipped with polar selecting magnet for receiving and polar transmitting contacts. Can be arranged also for neutral operation. Provided with automatic send-receive switch which is normally in receive position and operates to send position when any key is depressed. Uses 7.5 unit code with a speed of 400 operations per minute equivalent to 66% words per minute which is a line frequency of 25 cycles per second. Timing device stops motor if line is marking and idle for 1 % to 3 minutes. Motor runs on 24-volt storage batterie.
Army telegraph equipment, on following page)
117
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Nomenclature Dimensions and weight Power » Tubes D-c extension operation^
Dimensions in use (inches) Weight (pounds) Dimensions in case {inches) Weight in case {pounds)
Apparatus, Telegraph; Two-Tone Mark III 18 x 12 x 15)4 70 24v de, 3 to 5 amps, (teleprinter and 2-tone unit) 3-6V6 2-6C5 Switched simplex or 2-line simplex with monitoring teleprinter
Teleprinter Switchboard, 15-Line 25 Vi wide 18 high 21 deep 100 24v de, 2 amps, or 80 +80 volts, 20 milliamps. Switched simplex with v-f teleg. six channel duplex v-f s+sx No. 2 and 3, S+DX, terminal unit 80+80, local teleprinter
Teleprinter Switchboard, 40-Line 54 high 30 wide 30 deep 300 — — 24v de, 2 amps, or 80 + 80 volts, 20 milliamps — Same as above
a A-c power is 50 cycles.
b 2-line simplex similar to American 2-path polar.
Figure 3-83. British
118
CHAPTER 3. TELEGRAPH SYSTEMS
Max. line loss db No. channels Major components required per terminal Remarks
Main Items are: Apparatus Telegraph Two-tone, Teleprinter 7B (WD), Radio Sender and Receiver Additional Items for Certain Working are: Monitoring Teleprinter, Remote Control Unit “C”, Teleprinter Terminal Unit MK III or IV Portable equipment to provide teleprinter circuit over a radio link; includes sending and receiving features. Two-tone Apparatus when sending modulates carrier wave with one tone (1,560 c.p.s.) for marking and with another tone (840 c.p.s.) for spacing. Receiving side contains two band pass filters (1,560 c.p.s. and 840 c.p.s.) valve amplifier and rectifier. Modulator input circuit impedance is 600 ohms. When working simplex (radio), the radio transmitter (Wireless Set Nos. 12 or 33) may be controlled by Remote Control Unit C when two-tone unit and radio transmitter not located together. D-c extension may be to local teleprinter or remote teleprinter.
15 lines Operator Teleprinter No. 7B (WD), power Supply Units Rectifier No. 7 or storage batteries (24 volts) portable, or Supply Units Rectifier No. 6. Table mounted type of switchboard with capacity for 15 lines and 7 cord circuits. Simultaneous broadcasting up to six lines is provided for. Interconnects polar circuits operating switched simplex. Space signals used for calling switchboard and for disconnecting; both light line lamps at switchboard. Recall is by flashing. Station teleprinters are called by J Bell or by spacing. Switchboards can be worked together to increase capacity.
40 lines Same as above Floor mounted type of switchboard with capacity for 40 lines and 15 cord circuits. Other features same as 15 line teleprinter switchboard above.
Army telegraph equipment, (continued).
119
— .
; (c) Corrected coord
Collected coordinate
R AIV* AY BATTERY ___________
Reference Map «■*. Sheet
These ra.s L*ay guns are approx I n.at e l y IS CM At (e) the guns are adjacent, with Upp“y «« to rear. No damage to Uns train is A {c) are divided
. /he ckri of which three were
by four supply cars oi m
destroyed by direct bomb hit. No aypeien„ <1atoa«7& to cuus or their carries s»
& Sortie ioWT-Ter 1315 hours _________ . 12 June iyi4i.
..,; LJ 2 Trader Vans dlfJO
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rimor
V r a ■'< AS t 0
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Sc. M * f Tfi*W ^$9
11 .
* CM) '
W' 1 j?.?w
2 Tn K i .
4 k __j f^t f /a^ e I
Q/4- I
—FACSIMILE
SH I ' ■ I transceiver
r-POwER supply iffiK 31 i
J "J
‘OR v'
y ---, X
DEVELOPING s' T ■ j**-, ■. I 0H
TANK -------' LpACK OF IBM
BROMIDE
PAPER '• ' CM
.... * •'*
CONNECTING TELEPHONE
CO ILS-----
TL 53251
Figure 4-2. Facsimile Equipment RC-120 (page).
121
PARS.
401-402
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
minutes. Subject copy of larger size can usually be transmitted with this machine and other page machines by cutting it up into as many separate sheets as are required. It is described in TM 11-375B and TM 11-2252. Facsimile Equipments RC-120-A and RC-120-B include minor improvements in design, but can be used interchangeably with Facsimile Equipment RC-120. Converter CV-2/TX, described in TM 11-2252, may be used with these equipments to change from amplitude to frequency modulation for transmission on radio telephone channels.
(2) Facsimile Equipment RC—58—B. This is a machine (fig. 4-3) sending copy in the form of handprinting on tape at 50 inches per minute. It is described in TM 11—374. Transmitting and receiving amplifier equipment is included in a separate box.
(3) Facsimile Set AN/TXC-1. In general appearance and technical features, this equipment is similar to Facsimile Equipment RC-120. However, the drum and some associated parts are larger. It is used for sending weather maps and other copy up to 12 by 171/2 inches in about 20 minutes and is described in TM 11-375B. Converter CV-2/TX may also be used with this equipment. In view of the difference in picture sizes this equipment can not be used to send to or receive from Facsimile Equipment RC-120.
d. A facsimile network is in operation over a fixed radio system between Washington and the principal foreign theaters. Some notes on this are given in paragraph 402 f.
402. PAGE FACSIMILE.
a. General System. Transmission is carried out by exploring the subject copy, or material
RECORDER
AMPLIFIER -j SCANNER-,
r- WRITING
/ STAND
i ~ ■'■' ...
I «■ * g • *» » L' - i T '
I F '/If 4 *7 at ■ ^Jt*** ■ x
^^*******^
r..-7
I) *’ //
! TO RADIO
Zj/V EQUIPMENT
r< ’ iHHBI<
L.k
v (C( '-*W“ •
COVERS
RECT IFIER -
L-SPARE PARTS CHEST
TL 53250
Figure 4-3. Facsimile Equipment RC-58-B (tape).
122
PAR.
402
CHAPTER 4. FACSIMILE SYSTEMS
to be transmitted, with a beam of light along a set of closely spaced parallel lines and translating the blacks and whites of the copy into electrical signals by the use of a photocell. This process is called “scanning”. The electrical signal is transmitted to the remote point through a medium, which may be a wire circuit or radio link, in the form of some modulated carrier wave in the voice range that can be conveniently transmitted over an audio channel. At the receiving end the electrical signal is translated into marks on a record sheet which correspond to those on the original subject copy. The marks are placed on the record sheet by a mechanism that traces a parallel line pattern over the sheet corresponding to that at the sending end. In order that the scanning and recording occur at corresponding points in the two sheets, the two motions are synchronized by the use of an accurate local oscillator at each point.
b. Transmitter.
(1) The original subject copy is wrapped around a drum which is rotated in front of the scanning head. At the same time the drum moves axially each revolution by an amount equal to the scanning line spacing. A sketch of the arrangement is shown in figure 4-4.
PICTURE ELEMENT
BEING SCANNED
NONROTATING NUT, CONVEYING THRUST MOTION TO DRUM
ROTATING SHAFT WITH KEYWAY, KEYED TO END OF DRUM
SUBJECT COPY WRAPPED AROUND DRUM
LENSES
LIGHT SOURCE
PHOTO CELL
SLIDING PIN TO KEEP NUT FROM ROTATING
ROTATING SCREW SHAFT
DRIVE GEAR
TL 54775
Figure 4-4. Page sending machine.
The light signal input to the exploring photocell has a sustained constant value when a large area of uniform shade of the picture is being explored by the photocell. With a d-c anode supply the photocell output signal would indicate this by a constant value of direct current corresponding to the light input, and markings on the subject copy would be indicated by a
modulation of this direct current. Actually, though such a modulated direct current exists in the photocell, it is not used, and the signal is immediately translated into the amplitude modulation of an 1,800-cycle carrier current. The double sideband width is somewhat over 1,250 cycles, extending from about 1,175 to 2,425 cycles. This signal is in a form usuable for transmission over a wire line.
(2) Facsimile signals in general tend to use the frequencies in the voice band somewhat inefficiently, as illustrated in a qualitative manner in figure 4-5. Only that part of the
।
DIRECT CURRENT
SIGNAL AMPLITUDE
BAND RESULTING FROM MODULATION OFDIRECT CURRENT-TRANSMITTING OR RECTIFICATION OF--
CARRIER SIGNAL-RECEIVING
CARRIER CURRENT
SIDEBANDS RESULTING FROM MODULATION OF CARRIER CURRENT
TL 54776
Figure 4-5. Frequency disribution of a-m facsimile signal.
band is used which lies in the upper frequency range. The use of this comparatively narrow’ band prevents overlap and confusion between the lower sideband of the carrier signal and a band of frequencies one sideband width up from zero frequency. As mentioned in subparagraph (1) above, this latter band of frequencies is generated in the photocell. It is also generated again each time the signal passes through a nonlinear element in the transmission medium.
c. Receiver.
(1) The transmitting machine is utilized as a receiver by the use of equipment which is alternative to the scanning head. A choice of several processes is available for translating the received electrical signal into marks on the record sheet.
(2) The direct recording process is electrothermal. A stylus is brought to bear on the drum and makes black marks on a specially prepared gray paper (Teledeltos paper) wrapped thereon. At the close of the transmission the copy can be used immediately.
PAR.
402 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
(3) In the photographic process the exposure is made on a film or photographic paper (on the drum) by a modulated light beam from a glow lamp. Recording can be made on film or paper, and the record can be obtained either as a negative or as a positive, according to adjustments made at the sending end. The machine must in this case be operated in a dark room or in a light-proof bag, which can also subsequently permit insertion of the exposed photographic material into a processing tank through the use of armholes. Processing of the photographic material can then be accomplished in the tank in the light outside the light-proof bag.
(4) It is impossible to distinguish detail in the received copy which is finer than the width of the scanning line used in scanning the subject copy at the transmitter. In a general way the markings on the subject copy in an area of the length and width of the spacing between successive lines (elemental area, fig. 4-6)
Figure 4-6. Elemental area.
will be averaged together and reproduced at the receiver as an area of more or less uniform density in the record copy. Thus it is impossible to obtain more useful detail out of the received record copy merely by enlarging it.
(5) The choice of recording process to be used at the receiver is a compromise between simplicity of operation and the quality of the result. The photographic process, recording on a film negative from which subsequent positive prints are made, gives the best correspondence in reproduction of detail and in shades of gray from black to white to the original; and this method is needed for high quality work. It is also the only choice which easily permits multiple copies. The direct recording process is the simplest, at the expense of giving the least fidelity. It is probably to be
chosen for the majority of the work. The record sheet obtained from one transmission can be used for subject copy for another, but the loss of fidelity in such a retransmission is appreciable. Successive retransmissions degrade the appearance and usefulness of the material rapidly.
d. Synchronization. Extremely accurate tuning-fork-controlled local oscillators are used to control the drum drive motors at the sending and receiving ends. The consequence of a very small speed difference between the receiving and sending drums is quite serious. As an illustration (fig. 4-7), an error in frequency
1 l/96 IN
----8- 5/8 INCHES = 830 X 1/96 IN.
Figure 4-7. Skew caused by synchronization error.
OFFSET OF 1/96 IN BETWEEN SUCCESSIVE SCANNING LINES
of one part in 830, or 0.12 percent, causes an offset of one line width for every successive scanning line, and consequently a skew of 45° in the record copy. General standards set for commercial facsimile operation call for constancy to 10 parts in a million. It is also necessary to indicate the start of the picture by a suitable signal so that the sending and receiving mechanisms can start simultaneously.
e. Converter. For radio transmission Converter CV-2/TX is available to transform the amplitude-modulated (a-m) signal into a frequency-modulated (f-m) signal. When the system is lined up, a maximum amplitude of the input a-m carrier is translated into an 1,800-cycle output tone. A minimum amplitude of a-m carrier is translated into a 3,000-cycle tone. Intermediate values of a-m carrier are translated into intermediate tones. The output of the converter, therefore, consists of a wave of constant amplitude whose frequency shifts back and forth between 1,800 and 3,000 cycles, according to the input amplitudes and hence according to the lights and shades of the picture being scanned. The total band used,
124
PARS.
CHAPTER 4, FACSIMILE SYSTEMS 402-403
runs from about 1,200 to 3,600 cycles. Figure 4-8 gives a qualitative illustration of this frequency band. This f-m output signal replaces the voice current in a telephone radio link when the link is used for facsimile. Equipment is also provided in the same housing for translating an f-m signal back to an a-m signal for use at the receiving end. Translation in both
AUDIO SIGNAL AMPLITUDE
I 800 CYCLES (CORRESPONDS TO MAXIMUM AM SIGNAL)
3000 CYCLES (COR RES PONDS TO MINIMUM AM SIGNAL)
FREQUENCY
Figure 4-8. Frequency distribution of f-m facsimile signal.
directions simultaneously, however, is not possible. The converter is adapted to operate with both the RC-120 and the AN/TXC-1 machines. The converter is described in TM 11-2252.
f. Fixed Net Equipment. The facsimile equipment in operation between Washington and the principal theaters will send pictures 7 by 8V2 inches in 7 minutes, plus one minute for synchronization. The drum is 9.125 inches in circumference, rotates at 100 rpm, and advances 1/100 inch per revolution. The transceiver output is an amplitude modulated 1,800-cycle carrier. Two methods of radio transmission are in use. One employes a converter similar to CV-2/TX, with frequency shift from 1,000 to 2,500 cycles, in the audio signal to be transmitted via wire line and radio link. The other uses the amplitude-modulated signal to shift the frequency of a c-w radiotelegraph transmitter directly, with a white to black frequency swing of 1,500 cycles. In both cases the receiver converts to an f-m signal varying from 1,000 to 2,500 cycles, employing a total band from 300 to 3,200 cycles. This network utilizes equipment manufactured by Acme Newspictures Inc.
403. TAPE FACSIMILE.
a. This machine scans copy in the form of tape. The copy height is 14 inch and the total
width of the tape is % inch. Text is handprinted with pencil by the operator on a writing stand provided with guides and means for holding a roll of blank tape. , The copy is threaded through the sending machine which scans it along parallel lines running crosswise of the tape.
b. The sending and receiving machines are mounted in a single housing, and the receiver can be used to monitor outgoing signals if desired. The receiver uses direct electromechanical recording, in which the tape is pressed against an inked printing element to make the marks.
c. The machine handles the tape at the rate of 50 inches per minute and it is expected that about four words can be handprinted every 5 inches. It is impossible, however, to keep up the handprinting on the tape at more than some 15 words per minute. The scanning lines run 72 to the inch and are %-inch high.
d. The amplitude-modulated signals from the photocell pickup are converted to signals which are one of two frequencies: 1,650 cycles for black and 1,150 cycles for white. Either one or the other of these frequencies is transmitted, depending on whether the copy being scanned is black or white. At the receiving station, reception of these two frequencies operates an appropriate mechanical system for producing black and white.
e. Synchronization between sending and receiving ends is effected by a vibrator of approximately constant frequency at each end. The limitation on the speed difference between the two ends is made considerably more lenient than in the case of the page facsimile by printing two lines of received copy on the tape. Imperfect synchronization (fig. 4-9) results in
QU/CK
QUICK
0KU W' *
BfTOW^i
FOX FUMPS rox JUMPS
TL 54779
Figure 4-9. Double line reception on tape.
one line approaching an edge of the tape and eventually running off and coming back from the other edge. With two lines of record copy, however, one remains continuous and completely legible.
656935 0—45
10
125
PARS.
404-405
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Section II. TRANSMISSION MEDIUM
404. GENERAL.
Facsimile may be transmitted either by wire or by radio. A wire or radio circuit which is suitable for the transmission of a single voice channel is also suitable for facsimile transmission.
405. WIRE LINES.
a. In normal use, the facsimile system takes over the facilities of a telephone circuit in the transmission medium. The facsimile machine can be coupled to the telephone circuit in three ways, namely: through an attachment placed on the telephone receiver (earpiece of a handset), through a transformer connection, or by direct wire connection to the telephone line.
b. Facsimile is about as susceptible to attenuation-frequency distortion as telephone use of the same channel. Facsimile is, however, more susceptible to delay distortion, that is, variations in the transmission time of the various component frequencies of the signal through the band utilized in the transmission medium. Delay distortion is introduced by frequency selective elements in the transmission medium. Examples of sources of delay distortion are: loading in the wire line, filters, repeating coils, and phantom coils. The most common symptom of delay distortion consists of false lines in the received copy paralleling the edges of sharp boundaries between black and white.
c. Other defects to which facsimile transmission is particularly susceptible are interference from other communication channels, echoes, and sudden changes in over-all gain or
loss. The susceptibility of the facsimile system to these impairments depends, of course, on the quality of reproduction desired in the received copy. Limiting figures can be given for a high-grade photographic process; the requirements for the other processes will vary with the fidelity required for the character of the material being sent.
d. For general guidance a few limits which have been developed in facsimile experience with wire transmission are listed in figure 4-10. The limits are given for photographic and direct process recording on the equipment described herein, and for general information these are compared with limits for the best grade commercial photographic recording system. The envelope delay distortion listed means the difference between maximum and minimum envelope delay in the utilized frequency band. The envelope delay is the time of transmission of the envelope of an amplitude-modulated carrier wave, at the frequency of the carrier.
e. Frequency-modulated transmission is expected to be used over wire lines only with the tape facsimile machine. This type of transmission markedly reduces susceptibility to changes in over-all loss (fading), and somewhat reduces the effects of noise. Its influence on effects of delay distortion has not been completely investigated.
f. Facsimile signals may be sent over telephone carrier channels, with the same general limitations as in voice-frequency circuits. However, under some conditions, beat frequencies may arise which lead to bar or moire patterns on the record copy.
Commercial photographic recording Photographic recordings Direct process recording^
Sudden changes in over-all loss 0.2 db 0.2 db ldb
Noise—random (signal-to-noise ratio) 35 db 20 db 17 db
Noise—single frequency (signal-to-noise ratio) 50 db 30 db 20 db
Envelope delay distortion ±0.3 milliseconds ±0.3 milliseconds ±3 milliseconds
"RC-120 or AN/TXC-1
b RC-120, AN/TXC-1, or RC-58-B
Figure 4-10. Typical limits for facsimile circuit.
126
PARS.
406-408
CHAPTER 4. FACSIMILE SYSTEMS
406. RADIO CIRCUITS.
a. The principal defects of radio circuits which impair transmission in a facsimile system are:
(1) Interference from other radio channels.
(2) Static.
(3) Fading.
(4) Multipath transmission echoes.
b. The limitations on interference from other channels and from static, where the signal is amplitude modulated, are the same as those given under wire circuits. The use of a frequency-modulation signal, from the converter, gives some reduction, in susceptibility to this interference.
c. In radio systems, where the sky wave is sufficiently strong to be received, its changing relative phase with the ground wave, or the changing phase between several sky waves, causes fading. The difference in delay between the sky and ground waves, or between several sky waves, causes multiple pictures to be recorded at the receiver. This effect is called multipath echo, and facsimile is more susceptible to it than either telegraph or telephone communication just as it is more susceptible to delay distortion. For short circuits these defects are not so likely to be important. For the longer circuits where the sky wave comes in incidentally, or worse, where the sky wave is principally depended upon for the transmission, the defects become serious. The use of a frequency-modulated signal greatly reduces
impairments from fading. Its influence in reducing impairments from multipath echo is generally much smaller.
d. The quality of transmission which can be obtained over military radio circuits depends upon a number of adjustments, which are more critical for the picture system than for voice transmission. For example, careful adjustment of the percentage modulation is required to obtain good results. In general, facsimile service over a telephone radio circuit which is subject to fading will be satisfactory a smaller proportion of the time than will telephone service on the same circuit.
407. PRIVACY IN THE TRANSMISSION MEDIUM.
Privacy methods, aside from the use of preenciphered text for subject copy, have been found difficult to use effectively in facsimile transmission. The reason for this difficulty is that the edges of the picture usually show a characteristic discontinuity and that successive scanning lines show close correlation. This periodicity in the signal gives evidence as to the enciphering method used, and critical information for the deciphering of the material. No appreciable privacy can therefore be secured until this characteristic is completely hidden in the signal. Such thorough inter-spersal is difficult to obtain and rearrange for the legitimate receiver without a fairly substantial amount of apparatus and delicate adjustments.
Section III. FACSIMILE TEXT TRANSMISSION COMPARED TO OTHER FORMS OF COMMUNICATION
408. ELEMENTS OF COMPARISON.
a. General. Facsimile Equipment RC-120 is primarily designed to transmit sketches and diagrams which cannot be done by other forms of communication. However, where it is used to transmit text as such, it competes with these other forms.
b. Word Speeds. The word speed of text transmitted with the Facsimile Equipment RC—120 varies with the size of letters used. With direct recording, typewriter type is
about as fine as is practical? Waste space in the form of margins, paragraph indentations and extra space between lines, and the need for arranging messages on a fixed size sheet,
1 Much higher word speeds than typewriter type permits are theoretically possible if the subject copy is prepared in the form of fine clear printing from type, and photographic reception is used. Solid text of this kind can be transmitted with as much as 40 words per square inch or 300 words per minute. The processing required at both sending and receiving ends, however, makes this procedure generally impractical.
127
PAR.
408
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
reduce the word speed of the usual subject copy. In the facsimile system time must be allowed to change sheets on the drum at both ends, further reducing the word speed. A practical word speed with these allowances (30 percent for the former and 10 percent additional for the latter) is indicated in figure 4-11
Words per minute
Page facsimile with pica typewriter, single spacing, including average waste space, 7 words per square inch......................... 50
Tape facsimile, freely running (transmitting) 40
Tape facsimile, handprinting (to prepare copy for sending) ............................ 15
Start-stop teletypewriter, tape sending....... 60
Start-stop teletypewriter, keyboard sending. . 30
fashion without the use of intelligence in the discrimination.
(5) In the teletypewriter, as normally used on wire circuits, the misinterpretation of one pulse can cause errors in a number of successive characters. This can be caused by loss of synchronization or misinterpretation of a carriage-return signal (on a page receiver). However, for use over mediocre circuits, methods are available to overcome these objectionable effects, and with the use of them the teletypewriter suffers no handicap in this regard in comparison with facsimile.
(4) In the facsimile system, for freely running text, the loss of transmitted information caused by fadeout (not too prolonged nor too frequent) can be minimized by scanning the text vertically (fig. 4-12). This is because the
Figure 4-11. W ord speeds.
for Facsimile Equipment RC-120. Figures are also given for Tape Facsimile Equipment RC-58-B. These are compared with teletypewriter word speeds.
c. Frequency Band Widths. For effective transmission a facsimile circuit requires substantially a telephone band and displaces the telephone connection. Several telegraph circuits can be accommodated in an equal band width.
d. Noise and Fading on Mediocre Circuits.
(I) The frequency band width required for the facsimile system is several times as wide as that needed for a teletypewriter, the factor varying with the arrangement used. The former, therefore, is subjected to some 5 to 10 db more random noise than the latter, under the same noise conditions.
(2) Each facsimile character is formed out of a considerably greater number of signal elements than a corresponding teletypewriter character. The failure of a certain proportion of the signal elements to be registered clearly does not, therefore, render the character illegible, whereas it will cause an error in the teletypewriter. Further, the facsimile reception gives a complete record of the signal which permits intelligence to be used in cases of marginal legibility. The teletypewriter interprets the on and off signal in one definite
THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG'S TAIL. NOW IS THE TIME FOR ALL GOOD MEN TO COME TO THE AID OF THE
THE QUICK BROWN FOX JUMPS OVER THE LAZY
THE TIME FOR ALL GOOD MEN TO COME TO THE AID OF THE
ORIGINAL TEXT FADE-OUT WITH
HORIZONTAL SCANNING
THE QUICK I OWN FOX JUMPS OVER HE LAZY DOG’S TAIL. NOW IS THE TIME FC ALL GOOD MEN T( COME TO THE AID F THE
FADE-OUT WITH VERTICAL SCANNING
TL 54780
Figure 4-12. Effect of fade-out.
letters affected do not occur in succession in the sqme word. In the teletypewriter this cannot be done. The net result of all these considerations is that over a link of marginal quality, facsimile transmission may show an advantage over normal teletypewriter transmission.
e. Operating Considerations.
(I) The received copy obtained from a teletypewriter gives cleaner text than that secured from facsimile. Also the teletypewriter very easily permits the simultaneous making of a number of carbon copies. Where the message has to be relayed, the loss of legibility of facsimile copy in retransmission is a serious handicap. In the teletypewriter system the message can simply be received on a perforated tape which is utilized for automatic sending on the next link. If the message is already clearly typewritten, the facsimile system can use the sheet directly without retyping.
128
PARS.
__________________________CHAPTER 4. FACSIMILE SYSTEMS_____________________408-410
(2) Where the communication, however, is of the question and answer type involving to-and-fro conversation, the teletypewriter is at a considerable advantage because the message can be transmitted and read directly as it is being typed.
(F Kg K K
battery gB ggg
CABLE —|
battery AfZ
TELEPHONE -OUTER
repeater CASE
we^yL
SMnMxlF y_carrying
STRAP
TL 53192
Figure 5-8. Telephone Repeater EE-89-A.
ARRESTER
BLOCK COVER-y
TUBE COVER PLATE —,‘
g^c^h
ARRESTER BLOCK 26-Eg
ARRESTER BLOCK 27—>
BATTERY BA-23-i \ jW
BATTERY CABLE-, t ‘ Sg
battery 1 AW
separator .i PLATE-
battery ’S’
ba-36-
J Kgidn
tl 53193
cipally on nonloaded field wires (fig. 5-8). It will pass 20 cycle or 1,000-20 cycle ringing. The simplex circuit is carried through the repeater and is not brought out to terminals. TM 11-2006 covers the description and operation of this repeater.
b. Telephone Repeater EE-99-A. Telephone Repeater EE-99-A (part of Telephone Repeater Set TC—29—A (Voice-frequency)) is a small portable 4-wire repeater, now rated as Limited Standard, which may be available in some theaters (fig. 5-9). It is designed for use on field wires. The repeater will pass voicefrequency (such as 500-20 or 1,000-20 cycle) signaling. When 20-cycle signaling is used, the 20-cycle signal is passed over the phantom circuit (par. 511) derived from the two pairs of conductors. D-c telegraph can be operated over the simplex circuits except where 20-cycle ringing is required. Arrangements are included for providing a 2-wire termination on one side of the repeater, for use when the repeater is at a circuit terminal. TM 11-348 covers the description and operation of this repeater.
Figure 5-9. Telephone Repeater EE-99-A.
c. Tekphsr.3 Repeater TP-14-( ). This is a portable 22-type repeater (fig. 5-10) which became available in 1945. The repeater has built-in adjustable balancing networks and equalizers which are designed to permit operation on most types of Army wire lines. The repeater will pass voice-frequency signaling. Provision is made for bypassing 20 cycles around the repeater so that 20-cycle signaling
TL 54898
Figure 5-10. Telephone Repeater TP-14-C ).
139
PARS.
516-519
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
may be used when desired. Phantom or simplex circuits can be carried through or terminated at the repeater. Composite sets and composite balancing sets are not included. The repeater operates from 115-230 volts, 50-60 cycles ac, or 12 volts de and weighs 46 pounds, including the carrying case. Telephone Repeater TP-14-( ) is described in TM 11-2007.
517. TELEPHONE TP-9.
The range of nonrepeatered point-to-point circuits can be increased by use of Telephone TP-9. This telephone has fixed transmitting gain and adjustable receiving gain, and provides reversible one-way transmission under control of the push-to-talk switch on the handset. Information on this telephone and its application is in chapter 2.
518. PACKAGED VOICE-FREQUENCY REPEATER.
Packaged voice-frequency repeaters are provided in units of either one repeater (fig. 5-11) or three repeaters (fig. 5-12). Each repeater in a unit is arranged for use as either a 22-type or a 4-wire repeater. The repeaters include built-in composite sets, adjustable equalization for 2-wire and 4-wire circuits, and adjustable networks for balancing almost any type of 2-wire line. Each unit includes a power pack for a-c operation, and a bridging circuit to permit talking from a repeater to any other
REPEATER
LINE & CX BALAI NETWORK PANEL
COMPOSITE SET RAF
2CIRCUIT VOICE FREQUENCY RING EQUIPMENT UNIT
STATIC RINGING GENERATOR AND
ALARM--------
POWER SUPPLY PANEL-A-C POWER DISTRIBUTION OUTLET BOX--------------
JACK
22 £-
TL 53203
Figure 5-11. Packaged voice-frequency telephone repeater X-61821J,
LINE PROTECTORS AND DRAINAGE COIL
BRIDGING AND TELEPHONE SET PANEL
COMPOSITE SET PANELS
BRIDGING AND TELEPHONE .SET PANEL-------------
JACK FIELD
POWER SUPPLY PANELS
AC POWER DISTRIBUTION OUTLET BOX
REPEATER PANELS.......
TL 53204
Figure 5-12. Packaged voice-frequency telephone repeater X-61821K.
LINE &CX BALANCING NETWORK PANELS
repeater or to the circuit terminals. Two 1,000-20 cycle ringers are included in the cabinet with the single repeater unit. They may be used with any circuit in the office which requires a ringer. The 3-repeater unit does not include ringers. The packaged repeaters are designed for fixed plant service, the principal use being on open wire lines and lead-covered cables on a 2-wire basis, and on lead-covered cables on a 4-wire basis. The equipment and installation procedures are covered in TM 11-2028 and TM 11-2027.
519. COMPARISON OF REPEATERED AND NONREPEATERED CIRCUIT LENGTHS.
A comparison of the allowable circuit lengths for repeatered and nonrepeatered circuits is given for typical cases in figure 5-13. A single repeater in the middle of the circuit
140
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 519-520
is assumed. Where trunk circuits with several repeater sections in tandem are involved, the repeater sections will generally be shorter (par. 542). Repeater spacings for other types of facilities are discussed in paragraph 541.
Type of circut Circuit length (miles')
Non-repeatered With 2-wire repeater
Point-to-point circuits a, 30-db net loss
Wire W-110-B 11 15b
Wire W-143 25 37 b
080 C-S open wire pair 120 180
Trunk circuits a, 6-db net loss
16 ga., lead-covered cable 8 35
16 ga., loaded °, lead-covered cable 32 110
19 ga., lead-covered cable 5.5 24
19 ga., loaded °, lead-covered cable 17 58
080 C-S open wire pair 24 85
104 C-S open wire pair 33 115
104 Copper open wire pair 72 255
a Circuits are nonloaded except as indicated.
b These figures are for Repeater EE—89—A (21-type); all other figures are for a 22-type repeater with a 15-db gain for open wire and loaded cable circuits and 20-db gain for nonloaded cable circuits.
0 Loading 6000-88; that is, 88 millihenries at 6,000-foot intervals.
Figure 5-13. Comparison of maximum circuit lengths of non-repeatered circuits and circuits with a single repeater.
520. CARRIER SYSTEMS, GENERAL.
a. A carrier system makes it possible to obtain a number of independent telephone circuits over the same transmission path. This is accomplished by shifting the usual 200- to 2,800-cycle telephone band to another frequency range such as 3,200 to 5,800 cycles. This is similar to transmission over radio circuits except that radio circuits usually work on a double side band basis taking twice as much frequency space as the original voice band, whereas the wire carrier systems eliminate one side band and the carrier current, thus saving frequency space on the line and more effectively using amplifier power. The process of shifting the telephone bands and stacking them one above the other in the frequency range is carried out in the carrier terminal equipment which is always required for a carrier system. The operating length of carrier systems can be increased by tl^p use of carrier repeaters at intermediate points.
Army types of carrier systems are used on open wire and suitably designed rubber-covered wires, but ordinarily are not used on lead-covered cables.
b. Carrier operation is desirable because it permits maximum use of existing facilities, reduces the amount of open wire construction, and saves in shipping space and weight of materials. The carrier equipment can be transferred readily from one location or area to another as requirements change. The time required to establish a given number of carrier circuits on existing wire is much less than is required for stringing new wire.
c. Carrier systems are of three kinds which differ in the way the two directions of transmission required for telephony are handled. These three kinds are physical 4-wire, balanced 2-wire, and equivalent 4-wire. The particular type used has important reactions on the application and layout of carrier systems. All three kinds are used with tactical equipment. Fixed plant carrier systems using packaged equipment work only on the equivalent 4-wire principle.
d. Physical 4-wire systems use separate pairs and the same band of frequencies for each direction of transmission. The system uses two independent one-way paths like an ordinary 4-wire telephone circuit except that the frequency band extends beyond the voice range. Physical 4-wire systems are used for carrier on cables because this results in the lowest practicable top frequency and attenuation for a given number of circuits. When used on open wire lines, physical 4-wire systems are subject to high crosstalk between high-level outgoing currents of one system and low-level incoming currents of the same frequency on another system, unless repeater spacings are suitably reduced.
e. Balanced 2-wire systems use only one pair of wires and the same frequency band for each direction of transmission. Hybrid coils and balancing networks are used at terminals and repeaters to separate the two directions of transmission. The transmission path between terminals is like an ordinary 2-wire telephone circuit except for the higher frequencies used. Freedom from instability and singing is obtained by the balance between the lines and networks and by use of short repeater sections with only moderate gains. Balanced 2-wire operation is of use
656935 0—45
11
141
PARS.
520-521
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Carrier system No. of circuits No. of pairs Type of line Type of operation Approx. frequency range (.kilocycles')
A to B B to A
Spiral-four 4 2 CC-358-( ) or open wire Physical 4-wire 0.2-11.6 0.2-11.6
Carrier hybrid 4 1 Open wire Balanced 2-wire 0.2-11.6 0.2-11.6
Open wire converter 4 1 Open wire Equivalent 4-wire 20.8-32.2 0.2-11.6
Figure 5-14. Tactical carrier systems.
principally on open wire lines but can be applied also to other types of wires for short distances. The number of balanced 2-wire carrier systems that can be worked on an open wire line without danger of high crosstalk between different systems will depend on the repeater spacing, type of line, etc. (par. 523e).
f. Equivalent 4-wire systems use only one pair of wires but the frequency bands for the two directions of transmission are different, one band being above the other in frequency. Separation of the two directions at repeaters and terminals is done by means of filters. This avoids the disadvantages of 2-wire balanced operation while requiring only one pair of wires and retaining all of the transmission advantages of a 4-wire circuit. However, these advantages are gained at the expense of more than doubling the top frequency of the system. For this reason, equivalent 4-wire carrier operation is normally used only on open wire lines. As a given frequency band always transmits in the same direction for any system on the line, crosstalk is of the far-end type. Therefore, repeaters of higher gain can be used and a large number of systems can be worked on a line with suitably designed transpositions.
521. TACTICAL CARRIER SYSTEMS.
a. The types of tactical carrier telephone systems and the lines on which they are normally used are listed in figure 5-14. The spiral-four system using Telephone Terminal CF-l-( ) and Telephone Repeater CF-3-( ) is designed for use on Cable Assemblies CC-358-( ) but may be used also on open wire. The carrier hybrid system uses the spiral-four equipment plus Carrier Hybrid CF-7, which makes possible carrier operation on open wire on a pair per system basis. The open wire converter system using Telephone
Terminal CF-l-( ), Converter CF-4-( ), and Repeater CF-5-( ) is the most suitable tactical system for open wire, where commercial standards are to be approached.
b. Voice-frequency carrier telegraph systems can be operated over the telephone channels of these systems as discussed in chapter 3.
INSTRUCTION book POCKET
SPARE PROTECTORS
LINE COIL PANEL ANO
BINDING POSTS
MEASURING PANEL
line amplifier panel
equalizer panel
CHANNEL I PANEL
CHANNEL 2 PANEL
CHANNEL 3 PANEL
CHANNEL 4 PANEL
SHOCK MOUNTING
SIGNAL PANEL
SPARE TUBE PANEL
POWER SUPPLY A PANEL
POWER SUPPLY 0 PANEL
CONVENIENCE OUTLETS
TL 53193
Figure 5-15. Telephone Terminal CF-l-A.
142
PAR.
522
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES
[—POWER CORD
-BATTERY CORD
-CONDENSED INSTRUCTIONS
r-LlNE COIL AND i measuring
1 PANEL
PROTECTORS
FROM
EQUALIZER PANEL
■AB EQUALIZER PANEL
LINE AMPLIFIER PANEL
HANDSET
TL 53199
spare PROTECTORS
TALK AND SIGNALING PANEL
Figure 5-16. Repeater CF-3-A.
MOUNTING
522. SPIRAL-FOUR CARRIER SYSTEM.
a. General.
(1) The basic equipment units of the spiral-four carrier system are Telephone Terminal CF-l-( ) (Carrier), part of Telephone Terminal Set TC-21 (Carrier) and Repeater CF-3-( ) (Carrier), part of Repeater Set TC-23 (Carrier).
(2) Telephone Terminal CF-l-( ) and Repeater CF-3-A are shown in figures 5-15 and 5-16 respectively. The equipment is described in TM 11-341. Information on a complete 100-mile spiral-four system, Carrier System AN/TCC-2, is given in TM 11-2001.
b. On Cable Assembly CC-358-( ).
(1) The spiral-four carrier equipment is designed basically for use as a physical 4-wire system on Cable Assembly CC-358-( ). Figure 5-17 shows schematically the arrangements for nonrepeatered and repeatered circuits.
(2) Each system provides one voice-frequency and three carrier telephone circuits in the frequency range 0.2 to 11.6 kc. Transmission characteristics permit 6-db repeatered circuits about 150 miles long when the cable is aerial or on the ground, or about 400 miles long when it is buried. Transmission factors limiting the length, are loss variations caused by temperature changes, and noise. In practice, buried cable lengths have been considerably ■ less than 400 miles. Normal repeater spacings are about 25 miles; these are limited by noise and available repeater gain. When noise is low, somewhat longer spacings can be used with some complications in maintenance.
(3) When no intermediate repeaters are used, as in figure 5-17-A, circuit lengths up to 35 miles or more may be used by increasing the transmitting output at the terminals. Means for increasing the output are included in Telephone Terminals CF-l-A having serial
।--------- CABLE ASSEMBLIES CC-358-( ) CSPIRAL-FOUR CABLE)
CH 1 * * — _____________________________p _________________________________ ZZ CH I
CH. 2 TELEPHONE------------------------------* TELEPHONE — r H ,
— TERMINAL TERMINAL “
CH3~ CF-I-C ) CF-I-C ) —Cm a
(CARRIER) ---------..... ............ (CARRIER) ~
CM-4— “CH.4
NO INTERMEDIATE REPEATERS
I-----CABLE ASSEMBLIES CC- 358"( JCSPIRAL-FOUR CABLE) ___________
CH' = J_______________ I_________________________ ] tZCH.I
CH2ZZ TELEPHONE-------------------- REP-----------— ------- RER----------- *-------TELEPHONE —CH2
TERMINAL CF-3-( ) CF-3-( ) TERMINAL
(CAREER) ~|j . -KARB,E,C |J . CCARR^RJ-.IJ CE-.-O
CH4-- ~ CH.4
WITH INTERMEDIATE REPEATERS
B
Figure 5-17. Spiral-four cable carrier system.
TL 54785
143
PAR.
522
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
numbers greater than 516. Under favorable noise and crosstalk conditions, single section systems can be operated for lengths of 55 miles at 6-db net loss or 80 miles at 30-db net loss. The gain of the terminal is sufficient for this purpose. At or near these extreme conditions, singing may occur in cases of unusually poor near-end side-to-side crosstalk in the spiral-four cable.* 1
(4) Two d-c channels are provided over the two simplexes of the cable. Normally, one of these is used as a signaling channel to call in the intermediate repeater attendants. The other can be used for a telegraph circuit of one or two repeater sections.
c. On Wire W-143. The spiral-four system can be used on an emergency basis over two pairs of nonloaded Wire W-143 with repeater sections about 14 miles in length. There are some restrictions on the use of Wire W-143 for this purpose, as some characteristics, such as capacitance unbalance, may give noisy operation in certain areas having high static noise levels. A special equalizer is required if one or more intermediate repeaters are involved. This equalizer consists of an 11-milli-henry (mh) inductor in series with an 80-ohm resistor, shunted across the input of each repeater and terminal. It can be made up in the field, the inductor being obtained by the parallel connection of the four half windings of two 88-millihenry (mh) loading coils. Figure 5-18 shows the equalizer and the method of connecting the Coils C-114-A for this purpose. Satisfactory circuits of 6-db net loss can be obtained in this way for lengths up to about 100 miles under favorable conditions.
d. On Open Wire.
(7) The spiral-four system can be used as a physical 4-wire system on two open wire pairs. The method of setting up such a system is the same as for the spiral-four cable system, except that the instructions with the equipment do not give typical equalizer settings for
1 This condition can be remedied, when necessary, by keeping reels with poor crosstalk (crosstalk loss per reel less than 12 db greater than the gain of the terminal) at least 3 miles away from either end of the repeater section. Methods of measuring the crosstalk are described in paragraph 564. The least crosstalk loss at 11 kc for a cable reel meeting specification limits is about 43 db (1,650 mmf capacitance unbalance) ; the crosstalk loss at 11 kc corresponding to the rms capacitance unbalance in a reel is about 67 db. The crosstalk with such a long repeater section may also affect carrier telegraph operation, as discussed in chapter 3.
open wire circuits. These settings can be determined during the line-up tests except for the MILES dial of the equalizer which should be set on step 0 for copper wire and step 30 for copper-steel wire.
(2) The lines used may be combinations of open wire, Cable Assembly CC-358-( ), or Wire W-143 without serious effects on transmission except some increased loss. This makes the system useful in front areas where well-constructed open wire lines may not exist. Single systems may be operated on a nonrepeatered basis for lengths of 100 miles or more of open wire, giving four circuits on two pairs of wires. Circuit lengths can be increased by the use of repeaters. Two or more systems on the same line lead to crosstalk difficulties and require much shorter section lengths and repeater spacings for high-grade crosstalk performance. More detailed data on the allowable circuit lengths are given in paragraph 543b and figure 5-45.
I------------------------------1
CO'L C-II4 OR C-H4-A
I LI A A A A A A
COIL C-II4 OR C—114 -A L LJ f n , ■ LI I J
8O(t 5) OHMS
I______________________________I
NOTE : EACH COIL HAS 88 MH. THE FOUR WINDINGS IN PARALLEL PROVIDES II MH.
TO BINDING POSTS REC OF TELEPHONE TERMINAL CF-I-A OR AB IN, OR BA IN OF REPEATER CF-3-A
TL 54786
Figure 5-18. Locally made equalizer for IFire VF-143.
(3) If this system is operated on a physical 4-wire basis on an open wire lead carrying the open wire converter, type C (par. 528), type H (par. 527) or other equivalent 4-wire systems, high near-end crosstalk is likely to result, particularly if the spiral-four system is on a pair adjacent to that occupied by one of the other systems. Selection of pairs to reduce crosstalk is discussed in paragraph 530b.
e. On Loaded Paper-insulated Conductors. The spiral-four system can be operated in lead-covered cables on paper insulated conductors equipped with loading of sufficiently high cutoff frequency. The cut-off frequency of the loading should be about 25 percent greater than the highest frequency to be transmitted over the spiral-four system. Some European loading systems are designed for music cir-
144
PARS.
________CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 522-523
cuits and carrier systems, and have cut-off frequencies in the range 7,500 to 17,000 cycles on the sides or phantoms. These would permit using two to four channels of the spiral-four system, depending on the cut-off frequency. This use on underground cables, will provide circuits of stable net loss with a minimum of interruptions in service.
523. CARRIER HYBRID SYSTEM.
a. Carrier Hybrid CF-7 in combination with spiral-four equipment is used for balanced 2-wire carrier operation, using the same frequency band for each direction of trans-
TL 53200
Figure 5-19. Carrier Hybrid CF-7.
mission over open wire lines. This saves one pair as compared with physical 4-wire operation, but with restrictions on the length of the repeater sections and the required regularity of line construction.
b. Carrier Hybrid CF-7 (fig. 5-19) includes a repeating coil hybrid, a balancing network, protectors, and a composite set for deriving
two d-c telegraph channels. A description of this equipment is given in TM 11-2003.
c. Figure 5-20 shows schematically the layout of a carrier hybrid system.
d. Repeater section lengths must be kept short in this system to avoid singing difficulties. On well constructed lines with small irregularities, nonrepeatered circuits can be worked for 65 miles at 6-db net loss and 135 miles at 30-db net loss, on 80-mil copper-steel pairs. Longer lengths can be operated with repeater spacings of about 50 miles on this wire. If the lines are damaged or poorly constructed, and have changes in wire spacing or gauge, or have short lengths of inserted cable, the usable gain will be decreased. Such irregularities may reduce the maximum length of nonrepeatered circuits to not more than 45 miles at G-db net loss and 115 miles at 30-db net loss. Irregularities in line construction are likely to be more common in front areas and this characteristic of the carrier hybrid system should be allowed for in laying out systems in such areas. Detailed data on circuit lengths and repeater spacings are given in paragraph 543c and figure 5-46.
e. If more than one carrier hybrid system is operated on a line, near-end crosstalk will occur between oppositely directed paths. On new carrier transposed lines of Army construction, it will generally be possible to operate two carrier hybrid systems per crossarm with good crosstalk performance (par. 549c), or four per crossarm with crosstalk acceptable for forward areas. Existing lines may have poor crosstalk characteristics and operation of a number of systems will generally involve accepting higher crosstalk, increased circuit net losses, or reduced repeater spacings.
f. The carrier hybrid system can be used on Wire W-143 or Cable Assembly CC-358-( ) for moderate distances, as given in figure 5-46. If both pairs of the spiral-four cable are used for these distances, crosstalk between the two systems will approach the maximum
CABLE _
-----------------.ASSEMBLIES CABLE „ ____ i ASSEMBLIES.--------
— A r~l ----1—I--------1—I-----
CM8— T,'tL^™ALE-----------------°PE" WI"E----CARA----- ----CAM. <>™ »'« e.P.TnZ TELEPHONE----------------CH
-------- CF-I-C J HYB------------------HYB CF-3-C) HYB.------------------------ HYB TERMINAL ---- " 3----- (CARRIER) =:“CF’7 -------------------CF'7 ---(CARRIER)CF-7-------------------CF-7,(car'rU =CH ’
CH A---- ---- --------------------- ---------- ------- --------------------- O----
__________ ____________________________________________________________________________________________CH 4
Figure 5-20. Balanced 2-wire carrier hybrid system.
TL 54787
145
tolerable for forward areas. If one pair of Cable Assembly CC-358-( ) becomes damaged in a spiral-four system, operation on a balanced 2-wire basis in the faulty section can be used as an emergency method.
g. The carrier hybrid system can be converted to a physical 4-wire system or vice versa very easily, especially in the case of nonrepeatered systems. This allows considerable flexibility in the use of the two systems. Where sufficient pairs are available, physical 4-wire operation provides a more stable and less vulnerable system with wide latitude in the makeup of the line wires. The carrier hybrid system is for use where pairs are at a premium and the distance to be spanned is within the capabilities of the system as limited by line irregularities. Use of the system on very irregular lines in front areas is possible on a single section basis provided no attempt is made to insert large amounts of gain; that is, the system may be used to yield more circuits on a pair of wires but not to increase the range any large amount in such cases.
h. The carrier terminal and its associated hybrid can be separated and connections between the two made on a 4-wire basis. This is illustrated in figure 5-20, where Cable Assembly CC-358-( ) is shown connecting the terminals to the hybrids. This separation of the two units of equipment may be found desirable to avoid long cable lengths between the hybrid and the open wire line; for example, it may be desired to place the terminal in a less exposed location where it can be camouflaged. Separation of the two units in this manner should be avoided whenever possible as it makes it awkward to adjust the balancing network in the carrier hybrid.
524. PAIR-PER-SYSTEM OPERATION OF TELEPHONE TERMINALS CF—1—( ).
a. An emergency method for operating over open wire lines on a pair per system basis is shown in figure 5-21. This is a stop gap arrangement for use only when Carrier Hybrid CF-7 and the open wire converter system are not available, and there are not sufficient pairs to allow physical 4-wire operation.
b. It is not possible in this system to insert gain at either terminal, as this would cause circuit instability and singing. For satisfactory operation, the dial settings should be approximately as indicated in figure 5-21. With these settings the over-all net loss of each channel would exceed the line attenuation by about 9 db. If properly adjusted, the circuits will not sing under any line conditions.
c. The circuit lengths with this system are limited to about 25 miles on 080 copper-steel wire for circuits having 18-db net loss, and about 60 miles for point-to-point circuits with 30-db net loss. Distances about three times as long can be spanned on 104 copper wire, as indicated in figure 5-47. Any inserted cable would reduce these lengths by the insertion loss of the cable.
d. Except for the connections shown in figure 5-21, the procedures for setting up this system are the same as for ordinary spiral-four systems. However, a line-up of the system by means of testing current is not required and is not desirable. The various dials at each terminal should be set as indicated in the figure without regard to any over-all measurements. Small readjustments of the GAIN dials of the individual channels may be made as required to prevent the circuits from sounding tinny or to improve the volume, The sig-
146
PARS. 523-524 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
CHI . TRSG° T OPEn’VTrF'paTr "°TRSG CH I
O__e— ~ — _ __ -.
CH 2 ----- TELEPHONE TELEPHONE ------- CH 2
------ TERMINAL TERMINAL ~ '
_------ CF-I-C ) CF-I-C ) ----- _u_
CH 3 (CARRIER) [_.o (CARRIER) CH 3
CH 4 RECo-__ ___OREC CH 4
___________DIAL AND KEY SETTING AT EACH TERMINAL________
MILES DIAL DIAL I DIAL4 DIAL2 GAIN DIALS OUTPUT KEY REC. LEV KEY. O Oa O 4 20 (CH I TO 3) -HOdba NORMAL
22(CH. 4 ) A IF OUTPUT KEY IS NOT PROVIDED ON THE TERMINAL,SET DIAL 1 ON IO INSTEAD OF O.
TL 54786
Figure 5-21. Pair-per-system operation of Telephone Terminals CF-l-( ).
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 524-525
naling channel over the simplex is set up in the normal manner. The second simplex tap provided in the terminal equipment is not used, and no connections should be made to it.
525. OPEN WIRE CONVERTER SYSTEM.
a. The open wire converter system is an equivalent 4-wire system, designed for operation over open wire pairs without the limitations of the physical 4-wire and carrier hybrid
shows the converter and figure 5-23 the repeater equipment. The equipment is described in TM 11-2008.
sic. Panel , signaling CIRCUIT
A-C CONVENIENCE OUTLET
POCKET FOR
TECHNICAL manual
CONTROL PANEL
EQUALIZER
MODULATOR PANEL, MODULATOR CIRCUIT
CX PANEL, COMPOSITE SET
directional filters LOW PASS ON FRONT HIGH PASS ON REAR
COVER OVER COIL-TERMINALS
LINE COIL ANO BINDING POST PANEL
POWER SUPPLY
A-C ANO BATTER*
POWER CORDS T1ED FOR TRANSPORTATION
TL 51649
Figure 5-22. Converter CF-4 (2-wire to 4-wire).
AMP PANEL. HlGHGRC LOW GROUP AND RECEIVING AMPLIFIERS
spare tube and s PROTECTOR PANEL RECTIFIER RECTIFIERS FOR
SIGNALING CIRCUIT
AB EQUALIZER PANEL---
HIGH CROUP EQUALIZER
AMPLIFIER panel, HIGH-GROUP ANO LOW GROUP AMPLIFIERS
BA EQUALIZER PANEL-LOW GROUP EQUALIZER
TALK S, MONITOR PANEL'
CXA PANEL. COMPOSITE SET, LINE B
Directional FILTERS;— line; a, low pass on FRONT, HIGH PASS ON REAR
CXB PANEL. COMPOSITE-• SET,LINE B
directional filters — LINE B', LOW PASS ON FRONT, HIGH PASS ON REAR
RECTIFIER PANEL,-------
RECTIFIERS FOR
Signaling CIRCUIT
POWER SUPPLY panel----
A-C CONVENIENCE -OUTLET
A-C ANO BATTERY POWER CORDS TIED FOR TRANSPORTATION ——'
TL 51649
Figure 5-23. Repeater CFS (2-wire).
systems. This system uses Telephone Terminal CF-l-( ) (Carrier) ; Converter CF-4 (Carrier) 2-wire to 4-wire, part of Converter Set TC-33; and Repeater CF-5 (Carrier) 2-wire, part of Repeater Set TC-37. Figure 5-22
b. Figure 5-24 shows a schematic layout of a repeatered open wire converter carrier system. The transmission over the open wire line in one direction is 0.2 to 11.6 kilocycles (kc) and in the other is 20.8 to 32.2 kilocycles (kc).
CABLE CABLE
____________ASSEMBLIES ASSEMBLIES ---_________CC-358-( ) ------- CC-358-( )|--------------------------------
CH’— i r-------- ------- — ch ।
CH 2~“~“ TELEPHONE —---CONV. OPEN WIRE REP. OPEN WIRE CONV. — ■ || TELEPHONE---CH 2
TERMINAL CF-4 CF-5 ~ CF-4 TERMINAL
CH. 3 CP-I-C ) (CARRIER,---------------(CARRIER,----------------(CARRIER, CF-I-Q ) ---ch 3
(CARRIER} [J 2W-4W) 2W) 2W-4W)-------(CARRIER)
CH. 4 ________________________________________________________________________CH.4
Figure 5-24. Open wire converter system.
TL 54789
147
PARS.
525-526 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
c. Telephone Terminal CF-l-( ) is connected over two pairs of wire to Converter CF-4 and thence to the open wire line. At Converter CF-4 at one end of the system, the band of frequencies for one- direction of transmission is sent over the line without frequency change in the 0.2 to 11.6 kc range. The band of frequencies for the other direction is received from the line in the 20.8 to 32.2 kc range, then converted to 0.2 to 11.6 kc, and passed to the receiving side of the CF-1- ( ) terminal. At Converter CF-4 at the opposite end of the system, the functions of the two sides of the converter are interchanged: the band of frequencies for one direction of transmission is raised from 0.2 to 11.6 kc to 20.8 to 32.2 kc and sent over the line while the 0.2 to 11.6 kc band received from the line is passed on to Telephone Terminal CF-l-( ). Repeater CF-5 is used to increase the allowable length of system. It provides amplification for the 0.2- to 11.6-kc band in one direction and 20.8 to 32.2 kc in the other direction of transmission. The separation of the two frequency bands in both the converter and repeater is accomplished by means of directional filters (low-and high-pass) which are part of these units.
d. The system will provide four circuits per pair, and the circuit can be operated at 6-db net loss for distances up to about 1,000 miles (with some relaxation of crosstalk standards if systems are operated for such long distance on adjacent pairs). The normal repeater spacing on 080 copper-steel wire is 80 to 90 miles. Noise and available gain limit the repeater spacings. When used as a single-section system without repeaters, distances up to 135 and 200 miles can be spanned on 080 copper-steel wire, for circuit net losses of 6 db and 30 db, respectively. Additional data on repeater spacings are in paragraph 543e.
e. On 4-pair and 8-pair open wire lines transposed as outlined in TM 11-368 or TM 11-2253, each pair may be used for an open wire converter system. These will provide a maximum of 32 telephone channels on 8 pairs of wires. The system may be used on the same pole line with fixed plant packaged carrier systems and most foreign systems.
f. Combinations of the open wire converter system on open wire in tandem with the spiral-four system on Cable Assembly CC-358-( ) can be operated without bringing the channels down to voice frequencies at the junction point.
Converter CF-4 and Repeater CF-3-( ) are used at the junction in these cases. Converter CF-4 may also be used alone at the junction of the open wire and an entrance cable up to about a mile in length. This may be useful for camouflaging the approach to the carrier terminal and it avoids the transmission penalties of having the cable in the open wire line. A source of power is required for the converter.
g. Two composited d-c telegraph channels are provided, one of which is normally used for signaling purposes in maintenance of the system.
526. FIXED PLANT CARRIER SYSTEMS.
a. General. Fixed plant carrier telephone systems are the single channel type H and the 3-channel type C. These are equivalent 4-wire systems for use on open wire lines. Both are provided as packaged equipment.
b. Voice-frequency Circuit. In addition to the carrier channels, a telephone circuit can be obtained in the voice-frequency range on the same pairs of wires. This circuit is separated from the carrier channels by means of filters at each carrier repeater and terminal, and can be used nonrepeatered or equipped with 2-wire repeaters as desired. This is different from tactical equipment where the voice channel passes through the same amplifiers as the carrier channels.
c. D-c Telegraph. Two composited d-c telegraph circuits or one simplex telegraph circuit can be obtained over the same pair of wires used for the type H or type C systems.
d. Voice-frequency Carrier Telegraph. Voicefrequency carrier telegraph can be transmitted over the carrier telephone channels. The telegraph system may consist of the 6- and 12-channel packaged, equipment or the CF-2-A, CF-2-B, and CF-6 equipment.
e. Equipment Features. The packaged type H and type C systems are patterned after commercial systems but include special features desirable for Signal Corps use. The equipment is designed for a-c operation with built-in power packs. Each packaged unit has optional arrangements to permit its use under a wide variety of conditions. Provision is made for terminating the channels at voice frequencies on either a 2-wire or 4-wire basis. The 4-wire termination is used where a circuit consists of type C, type H, or 4-wire voice-frequency sections permanently connected in tandem. It is
148
PARS*
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 526-527
PACKAGED PACKAGED
VOICE-FREQUENCY REPEATER VOICE-FREQUENCY REPEATER
-----VOICE ____ VOICE _______________REP. ~T~ ex------------------------------ex _-] r— rep ZZZZ EQ PT._______________________________________________________I I I I-EQPT
________________________ JI |R ' T| |R t-" -----------------------------------------_j— '—V—' _ TO D-C TO D-C •- -J
LF TELEG. TELEG LP -------
---------- -------- EQPT. EQPT ----------- -------------
___ H CARRIER _---H CARRIER ------------------ TERM.-HP - ------------------------- HP—= TERM- =
PANEL ----- ----------------------------------- PANEL
H CARRIER H CARRIER
LINE PANEL LINE PANEL
CX-D-C TELEGRAPH COMPOSITE SET.
HP-HIGH PASS LINE FILTER, PASSES FROM 4,000 CYCLES UP.
LP —LOW PASS LINE Fl LTE R, PASSES FROM 0 TO 3,000 CYCLES
TL 54790
Figure 5-25. Type H system and voice-frequency circuit on open wire.
also used when voice-frequency telegraph systems are applied to the channels.
f. Transmission Data. Transmission data for the type H and type C systems are given in paragraph 543e.
527. TYPE H SYSTEM.
a. The type H system provides one carrier circuit in the frequency range 4.0 to 6.9 kc for West to East transmission and 7.4 to 10.3 kc for East to West. Figure 5-25 shows the general arrangement of a nonrepeatered system in association with a 2-wire voice-frequency telephone circuit.
Figure 5-26. Type H carrier terminal panel X-66217A.
b. The type H systems are normally used as single section systems. Circuits having 6-db net loss can be obtained for lengths up to 145
miles on 104 copper-steel wire. The circuit lengths can be increased by use of a type H carrier repeater. Corrections for transmission variations with temperature and weather are made manually, when necessary.
Figure 5-27. Type H carrier repeater panel X-66217B.
c. The major components of the packaged type H system are shown in figures 5-26 and 5-27. The terminal is universal; that is, it can be arranged as an East or a West terminal by throwing a switch. The terminal is also arranged so that two terminals can be associated to provide a 3-channel system (voice plus 2 carrier) for physical 4-wire operation over suitable wire or radio systems. The packaged type H equipment does not include protectors or composite sets. Protectors can be provided from the line terminating and simplex panel described in TM 11-2020. Protectors and composite sets can be provided by associating the type H equipment with the packaged voice-frequency repeater or the line terminating and
149
PARS.
527-528
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
1 ;'±±
PROTECTORS
24 VOLT RECTIFIER’
150 VOLT RECTIFIER-
CHI VOLUME LI MITER-
CH 3 VOLUME LIMITER,
VOLUME LIMITER
BATTERIES------
LINE FILTER
COMPOSITE SETS
LINE FILTER BALANCE NETS AND 17 DB PADS
ALARM CIRCUIT RELAYS-
SPARE PARTS
POWER OUTLETS-
LINE ANO POWER BAY
TERMINAL BAY
• BASIC EQUALIZER AND GRID BATTERIES
THANSM IT ting AMPLIFIER
&-PILOT CHANNEL
| REGULATOR
•RECEIVING AMPLIFIER
H--CH1 MODULATOR AND
B DEMODULATOR
■CHS MODULATOR AND OF MODUL ATOR
!~ch3 modulator and DEMODULATOR
K-CH2 BAND FILTERS
CH 3 BAND FILTERS
-POWER OUTLETS
TL 53210 t
Figure 5-28. Packaged type C carrier telephone terminal (East terminal X-61819P; JFest terminal X-6T819R).
composite panel described in TM 11-2031. The type H system and its installation are covered in TM 11-2025 and TM 11-2038.
528. TYPE C SYSTEMS.
a. Type C systems provide three high-grade carrier channels in the frequency range 6.5 to 15.7 kc for the East to West transmission and 18 to 28.2 for West to East. The type C packaged terminal and repeater are shown in figures 5-28 and 5-29 respectively. A schematic of a repeatered type C system with a voicefrequency telephone circuit on the same pair of wires is shown in figure 5-30.
b. Type C systems have automatic regulation to take care of transmission variations and can provide circuits having 6-db net loss for practically any length up to 1,000 miles or
more. Maximum repeater spacings of about 155 miles can be used on 104 copper-steel wire, the limitations being noise and available gain.
c. Type C systems can be operated on all pairs of U. S. Army 4-pair and 8-pair lines transposed for 30-kc operation. On other types of lines suitable carrier transpositions are required and pairs may need to be selected for minimum crosstalk. The packaged type C system is arranged so that either of two frequency allocations can be used. In the CS-frequency allocation (fig. 5-33) the channels in the high-frequency group are transmitted as lower sidebands; in the CU-frequency allocation these channels are transmitted as upper sidebands. This feature is provided to reduce crosstalk effects as crosstalk between upper sidebands on one system and lower sidebands on another system will not be intelligible.
150
PAR.
528
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES
PROTECTORS---
FUSE PANEL --
ALARM LAMPS
W-E PILOT REGULATOR
24 VOLT RECTIFIER
e-w pilot REGULATOR
ISO VOLT RECTIFIER-
WEST line FILTER.
JACK PANEL
PAD PANEL
WEST COMPOSITE SET
WEST L F
BALANCE NETS -
ALARM RELAYS —
NETWORK S. equalizer panel
W-E IN DIRECTIONAL FILTERS
EAST LINE FILTER
E-W OUT DIRECTIONAL FILTERS
East
COMPOSITE SET
EAST L F
BALANCE NETS’
SPARE PARTS
VXTJj
___ .2: '*******■'
I |^| WW” ;
W-E AMPLIFIER
BASIC EQUALIZERS
GRID BATTERIES
E-W AMPLIFIER
E-W IN DIRECTIONAL FILTER
W-E OUT DIRECTIONAL FILTER
POWER OUTLETS
POWER OUTLETS
LINE AND POWER BAY
REPEATER BAY
TL 53211
Figure 5-29. Packaged type C carrier telephone repeater X-61819S.
TYPE C CARRIER TERMINAL TYPE C CARRIER REPEATER TYPE C CARRIER TERMINAL
CH 3 —T ~f I | | I______I | » | | | | _ I I | _ | I -'l— ch 3
> TERM -----^HPLdJCX L-----JCxttZjHPtZ REP- Zj HP fTZ CX ~ jcxttrjHP TCD.. C
cH2-{—: EQPT |—r T2j TIT eqpt. L__r T_T 1LT L_J teEqPt>ch2
ch । -f~q ।—I j—j —. .—. c=>-ch i
— lpJ l—jLptzzn nzz lp zJ L_jlpl~
---- I Ir / \tI,Ir z stI IR, \tI |R z
__ VOICE J TO D-C TO D-C unirc „n.rrr TO D-C TO D-C
-- PPP TELEG teleg. v°'S5 —J L_ZV°'CE teleg teleg. —VOICE - REP----------------------------------------------------------------------------------EQPT. EQPT REP REP EQPT EQPT REP
nr nr
CX-D-CTELEGRAPH COMPOSITE HP-HIGH PASS LINE F I LTER,PASSES LP-LOW PASS LINE FILTER, PASSES
SET
FREQUENCIES FROM 6,000 CYCLES 0-5000 CYCLES
UP
Figure 5-30. Type C system and voice-frequency circuit on open wire.
TL 54791
151
PARS.
528-530
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
d. The packaged units include composite sets for deriving d-c telegraph circuits, line filters for separating the carrier from the voice circuit, and volume limiters for the telephone channels when a voice-frequency carrier telegraph system is operated over another channel. A type C carrier transfer panel is available as a separate unit. This consists of line filters and associated equipment to permit separating the type C from the voice circuit at an intermediate point in a repeater section (par. 532).
e. The type C system and its installation are described in TM 11-20^6 and TM 11-2023. The carrier transfer panel is covered in TM 11-2031.
529. SIGNALING.
Voice-frequency signaling must be used on all carrier circuits, on all voice-frequency circuits equipped with packaged 22-type or 4-wire repeaters, and on all composited circuits. The 1,000-20 cycle ringers used by the Signal Corps are normally the EE-101-( ) or the packaged ringers X-61820A and B. Ringer TA-3/FT provides either 1,000-20 or 500-20 cycle ringing, the latter being used when operating with British or European equipment requiring this type of ringing. Twenty-cycle signaling can be used on nonrepeatered, noncomposited circuits, and on voice-frequency circuits equipped with Repeaters EE-89-A, EE-99-A, or TP-14-( ).
530. SYSTEM COORDINATION ON OPEN WIRE LINES.
a. Repeater Locations. When different kinds of telephone and telegraph systems are used on an open wire line, there are certain features of system layouts which should be coordinated. It is desirable to locate all telegraph, voice, and carrier repeaters at the same points. This centralizes maintenance and is desirable from a transmission standpoint as it reduces the possibility of excessive level differences between systems, which would produce crosstalk.
b. Frequency Coordination.
(1) It is desirable that transmission within any carrier-frequency band be in the same direction on all carrier systems on a line. When this is arranged the frequencies are said to be coordinated. Frequency coordination tends to prevent the high near-end crosstalk which would occur if currents of the same frequency were at high level on one pair and at a low
level on another pair at the same point on the line. Charts showing the frequency allocations for various types of carrier systems are in paragraph 534.
(2) The frequency bands of the open wire converter system and type C, and of type C and type H, can always be coordinated. The frequency bands of the open wire converter system and type H do not coordinate but both systems can generally be operated on the same U. S. Army line on nonadjacent carrier transposed pairs, if transmission from the B terminal to the A terminal (0.2- to 11.6-kc band) of the open wire converter system is in the same direction as transmission from the East terminal to the West terminal (7.4- to 10.3-kc band) of the type H system.
(3) The spiral-four carrier system operating on a physical 4-wire basis on an open wire line uses the same frequency band in both directions of transmission. Where more than one of these systems is operated on the same crossarm, it is important that the adjacent pairs used in the two systems be operated in the same direction to keep level differences between these pairs at a minimum. Such an arrangement is illustrated in figure 5-31-A.
(4) The carrier hybrid systems on open wire use the same frequency band in both directions of transmission on one pair and therefore permit no choice in how the systems should be pointed relative to each other or to other systems. Expedients used for keeping crosstalk satisfactory with more than one of these systems on a line are: reduced repeater gains and spacings, and selection of pairs, usually based on obtaining the maximum physical separation between pairs carrying the same frequency bands in opposite directions. Such arrangements are illustrated in figures 5-31-B and -C, which apply when two systems are to be operated per crossarm. As many as four systems per crossarm may be usable where the crosstalk standards for forward areas (par. 549b) apply.
(5) The methods of assigning pairs for spiral-four or carrier hybrid systems per crossarm shown in figure 5-31 are for lines having American types of carrier transpositions. Some other method of assignment may be found desirable on other types of lines. On lines with barrelled squares, crosstalk between pairs in horizontally or vertically adjacent squares is worse than for combinations with more sepa-
152
ration. When 10-pin crossarms are used the pair formed by the two wires adjacent to the pole, that is, the pole pair, should not be used for carrier.
(6) As another example of system pair assignments, assume that a type C system is operating on one pair of a line and it is desired to add one spiral-four system working physical 4-wire on two other pairs. A large level difference will exist between the low-frequency group (East to West) of the type C and the spiral-four frequency band transmitting West to East, since the frequency bands are practically the same and the directions of transmission are opposite. Therefore, the pair used for West to East transmission on the spiral-four system should be selected to have the greater crosstalk loss into the type C pair. In the absence of measurements or other data on transpositions, it is a fair supposition that pairs far apart will have the least crosstalk.
(7) Where the repeater section lengths are much shorter than the maximum allowable, the need for using the segregation arrangements shown in figure 5-31 is decreased, because the level difference is reduced by the amount of reduction in line loss as compared to the maximum.
c. Level Coordination. When different types of systems are operated on the same line, the output levels should be made about the same on all systems for a given frequency range on the line. This usually gives optimum results from a crosstalk standpoint. If a branch line joins a main line at an intermediate point in the main line repeater section, or if a repeater or carrier terminal is used at an intermediate
point, readjustment of system levels may be required to equalize the levels at the intermediate point. Means for making such adjustments are included in the carrier equipment.
531. CABLES IN OPEN WIRE LINES.
a. Incidental cables in open wire lines will require consideration in planning and construction in order to avoid undesirable transmission reactions. Nonloaded cable in particular has a much lower impedance than an open wire pair and when used in the line can be an important source of increased transmission loss and crosstalk. Incidental cables also cause irregularities in the line impedance which limit the usable repeater gains on 2-wire circuits.
b. Incidental cable should be avoided by the use of open wire construction to the greatest extent practicable. Long span open wire construction can be used for road and river crossings. The aerial spaced pair construction described in paragraph 504 is desirable where use of insulated wire is necessary, such as through foliage which cannot be kept clear of the line. The impedance of this construction approximates open wire line impedance and thus minimizes reflection effects.
c. When cables are used, the transmission effects will depend on the type of system. With spiral-four equipment operated physical 4-wire, the principal effect will be an increase in the transmission loss of the line. For carrier hybrid operation, cables will reduce the balance obtainable between the line and network, and in general will allow use of only moderate gains. In the open wire converter, type C, and type H systems the important effects are increased crosstalk and transmission loss.
153
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 530-531
/—SYSTEM I—v—SYSTEM 2—SYSTEM SYSTEM SYSTEM SYSTEM
A-B B-A/\B-A A-B I /X 2 I Z\ 2
,? ?l l?-i rt................?....? ?l 1 .... ? r? ?.. ? ?l I?...??
/—SYSTEM 3—\ /—SYSTEM4—\ SYSTEM SYSTEM
A-B B-A B-A A-B 3 4
!? ? ? ?l I? ! ? ? ??!]?? ? ? [
A B C
NOTES:
I. A SHOWS OPTIMUM ASSIGNMENTS FOR SPIRAL-FOUR CARRIER SYSTEMS.
2. B AND C SHOW OPTIMUM ASSIGNMENTS WHEN CARRIER HYBRID CF-7 IS USED WITH SPIRAL-FOUR EQUIPMENT. ___
TL 54792
Figure 5-31. Pair assignments for spiral-four and carrier hybrid systems on open wire.
PARS.
531-533 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
d. Allowable lengths of incidental cables for various types of systems are discussed in paragraph 545. When cables are used nonloaded, the lengths tend to be short, especially for carrier operation. By use of loading, the impedance can be increased and much longer lengths are usable. Suggestions for loading incidental cables in tactical systems and reference to carrier loadings for fixed plant systems are given in paragraph 545.
e. In using pairs on an existing open wire line, a check should be made to see whether all loaded cables included will transmit the desired frequency band. Carrier operation is not possible over cable pairs with voice-frequency loading because of the cut-off effect referred to in paragraph 512a. The cut-off frequency of Cable Assembly CC-358-( ) is not high enough to pass the frequencies required for the open wire converter and type C carrier systems.
532. DROPPING CIRCUITS ON CARRIER PAIRS.
a. In laying out circuits to meet particular traffic demands, it may be advantageous to use some of the channels of a carrier system for circuits of less than the complete system length. For example, the system may run from A to C, and a circuit from A to B, as well as one from B to C, may be needed. This can be obtained by dropping circuits in the ways described below.
b. One or more channels can always be dropped at an intermediate point on a carrier route by installing terminals back-to-back; that is, by terminating a carrier system at voice frequency in both directions at the intermediate point.
c. Arrangements are provided for bridging at repeater points on the No. 1 channel of the open wire converter system. A similar bridge can be made on the voice-frequency channel of spiral-four systems by means of a simple modification of the equipment described in Change 1 to TM 11-341 dated 15 February 1944. A short voice-frequency extension can be used from the repeater point. This provides a comparatively high net loss circuit (20 db or more) from the bridge to either terminal or to a bridge at another repeater. As the voice-frequency or No. 1 channel is normally used in routine maintenance of these systems, coordination of use of the circuit for maintenance and message purposes will be necessary.
d. On pairs with type H or type C carrier systems, the voice-frequency circuit is separate at the carrier repeater points and may be bridged or terminated as desired. By the use of carrier transfer panels and line terminating and composite panels (or line terminating and simplex panels), the voice-frequency circuit can also be separated and terminated at an intermediate point in the carrier repeater section.
e. A voice-frequency bridge with short extension can be made on any line at points between repeaters by means of Telephone Unit EE-105. The loss between the bridge and the circuit terminal will be high in most cases (20 db or more depending on the location of the set) and in the case of the tactical carrier systems, will require coordination in use of the circuit for maintenance and message purposes.
533. CIRCUITS IN TANDEM
a. It will be necessary on occasion to connect telephone circuits permanently in tandem in order to build up longer circuits. The connections between circuits can be made with the individual circuits terminated at voice frequencies on either a 2-wire or a 4-wire basis. It is preferable to connect the circuits together on a 4-wire basis because this will permit lower net losses and give better overall transmission.
b. Telephone Terminal CF-l-A is arranged only for 2-wire termination but the modifications described in TM 11-2001 can be made when it is necessary to provide 4-wire terminations of the channels. Future manufacture of this equipment, starting early in 1945, will include key arrangements to simplify the setting up of either 2-wire or 4-wire terminations. Voice-frequency repeatered circuits or type C and type H carrier systems, set up by means of packaged equipment, can be terminated either 2-wire or 4-wire.
c. When two circuits are connected together on a 4-wire basis, adjustment of the gains and losses at the junction point will be necessary. The method of making these adjustments varies with the type of equipment and is described in the manuals on the equipment. The principles involved are illustrated in figure 5-32 where circuits Nos. 1 and 2 may* be any types of circuit, wire or radio, terminated on a 4-wire basis at their junction. Assume first that circuits Nos. 1 and 2 are terminated
154
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 533-534
on a 2-wire basis and lined up for operation as separate circuits, with normal gains and levels for each circuit. Then when the two circuits are connected in tandem on a 4-wire basis as shown, gains or losses represented by P and P' need to be inserted at the junction point. The gain or loss of P should be such that the transmission level at the input of C will be the same as when circuit No. 2 is terminated on a 2-wire basis for operation alone. Likewise, the gain or loss of P' should make the transmission level at the input of C' the same as when circuit No. 1 is terminated on a 2-wire basis for operation alone. The gain or loss represented by P and P' is obtained by adjustment of pads (provided in some types of equip-
4-WIRE ^JUNCTION z
H-----CIRCUIT NO. I----•+«----CIRCUIT NO. 2-----
I
I
A B pl C D
l— HYBRID — NETWORK NETWORK — HYBRID —I
1 L—__J I I
j--1 ।-- F» --------1 j—।
D' C B' A'
TL 54965
Figure 5-32. Four-wire circuits connected in tandem.
ment), and by changing the gain of C and C'. The combination circuit should be made to have the same net loss in the two directions of transmission by changing the gains at D and D', as required. This general method of setting up 4-wire connections is applicable where circuits Nos. 1 and 2 are capable of operating separately at net losses of 6 to 9 db each. If the circuits involved cannot operate at net losses as low as this, or if the net losses of the two circuits are widely different, it may be necessary to change the gains at C and C' or even at A and A', to avoid singing difficulties on the built-up circuit. Special cases of this kind may be met if one of the circuits is a 2-wire voice-frequency or type H carrier circuit.
d. When circuits are connected together permanently on a 2-wire basis, a modification of the normal adjustment of circuit net losses is desirable to reduce the loss of the over-all
connection. Designating the two points to be connected as A and B, the channel receiving gains at the intermediate point should be increased so that, the transmission losses from A and B to the intermediate point are 0 db and the losses from the intermediate point to A and B are 6 db. This will give an over-all net loss of 6 db in each direction as compared with a value of 12 db which would be obtained if the two circuits were adjusted in the normal manner. If three circuits are permanently connected in tandem, the end circuits in the connection would be adjusted in the manner described, and the middle circuit set up to have 0-db loss in each direction. This will give a 6-db over-all loss instead of 18 db. The foregoing assumes that the individual circuits are each capable of working at 6-db net loss when operated alone, and that the wiring between the circuit terminals at a junction point is short.
e. It is important to coordinate the type of ringing equipment used at the terminals of a built-up circuit. The ringing equipment at the two ends does not have to be of the same nomenclature but it must be designed to receive and transmit the same kind of signals over the circuit. Voice-frequency signaling over U. S. Army lines is normally 1,000-20 cycles. The British use 500-20 cycles and sometimes unmodulated 500 cycles. European circuits may also use 500-20 cycle ringing. If the ringers at the two ends are of the same type, it is not necessary to provide any ringing equipment at intermediate junctions in the built-up circuit. If ringers of the same type are not available at the two ends, coordination may be effected by providing suitable ringers connected back-to-back at an intermediate point. Thus, a circuit might be equipped with 500-20 .cycle ringers at each end and connected to another circuit equipped with 1,000-20 cycle ringers. A 2-wire termination of each circuit at the junction is necessary in this case.
534. FREQUENCY ALLOCATIONS OF CARRIER SYSTEMS.
a. The frequency allocations of various American, British, and French carrier systems are shown in figures 5-33 to 5-35 inclusive. These also show the normal output levels on the line. The information in these figures will be useful in coordinating the directions of transmission and output levels of different systems as discussed in paragraph 530.
155
PAR.
534_____________________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING__________________________________________________
b. The frequency allocations of Japanese available information in technical magazines and German civilian systems are shown in and there may be some other types of carrier figures 5-36 and 5-37. These are based on systems (including coaxial cable systems).
normal
OUTPUT
SYSTEM db d
r_____________________________US- SIGNAL CORPS
a-bIand B-A I
> 59 0.85 11.8
CF-l-( ) o| __________ ____If,_____4 I___
CF-l-( (PLUS CF-7 - 4 j I CH '"I lCH 11 I CH 3 111 CH 4.1 |
B-A A-B
5 9 8 85 11.8 20 65 26.55 29 5 3 2 45
cf-i-( )pluscf-4®_*£chT] [chZ]|[cK3]|[chZ1| carrier | GhT] GEZI |GhT]|[ch4]|
______ W-E 715 E-W
TYPE H +16 | VO I CE| | | | | |
E-W A W-E b I
6 3 9.4| 12 9 20 7 24 4 28.4
''cs +18 IVOICEI CH 3 ||| CH 2 | |[~CH I | | CH 2 || | CH I || | CH 3 11
TYPE C- E-W 8- W-E c
6-3 9 4| 12-9 17 7 214 25 4
^CU +18 IvOICeI p CH 3 l| I CH 21 | l~~CH I I 11 CH2 I CH I | ||| CH3 |
o 5 10 15 20 25 30 35 40
d FREQUENCY-KILOCYCLES
. PILOT FREQUENCY 9.45KC
PILOT FREQUENCY 24-35KC
C PILOT. FREQUENCY 2I-45KC
d WITH i MILLIWATT TRANSMITTED FROM SWBD OR CKT TERMINAL
BRITISH SIGNALS
B-aI 6;° A-B~
1 +1 +20 IvoiceI | |TI I
A-B AND B-A
60 9 21 12.5 16 0
1 + 4(4 WIRE) + 5 jVOICEl | CH 2 |f [~CH 3 |f |~CH~4~|f | CH 5 |f
8-A A-B
60 9k2 12^5 160 17.8 21.3 246 278 33.8
(3tlKC GrTcARR.) +5d [CHT]J[CHT]jrCH4]| (CH5jf |EhU |[CHZ]|[CH3]|[cHZj f CARRIER
B-A A-E
60 92 12.5 160 19 22.5 125.8 290 35.0
(35KC gr^carr.) +5 * S GEZ f GEZI J GEE] f [CH5J f J GEE] f [Tha] f [chT] | GEZ Carrier
A-B b B-A b |
6.3 9.4| 129 ?0-7 244 28.4
sos-3-f +i8 IvoiceI f|cH 3 |f|~CH 2 | f|ch 1 | | ch 2 if I ch 1 |f |ch 3 if
A-B C B -A C
7 7 | 10 9 14 3 . 198 23.7 • 27.7
S0T-3-F +18 IvoiceI f|CH 3 | f|CH 2 | f| CH I | f|| CH 2 | fl CH I 1 "|ch 3 I
0 5 10 15 20 25 30 35 40
FREQUENCY- KILOCYCLES
2 +I8dbm OUTPUT MAY BE OBTAINED BY AN ADDED AMPLIFIER
D PILOT FREQUENCY' A-B I2-85KC;B-A 28-45KC
C PILOT FREQUENCY: A-B I4.25KC;B-A 27-65 KC TL 54793
Figure 5-33. Frequency allocations of U. S. Army and British Army carrier telephone systems.
I
156
PAR.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 534
______________________U S SIGNAL CORPS I I I I I
TYPE B t A A7B
dp J?
Op -P X' v*
Mil Illi
CHANNEL-------*4 3 2 1 1 2 3 4
ByA A-B
Z4251275 ' Z 2125 2295 X
I I II
CHANNEL-* 5 6 5 6
E-W AND W-E
FIXED PLANT ' f ~ ~ 7
system dp # f T I 5PART OF VOICE CHANNEL J
(TH-l/TCC-ll ----------j j । I 'I ।-------------------j-------
500 1000 1500 2000 2500 3000
FREQUENCY - CYCLES
BRITISH SIGNALS
। 2Z ! 1
VOICE CHANNEL SPEECH PLUS _ | 1----------------------------------------------------------J
SIMPLEX 2300
| VOICE CHANNEL | | 1
B-A A-B 1680 I860
SPEDEUPHLEXUS I PART 0F VOICE CHANNEL | | ) PART OF VOICE CHANNEL |
B-A A-B
I I 3 CHANNEL &_„O O°_<,O° J? oP°
DUPLEX GRP. I «. 4 P P P P P P ? ? ? ? ?
GRP. 2 (PROVIDES
3 0RsyStem^NEL
° CHANNEL-*! 2 3Z x4 5 6Z x6 5 4zX3 2 lz
GROUP I GROUP 2 GROUP 2 GROUP I
B-A A-B
rfP 0-°' z z z z z ~EL I I I I I I 1 I 111 I
CHANNEL-* I 23456 654321
I I I I I
500 1000 1500 2000 2500 3000
FREQUENCY-CYCLES TL 54795
Figure 5-34. Frequency allocations of U. S. Army and British Army voice-frequency telegraph systems.
656935 O—45--12 157
NORMAL OUTPUT TYPE FACILITY db
CS OPEN WIRE +181 cauc - „ - ARMV
OPEN WIRE +161 SAME AS U-5- ARMY SYSTEMS
| 6.87 103
W-E | E-W J
D OPEN" WIRE +16 CHAN.---*4 11 | | |
E-W W-E
7-6 106 13.9 161 19.8 23-7
- CN OPEN WIRE +18 CHAN.—»| 3 | a | I "2 I ' I ' "| 3 ]
। 6.0
E-W 8c f
W-E 4-W CABLE +43 Fvd7CE~l I' I
PHANTOM ----* 1----1 1
0 5 10 15 20 2 5 30
FREQUENCY-KILOCYCLES
Figure 5-35. Frequency allocations of French carrier telephone systems. L 54794
NORMAL OUTPUT type Facility db
/-------- ONE DIRECTION----------\ /----—-----OTHER DIRECTION--------\
7.6 105 13 8 16 1 19 8 23.7
N0.I OPEN WIRE CHAN.---3 | 2 [ l" || 2 | I | 3 [■«--CHAN.
62 93 129 208 24 3 28 4
NO 2 OPEN WIRE CHAN.---3 | !p—"a ''] I 1 F " 2 l' 3 ------CHAN.
7.6 105 13-8 19.9 237 27-7
CR OPEN WIRE CHAN. »| 3 2 |~ "T ' 11 CHAN.---2 ' | ' l' "I 3
/--------------------------EAST TO WEST AND WEST TO EAST---------------------------
3 7 II 15 19 23 27
4-WCABLE +5 CHAN.----------4---»1 ' I 1^ 1 2 1 3 | ~4~" || F~ 5......il I 6
''pilot x
__________________I___________I__________________I I I I I
0 5 10 15 20 25 30
FREQUENCY - KILOCYCLES
! ! ■ - ( -——।--------------------------------------------------,---------------,------
/---ONE DIRECTION-----\ /— OTHER DIRECTION -\
35 389 42.8 491 53.2 57.3
HF OPEN WIRE I I I | 2 || I 3 L-CHAN.I I । | 2 | 3 il-CHAN.
/-----------------W-E ---------------------\ /—-----------------E —W----------------------x
33 37 41 45 49 53 57 63 67 71 75 79 83 87
NO.3 OPEN WIRE +10 to Im !m Im Im Im J— chan-Jpo Im Im Im Im Im I 'pilot' 'pilot'
/----------------- W-E --------------------x ,---------------------- £-w ---------------------\
33 37 41 45 49 53 57 63 67 71 75 79 83 87
no.4 open wire +io I r~r~il r~2~il mil rml rml mil*—chan. I Im Irm lr~b~i Irm Irm Im—chan.
'pilot' 'pilot'
___________________________________I I I I I I
30 40 50 60 70 80 90
FREQUENCY-KILOCYCLES
Figure 5-36. Frequency allocations of Japanese carrier telephone systems. TL 5*797
158
PAR.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 534
NORMAL
TYPE FACILITY OUTPUT db
I I I I I I I-----------------------------------------------------------------
60
A-B & B-A
L 4-W CABLE +43 | ~| | |
5 0
A-B Tb-A
EI.E2 OPEN WIRE p----1||-]
6.4 103
A-B | B-a|
E3 OPEN WIRE |----11 |-||
/-----a - B---\ z------B-A ----\
6.3 9.4 12 9 20.7 24 4 285
Tl OPEN WIRE +17.4 CHAN. -l~T~ilr2~l !fT~] ["Til m! ml-
/-----A-B---\ /------A-B---------\
7.7 10.9 14-3 19 8 23.7 27 7
T3 open wire +174. tmlmi lr~r~i In Im |~n
,------A-B ----x ,------B-A----\
6 9 12 18 21 24
mek3 open wire +17.4 CHAN—Jrr-]|f-g-|lr5~i ImlrmlmH—chan.
A-B B-A
44 sa
EK OPEN WIRE +174 l
i I i i r~i
/-------------- A-B ---------------—x ,------------- B-A —--------------x
6 9 12 15 18 21 24- 27 36 39 42 45 48 5, 54 57
mek open wire chan —JtmlcolciD^imlralfmlczolcgZ IrmlmlmlrmIrmlmlfrnilrm
,------------------------ A-B AND B-A -----------------------------x
12 16 20 24 28 32 36 40 44 48 5a 56
V 4-W CABLE *4 S CHAN--Jl ' I 3~~1~~4~~1 S I fe ^1---7-S ||----9--।--Io-1-n--|r7F~|
__________I___________I__________I I I I |
0 8 16 24 32 40 48 56 64
FREQUENCY - KILOCYCLES
n i i i i i i i i t । ।—i—।—।—
/----------A—B ----------\ /-------- B-A ----------x
60 68 76 84 92 108 116 124 132 140
mk open wire +,3o Jn ci (Ju Jsj Jg r4n r4n r4n i~Ui r4n
।
,—————A-B -----------------------y ,-------------B-A ----------------x
4 8 54 60 6 6 72 78 84 90 III 117 123 129 135 141 147 153
pilot 'piloF'
_____I____I_____I_____I___I_______I l l i i i i i r i
40 48 ^>6 64 72 80 88 96 104 112 120 128 136 144, 152 160 160
Tl 5479#
Figure 5-37. Frequency allocations of German carrier telephone systems.
159
PARS.
535-538________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Section V. TRANSMISSION DATA
535. GENERAL
This section gives data for use in estimating the transmission results obtainable with various combinations of wire and equipment. Transmission guides in the form of talking ranges, repeater spacings, etc., are given to indicate the types of circuit layouts which should give satisfactory transmission results under representative conditions. The data are given in tabular form in figures 5-38 to 5-48 inclusive which are collected under paragraph 544.
536. ATTENUATION AND IMPEDANCE.
a. The attenuation at various frequencies and the 1,000-cycle impedance of various types of lines are given in figures 5-38 to 5-40, inclusive.
b. The losses in figure 5-38 are for open wire lines of the type referred to in paragraph 505b, and described in detail in TM 11-368 and TM 11-2253. Lines with different wire spacings will have somewhat different attenuations and impedances but these differenceswill be unimportant for most purposes. The figures assume lines in good condition without much leakage and do not allow for the presence of ice, hoar frost, or wet snow on the line wires. If tree branches, vines, or other foreign materials are allowed to touch the wires, the losses may be much greater, the circuits may be quite noisy, and d-c telegraph circuits may be unusable. When ice or snow covers the wires the losses also will be much greater, particularly at carrier frequencies.
c. Some foreign lines will have conductor sizes different from those listed in figure 5-38. The attenuation of such lines can be estimated approximately by interpolation between the figures given. The attenuation of a phantom circuit is about 0.8 of that of the corresponding side circuit. Chapter 9 gives the relation between the diameters of American and foreign conductors.
d. Nonstabilized rubber-covered wires are greatly affected by moisture on the wires, largely because this increases the capacitance between wires. However, if the insulation of wires is not maintained the leakage losses will be greatly increased. In addition, series resistance may develop, particularly at splices where the wires tend to oxidize to form a high-
resistance contact; large additional losses and excessive noise may be introduced in this way. The losses of field wires used as pairs are not much affected by occasional contacts with tree branches and other material.
e. The transmission data in figure 5-40 are for common types of American civilian loading systems which may be used in some military installations. Similar data on foreign loading systems are in TM 11-487.
537. BRIDGING LOSSES.
a. It will sometimes be necessary to add a bridged connection to a voice-frequency circuit. The losses caused by such connections are given in figure 5-41. The loss to through transmission is the loss added to the through circuit by the bridged connection. The loss from the line to the bridged circuit is the loss in power received at the bridged line as compared with the power that would be received if the through line did not extend beyond the bridging point.
b. If there are several bridges, the total added loss in the through circuit will be the sum of the separate bridging losses. The loss will be somewhat less if the bridges are close together. The losses of figure 5-41 apply when the bridged line is long, that is, with a loss of at least 6 db. Short bridged lines terminated in Telephone EE-8—( ) will cause bridging losses intermediate between the values shown for the facility and Telephone EE-8-( ).
c. Bridging losses will vary considerably with frequency. A Telephone EE-8-( ) bridged across an open wire pair may cause a loss to through transmission of 10 to 15 db at 500 cycles (ch. 2). This will be particularly important if 500-20 cycles signaling is used on a pair.
538. LOSS OF CABLES INSERTED IN OPEN WIRE LINES.
The loss added by nonloaded cables inserted in open wire lines consists of the attenuation of the cable plus reflection losses. At carrier frequencies, the reflection losses are large because the impedance of nonloaded cable is much lower than the open wire pair impedance. The exact computation of the added loss is complicated but an approximate method, accurate for most purposes, is given in figure 5-42. As an
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CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 538-541
example of the use of figure 5-42, the loss added by inserting 2,400 feet of 19 gauge nonloaded cable in an open wire pair would be 24 X 0.22 = 5.3 db at 27 kc. The loss added by 3,200 feet would be 4.0 -|- X 3.0 = 5.8
O,2o0
db. The value 3.0 db per mile of 19 gauge cable at 27 kc is derived, by interpolation, from figure 5-39. The reflection losses and multiplying factors for frequencies other than those given in figure 5-42 can be estimated readily by interpolation.
539. EQUIPMENT LOSSES.
Equipment at terminals or intermediate points may introduce appreciable losses which must be allowed for. Switchboard losses may also be important in the case of switched circuits. Typical equipment losses are given in figure 5-43.
540. TRANSMISSION RANGES FOR NONREPEATERED VOICE-FREQUENCY CIRCUITS.
Figure 5-44 shows maximum talking ranges for various kinds of nonrepeatered voice-frequency circuits. These are shown for 6-, 18-and 30-db circuits, which are suitable respectively, for via trunks, terminal trunks, and point-to-point circuits. For pairs whose losses vary from dry to wet, the wet condition is assumed. The lengths given assume wire in good condition, without excessive leakage or high-resistance joints. Any incidental losses, discussed in paragraphs 537 to 539 inclusive, will reduce the talking range.
541. TRANSMISSION RANGES FOR REPEATERED VOICE-FREQUENCY CIRCUITS.
a. General. Talking ranges for repeatered voice-frequency circuits are given in figure 5-44. The following subparagraphs discuss the factors involved in the use of the data.
b. Telephone Repeater EE-89-A. The principal usage of this repeater is expected to be on nonloaded rubber-covered wires. The repeater can be used on open wire pairs if the line impedances are sufficiently uniform and the low power output of the repeater is not a limitation. The circuit lengths applying for this repeater in figure 5-44 assume that the repeater has 12- to 15-db gain and is located at the center of the circuit. In cases where the repeater cannot be located near the center point, the range should be reduced so that twice the dry weather loss on the short side of the re
peater exceeds the one way repeater gain by at least 6 db. This consideration will be important only on low net loss circuits. In a specific circuit, the gain actually realizable may differ somewhat from the assumed value and may be higher if the line impedances on each side of the repeater are closely the same.
c. Telephone Repeater TP-14-( ). The repeatered talking ranges given in figure 5-44 apply for this repeater except on certain types of lines where the range may be reduced because of limitations of available gain (18 db at 1,000 cycles) or balances obtainable with the networks provided in the repeater. These exceptions are covered by the notes of figure 5-44. Except for these, the application of the repeater is governed by the same transmission considerations as for the packaged voice-frequency repeater, discussed in subparagraph d below.
d. Packaged Voice-frequency Telephone Repeater.
(1) The data given in figure 5-44 apply for a packaged voice-frequency repeater operated as a 22-type repeater at the center of a circuit. Singing and crosstalk are the principal limitations on the usable gain of such a repeater. Figure 5-44 is based on gains of 20 db for nonloaded paper-insulated cable or nonloaded stabilized wire and 15 db for open wire lines, which are assumed of moderately uniform construction and impedance. Gains of 20 db could be used on the high-grade fixed plant open wire lines described in TM 11-2253. This would permit longer repeater spacings as discussed in detail in TM 11-2022. Usable gains would be lower than are assumed in figure 5-44 if the lines have large impedance irregularities or excessive crosstalk.
(2) Although figure 5-44 is for a repeater in the center of the circuit, approximately the same range could be obtained with a terminal repeater at each end of the circuit.
(3) If the desired length of circuit is greater than shown in figure 5-44, more repeaters may be added. The following shows approximately the amount of total gain usable in various numbers of repeaters: one repeater, gain G; two repeaters, 1.9G; three repeaters, 2.6G; and four repeaters, 3.3G. This assumes that the distance from the end repeaters of the circuit to the circuit terminal is equal to one half the normal spacing between repeaters. From these factors and from the differences
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
between repeatered and nonrepeatered ranges in figure 5-44, the allowable lengths of circuits with various numbers of repeaters may be estimated on stabilized wire. For example, for nonloaded Wire W-143 the nonrepeatered range for a 6-db net loss circuit is 5 miles, and the similar range for one central repeater is 22 miles or a difference of 22 — 5 = 17 miles. The allowable length for two intermediate repeaters is, therefore, 5 + 1.9(17) = 37 miles and for three intermediate repeaters is about 5 4- 2.6(17) = 49 miles. General rules for assigning gains to the various repeaters in a circuit are given in paragraph 546.
(4) On nonstabilized wire, the same method may be used but with the further restriction that the net loss in dry weather should not become less than 3 db at any time. This will limit the range of nonstabilized wires. Also, for some of the longer lengths bf repeatered open wire circuits, some manual regulation would be necessary under extreme weather conditions in the case of nominal 6-db net loss circuits.
(5) The margin against singing would be appreciably degraded by operating circuits at net losses lower than 6 db. No repeatered 2-wire line should be operated at a net loss lower than 3 db under the extreme attenuation variations likely to occur with weather and temperature changes.
(6) The data given in figure 5-44 for lead-covered cable pairs are for circuits in forward areas where crosstalk standards may be relaxed. Repeater spacings for trunk circuits in rear areas are discussed in paragraph 542.
542. VOICE-FREQUENCY LEAD-COVERED CABLES.
a. Small Cables.
(I) Lead-covered cables installed by the Army are expected to be of the 7-, 12-, or 27-quad size in most cases. These cables are used principally for 2-wire and 4-wire voice-frequency repeatered circuits in rear areas, but some use for them may be found in forward areas when conditions are reasonably stable. If both directions of the 4-wire circuits are to be operated in the same cable, 4-wire segregation arrangements similar to figure 5-85-B should be used. With such segregation, average repeater spacings up to about 40 miles for 19 gauge, 6000-88 loaded circuits, or about 70 miles for 16 gauge, 6000-88 loaded circuits may be used for 2-wire and 4-wire circuits in
American type cables of the 7- to 27-quad sizes. By using two small cables with oppositely bound 4-wire paths in different cables, higher repeater gains can be used with good crosstalk performance. This assumes that there are no 2-wire circuits in the cables. Under these conditions the above repeater spacings may be doubled, provided repeaters of sufficiently high gain are available and unusual noise conditions are not encountered, such as noisy open wire pairs tapping into the cable near repeater inputs.
(2) If the phantom is not used, capacitance unbalance corrective work during installation will not be necessary. To obtain highgrade crosstalk performance between pairs, splicing should be such as to equalize the exposure between the pairs. By this is meant that any two pairs through the spliced cable should, in so far as practicable, appear a minimum number of times as pairs of the same quad, pairs in adjacent quads, etc. The 2-wire repeater balances obtainable tend to be low, because of large capacitance deviations from pair to pair. These deviations can be improved by cutting long reel lengths at 750 or 1,500 foot intervals, and resplicing so as to equalize the pair capacitances. Splicing at these shorter intervals would also improve the crosstalk performance. Such splicing may not be practicable, however, in many Signal Corps installations.
(3) Assuming that a cable of the 7-to 27-quad size is used for 2-wire and 4-wire circuits, with the repeater spacings and methods of segregation and splicing referred to in subparagraphs (1) and (2) above, crosstalk considerations make it desirable to restrict the 2-wire circuits to lengths of one repeater section and 8-db net loss, or two repeater sections and 11-db net loss. The 4-wire circuits can be operated at net losses of 6 to 8 db (depending on the cable size, etc.) for lengths of about 500 miles. If segregation of the oppositely bound 4-wire paths is not used, the net loss of 4-wire circuits would need to be increased about 6 db to obtain crosstalk performance equivalent to that with segregation. If the average repeater spacings are in excess of those in subparagraph (1) above, the circuit net losses would need to be increased 1 db for each increase of 1 db in the repeater section loss, in order not to degrade crosstalk performance.
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CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 542-543
b. Large Cables. Large lead-covered cables (up to 300 pairs or more) may be taken over from the enemy or installed in stable areas where large numbers of circuits are needed. Special techniques and tools are required to install and maintain these cables. Special engineering is also required and this should be done well in advance of the time the cables will be used. The repeater stations will be located at fairly regular intervals which may be 35 to 100 miles, depending upon the wire gauge, loading, and transmission requirements. When existing cables are used to provide Army circuits, the best transmission results will be obtained if the Army circuits are laid out with the same repeater gains, etc. as the civilian circuits previously in operation. Information on rehabilitation of damaged long distance cables is covered in section VII.
543. CARRIER REPEATER SECTION LENGTHS.
a. General.
(1) Figures 5-45 to 5-48, inclusive, give circuit lengths and repeater spacings for carrier systems. The tables cover both single section and repeatered systems for circuit net losses of 6 db and 30 db. Lengths for other net losses, or net losses for other lengths, can be estimated by straight line interpolation between the figures. In some cases, the net loss of 30 db applies to the top channel of a system and lower net losses may be obtainable on other channels. Also, in some cases the net loss could be reduced at the expense of increased noise. The figures are based on the crosstalk and noise standards for rear areas, discussed in section VI and in chapter 12, and consideration of the available gain in the equipment.
(2) If the length of a nonrepeatered system approaches that given for 30-db net loss circuits, and if a teletypewriter is used on voice-frequency carrier telegraph channels, considerable telegraph errors due to atmospheric static may occur in the season when thunderstorms prevail. With the spiral-four carrier system, telegraph transmission may be improved under this condition by the use of telephone channel 2 instead of channel 3 because of the lower line loss of channel 2. Other expedients are repeated transmission of the message, or the use of manual telegraph during periods of high static.
b. Spiral-four Systems. Figure 5-45 applies co the physical 4-wire operation described in paragraph 522. In the case of the open wire system,
figures for two systems on a line are governed by crosstalk. Line construction described in TM 11-368 or TM 11-2253, and crosstalk standards per paragraph 549c, are assumed. Where crosstalk standards can be relaxed, longer section lengths are possible for 2-system operation on such lines. However, where existing open wire lines of other types are used, crosstalk may be inherently high and it may be necessary to adhere to the lengths given for 2-system operation and also accept poorer crosstalk.
c. Carrier Hybrid Systems.
(1) Figure 5-46 applies to the carrier hybrid system described in paragraph 523. In this case, no particular distinction has been made in the table between one- and 2-system operation on the line. The lengths indicated will allow 2-system operation on outside pairs of lines of the type described in TM 11-368. On adjacent pairs, the lengths should not exceed the values for 2-system operation in figure 5-45 and even at these lengths the crosstalk performance is likely to be poorer than indicated in paragraph 549c.
(2) Figure 5-46 gives section lengths for two values of repeater balance: 25 db and 15 db. The 25-db balance would apply to a well constructed line, without changes in wire gauge and spacing, and with inserted cables limited to the lengths and types discussed in paragraph 545. The 15-db balance is for a line of moderately poor construction with inserted lengths of cable, etc. It does not represent the worst condition that may be encountered.
d. Pair-per-system Operation of Terminals CF-l-( ). Figure 5-47 applies to the arrangements described in paragraph 524. The maximum circuit lengths for open wire assume that there are no incidental losses due to inserted cables, etc. Allowance should be made for such losses in laying out these systems.
e. Equivalent 4-wire Systems. Figure 5-48 gives data for the open wire converter, type H, and type C systems described in paragraphs 525, 527, and 528 respectively. The lengths are based on noise limitations and available gain and should be considered as maximum values. If the lines include any long lengths of cable or other sources of loss besides the open wire pair, the spacings should be shortened in proportion to the excess loss. The type C automatic regulation will be inoperative at the lengths given for nonrepeatered systems and 30-db net loss.
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544
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
544. TABULAR DATA.
Figures 5-38 to 5-48, inclusive, give data covering the transmission characteristics of wires and wire-line circuits. Information cov
ering the physical characteristics of these wires together with construction data are given in chapter 9. Further information is given in TM 11-487.
Description* D-c resistance (ohms per loop mile) 1,000-cycle impedance (ohms) Condition of wire Approximate attenuation11 (db per mile)
1 kc 8 kc 11 kc soke 30 kc
080 Copper 17.5 680-j235 Dry 0.11 0.13 0.14 0.16 0.19
Wet 0.13 0.15 0.17 0.20 0.24
104 Copper 10.3 614-jl45 Dry 0.074 0.089 0.099 0.13 0.15
Wet 0.083 0.11 0.12 0.16 0.19
128 Copper 6.8 580-j97\ Dry 0.052 0.071 0.080 0.11 0.13
Wet 0.061 0.088 0.100 0.14 0.16
165 Copper 4.1 545-j60 Dry 0.034 0.056 0.064 0.084 0.10
Wet 0.042 0.072 0.083 0.11 0.13
080 40% C-S 42.8 791-j481 Dry 0.23 0.31 0.32 0.33 0.33
Wet 0.25 0.34 0.35 0.36 0.37
104 40% C-S 25.3 686-j335 Dry 0.16 0.20 0.20 0.21 0.21
Wet 0.18 0.22 0.23 0.24 0.24
128 40% C-S 16.7 613-j227 Dry 0.12 0.14 0.14 0.14 0.15
Wet 0.13 0.16 0.16 0.17 0.18
104 30% C-S 33.8 740-j418 Dry 0.21 0.28 0.28 0.29 0.29
Wet 0.22 0.30 0.31 0.32 0.33
128 30% C-S 22.3 649-j291 Dry 0.15 0.19 0.20 0.20 0 20
Wet 0.17 0.22 0.22 0.23 0.24
083 GI 130 l,380-j830 Dry 0.36 1.2 1.4 2.1 2.5
Wet 0.37 1.2 1.4 2.1 2.5
109 GS 75 l,230-j630 Dry 0.30 1.1 1.3 1.7 2.0
Wet 0.31 1.1 1.3 1.7 2.0
• C-S denotes copper-steel. Percentage is conductivity relative to copper. GS denotes galvanized steel, GI denotes galvanized iron.
b Attenuations are foi» side circuits at 70°F and assume use of Insulators IN-15 and IN-128 in good condition, that
trees, brush, etc., do not touch wires, and that recommended construction practices are followed. Pole spacing is assumed 200 feet except for 080 copper and twin pairs for which 150 feet is assumed. Pin spacing in all cases is assumed to be 8 inches.
Figure 5-38. Transmission data on open wire lines (continued on opposite page).
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CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES
Description D-c resistance {ohms per loop mile) 1,000-cycle impedance {ohms) Condition of wire Approximate attenuation* {db per mile)
1 kc 8 kc 11 kc 20 kc 30 kc
Twin pairsh (rubber-covered wires')
W-110-B open wire 93 Dry 0.43 0.66 0.68 0.70 0.73
Wet 0.46 0.68 0.71 0.75 0.79
W-110-B tree 93 Dry 0.44 0.68 0.70 0.75 0.80
Wet 1.1 1.6 1.7 2.1 2.6
W-143 open wire • 17.5 Dry 0.13 0.14 0.14 0.16 0.17
Wet 0.14 0.16 0.17 0.20 0.23
• Attenuations are for side circuits at 70°F and assume b Two wires of one pair used in parallel form one side of use of Insulators IN-15 and IN-128 in good condition, that the circuit and two wires of another pair form the other side, trees, brush, etc., do not touch wires, and that recommended also known as spaced aerial pairs (par. 504). The open wire construction practices are followed. Pole spacing is assumed twin pair is assumed to be strung like open wire on insulators 200 feet except for 080 copper and twin pairs for which 150 and poles with 8-inch spacing. The tree twin pair is made of feet is assumed. Pin spacing in all cases is assumed to be two Wire W-110-B pairs tied to trees, the spacing varying 8 inches. from 8 to 24 inches- Attenuations apply when there are few contacts with foliage, etc.
Figure 5-38. Transmission data on open wire lines (continued).
Type Loading • D-c resistance^ {ohms per loop mile) Capacitance {mf per mile) 1,000-cycle impedance 0 (o/wis) Approximate attenuation^ {db per mile)
1 kc 8 kc 11 kc 20 kc 30 kc
Lead-covered paper-insulated cable
16 ga. sided nonloaded 42 0.062 255-j214 0.73 1.36 1.43 1.63 1.87
19 ga. sided nonloaded 86 0.062 345-j317 1.08 2.37 2.55 2.84 3.07
19 ga. pair nonloaded 86 0.084 295-j273 1.26 — — — —
22 ga. pair nonloaded 171 0.082 416-j399 1.79 — — — —
24 ga. pair nonloaded 274 0.072 558-j542 2.14 — — — —
24 ga. pair nonloaded 274 0.084 517-j503 2.31 — — — —
26 ga. pair nonloaded 440 0.069 718-j706 2.67 — — — —
16 ga. sided 6000-88 50 0.062 l,120-j53 0.19 — — — —
19 ga. sided 6000-88 94 0.062 l,125-jl03 0.36 — —— — —
• The type of loading is shown by a number representing the wire distance between loading coils expressed in feet followed by a number representing the inductance of the loading coil expressed in millihenries. b The data in this table apply at a temperature of 70° F. 0 For loaded circuits, the 1,000-cycle impedance is for the midsection point of a loading section, that is, a point midway between two adjacent loading coils. d These are quadded cables; all others are nonquadded.
Figure 5-39. Transmission data on wires and cables (continued on following page).
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Type Loading » D-c resistance*1 (ohms per loop mile) Capacitance (mf per mile) 1 .OOO-cycle impedance 0 (ohms) Approximate attenuation*1 (db per mile)
1 kc 8 kc 11 kc SO kc SO kc
Rubber-covered wire and cable
W-130-A wet nonloaded 590 0.28 432-j372 6.5 14.5 16.5 19.0 22.0
W-130-A dry nonloaded 590 0.09 775-j697 3.5 8.0 9.0 10.5 12.5
W-130-C wet nonloaded 590 0.15 560-j540 4.5 11.0 12.0 14.0 16.0
W-130-C dry nonloaded 590 0.06 900-j860 2.9 7.0 8.0 9.0 10.5
W-130 wet nonloaded 590 0.19 505-j475 5.0 12.5 13.5 16.0 18.5
W-130 dry nonloaded 590 0.07 890-j850 3.0 7.0 8.0 9.0 10.5
WD-3/TT nonloaded 590 Characteristics approximately the same as Wire W-130
W-110-B wet nonloaded 186 0.18 300-j270 2.8 6.4 7.2 8.9 11.2
W-110-B dry nonloaded 186 0.07 485-j440 1.7 3.7 4.0 4.6 5.2
W-110-B wet 5280-88 195 0.18 775-jl05 1.6 — — — —
W-110-B dry 5280-88 195 0.07 l,175-jl80 0.8 — — — —
W-50 wet nonloaded 26 0.24 112-j81 1.0 1.9 2.1 3.0 4.2
W-50 dry nonloaded 26 0.07 215-jl47 0.55 0.85 0.9 1.05 1.25
W-108 wet nonloaded 180 0.24 253-j238 3.2 7.9 8.9 10.9 12.3
W-108 dry nonloaded 180 0.13 337-j319 2.3 5.7 6.3 7.2 7.6
W-108-A wet nonloaded 230 0.24 285-j268 3.6 9.3 10.5 13.1 15.0
W-108-A dry nonloaded 230 0.13 380-j364 2.7 6.7 7.5 8.8 9.5
W-143 nonloaded 35 0.21 130-jl05 1.2 2.1 2.2 2.5 2.9
W-143 3300-88 48 0.21 870-j20 0.32 — — — —
WC-548 side nonloaded 71 0.12 235-j200 1.3 2.5 2.7 3.0 3.4
CC-358-( )side 1320-6 77 0.12 475-jl05 0.75 0.85 0.95 — —
CC-358-( )phantom nonloaded 39 0.27 130-j85 1.3 2.5 2.7 3.5 4.4
CC-345 nonloaded 90 0.14 240-j220 1.7 3.7 4.0 4.6 5.0
CC-355-A nonloaded 90 0.14 240-j 220 >.7 3.7 4.0 4.6 5.0
a The type of loading is shown by a number representing the wire distance between loading coils expressed in feet followed by a number representing the inductance of the loading coil expressed in millihenries.
b The data in this table apply at a temperature of 70° F. Data are approximate as the electrical characteristics of
these wires are subject to variations because of material substitutions and difficulties in controlling manufacturing processes.
e For loaded circuits, the 1,000-cycle impedance is for the midsection point of a loading section, that is, a point midway between two adjacent loading coils.
Figure 5-39. Transmission data on wires and cables (continued).
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CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 544
QUADDED CABLES a
Loading b Nominal0 impedance (ohms) Cut-off frequency (cycles) Attenuation, 1,000-cycle, 55° F (db per mile)
19 ga. 16 ga.
B-88-50-S 1,550 5,600 0.28 0.16
B-88-50-P 930 5,900 0.23 0.14
H-174-106-S 1,550 2,900 0.28 0.16
H-174-106-P 950 2,900 0.22 0.13
H-172-63-S 1,550 2,900 0.27 0 16
H-172-63-P 750 3,700 0.28 0.16
H-88-50-S 1,100 4,000 0.35 0.19
H-88-50-P 650 4,200 0.30 0.16
H-44-25-S 800 5,600 0.47 0.25
H-44-25-P 500 5,900 0.30 0.21
B-22-N 800 11,000 0.45 0.24
H-44-N 800 5,600 0.47 0.25
H-88-N 1,100 4,000 0.35 0.19
NONQUADDED CABLES'3
Gauge cable (B&S) Loading Nominal* impedance (ohms) Cut-off frequency (cycles) Attenuation, 1,000-cycle, 68° F (db per mile)
26 H-88 1,050 3,800 1.68
24 H-44 750 5,300 1.46
H-88 1,050 3,700 1.13
B-88 1,450 5,300 0.86
22 H-44 700 5,000 1.04
H-88 1,000 3,500 0.79
B-88 1,400 5,000 0.60
B-135 1,700 4,000 0.48
19 H-44 700 5,000 0.56
H-88 950 3,500 0.42
B-88 1,350 4,900 0.34
B-135 " ' 1,700 3,900 0.26
8 Capacitance of quadded cables: 0.062 mf per mile (side) 0.102 mf per mile (phantom).
b The first letter indicates the coil spacing (H = 6,000 ft. and B = 3,000 ft.): the first and second numbers indicate the inductances (millihenries) of the side and phantom loading coils, respectively; and the last letter indicates whether it is a side circuit (S), a phantom circuit (P), or a nonphantomed pair (N).
0 For loaded cable Z = 4 CC-358-O *---420 FT.--
~ r-T—I i—r—1 f—r-1 [—]—] I
—O--------------------------*--------------— ---------X----'W----------------O
OPEN O-------------xMLr— -------*--------------— iMz------------* vWlr —————IO OPEN
lw,'nree -o---------------yy---_*----------yy- ------------------X----------------------O--- LINE
O —----- 00------X---------JLftz- —------JUL-----X dbb- O
SPLICE I I J SPLICE
B
SCHEMATIC-MULTISECTION LAYOUT TL 5479B
Figure 5-50. Improvised loaded cable, 12-kc band, for inserting in open wire.
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PAR.
545 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
l^^o^TING^r_____FRACTIONAL CABLE ASSEMBLIES CC-358-( ) _ L CONNECTING I
WIRES i INCLUDING CONNECTORS *+"— WIRES
II II
|<-3FT. APPROX, 105 FT----p-----105 FT.----------------»|*3FT. APPROX.-*|
.LINE PROTECTOR I I LINE PROTECTOR. । I
| | f WHEN REQUIRED । | WHEN REQUIRED V ■
—--------R4—-—-4-——144-------------------------------6___
OPEN Sx y-----W2 X-xOOrJ_T a W2 /a
WIRE -T V T —---------a, cp open
line 1 A------B!--------- ----Bl-A, J-H tISI
—0--------rn-------------------* 3~t -is ------------------------------------
H A TO D DIRECTION
Z o
2 +10 --------------------------------------------
2
7 ,+6 ,+6
< +5---------------------------7--------V---------
a / +4 / /
*" / / /
0-------/-----------/--------7^-------------7
/ / -4 -A
5 /
*-8 /
-'°------------k-----------------------------
-15 -----J-----------------------------------
D TO A DIRECTION
TL 5498 9
Figure 5-53. Transmission level diagram.
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CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 546-547
546. REPEATER GAINS ON VOICEFREQUENCY CIRCUITS.
a. The repeater gains in a voice-frequency circuit must be adjusted so that singing will not occur and there will not be excessive overloading, noise, or crosstalk. Within these limitations, the overall circuit net loss should be adjusted as nearly as possible to the desired value and should be the same in both directions of transmission. Since repeaters will be located near towns or other convenient points, the distance between repeaters may not be uniform and the gains will therefore be different at different repeaters. For the same reason, the gains at any one repeater may be different in the two directions of transmission. General rules for assigning repeater gains on either 2-wire or 4-wire circuits are as follows.
(7) The transmitting gain (in the direction transmitting away from the switchboard) of the first repeater in a circuit should provide a transmission level (ch. 12) at the repeater output of +6 db for 2-wire circuits and 4-10 db for 4-wire circuits.
(2) The gain of an intermediate repeater in a given direction of transmission should not exceed the loss of the preceding line section. It may be made equal to the line section loss either on 4-wire circuits, or on 2-wire circuits if singing conditions permit. This will make the transmission level at the output of any of the intermediate repeaters not greater than -j-6 db on 2-wire circuits and 4-10 db on 4-wire circuits.
(- circuit from the input at A to the amplifier
—A-------------------Ixx _____________4o output at B is -4 db. On the disturbed circuit
u------crosstalk there is a gain of 21 — 6 = 15 db from the
A ’ bic* 1 d L°SS point of coupling at B to the output at A, since
!____________________/ /__________ the level at A is higher than the level at B.
5-jl loss • The sum gains an^ losses in the trans-
_________L * ____________ mission path between the two circuits at point
I— 9_db GAIN__________________________A is as follows:
TL 54883 . -4 - 40 4- (21 — 6) = -40 4- 11 = -29 db
Figure 5-56. Loss or gain in crosstalk path. Since the crosstalk coupling of 40 db at point
... ... ,. . __ .. . , . B appears as a crosstalk coupling of 29 db at
at point A will then be. a 32-db loss, that is, crosstalk amplification is 11 db. The
e sum of two 4-db gams and a 40-db cross- above expression may be written as follows:
talk loss, lhe sum of the two 4-db gams, that T y _i_ r t xr a v t t । at is, the gam from the sending terminal of the where L1 indicates the level at point B on the disturbing circuit to the point where the cross- disturbing circuit, L2 the level at B on the distalk loss is given, plus the gain from this point turbed circuit, N2 the net loss of the disturbed on the disturbed circuit to its receiving ter-
minal, is called the crosstalk amplification, transmission level diagram a to c on disturbing circuit This amplification may, in particular cases,
turn out to be a loss rather than a gain. If there zero level -i _4 gdb
is a known crosstalk loss between two circuits
in a particular section of line or piece of ap- \l-21 ^""J-2.1
paratus, it is necessary to know the crosstalk crosstalker—hx--------—tx.— -----xn crosstalk
amplification in order to determine the cross- A B; c loss
talk loss from the sending terminal of the listener* dx ^^^level^*
disturbing circuit to the receiving terminal -6dt>-i
of the disturbed circuit. It is this latter cross-
talk loss which is of interest in judging the "2I ”21
crosstalk performance of the circuits. Cross- transmission level diagram q to a on disturbed jircwt
talk losses between paits of two repeatered Figure 5-57. Near-end crosstalk amplification.
circuits at various points in their length can
be brought to a common base by subtracting circuit, and X the crosstalk loss at point B. from each the proper crosstalk amplification It is evident from the above that the crosstalk Crosstalk losses, thus reduced to a common amplification equals Lx — L2 4- N2. If the net base, may be combined (par. 563) to obtain loss of the disturbed circuit were zero, the the total crosstalk loss. Crosstalk amplification crosstalk amplification would be simply Li — L2. values may.be readily deduced from transmis- The crosstalk loss plus Li - L2 is called the sion level diagrams as discussed in the follow- equal level crosstalk loss, that is, the crosstalk ing subparagraphs. loss between circuit terminals when the levels
b. Near-end Case. Figure 5-57 indicates two of the two circuits at this point are alike, paralleling 2-way circuits, equipped with Couplings at various points may be reduced to
182
PAR.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 550
a common base by computing the equal level crosstalk loss corresponding to each one. This merely involves noting the level difference on the level diagrams for each point of coupling and adding it to the corresponding crosstalk loss. The equal level crosstalk between circuit terminals plus the net loss of the disturbed circuit gives the crosstalk coupling between circuit terminals for any assumed or chosen net loss.
TRANSMISSION LEVEL DIAGRAM ON DISTURBING CIRCUIT
kH7 p<+l7
ZERO LEVEL —* ___6db
\ _20 \l-20
CROSSTALKEF. ->---------{>--------/>-
* q /» / 40 d b
A D v ''CROSSTALK LOSS
MAIN TALKER -[> ----------{> T>~«.L ISTENER
kH7 [A!7
ZERO LEVEL —* I 6db
^-20 ^d-20
TRANSMISSION LEVEL DIAGRAM ON DISTURBED CIRCUIT TL 54806
Figure 5-58. Far-end crosstalk amplification.
c. Far-end Case. Figure 5-58 indicates two paralleling circuits between points A and C transmitting in the same direction. These circuits are assumed to be alike and have the same level diagram. It is assumed that there is a crosstalk loss of 40 db at point C. Since this loss occurs at points of equal level the equal level crosstalk is 40 db and the crosstalk between circuit terminals at point C is 40 db plus the net loss of the disturbed circuit, that is, 46 db. The crosstalk loss indicated at point C might be due to a lumped coupling or might be the loss, measured at C, due to distributed couplings along the length B to C. A common method of measuring such coupling involves energizing the disturbing circuit at B and comparing the powers received at C on the disturbed and disturbing circuits. The latter is called output-to-output or unamplified far-end crosstalk loss. Data in this form are often more convenient to obtain and analyze than input-to-output far-end crosstalk losses. In a more general case, the levels of the two circuits at point C would be different and the equal level crosstalk loss would not be equal to the unamplified far-end crosstalk loss.
d. Repeater Spacing. In figures 5-57 and 5-58 circuit net losses of —6 db and unamplified
crosstalk losses of 40 db are assumed in both cases. The line section losses and repeater gains for the far-end case (fig. 5-58) and for the near-end case (fig. 5-57) are 37 db and 17 db, respectively. The repeater gains for the near-end case are thus 20 db smaller than those for the far-end case. With the same crosstalk loss and 20 db smaller repeater gains the input-to-output near-end crosstalk, however, is 17 db poorer than the input-to-output far-end crosstalk. It is evident from this that the gain introduced by repeaters tends to increase the seriousness of near-end crosstalk. Hence near-end crosstalk is a factor tending to limit repeater section lengths on voice-frequency circuits, and on carrier circuits transmitting the same frequencies in both directions, such as the carrier hybrid system. With systems like the type C carrier system, which use different frequency bands in opposite directions, far-end crosstalk is normally the predominating type. An exception, as explained later, is interaction crosstalk around the repeaters. Since the transmission levels on disturbing and disturbed circuits involved in far-end crosstalk coupling are equal for like types of circuits, these repeater gains do not increase the seri ousness of far-end crosstalk and such gains are limited mainly by noise considerations.
e. Avoidance of Unusual Level Differences. With repeatered circuits transmitting the same frequency in both directions, crosstalk amplification due to level differences is inevitable. The rules for repeater spacing given in section V of this chapter are intended to suitably limit crosstalk amplification. With carrier systems such as type C, which transmit a given carrier frequency in only one direction, it is usually possible to avoid level differences, and it is important to do so. If one of two such systems has a relatively higher transmitting level, an unusual level difference is created, and the equal level crosstalk loss from the high-level to the low-level circuit will be less than if both circuits had the same transmitting levels. If a branch line joins a main line at an intermediate point in the main line repeater section, a level difference may be created and readjustment of the repeater output levels may be necessary to avoid it. If two circuits are repeatered at different points, differences in level will occur which will increase the amplified crosstalk from the higher-level to the lower-level circuit, and level adjustments to
183
PARS.
550-551 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
decrease these differences may be desirable. Where two circuits have the same repeater points but are of different loss per unit length, the best crosstalk results are obtained if the levels are so adjusted that they will be the same at the middle of the repeater section.
551. TRANSPOSITION THEORY.
a. If there were on a pole line, only a single pair of similar wires arranged in a horizontal plane and distant from sources of electrical disturbances, there would be little need for transpositions. Such sources would induce substantially equal voltages in the two wires and cause equal currents returning through the earth, and but little differential interfering current in the circuit composed of the two wires. Most of this differential current would be due to chance differences between the wires, that is , differences in sag, in diameter, in the quality of the joints, etc. Such chance irregularities in construction would not be systematic and, therefore, the interfering current would not ordinarily be reduced by transpositions.
b. When there are several telephone pairs on a pole line, the two wires of a pair can not be equally distant from all other wires on the line. Transpositions are necessary, therefore, to equalize the voltages induced in the two wires of a pair from transmission of speech, telegraph, or noise currents over various combinations of other wires on the line or over these wires with ground return.
c. To equalize the distance between two wires of a pair and a third paralleling wire it would only be necessary to transpose the pair once at the center of a long length. This would not be satisfactory from the crosstalk and noise standpoints because of the attenuation in magnitude and change in phase of the transmission currents as they proceed along the line. In figure 5-59 two near-end crosstalk paths are indicated by dotted lines, one for each half of the circuit. The transposition reverses the direction of the crosstalk current due to the second half of the line and the two crosstalk currents tend to annul. The two crosstalk currents will be out of phase by twice the phase change in the distance from the crosstalker to the transposition. If the frequency were 30 kc and the distance out to the transposition were V/2 miles the phase change out and back would be about 180°, and the two crosstalk currents would tend to add rather
than to subtract. Because the phase change per unit length increases about directly with frequency, the maximum permissible distance between transpositions depends upon the top frequency to be transmitted.
d. Since the far-end crosstalk paths indicated by dash lines in figure 5-59 are alike in attenuation and phase change, it might be thought that far-end crosstalk would be neutralized by a single transposition in a long length. Near-end crosstalk occurs, however, from the first pair to some other circuit and from this third circuit back to the second pair. If there are only two pairs on a line the important tertiary (third) circuit is the phantom of the two pairs. In order to minimize near-end crosstalk to all tertiary circuits and thus minimize the resulting far-end crosstalk component, each pair must be transposed frequently. Crosstalk involving coupling via tertiary circuits is called interaction crosstalk.
I| “12
...x? z
-Ii )\ i2/'
------------------------
TL 54804
Figure 5-59. Crosstalk with a single transposition.
e. Interaction crosstalk is particularly important at carrier repeater points, since the crosstalk path is from high-level repeater outputs to the tertiary and from the tertiary to low-level repeater inputs. The crosstalk in this path is thus amplified by the gain of the repeater. A similar path at the middle of the repeater section would be at a point of approximately zero level difference. Interaction crosstalk may occur from a repeater output to its own input and cause singing if the gain is large.
f. Various devices (TM 11-368) are used to suppress interaction crosstalk. To prevent repeater singing at frequencies above the operating range and consequent overloading of the repeater, Repeater CF-5 (carrier) is provided with a roof filter. Singing or crosstalk within the operating frequency range may require suppression measures. These measures are not needed when carrier systems restricted to a top frequency of about 12 kc are used on U. S.
184
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 551-552
TALK ------------------------------' -k
___\ "x.__________________________7
I___v-^R E FLECTION CROSSTALK,
; COUPLING
______Z.'Z.'Z.'Z.-----------LTZ~L?X l 15 ten
IMPEDANCE VFAR-END CROSSTALK
MISMATCH
COUPLING
Figure 5-60. Reflection crosstalk.
TL 54803
Army lines (TM 11-368 and TM 11-2253) or on other lines designed for a* top frequency of about 30 kc. When carrier systems with top frequencies of about 30 kc are used on U. S. Army lines some of the following suppression measures may be necessary: insertion of suppression coils in the other pairs and simplex legs; reduction of ground resistance at repeater points; and limitation of repeater section lengths.
g. When a particular frequency band is sent in only one direction on a line, far-end crosstalk is the controlling type. However, as indicated in figure 5-60, unless the pairs have terminating impedances which give a reasonably good match with the impedances of the open wire line, near-end crosstalk may be reflected
and appear as an important component of the far-end crosstalk. For this reason it is important to avoid impedance mismatches either at repeater points or at points where cable or rubber-covered wire is inserted in open wire lines (par. 545).
552. TRANSPOSITION TYPES.
a. The American, and to a considerable extent the British, system of transposing involves having all wires on a pole line normally parallel and transposing one or more of the pairs at suitable intervals. The transposition patterns used are called fundamental types and are shown in figure 5-61.
b. The letter designations are the conventional shorthand method for describing the transpositions in a pair of wires. This may be useful in obtaining information from headquarters regarding additional pairs which it may be planned to string on an existing line. In such cases the transpositions in the existing pairs may be described by the letters. For example, the set of transpositions for pair 1-2 of the U. S. Army line is type A, because this
0 I 2 3 4 5 6,7 0 NOOF
I I I I I I I_I I__| I I II I I I I I I I I I I I I I I I I I type tptl
c 29
e e 27
f F 26
9 ^|CZ>Ezaj; j. 9 25
h . 4- I —I—h 24
i wi|c_!—i 23
J J 22
: a 21
O 0 17
A^^^ZZfZDj^WpZZZD^^KZZ=>^^’GZZZ>|2Z^>CZZtz>S^^p±ZZ>^^3tzZZZ A 15
c —L | !——xzz&zzz^———I—C 13
PZ^EZae=|ZZjg^2K_.| .I YW^T-! I ^777777?^-p-jb/ZZ/ZZ- D 12
F 7ZZZZZZ2*.—1 -1—iG222ZZ2ip^—^A,272///7\2/23)t—' 1 '^7777777^727P27NC—i--1-1 j—F 10
j S/X/jfeaL i.. l ■ I . Lf। 1 ^T^zzLzLzLzz j I
‘ „j__ 1 I | ~ K 5
L ZZZZ/ZZZZZZZA^—1-1__. | I ZtZ^47/4W|Z//2^Z I I , L 4
M'222>222)222>2222)/22/2J22)222>222^-{-1~ 1 1 । 1 .^777^2)/22)222)/222\222\277it~^ 1 | I I 1-1- M 3
^22>/22)l2^)7777\>72^777ir-"\ I I —l—‘ — „ I I ^222)2222222^222)27777777777, N 2
Oi/z/\///\222A222/22222222Af222)22/2/22)2223222222277T777)’27/77777277Ac. । "'f 1 I 1 I I I I O I
Figure 5-6. Fundamental types in 32 transposition intervals.
TL 54 8 07
185
PARS.
552-553
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
pair has 15 transpositions in 32 intervals (fig. 5-61). Similarly, the type for pair 3-4 is I, since in this pair there are seven transpositions in the 32 intervals. The transposition at the end of the last interval is not counted here, but is reckoned as an S-pole transposition (subpar. d); Since capital letters and small letters denote materially different types of transpositions, great care must be used in transmitting the information by means of these letters. To properly use the shorthand method it is necessary to specify the transposition types on the various pairs and the number of pole spans involved or the length of line and average pole spacing. The types with relatively few transpositions can exist in shorter lengths of line than the types with more transpositions. For example, type M could exist in four transposition intervals, or a minimum of eight spans with rolling transpositions, which require two spans per transposition. Type A requires 32 transposition intervals or 64 pole spans.
c. Other patterns may be obtained by using more transposition poles. The usual method of designating patterns with more than 32 intervals is to indicate additional transposition poles by subscripts; for example, ai means that there are 32 additional transpositions at the mid-points of the 32 transposition intervals in figure 5-61, giving a total of 63 transpositions for at. The subscript 2 indicates two additional transpositions at the first and third quarter points of the transposition intervals in figure 5-61. Subscript 3 means transpositions at all three quarter points.
d. It is convenient to divide a line into transposition sections. Within a transposition section each pair is transposed using one of the fundamental types on one pair, a different fundamental type on a second pair, etc. The end of a section is sometimes called a balance point and is a suitable point for branching circuits or for junctions of lines with different transposition arrangements. The pole at the end of a transposition section is traditionally called the S pole. Transpositions in some of the pairs are often specified at S poles, since if the line consists of a succession of similar transposition sections the crosstalk coupling may be improved in this manner.
e The crosstalk between two transposed pairs depends considerably upon the relative type, that is, the fundamental type on one pair relative to that on the other. To obtain
the relative type, count the number of points within a transposition section where there are transpositions in one pair or the other but not in both. For example, consider pairs 1-2 and 13-14 of the U. S. Army line (figs. 5-63 and 5-64). Within the full transposition section there are 12 points where pair 1-2 is transposed and pair 13-14 is not, and 16 points where pair 13-14 is transposed and pair 1-2 is not. Hence there are 28 relative transpositions; these correspond to type d (fig. 5-61). The relative P means that all transpositions in both pairs are alike, which is undesirable. To a lesser degree it is undesirable to use a regular succession of the same relative types such as 0, M, I, A, a, an a3. Of these relative types, O is least desirable; the desirability increasing in the order named.
f. The maximum transposition pole spacing to properly control crosstalk is a function of the top frequency. For a 2-crossarm line the following rough rules may be used:
Voice frequency...........1 mile
12 kilocycles..........1,300 feet
30 kilocycles.............600 feet
g. It may be desired to add wire to lines with French or Italian transpositions. If the special hardware required is not available it may be necessary to transpose the new wire as per instructions for the U. S. Army line. In adding wire transposed American style to a line whose transposition plan is not well understood, it is best to transpose the new wire at points different from those used for the old wire, in order to avoid considerable parallels between old and new pairs which by chance are so transposed that the crosstalk coupling tends to accumulate. For example, French long distance lines (par. 561) have points four pole-spans (200 meters or 656 ft.) apart where the pairs may be rotated a quarter turn. If pairs are added under the American plan, it would be best to have the transposition poles three pole-spans apart, unless it is practical to make a careful study of both transposition plans.
553. NEW OPEN WIRE LINES.
a. A simple transposition scheme has been devised for use with U. S. Army open wire lines. The lines and the transpositions are described in TM 11-368 and TM 11-2253; the transpositions are described herein and in TB Sig 73. They are suitable for carrier operation up to 30 kc on all pairs on two standard 4-
186
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES
PAR
553
pair 88-inch crossarms, thus permitting 32 telephone channels on a single pole line. Pair 7-8 of these lines is suitable for operation up to about 150 kc. Short 2-pair crossarms for light traffic routes can be obtained by sawing 88-inch crossarms in half.
b. The expected crosstalk performance is that given in paragraph 549c for circuits up to 1,000 miles on the eight pairs, provided carrier systems like the CS and CU (par. 528c) are used. Equally good performance on 4,000 to 5,000 mile circuits is possible on selected pairs or channels. If equally good performance on all pairs of very long lines having two or more crossarms is required, information on suitable transpositions may be obtained through Army Communications Service.
c. The transpositions are made by tying the two wires of a pair into two grooves in Insulator IN-128, which is a special transposition insulator sometimes called TW. The two wires are tied on the same side of the insulator. This is known as a rolling type of transposition. Figure 5-62 shows a rolling type transposition using Insulator IN-128. It also shows a rolling type transposition on a drop bracket and a point type transposition. The point type transposition is completed over a few inches, while the rolling type requires two spans for completion. Point type transpositions using special hardware are worth while on long commercial multiarm carrier lines. The design of the U. S. Army line is such that the systematic effect of rolling type transpositions on crosstalk is greatly reduced. For this reason use of Insulator IN-128 at transposition points on Army lines will result in crosstalk performance only slightly poorer than that with point type transpositions. If drop bracket transpositions were used, the crosstalk for the worst pair combination would be about 6 db poorer than with Insulator IN-128, and the crosstalk, oh the average, about 3 db poorer. While the use of drop brackets might be expedient for some of these lines, their use should obviously be avoided on long lines on which good crosstalk performance is required.
d. Figure 5-62 also indicates an improvised tandem transposition using two Insulators IN-128. There has been concern about wire hits resulting from transposing on a single Insulator IN-128 when it is desired to use pole spacing around 200 feet, and when the available personnel cannot be expected to properly
equalize the sags of the two wires of a pair. The tandem transposition may be of interest in such situations as an alternative to the drop bracket transposition. The hardware required with the former is simpler, and the crosstalk characteristics are about like those for transpositions made with a single Insu
lator IN-128. Suitable spacings between the two Insulators IN-128 are 12 inches on straightaway line sections and 8^2 inches on corners up to 30 degrees away from the straightaway. For transpositions at corners with greater angles, it would be necessary to use two pole spans to make the turn. For the hardware, a break iron with four holes might be improvised and short shank steel pins with wooden cobs similar to those used
187
pm
■ O ' ' Ov UO 0
' Rnr
TOP VIEW
TRANSPOSING ON POINT TYPE BRACKETS
WIRE A ____ __________________________WIRE B
-------------C7_
„c B ----— TOP VIEW -----------
------
IP
SIDE VIEW ROLLING TYPE , TRANSPOSING ON DROP BRACKETS
WIRE A________________________________WIRE B
XoP VlPP --
A p .
B f
TIE BOTH WIRES TO THE-' K/J
SAME SIDE OF INSULATOR
SIDE VIEW
ROLLING TYPE,TRANSPOSING ON INSULATOR IN-rl2B
WIRE A WIRE B
u ‘
n TOp ViPv o
e-q— TT
SIDE VIEW
TRANSPOSING ON TWO TANDEM INSULATORS IN-128
TL 54808
Figure 5-62. Methods of transposing a pair of wires.
PAR.
553
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
with drop brackets could be used. The tandem, transposition could also be made by mounting wooden pins on a wooden support such as a section of crossarm. The horizontal spacing between the two wires of a pair at one of the Insulators IN-128 is about 2^ inches. Tie wires at the two insulators are not necessary.
The line wires may be easily sprung into the grooves of the two insulators. However, this reduces the sag in the two adjacent spans by 2 to 3 inches for spans between 200 and 150 feet in length. In stringing wires the tensions should be adjusted as far as practicable to obtain normal sag after transposing.
PIN SPACING
p— —16” —8"-*b—|6" —4*~ 8"~4‘—ib” —+- 8‘‘H
TRANSPOSITION POLES
OABACABADABACABADABACABADABACABASABACABAD etc. * * * *
J.ZZGZGZGZGZGZGZGZGZGZGZZZGZGZGZGZZDGZGZGZC ’ZZZZGZZZGZZZGZZDGZZZGZZZGZZDGZZDGZZDGZZDG
Izgdgdgdggcggzgzgdgdgdgdgggzgggdgzgdgdgzg:
,’0ZZGZZZZZZZGZZZGZZZGRZDGZZZ>GZZDGZGDGZZZCZ:
■*----FULL TRANSPOSITION .SECTION*ABOUT 3.6 MILES *-*- *
ZERO NOTES:
POLE |. NOMINAL DISTANCE BETWEEN TRANSPOSITION POLES IS 600 FT.
2. TIE WIRES TO SIDES OF INSULATORS AWAY FROM THE POLE.
* IN TACTICAL CONSTRUCTION, THESE POLES ARE DESIGNATED "C” POLES ON ONE-CROSSARM LINES. TL 54309
Figure 5-63. U. S. Army line, transpositions for first 4-pair crossarm.
PIN SPACING
X a1*-*}*—16" —®" X—ie>" —8" “*t*—lfeM —
TRANSPOSITION POLES OABACABADABACABADABACABADABACABAS ETC
'ii ZZCZZZCZCZGZZZCZZZCZZZCZGZCZZZZZ
13 —s/-v--xr-x<^z----v--xz-xz-xz-xz-xz-y-xz-xry-xz-y-xr
14 _^x-A-zk-zx_zx_z<-ZX-Z<-zx_ZL^zx-zX-A-y<^x_A-A--A-
ZZCZCZCZZZCZZZCZZZCZCZZZZZCZZZCZ
-------FULL TRANSPOSITION SECTION ABOUT 3-b MILES -•
ZERO
POLE
I.FOR TRANSPOSITIONS AT 'S" POLES SEE FIGURE 5-6S.
2.SPACE CROSSARMS 3 FEET.
3.F0R TRANSPOSITIONS IN PAIRS 1-2 TO 9-10 SEE FIGURE 5-63. NOMINAL DISTANCE BETWEEN TRANSPOSITION POLES IS 600 FEET TL 54810
Figure 5-64. U. S. Army line, transpositions for second 4-pair crossarm.
188
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 554-555
1-2 —4—1-----1. -I- + ■■+ ------------------------------------
3-4 ------U--FF-FF--,i-FF-ii-IF----IF-IF-Ir-IF-IF-■ F—I IF-:-IF
7-g ----—-----------—-------— — — — — — —---------------— — -
g-IO ---u-is IF--IF-IF-11-IS-IF-IF->■ 'I--t-IF-IF--IF IF IF-1F-H
11-12 --U--F— !-----IF-IF-IF-1-IF--IF—F!----FF-IF----IF —I!-U-i:
13-14-----IF-— — -------IS—-IF-----IF—---------IE----IF----IF-
17-18-----— — —-------------— ■—------— -— ----------------— ■
I9-2O|-------—- ■—f—| -------------------------------------1— :
SI 32 SI S3 SI S2 SI S2 SI S2 SI S3 SI S2 Si 52 Si S2 SI ETC
ZERO POLE x INDICATES TRANSPOSITION
- INDICATES NO TRANSPOSITION
TL 54811
Figure 5-65. U. S. Army line, transpositions at S poles.
554. U. S. ARMY LINE, NORMAL TRANSPOSITION SECTIONS.
The transposition arrangements are shown on figures 5-63 to 5-65 inclusive. Figures 5-63 and 5-64 indicate a succession of similar transposition sections each about 3.6 miles in length and ending in an S pole. Transpositions at S poles for pairs on both the first and second crossarms are shown on figure 5-65. For the first crossarm the transpositions are alike at all S poles. The drawings also show the spacing of the wires and of the transposition poles.
555. U. S. ARMY LINE, SHORT SECTIONS.
a. General. In addition to the nominal 3.6-mile transposition sections indicated on the
above figures, it may be necessary to use short transposition sections because of unavoidable discontinuities in a uniform succession of long sections. On a line where crosstalk standards are relaxed, a short section may consist of any part of a long section. Special short sections for better grade lines are described in subparagraphs b and c below. On the best lines, the number of discontinuities requiring short sections is reduced to a practical minimum. The short sections discussed in TM 11-368 (tactical lines) are usually parts of long sections. The short sections of TM 11-2253 (fixed plant lines) have, in most cases, different transposition arrangements than a part of a long section with the same number of transposition poles. The planning for the short sections specified for tactical lines is simpler but the short sections specified for fixed plant lines give better crosstalk results. In any short section of a line, the transpositions in all the pairs should follow the same short section scheme.
b. Short Sections for Tactical Lines.
(1) A suitable short section consists of any whole number of eighths of a full transposition section, but short sections of lesser length may be created. A normal one-eighth section is 2,400-feet long, but a length having not less than eight spans of wire may be used
------DIRECTION OF L I N E OF CONSTRUCTION
LONG SECTIONS
SHORT SECTIONS AND CABLE
LONG SECTIONS.
| CABLE , END SEC.
A WIRE ____________B_______ _____B___________________________B_________
______B_WIRE_____> \ A A/ ; \ A cr t— cn_o
O !n°p o ? or °
a. “-ui i-
V) ulmV) O u Zz <-> O u-coO
NOTES:
I. AT s POLES TRANSPOSE PER FlG5-65(EXCEPT SEE NOTE 4). O POLE BEGINS A LONG SECTION.
2. WIRE AON THE FIRST POLE BEYOND THE O POLE SHOULD BE ON THE SAME PIN AS IT IS ON THE FIRST POLE BEYOND THE PRECEDING S POLE.
3. SHORT SECTIONS CONSIST OF ONE OR MORE 1/8 THS OF FULL SECTION. ON TWO CROSSARM LINE THE TRANSPOSITION POLES ARE SPACED 450' OR LESS. ANY I/8TH MAY BE SHORTENED TO AS FEW AS 8 SPANS. IN 3 TO 7 SPANS USE END SECTION. ONE OR TWO SPAN END SECTIONS ARE LEFT UNTRANSPOSED.
4.IN END SECTIONS TRANSPOSE PAIRS 3-4,9-10,11-12,17-18. FOR A PAIR TRANSPOSED WITHIN A 3’SPAN END SECTION, IF DRAWINGS CALL FOR TRANSPOSITIONS AT BOTH C (ORS) ANDO POLES, OMIT BOTH; FOR A TRANSPOSITION AT 0 POLE AND NONE AT C (ORS), LOCATE THE TRANSPOSITION WITHIN END SECTION TWO SPANS BEFORE THE O POLE.
TL 54812
Figure 5-66. U. S. Army line, transpositions at junctions between long and short transposition sections.
656935 0—45-
14
189
PAR.
555
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
as an eighth section. This eighth section limitation is desirable to minimize the number of spans on a one-arm line in which the two wires of a pair are abnormally spaced because they are pulled together at Insulator IN-128. In the case of a 2-arm line the limitation is necessary in order to avoid transpositions on adjacent poles in some pairs on the second arm.
(2) On one-arm lines, if seven spans or less are to be treated, the length is regarded as an END section. An END section consisting of one or two spans is left untransposed. In an END section of three to seven spans, certain of the pairs are transposed at approximately the middle as indicated by note 4 of figure 5-66. This figure is an illustration of the use of short sections, It shows but a single
pair of wires which requires a transposition as per figure 5-65 at an S pole completing a long section, and at which a short section or series of short sections starts. While the transpositions as per figures 5-63 to 5-65 are not shown on figure 5-66, except for the transposition at the S pole, such transpositions should be installed at all transposition poles except in the special case covered by note 4 of figure 5-66. In a 3-span END section, it is not possible to transpose a pair within the section and at both terminal poles of the END section, because the transpositions require two spans for completion. For this reason certain transpositions which would normally be placed at the terminal poles of END sections as per figures 5-63 to 5-65, must be omitted with 3-span
SHORT SECTION-64 SPANS
FIRST END
POLE POLE
ABACABADABACABADABACABADABACABA
I- 2------if-----------:(■-----------„--------------JE----
3-4---if-----if-----it—----if-----if-3E--if------if-iE----
7-8 -if---it-if-it--if-if--if--if-j;-iE--js-j;---;;-je-j;-j;_
9-i° -[--I I I I I I I I H-i-------------5[------;f-------
f
SHORT SECTIONS-32, 16, 8 AND Z TO 7 SPANS
32 SPANS 16 SPANS 8 SPANS SPANS
F,RST END FIRST END FIRST END u
P0LE POLE POLE POLE POLE POLE
ABACABADABACABA ABACABA ABA So^ozp u.0.2a. uL
I _ 2-----if------------if----- ---------if----- -------JE_
3-4 if if--if----if--■'-if-- ---if-Ji--j;- ------ —if—
7-8 —if---if--if-if-if--if-if--JE- —jE-JE----JE--JE- —jj-. j—----
9-10---f—-----if----if-----if---------if-----jf- ---jf- —j.
NOTES-
I. SHORT SECTIONS SHOULD BE COMBINED AT THE END OF THE LAST FULL AS SHOWN IN FIGURE 5-69. TRANSPOSITION SECTION. THIS WILL
~ RESULT IN THE WIRES ENTERING
2. WHEN SHORT SECTIONS ARE COMBINED THE NEXT FULL’SECTION IN THE
THE END POLE OF ONE SECTION SERVES SAME PIN POSITIONS THEY WOULD AS THE FIRST POLE OF THE ADJACENT HAVE OCCUPIED IF THE SHORT SECSECTION. TION OR SECTIONS DID NOT EXIST.
3 AT THE END OF A SHORT SECTION WHEN 4. NOMINAL DISTANCE BETWEEN TRANSNO OTHER SHORT SECTION FOLLOWS, OR POSITION POLES IN SHORT SECTIONS AT THE END OF A COMBINATION OF IS 300 FEET (2 SPANS), EXCEPT IN
SHORT SECTIONS, TRANSPOSE AT THE 2 TO 7 SPANS WHERE THE DISTANCE
END POLE SO THAT THE WIRES ON THIS WILL BE FROM I TO 4 SPANS POLE OCCUPY THE SAME PIN POSITIONS
AS THEY HAD UPON LEAVING THE S POLE TL 54813
Figure 5-67. Transpositions for first crossarm, U. S. Army fixed plant short sections.
190
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES
PAR.
555
END sections. The standard S-pole transpositions are placed at the S pole preceding a short transposition section or succession of short sections. The transpositions at the last pole of such a short section arrangement are so made that each wire has the same pin position just beyond this pole as it has just beyond the preceding S pole which terminated a long section. Thus, the full transposition sections will have the wires of each* pair connected together in the same way as if the short transposition sections and any associated insulated wire or cable inserts did not exist.
(3) Short transposition sections for a 2-crossarm line are handled in a similar fashion except that the transposition interval should be reduced from 600 feet to not more than 450
feet in an eighth section. Any whole number of eighth sections or shortened eighth sections may be used to transpose a special length. The END section is handled in the same way as with a one-crossarm line. One transposition is placed in each of pairs 3-4, 9-10, 11-12, and 17-18.
c. Short Sections for Fixed Plant Lines. Figures 5-67 and 5-68 ( taken from TM 11-2253) show the transposition arrangements. Short sections for 8, 16, 32, and 64 spans are shown, the transposition pole spacing being two spans (nominally 300 feet). The 2-7 span section is the same as the END section discussed above except that TM 11-2253 (unlike TM 11-368) specifies transpositions on Insulator IN-128 at the midpoint of a 2-span END section.
SHORT SECTION-64 SPANS FIRST END-
POLE POLE
ABACABADABACABADA BACABADAB A C A B A
11-12---if---if-if---if-if-if-if-------if---if-if if---if if if-if-
13-14-------if-----if-----if------if-----if-----if------ft-----
17-18 --if-----it--if-it------if-if--it-----it-----it -y---it--
19-20 I |-1’I I I y-1-|-|-|-| ■ I-| y- |- I Illi rf~l~|-|~l l~rr~
SHORT SECTIONS-32,16, 8 AND 2 TO 7 SPANS 2 TO 7
32 SPANS 16 SPANS 8 SPANS SPANS
FIRST END FIRST END FIRST END
POLE POLE POLE POLE POLE POLE rO^oZo
ABACABADABACABA ABACABA ABA “■
11-12 if--if-if--if--if-if--it- —if-----if-it--if— --------- —if—
13-14-------if-----if-----it--— —--------if-----if—L — —it--it- -----
17-18---if-----if--if--if -—it---—----------st------------it-- —it-
19-20 -------------if--------------------it--if--it- ------- -------
notes:
I. SHORT SECTIONS SHOULD BE COMBINED OCCUPY THE SAME PIN POSITIONS AS AS SHOWN IN FIGURE 5-69. THEY HAD UPON LEAVING THE S
POLE AT THE END OF THE LAST FULL
2. WHEN SHORT SECTIONS ARE COMBINED, TRANSPOSITION SECTION. THIS WILL
THE END POLE OF ONE SECTION SERVES RESULT IN THE WIRES ENTERING THE
AS THE FIRST POLE OF THE ADJACENT NEXT FULL SECTION IN THE SAME
SECTION. AT THIS POLE TRANSPOSE PIN POSITIONS THEY WOULD HAVE
PAIR 19-20. OCCUPIED IF THE SHORT SECTION
OR SECTIONS DID NOT EXIST.
3. AT THE END OF A SHORT SECTION WHEN
NO OTHER SHORT SECTION FOLLOWS, OR 4. NOMINAL DISTANCE BETWEEN TRANS-AT THE END OF A COMBINATION OF SHORT POSITION POLES IN SHORT SECTIONS SECTIONS, TRANSPOSE AT THE END POLE IS 300 FEET (2 SPANS), EXCEPT IN SO THAT THE WIRES ON THIS POLE 2 TO 7 SPANS WHERE THE DISTANCE
WILL BE FROM I TO 4 SPANS.
TL 54814
Figure 5-68. Transpositions for second crossarm, U. S. Army fixed plant short sections,
191
PARS.
555-556
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
No. of spans Use short sections
2-7 2 to 7
8-9 a 8
10-15 8 and 2 to 7
16-17“ 16
18-23 16 and 2 to 7
24-25“ 16 and 8
26-31 16 and 8 and 2 to 7
32-33“ 32
34-39 32 and 2 to 7
40-41“ 32 and 8
42-47 32 and 8 and 2 to 7
48-49“ 32 and 16
50-55 32 and 16 and 2 to 7
56-57“ 32 and 16 and 8
58-63 32 and 16 and 8 and 2 to 7
64-65“ 64
No. of spans Use short sections
66-71 64 and 2 to 7
72-73“ 64 and 8
74-79 64 and 8 and 2 to 7
80-81“ 64 and 16
82-87 64 and 16 and 2 to 7
88-89“ 64 and 16 and 8
90-95 64 and 16 and 8 and 2 to 7
96-97“ 64 and 32
98-103 64 and 32 and 2 to 7
104-105“ 64 and 32 and 8
106-111 64 and 32 and 8 and 2 to 7
112-113“ 64 and 32 and 16
114-119 64 and 32 and 16 and 2 to 7
120-121“ 64 and 32 and 16 and 8
123-127“ 64 and 32 and 16 and 8 and 2 to 7
“No transpositions made in last span.
Figure 5-69. Combinations of U. S. Army fixed plant short transposition sections.
Figure 5-69 (from TM 11-2253) shows how to lay out short sections for lengths from 2 to 127 spans. Note 3 of figures 5-67 and 5-68 gives instructions similar to those of note 2 of figure 5-66. These instructions require transpositions in some cases at one or both of the S and 0 poles which are at the ends of a short section or series of short sections. While TM 11-2253 does not specifically cover this point, it should be noted that when a 2- or 3-span END section terminates at an 0 pole (start of long section), or has an S pole (end of long section) on one end and 0 pole on the other, the rules of TM 11-2253 may call for transpositions in certain pairs on adjacent poles. Since this is impossible with rolling type transpositions, proceed in the following manner. If the drawings call for transpositions in a pair at both ends of and within a 2- or 3-span END section omit the transpositions at the ends. If the drawings call for transpositions
in a pair at one end of and within a 2-span END section omit both transpositions. For the same situation with a 3-span END section, space the two transpositions two poles apart. It should be noted that the transposition arrangements at A, B, C, or D poles in short sections may not be the same as those used on similarly designated poles in full sections. Confusion may be avoided by associating some modifying symbol with the pole letters for short sections. For example, small letters or a circle around the capital letters might be used.
556. U. S. ARMY LINE, TRANSPOSITION POLE AND WIRE SPACING DEVIATIONS.
a. The following standards regarding deviations apply to rear area plant. For construction close to the front and relaxed crosstalk standards, small pole and wire spacing deviations are not important.
192
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 556-557
b. The actual spacing between any two successive transposition poles minus the intended average transposition pole spacing (600 ft., etc.) is called the deviation. The following are suitable standards: the maximum deviation should not exceed 100 feet; only a very small percentage of the deviations should approach 100 feet; the sum of all deviations (regardless of signs) divided by the total number of deviations should not exceed about 33 feet. A more precise rule, which permits a few very large deviations when necessary, is as follows: the sum of the squares of the deviations (in feet) in a given length of line (not longer than a repeater section nor shorter than a transposition section) should not exceed three times the given length of line (feet). However, any single deviation greater than about 400 feet should be avoided. In order to take care of local conditions when necessary, the intended average spacing may be changed at an S pole, but should not be changed between S poles.
c. The distance between the highest and lowest wires on a given crossarm, as measured at the lowest point in a span, is called the sag difference. For a one-crossarm line a maximum sag difference of 5 inches is permissible. For a 2-crossarm line the maximum sag difference should not exceed 3^2 inches and only a very small percentage of the differences should approach 3b£ inches. The average sag of the first crossarm wires in a given span should be as nearly as practicable the same as the average sag of the second crossarm wires in the same span.
557. U. S. ARMY LINE, ARRANGEMENTS FOR JOINT ENTRANCE OF TWO LINES.
a. Situations may arise where it is impracticable to avoid joining two U. S. Army lines for a short distance; for example, it might be necessary to bring two 2-arm lines into a station over a 4-arm line. Where 3-arm or 4-arm joint line sections are unavoidable they should be constructed to give the necessary physical clearance and strength, and certain precautions are necessary to obtain suitable carrier frequency crosstalk performance (par. 549c). The joint sections should not ordinarily be more than 3.6 miles long (one full transposition section) ; the pole where the two lines join should be at or within about two spans of an S pole or the terminal pole of a fixed plant or tactical short section; and transposition arrangements, pair assignments, and
avoidance of transmission level differences, as discussed in the following subparagraphs,, are required. It is assumed that standard 88-inch crossarms spaced«3 feet apart are used; if the spacing is 2 instead of 3 feet, the coupling loss will be 3 to 6 db less. The combining of two lines more than once is undesirable for crosstalk reasons.
b. To avoid the complication of additional transposition patterns, it is recommended that pairs on the third arm be transposed like those on the first arm and pairs on the fourth arm be transposed like those on the second arm. This results in transposing pairs alike on alternate arms. To obtain the maximum separation and crosstalk loss between such like-transposed pairs, it is recommended that pair 29-30 be transposed like pair 1-2, 27-28 like pair 3-4, 39-40 like pair 11-12, etc. The order of the transposition patterns on the third and fourth crossarms is reversed with respect to the order on the first two arms; that is, the patterns are allocated from right to left instead of from left to right. The crosstalk improvement resulting from this reversal is about 6 db at 30 kc and as much as 15 db at 11 kc.
c. The minimum output-to-output far-end crosstalk loss would be about 60 db at 30 kc. The far-end crosstalk loss between circuit terminals is greater than this by an amount equal to the net loss of the disturbed circuit and less by any level difference existing at the office end of the joint line. Unless there is an unusual level difference, the far-end crosstalk loss between circuit terminals should be above 60 db, the allowable value for fixed plant construction. Since a coupling loss as little as 60 db may exist in one joint section, several such sections in a telephone line are obviously undesirable.
d. As noted in TM 11-2022, a serious crosstalk problem occurs if it is attempted to operate carrier systems of maximum frequency of about 30 kc in opposite directions over the same pole line in entering an office. Such operation should be avoided except under extraordinary circumstances, since the repeater spacings given in paragraph 543 involve near-end crosstalk amplification of from about 25 to 40 db and it is difficult to find two pairs on the same line which would give satisfactory crosstalk loss between circuit terminals. For example, 80-db unamplified crosstalk loss would result in only 45-db loss after 35-db crosstalk
193
PARS.
557-558
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
amplification. However, with a 3- or 4- crossarm line it might be practical to operate two opposite directional carrier systems for about 2 miles or less, provided these systems utilized pairs on opposite sides of the poles with at least one intervening crossarm and provided the pairs had at least three relative transpositions per mile (such as pairs 7-8 and 21-22 of the U. S. Army line). The crosstalk coupling before amplification might be expected to lie between 85 and 90 db. Under such circumstances the use of dissimilar systems such as CS and CU is desirable since these involve only unintelligible crosstalk, for which a 6 db smaller crosstalk loss is permissible. Omitting the proviso for an intervening crossarm would probably decrease the crosstalk coupling loss by about 6 db, with a 4-, 3-, or 2-arm joint line section.
e. If CF-1 or CF-7 carrier systems are to be routed over a joint line section, fixed plant transpositions should be used within the joint section on all pairs. Suitable pair assignments for CF-1 and CF-7 systems on a 2-arm line are given in figure 5-31; the same assignments are recommended for the third and fourth crossarms of a joint line section. For example, CF-7 systems could suitably go on pairs 1-2, 7-8,13-14, and 19-20; and on pairs 21-22, 27-28, 33-34, and 39-40. With these assignments, the unamplified near-end crosstalk loss at 11 kc (approximate midband frequency for top channel) is not likely to be less than about 75 db. The crosstalk amplification, for the repeater spacings given in paragraph 543, amounts to around 12 to 17 db; hence the crosstalk loss after amplification is expected to be not poorer than about 60 db.
f. If the above pair assignments are not adhered to and if the joint line is transposed to fixed plant short sections, the 11 kc near-end crosstalk between vertically adjacent pairs on the second and third arms may be 3 to 10 db poorer than the crosstalk with the above pair assignments. If the joint line is transposed to a 3.6-mile transposition section, the 11 kc near-end crosstalk between pairs 11-12 and 21-22 and between pairs 13-14 and 23-24 will be about 20 db poorer than the crosstalk with the above pair assignments. This is about as bad as the crosstalk in a repeater section between horizontally adjacent pairs.
g. Ii for some reason it becomes necessary to use joint lines for several 3.6-mile sections, the S-pole transpositions shown in figure 5-70
are recommended. The purpose of S-pole transpositions is to adjust the relative phases of the crosstalk contributions from several 3.6-mile sections so that they will tend to cancel at the repeater input. S-pole transpositions do not reduce crosstalk resulting from irregularities in construction, but are effective in reducing crosstalk controlled by transposition types when the line consists of a succession of full transposition sections uninterrupted by
Pair S-pole transpositionsa
21-22 — — — X — — — X
23-24 X —• X X X — X X
27-28 — X — X — X — —
29-30 X — X — X — X X
31-32 — X — X — X — X
33-34 — X — — — X — —
37-38 — — — — — — — X
39-40 — — — X — — — —
S pole SI S2 SI S3 SI S2 SI S4
a X = transposition
— = no transposition
b Transpositions within 3.6-mile sections on third and fourth crossarms have patterns reversed from those on first two arms; that is, pair 21-22 is transposed like pair 9-10, etc. After eight S poles, repeat the S-pole transpositions shown above.
Figure 5-70. S-pole transpositions for third and fourth crossarms on poles carrying two U. S. Army lines.
intermediate short sections, lengths of inserted cable, or other discontinuities. When the line is well constructed and free from discontinuities, and the S-pole transpositions of figure 5-70 are used, it is estimated that on the worst pair combinations the crosstalk in one repeater section will be little poorer than in a single 3.6-mile joint line; under other circumstances the crosstalk in a repeater section or a line several transposition sections long may be considerably poorer than in 3.6 miles.
558. USE OF lO-FOOT CROSSARM.
a. A 10-foot, 10-pin crossarm often used in the Bell System is known as the type A. Stocks of such crossarms may be available abroad. The pin spacing of the type A crossarm, in
194
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 558-559
inches, is as follows: 12, 12, 12, 12, 16, 12, 12, 12, 12. A one- or 2-crossarm line using type A crossarms and drop brackets, and U. S. Army line transpositions and crossarm spacing, would have crosstalk about 9 db worse than that of the standard U. S. Army line. Of this increase, about 6 db is chargeable to the pin spacing and about 3 db to the drop brackets. A further increase of about 3 db would be brought about by 2-foot spacing between crossarms instead of 3-foot spacing.
b. The alternatives listed in subparagraphs (1) to (4) below are available for improving the crosstalk with the type A crossarm.
(1) Convert the type A arm to a 4-pair, 88-inch arm by boring four new holes and cutting off the excess length on each end.
(2) Convert the type A arm to a 4-pair, 10-foot arm by boring four new holes to give the following pin spacing, in inches: 8, 28, 8, 24, 8, 28, 8.
(3) Convert the type A arm to a 4-pair, 10-foot arm by using all the existing pins except Nos. 3 and 8, to give the following pin spacing, in inches: 12, 24, 12, 16, 12, 24, 12.
(4) Convert the type A arm to a 5-pair, 10-foot arm with 8-inch spacing between wires of each nonpole pair by boring four new holes and thus obtaining the following pin spacing in inches: 8,16, 8,16,16,16, 8,16, 8. Type CW (wood pins) and type CS (steel pins) 10-foot arms are already bored in this manner.
(5) These alternatives rank in the following order of merit: (2), (4), (1), (3), as regards the improvement in crosstalk between nonpole pairs. Use of standard Bell System transposition types instead of the U. S. Army types would not give enough crosstalk improvement on a one- or 2-crossarm line to warrant the additional complexity and increased number of transpositions required. If 10-foot crossarms are used, the type of construction must be made sturdy enough to withstand the increased stresses as compared to those with 88-inch crossarms.
c. If for some reason pole pairs must be used on the type A crossarm, the transposition types given in figure 5-71 are suggested for pole pairs when the U. S. Army transpositions are used on the nonpole pairs; the pole pairs should be used for voice-frequency operation only. The information for pole pairs on
the third and fourth crossarms assumes that the nonpole pairs on the third and fourth arms have reversed transposition patterns as compared to those on the first and second arms (par. 557). The crosstalk between nonpole pairs with type A crossarms and such usage will, of course, be substantially poorer than that stated for 88-inch crossarms in paragraph 557.
Transposition types a
Pair Full section Fixed plant short sections S-pole transpositions
64 spans 32 spans 16 spans 8 spans 2-7 spans
5-6 K J M 0 p p —
15-16 G K N M p p —
25-26 M L M 0 0 0 X
35-36 L M N M p p —
a Types of transpositions are shown in figure 5-61.
Figure 5-71. Transpositions for pole pairs for short voice-frequency circuits.
d. When the type A crossarm is used in commercial circuits, carrier-frequency crosstalk can be reduced by the use of four different frequency allocations for type C carrier, instead of the two allocations (CS and CU) available with packaged type C systems, or the single allocation used with tactical carrier systems.
559. BRITISH ARMY LINES.
a. Two 4-way or 8-way Arms. The British Army has a transposition system and short crossarm very similar to those used in the U. S. Army line. (Four-way in this connection means four conductors per crossarm.) This system is indicated in figure 5-72. The transpositions are arranged somewhat differently in the British and the American systems. The wire numbering is different and the British system does not contemplate the use of carrier systems on the two outside pairs of the second arm. Pair 5-6 of the British system is suitable for operation of carrier frequencies up to about 150 kilocycles.
b. Multi-airline (MAL). In some theaters, the British have used a light and rapid tactical construction known as multi-airline (par. 505d).
195
PAR. 559 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
PIN SEE
NUMBERING NOTE 6
ABAGA8A0ABACABADABAC ABADASACABAC ABACABADABACABADABACA6ADABACABA^( S/2
iST _ 34
CarmS % ■-
7/b----3t--)f---33-Z--;E-------;E-)f-jj-------j'----j!---------;f--■ ,,
u/i2 —-■-it—; Hr-iH Hr-iH Hr---)rH Hr---!HH!---3 H Hr-J Hi Hr---iH 3
2nd i3/(4 -M--)«HX--X--X--^*H--K--)e^-X--K--*H(--K--X--Mr4(--X--M--HF)(--X--K--Wr>e-K--K--ierX--)e ir CROSS “ |S/ ___________________________ ____________________________
arm Z|6 ' -> -■ :t1—Hr--------::-----ir----f——:t---it-:H I !r
Ksh- I l f I I l-l I I-I 11 l-l-t-l-l l-l-1 i I I I 11 I I j: ■ ■’ DESIGNATION —~~* ^ABACABADABACABADABACABADABACABAEABACABADABACABADABACABADABACABAS/ 5/
I I I I I I I I <000> MILES --•> 0 12 3 4 5 6 7 8
NOTES: I. THESE TR ANSPOSITIONS ARE SUITABLE FOR APPLICATION POSITION SECTION OF WHICH IT FORMS A PART. THE
TO ROUTES HAVING CROSS SECTIONS SHOWN THAT IS AVERAGE DEVIATION FOR ALL IN T E R VA L S CO MPRISING
FOR TWO 4-WAY OR TWO 8-WAY ARMS. SECTION SHOULD NOT EXCEED IO YARDS.
2. THE DESIGN IS INTENDED FOR APPLICATION TO SECTIONS 6. USE S/oDD OR S/EVEN TRANSPOSITIONS AT END OF
APPROXIMATELY 8 MILES BUT NOT EXCEEDING 8^ MILES ALTERNATE TRANSPOSITION SECTIONS.
T IT WILL BE NOTED THAT IF ONLY ONE B-WAY ARM IS
3. WHERE NECESSARY THE SECTION MAY BE TERMINATED AT USED, THE T R ANS POSIT IO N S O N THE "C" AND "D" POLES
ANY NOMINAL I MILE POINT THAT IS ANY D,E,OR SPOLE. ARE IDE NT IC A L, B U T THE POLES SHOULD STILL BE LET-
4. RESIDUAL SECTIONS LESS THAN ONE MILE IN LENGTH TERED “C"AND"D" CORRECTLY, IN ORDER TO CATER FOR
SHOULD BE DEALT WITH BY USING ONE-EIGHTH OF THE THE LATER APPEARANCE OF A SECOND ARM.
SECTION (S/o TO D) THE POLE SPACING BEING ADJUSTED 8. IF THE ROUTE HAS TO CHANGE FROM 4-WAY TO 8-WAY OR
IF NECESSARY TO SECURE EIGHT SUBSTANTIALLY EQUAL VICE VERSA FOR A FEW POLES FOR CONSTRUCTIONAL
INTERVALS. REASONS, THE CROSSING OF THE WIRES SHOULD CARRY
5. TRANSPOSITION POLES SHOULD BE SO LOCATED THAT THE 0N AS IF NO CH*NGE HAD BEEN MADE. LENGTH OF ANY TRANSPOSITION INTERVAL (NORMALLY '9. PIN SPACING :-O 8’ o 16* 0 8*0 (8* 0 8* 0 16* 0 8*0
220 YARDS) DOES NOT DIFFER BY MORE THAN 25 TWO FEET BETWEEN CROSSARMS.
YARDS FROM THE AVERAGE INTERVAL FOR THE TRAN«.
TL 548 18
Figure 5-72. British Army line transpositions (rearrangement of British Signals drawing).
SoABACABADABACABAEABACABADABACABAS|
1 PAIR I -HHHHHt------ih-it--it—HE---if—i!-if------55——Jf-iHHHHHHH-
2^-Zi pair 2---------------u-------------n-------u------------------------n---
3^--^ PAIR 3 -HHHHHHHI-------------iHHHHHHt—iHHHHHHf-HHHHHHHH
4^-^ PAIR 4-------------it-----ii It—«--------it-Hf it------it-Hf-Ht-------3!
2 - WAY -------------------8 MILES------------------------------►
ARMS
NOTES: I. TRANSPOSITION SECTION IS 8 MILES LONG.
2. INTERVAL BETWEEN TRANSPOSITION POLES IS 1/4 MILE.
S0A B A C A B A D A B A C A B A E A B A C A B A D A B A C A B A S|
A PAIR I -ii--------Ini-------------------it--------------H----------------
I 2
* —4------T* PAIR 2---------- ft------------n------------it------------------if--
3 4
*■ ■■■■*-*--* PAIR 3 -Ht—Ht--iHHHHt----IHHI--------If—it--It-If-----IHHt---31-if----3H-
5 6
* ' ' *--4--* PAIR 4 --it-ae——it——JI-it-it—Ht—HHHE--------it-iE—HE—HE------If—If—If—
7 ®-
4 4-----4 4 PAIR 5-------it-----If—«--it-------it--it--------if—Ht-3E-------if-
pair 6----ae——at——at-----3t—he-he-----st--it—;t--------it--it--if-
4-WAY
ARMS PAIR 7 --iHHf--)HHt--iHHFHHHHHHHt—iHHH-it-iHt--3HHt—
PAIR 8 iHHt iHHHHHHr--3HHHHHHt------------------31—i H H H t-i H F-i H t—t|t-—
-•-----=-------------8 MILES------------------------------►
NOTES’-I. TRANSPOSITION SECTION IS 8 MILES LONG.
2. INTERVAL BETWEEN TRANSPOSITION POLES IS 1/4 MILE.
3. THIS SYSTEM USEFUL FOR MAL ROUTES. TL 54817
Figure 5-73. British flat transposition system (rearrangement of British Signals drawing).
196
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 559-561
The most common arrangement involves two 12-inch spaced pairs on two crossarms 12 inches apart. The two pairs are usually not transposed. The far-end crosstalk is apt to be unimportant except when wire sag differences are very marked. The near-end crosstalk makes it difficult to use both pairs simultaneously for voice-frequency circuits or for carrier systems using the same carrier frequencies for both directions of transmission. Less difficulty would be expected with carrier systems such as type C which uses different carrier frequencies in the two directions. This assumes^ however, that large impedance mismatches do not exist at the terminals or at intermediate points since such mismatches would cause serious reflections of near-end crosstalk. Sometimes 4-pin crossarms are used on the multi-airlines. Horizontally adjacent wires are used as pairs. Point-type transpositions are used. Suitable transpositions for voice-frequency operation are given in figure 5-73 which is a rearrangement of a British Signals drawing.
c. Line with Rotating Pairs. The British have also used a more substantial line construction involving two short crossarms one foot apart. Each crossarm has a 12-inch spaced pair on each side of the pole and therefore there are four wires arranged on the corners of a square on each side of the pole. Diagonally opposite wires in a square are used for the two wires of a pair. Each square is rotated a quarter of a revolution in one span at specified intervals. For example, one square might be rotated at intervals of 5 spans and the second square might be similarly treated except that every fourth rotation would be omitted in order to reduce crosstalk between pairs in different squares. While experience has shown that the crosstalk with such an arrangement is rather poor, it might be expedient to use this construction for moderate distances (about 100 miles) for voice or even for carrier operation. An advantage is that no special hardware or insulators are required. A disadvantage is that wires with only one 1-foot vertical separation cross at the center of each span, with consequent chances of wire hits.
560. DIFFERENT LINES IN TANDEM.
It may be necessary to use sections of line in tandem, some of which are transposed to the American system and others to a British system. If the type of transposition system changes between repeaters, a full transposi
tion section of one type of transposition system should be completed (with the aid of intervening short sections, if necessary) before starting in with a full section of the other type of system.
561. EXISTING LINES.
a. Existing lines will be found which are not transposed according to TM 11-368 or TM 11-2253. They may be transposed by the British method (par. 559) or by the French and Italian methods shown in figures 5-74 to 5-79, inclusive. If it is desired to use such lines
or fragments of them and to add wire to them, and the special hardware required for the foreign type of construction is not available, it may be desired to fill in gaps with American construction. In such a case the best way is to terminate the American construction in an S pole of a long section or in a complete short section and to terminate the foreign line at a balance point. Filling in gaps in existing lines may involve connecting together pairs of different conductivity or gauge. Reflections occur at such junctions but these are not apt to affect
197
,\y
DIAGONALLY OPPOSITE WIRES CONSTITUTE A PAIR
TRANSPOSITION ARRANGEMENTS
GROUP
9/10_________________—._____:------1
| I 2
< 9/11 3
2 9/12+
u. 7/8 5
O -----------------—-----
id 7/9 6
id 7/10___________________________ 7
5 3/5----------------------------- 8
3/6 9
SPANS I 2 3 4 5 6 7 8 9 10 II 12 13 14 IS 16
--------- 90° ROTATION IN EACH SPAN <50 METERS)
--------- NO ROTATION
(o\ •2XI f»2'
90° ROTATION =
(•a" oij [o r •a]
IAIPOLE 2HCPOLE TL 548|8
Figure 5-74. S.E.T. Italian 9-group telephone line.
PAR.
fe1-ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
a । . a 2 . the corners of a square. Diagonally opposite
L~ -- Sf i wires in a square are used for a pair. With the
' Z Z \ Italian 9-group line construction (fig. 5-74),
» the squares are rotated rather continuously,
\*Z \V there being a 90° twist in each span. There are
/A\ Z^X' certain omissions of these twists, presumably
diagonally oppos.te Cr°!Stalk bet.ween different squares.
WIRES CONSTITUTE A PAIR ine Italian 4-group line of figure 5-75 has
180° rotations in two spans at intervals of 500 meters (1,640 feet) or more. The 4-e-roun group hne of figure 5-76 has 90° twists in one span
I at intervals of 6 or 12 spans. With the French
plan of figures 5-77 and 5-78, there is usually a 90° twist in two spans at each fifth pole. This requires special hardware at the center
3 55 °f the two spans. There is sometimes a 180°
, twist in four spans as indicated on figure 5-78.
The French plan of figure 5-79 uses a 90° twist spans-o IO 20 30 40 50 60 70 bo oo in two spans at intervals of 0.25 to 1 kilometer
9o° rotation= p° 4 [2* <»il as m(hcated by arrangements A to D. When
[z'» oij [|6 •z] there are more than four groups on a line 180°
i-sipole zap pole twists in four spans are superposed at 4-kilo-
DISTANCE (d) = 5OO METERS (1640 FEET)
TL 54819
Figure 5-75. CIRCOLO Italian State 4-group telephone line. Zi p
°l A >2 a B • oC . o D
\ Z X Z \Z Xy*
crosstalk seriously. They may have a notice- '~Z\ , ~ z*\ —/< 1 *
able effect on the balance at a 22-type repeater 2 1 X°—r~
point. The poorest return loss due to such a J
junction would be about 23 to 26 db. If it is X^Z X°Z X*Z XBZ desired to add wire with the American type Z^X rz> xx letters A to D. If a line has more than four
-D x*—------—"-------------------------------1-—° xx crossarms or if a crossarm has more than four
'z o_______________o___«_____JS__Jf_xx <> groups, then the fifth, sixth, etc., are treated
2np d <>---k— ■ —ax <> like the first, second, etc. Carrier systems may
X-ARM । a <> k k o -j: x xx o be worked on selected pairs according to some
reports. The two pairs in a square are in planes ro b ..........” 1-—*■—*x o a^ ^S’bt angles and tend to be noninductive to
x-a'rm' c <>-Ji---------------------Jt—it—xx——is if xx <> each other. Measurements in the United States
o <•--—**——** <> have indicated that this tendency may be off-
s „___3t____3,__,,_(1 Xx set to a considerable extent by irregularities
4th d xx—if--if-----------if—xx—if----------if—if—o xx in wire or pole spacing. Not all the pairs in
X ARM b •*"—v—T "—’■ r—r xx different squares are, in principle, noninduc-
k x|x j j *|* ” xx tive each other and therefore not all the
o ik 2k 3k 4K 5k 6K 7k \si , 32/ squares are rotated alike.
SEE NOTE 2
N0Tr T„E HOMINAL 0,3TANCE BETWEEN THE K POLES .3 . KILOMETER 'f F’KUre 5-80;A K'™3 3 r0U8h method Of .5/8 mile). estimating the far-end crosstalk loss of the
2 .the sequence of s poles is si,s2,si,s2 si etc. French and Italian lines for like carrier chan-
4 xxoso-ROTATiRN in 4 spans. * nels of Wb Pet loss- The data in this figure
5 o=no rotation •£ °•’ u„oi' o>’ *2 were obtained from measurements made on a
L- pole] [2 । pole] [3 polJ short length of line in the United States on
G-^p(j 10 i '* which the wires had been arranged in squares
s. the transpositions,for every B _.._,p____________ with 90° rotations in each span, and from a
20 SPANS BETWEEN THE KILO- xj 1 j x • 1 J? XT TT O A 1 • rrvi > 1 ,
METER POLES ARE AS SHOWN yC -0---’f ?-------------1 held trial of the U. S. Army line. The table in-
_ * * dicates that the crosstalk loss between pairs in
H 20 SPANStl sJ22 the same square is especially low and that the
Figure 5-78. French telephone lines in North Africa, crosstalk 1OSS between pairs in adjacent
transposition arrangements. squares may be higher, although not SO high
lettering of groups
aX aX BX
cX °x bX
azxs bX iK
D £ Ax>\ B C^> 1 |
• B --if—If—If-it—il—Jt----------il—JI—it-||—it—is- 2NDCROSSARM _^J,_L J, 1 ,,
G I ii if it if------------if if-)■----1; 3RD CROSS ARM (l—. j——o—t i—i> i—it—<>
D ■t--------'■--------«--------------------------4TH CROSS ARM
* QUARTER TURN (90°) —HALF TURN (180°)
—O—ROTATION OMITTED
TL 54823
Figure 5-79. French rotation transposition system (rearrangement of British Signals drawing).
199
PAR.
561 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
_____ Minimum par-end crosstalk loss between circuits of 6-db net loss a
Type of line Crosstalk loss for 100 miles (db)b Miles for minimum crosstalk loss
60 db 50 db
12 kc 30 kc 12 kc 30 kc 12 kc 30 kc
U. S. Army, one crossarm Adjacent pairs 74 66 2,500 400
Other combinations 78 70 6,300 1,000
Foreign Pairs in same squares 57 49 50 10 500 100
Pairs in adjacent squares 66 58 400 63 4,000 630
A
Minimum near-end UN AMPLIFIED crosstalk loss IN 100 MILES'1
Type of line Crosstalk loss for 100 miles (db)
12 kc 30 kc
U. S. Army, one crossarm Adjacent pairs 65 56
Other combinations 70 70
Foreign Pairs in same squares 48 37
Pairs in adjacent squares 56 50
a The crosstalk loss figures assume that any systematic coupling between pairs in different squares is sufficiently reduced by rotations. This assumption is dubious at carrier frequencies particularly above 12 kc when the rotations are
B
more than about 500 meters (1,640 feet) apart.
b For double the length subtract 3 db and for half the length add 3 db etc., that is subtract 10 log (L-J-100).
Figure 5-80. Crosstalk estimates, U. S. Army versus French or Italian lines.
as for the American system. As noted in the table, the estimates assume that systematic coupling between pairs in different squares is made negligible by rotations. In cases where the transposition intervals are large compared with those recommended in paragraph 552f, or where transposition pole spacing irregularities are large, the coupling between such pairs may be poorer than shown in the table. Experience with rehabilitated lines in one theater was, that because of difficulty in establishing sufficiently exact transposition intervals the crosstalk between pairs in adjacent squares was poorer than between pairs in the same square. Where the crosstalk standards of paragraph 549c are to be met, it is advisable to avoid using the same or adjacent squares for two carrier systems of the 2-wire or equivalent
4-wire types and to place such systems as far apart on the line as feasible. If carrier systems are to be placed on adjacent pairs on the U. S. Army line or on pairs in the same square or adjacent squares in a rotated square line, it is desirable to use unlike carrier systems such as the CS and CU (par. 528c). The crosstalk between such systems is unintelligible and the tolerable crosstalk loss is about 6 db less than that for like carrier systems. Figure 5-80-B gives some coupling figures for unamplified near-end crosstalk. The tabular values may be translated to crosstalk loss between circuit terminals as per paragraph 550. Voice-frequency coupling losses will be about 10 db more than those listed for 12 kilocycles in figure 5-80. Since the performance at carrier frequencies on these foreign lines is dubious, crosstalk
200
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 561-563
Type of paper-insulated cable a Pair-to-pair combination Rms capacitance unbalance (mmf per 0.1 mile) Minimum crosstalk loss in 1 mile of cable (db)
Nonloaded 30 kc Loaded 30 kc
Multiple-twin Side-to-own-side 20 70 54
Spiral-four Side-to-own-side 40 64 48
Multiple-twin Adjacent quads 15 73 57
Spiral-four Adjacent quads 2 90 74
Multiple-twin 3-quad to 9-quad layer 7 79 63
Multiple-twin 9-quad to 15-quad layer 5 82 66
a Definitions of multiple-twin and spiral-four are given in paragraph 506b.
Formulas for 1 mile of cable or less:
Nonloaded cable; minimum crosstalk loss
db = 120-20 log [CFVTOL (1-0.028 FL)]
Loaded cable; minimum crosstalk loss
db = 120 - 20 log (CFVlOL)
Figure 5-81. Minimum crosstalk loss due to capacitance unbalance.
C = root mean square (rms) capacitance unbalance (mmf per 0.1 mile)
F=frequency (kc)
L= length (miles)
Values and formulas apply particularly to equal level far-end crosstalk but are sufficiently accurate to estimate unamplified near-end crosstalk.
measurements may be necessary to obtain suitable pairs. Improvised methods of measuring crosstalk are described in paragraph 564.
562. CROSSTALK IN ENTRANCE AND INTERMEDIATE CABLES.
a. Low crosstalk loss between paper-insulated cable pairs used in open wire carrier circuits must be avoided. For this reason it is generally necessary to avoid using both sides of the same cable quad, two pairs in adjacent multiple-twin quads, or pairs in adjacent layers containing fewer than about 15 multiple-twin quads.
b. Figure 5-81 gives estimates of the minimum crosstalk losses (equal level far-end crosstalk) for such pairs in one mile of cable. The formulas in figure 5-81 may be used where estimates of crosstalk losses are needed for other frequencies, shorter lengths, or other capacitance unbalances. The estimates and formulas also apply with fair accuracy to unamplified near-end crosstalk in one-mile or shorter cables since attenuation may be neglected in such short lengths. It is assumed that the cable pairs are directly connected to the open wire or to terminal,apparatus having an impedance of about 600 ohms, because impedance match
ing devices will probably not be used at such junctions. If loaded cables are used, their cutoff frequency must be sufficiently high to permit satisfactory transmission of the top frequency of the carrier system.
c. To determine the crosstalk loss between circuit terminals corresponding to the figure 5-81 values, follow the methods in paragraph 550. This loss may then be compared with the estimated crosstalk loss (between circuit terminals) in the open wire to determine whether the over-all performance will be materially degraded by use of the cable. If there are several cables in a carrier repeater section, the total crosstalk loss for all cables should be computed as per paragraph 563.
563. COMBINATION OF CROSSTALK LOSSES.
Figure 5-82 indicates a method of combining two crosstalk losses (between circuit terminals or on some other comparable basis) to determine the total loss when the crosstalk currents are expected to combine at random. The difference between two losses is used to determine a value in db to be subtracted from the smaller of the two to get the total effect. The chart may be used for combining any number of crosstalk losses taking two at a time.
201
PAR.
564
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
A B A B A B
From To From To From To
0 0.1 3.0 2.2 2.5 2.0 6.1 6.7 0.9
0.1 0.3 2.9 2.5 2.7 1.9 6.7 7.2 0.8
0.3 0.5 2.8 2.7 3.0 1.8 7.2 7.9 0.7
0.5 0.8 2.7 3.0 3.4 1.7 7.9 8.7 0.6
0.8 1.0 2.6 3.4 3.7 1.6 8.7 9.6 0.5
1.0 1.2 2.5 3.7 4.0 1.5 9.6 10.8 0.4
1.2 1.4 2.4 4.0 4.4 1.4 10.8 12.3 0.3
1.4 1.7 2.3 4.4 4.8 1.3 12.3 14.5 0.2
1.7 1.9 2.2 4.8 5.2 1.2 14.5 19.4 0.1
1.9 2.2 2.1 5.2 5.6 1.1 19.4 Inf. Zero
5.6 6.1 1.0
A = arithmetic difference in db
B = number of db to subtract from smaller loss
Figure 5-82. Method of combining two crosstalk losses.
564. IMPROVISED METHODS OF MEASURING CROSSTALK.
a. General. Since apparatus specifically designed for measuring crosstalk is usually not available in the Army, improvised measuring methods with apparatus more generally available are described below. Figure 5-83 gives several arrangements for measuring near-end and far-end crosstalk coupling, in terms of db crosstalk loss, using apparatus of the types listed in figure 5-84. In these arrangements the wiring should be carefully laid out to avoid crosstalk in the test apparatus, by preserving pairing and by separating high-level from low-level circuits. The arrangement should be tested with 600-ohm resistors replacing the telephone lines shown in the figure, to determine whether the crosstalk in the test apparatus is insignificant. The circuit arrangements for near-end crosstalk are devised to measure the insertion loss between 600-ohm resistances, that is, the loss caused by connecting the input of the disturbing circuit to a 600-ohm transmitting circuit and the output of the disturbed circuit to a 600-ohm receiving circuit instead of connecting the transmitting circuit directly to the receiving circuit. Far-end crosstalk as usually measured (including the arrangements
shown in figure 5-83) is the crosstalk loss between the far ends of the disturbing and disturbed circuits (here assumed to be co-termin-ous); that is, measured far-end crosstalk. The loss measured is the input-to-output insertion loss between 600-ohm resistances less the insertion loss of the disturbing circuit between 600-ohm resistances. Corn 3tions to measured far-end or near-end crosstalk, to express them in terms of equal level crosstalk, can be made in accordance with the principles in paragraph 550. In measuring crosstalk on carrier or repeatered circuits, the output of the testing oscillator must be limited so as not to overload the repeaters or terminal equipment. An input of zero dbm (1 milliwatt) at zero transmission level is safe.
b. Types of Apparatus and Methods. Figure 5-84 lists some portable apparatus which can be used in the testing arrangements given in figure 5-83. The oscillators, detectors, and attenuator listed in figure 5-84 are designed for a 600-ohm impedance. They may be used directly on lines of approximately this impedance, as indicated in figure 5-83. For measurements of crosstalk on other circuits, these testing arrangements should preferably be modified by using impedance matching arrangements to match the lines to the measuring apparatus, and the lines should be properly terminated in approximately their characteristic impedances. In measuring far-end crosstalk, if the oscillator-end termination of the disturbed circuit, or the detector-end termination of the disturbing circuit, badly mismatches the line, there will be a reflected nearend-crosstalk component in the far-end crosstalk measurement. Crosstalk measurements with the apparatus shown in figure 5-84 should be made at several frequencies, except for far-end crosstalk on voice-frequency circuits, where a 1,000-cycle measurement is sufficient. Otherwise, on voice-frequency systems and at voice frequencies on channels of carrier systems, measurements should be made at 500, 1,000, and 2,000 cycles; and on carrier systems, at carrier frequencies corresponding to 500, 1,000, and 2,000 cycles in the voice channels of the disturbing circuit; and the rms (root mean square) value taken. This is obtained by averaging the power ratios (less than unity) corresponding to the db of crosstalk loss measured (ch. 12) and taking the db value corresponding to this average ratio.
202
PAR.
CHAPTER 5, VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 564
NEAR END CROSSTALK | MEASURED FAR END CROSSTALK
. ____________________________EAR BALANCE METHOD____________________________
OSCILLATOR OSCILLATOR
a4RDT. SWITCH --I--- ---- / ----------- D-P.D.T. SWITCH —i
-----------F 1 o"i“r° ----------------H------------------1\
_____I | ' , ' D,STURBING 600'"> DISTURBING ATTENUATOR _____|-1,
ATTENUATOR J 1-0 °“^ I V ' \ 1
__Q ; rO----------------------O-. j—O------------------------------ Li
I I 1 j | DISTURBED 600'" > >600“ DISTURBED
u- J-TTLc------------------oJ -----------------------------1 ---J-j
R < R > A J*
I 1 R> R>
L >300*
< <* FlRECEIVER
0=^2) —-----------------------------T
300 > >300"--- DISTURBED 600 >
I-------- -------o------------O—J
DIAGRAM B METER METHOD
OSCILLATOR OSCILLATOR
■ ____^-4PD.T. SWITCH
j ! ^DISTURBING 600"^ DISTURBING ^-4P.D.T. SWITCH
E5 I O— 1 " - " O—I I—O—{—<5 O O I
MO: _____________________a
> ■ DISTURBED 600 > 1 I [________ 1 *
; Q- q-Tq ; < , i ; ATTENUATOR
MEASU-g -ATTENUATOR* h 600 ^ DISTURBED IL [T'e'asUR|NG |
— "WHEN NECESSARY l—p. p,,.. SET
__________________DIAGRAMED________________________________________DIAGRAM F____*WHEN NECESSARY
OSCILLATOR OSCILLATOR
I I | ^4P.D.T. SWITCH , | 4PD.T. SW1TCH
I---4-----1* —o____________________ o I DISTURBING F r - ~ l~ ~i--t *"
i o 04—* L 1 " o—o, o o ;
j [ DISTURBING 600“^ jV T A [
E—-e-—' o-]- । „ I ' I y Co । ----------------
I 1 I 1 ATTENUATOR
I j -Q n . । i
O । I I 1—0----- C>—i" ° 0 Qi _____________
J ; DISTURBED 600-g Mo> DISTURBED J 'L r 1 1
L-r FT .sru,-------------------------------J t______________ ,
I _________ ___________ VVV-' REPEATER
—1 AMPLIFIER - • I I
ATTENUATOR OR DETECTOR ---’—1---
— REPEATER — ---------- ------------ ----------- DETECTOR
DIAGRAM E DIAGRAM G --------
TL 54824
Figure 5-83. Circuit arrangements for measuring crosstalk loss.
203
PAR.
564 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
c. Ear Balance and Meter Methods. Figure 5-83 gives two types of set-ups for measuring crosstalk: an ear balance method (diagrams A to C) and arrangements using meter indicating measuring sets (diagrams D to G). The ear balance arrangements are necessarily confined to measurements on voice-frequency circuits or at voice frequencies on channels of carrier systems. The meter method may be used for measuring crosstalk at voice or carrier frequencies, the limitations depending on the frequency and sensitivity range of the particular apparatus used.
d. Ear Balance Methods. Diagrams A, B, and C show three testing arrangements for measuring crosstalk using the ear balance method. This method consists of listening to the testing tone on the disturbed circuit via the crosstalk path, then switching to the oscillator circuit and adjusting the attenuator until the tone is of equal intensity. The number of db inserted in the attenuator may then be read as the crosstalk loss. Resistors R should be chosen so that the resistive component of the impedance of the receiver plus 2R is about 600 ohms at 1,000 cycles. The two resistors should be as nearly alike as practicable, preferably within 2 percent and a difference of more than 10 percent should be avoided. Suitable approximate values of R are given below for various receivers available in the Army.
Receiver Approx. 1,000-cycle receiver impedance R Total
R-22 (single receiver part of Head and Chest Set HS-19) 150 + j260 200 550 + j260
HS-30-C ) (double, insert type receivers) 130 + jl50 250 630 + jl50
Diagrams A and B are for near-end crosstalk measurements. Diagram A, the simplest arrangement may be used satisfactorily in the absence of high circuit noise. Diagram B uses an arrangement which allows noise, present on the disturbed circuit, to be heard in both positions of the oscillator. This arrangement permits a more accurate balance to be made in the presence of high noise than is possible with the arrangement in diagram A. The 300-ohm resistors prevent error in measuring the crosstalk insertion loss when the impedance of the disturbed circuit is quite different from
a 600-ohm resistance. For example, without the resistors and for a line impedance of 1,200 ohms resistance, the measured crosstalk loss would be 2.5 db too great. Evidently the resistors can be considerably below 300 ohms without causing large errors. The two resistors in different wires and on the same side of the receiver should be alike, however, and preferably within 2 percent. No padding resistors in series with the receiver are necessary. In diagram C (the arrangement for far-end tests) at least 10 db should be left in the attenuator so that the disturbing line may be properly terminated when listening is done on the disturbed circuit.
e. Meter Methods.
(1) Diagrams D, E, F, and G give crosstalk testing arrangements using meter indicating detectors. The measuring method for diagrams D and F consists of obtaining a measurement of the oscillator output power on the measuring set, then switching and measuring the power of the test frequency on the disturbed circuit. The difference in the two readings in db is a measure of the crosstalk loss. The method for diagrams E and G is to adjust the attenuator, with the switch in the oscillator position, until a meter deflection is obtained on the detector. Then switch to the disturbed circuit and again adjust the attenuator until the same meter deflection is obtained. The difference in the attenuator settings will be a measure of the crosstalk loss in db. A precaution must be taken to be certain that the detector or measuring set on the disturbed circuit is measuring the testing frequency and not noise. This should be checked by switching the oscillator on and off. If the received power with the oscillator off is at least 9 db less than that with the oscillator on, the error introduced by the noise is less than 0.5 db. By applying a correction, crosstalk may be measured in the presence of somewhat higher noise. Measure on the disturbed circuit with the oscillator on, and again with it turned off. Com- • pute the apparent crosstalk loss with the oscillator on; make a similar computation using the disturbed circuit reading with the oscillator off and the same oscillator power reading. Find the db difference between these apparent crosstalk losses, and use it in the table below to obtain a db correction. Add the correction to the apparent crosstalk loss with the oscillator turned on, to obtain the real crosstalk loss.
204
PAR.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 564
Apparatus • Frequency range (cycles) Range (db) Input or output impedance (ohms)
13A transmission measuring set 30- 20,000 4-10 to —45 dbmb 600
32A transmission measuring set 150-150,000 4-35 to —35 dbm 135 or 600
2B noise measuring set (Stock No. 3F4265) 60- 12,000 4-25 to —99 dbm at 1,000 cps 600
17B oscillator (Stock No. 3F3570-3 ) 50-150,000 4-18 to 0 dbm 135 or 600
19C oscillator 30- 15,000 up to 4-6 dbm 600
51A oscillator 2,000- 79,000 4-16 to —75 dbm 135°
5A attenuator 0-100,000 1 to 81 db loss 600
Telephone Repeater EE-99-A Voice 35 db gain for each of two amplifiers, at 1,000 cycles 300d
Telephone Repeater TP-14-( ) Voice 18 db gain at 1,000 cycles 600
a All except last two items are Western Electric Company to obtain 600-ohm output.
designations. d At least 6 db should be left in the attenuator when placed
b Dbm = db referred to 1 milliwatt. at the input of this repeater, to avoid errors due to mismatch-
0 Use 135:600 ohm coil in 32A transmission measuring set ing.
Figure 5-84. Apparatus usable in improvised crosstalk measurements.
For example, if the apparent crosstalk loss determined with the oscillator on is 50 db and with the oscillator off is 52 db, the difference is 2 db. From the table below, the correction to be applied to the 50 db reading is 4 db giving a true crosstalk loss of 50 + 4 or 54 db.
Difference in db: 6 to 9 4 to 5 3 2 1.5 1
Correction in db: 1 2 3 4 5 7
(2) Diagrams D and F are crosstalk measuring arrangements for use where a Western Electric Company 2B noise measuring set is available; or for measuring small crosstalk losses with a Western Electric Company 13A or 32A transmission measuring set at frequencies indicated in figure 5-84. For an oscillator output of 0 dbm (1 milliwatt) a maximum coupling loss of 45 or 35 db may be measured using the 13A or 32A set respectively. The Western Electric Company 2B noise measuring set may be used for measuring considerably greater values of crosstalk loss at frequencies up to around 12,000 cycles. For measurements on pairs without repeaters or terminal apparatus, larger values of crosstalk loss may be measured by using higher oscillator outputs.
(3) Diagrams E and G give crosstalk measuring arrangements to permit measurement of higher values of crosstalk loss. A repeater or amplifier, such as Telephone Repeaters EE-99-A or TP-14-( ) for voice frequencies, is used ahead of the detector to increase its sensitivity. In using Telephone Repeater EE-99-A in this measuring set-up, at least 6 db must always remain in the attenuator ahead of it to avoid inaccuracies due to the mismatch between its 300-ohm input and the rest of the measuring circuit. The equalizer networks in the repeater may be switched in, when necessary, to provide low- and high-frequency noise reduction.
f. Use of Telephone Terminal CF—1—( ).
(1) Telephone Terminal CF-l-( ) can also be used to measure crosstalk at the frequencies which are obtained when the 1,000-cycle test tone is sent on one or more of the four telephone channels. For measuring near-end crosstalk, the transmitting portion of the terminal is connected to the disturbing circuit, and the receiving portion to the disturbed circuit; the crosstalk is amplified by the receiving portion of the terminal and read on the db meter associated with the terminal;
656935 0—45
15
205
PARS.
564-565 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
and the nominal gain in the terminal is allowed for in converting the measurement into crosstalk loss.
(2) The procedure is as follows. Send normal testing power into the channel chosen for test. Set the OUTPUT key, where provided, in the NORMAL position. In the case of Carrier Terminal CF-l-B, set the channel 2 WIRE-4 WIRE key to the 2 WIRE position. Set REC LEV key in the operated position. Set MILES dial on step 0, dial 1 on step 30, dial 2 on step 4, dial 4 on step 14. Set the switch on the MEAS panel to measure the 2-wire output of the channel under test. Adjust the GAIN dial so as to obtain a deflection on the db meter. Add the setting of the GAIN dial, the reading of the db meter (upper scale, neglecting the minus sign), and the appropriate constant from the following table, to obtain the approximate crosstalk loss in db.
Channel Test frequency at output of carrier terminal (kc) Constant to be added
1 1.0 7
2 4.9 11
3 7.85 15
4 10.8 21
For example, if channel 4 is used, and the GAIN dial is on 30, and the meter reads -20, the crosstalk loss is 30-f-20-|-21=71 db. If the GAIN dial is set on its top step (step 45), the gain may vary by about ±3 db from its nominal value on account of the small amount of feedback in the receiving amplifier with this setting; and there will be a corresponding uncertainty in the crosstalk measurement.
(3) When this method is used to measure the side-to-side crosstalk in a single Cable Assembly CC-358-( ), the cable assembly should normally be connected to Telephone Terminal CF-l-( ) through a Cable Stub
CC-356 which has low crosstalk, as determined by a separate test. If the far end of the cable assembly or cable stub is left unterminated for simplicity in testing, and the crosstalk is due to capacitance unbalance, the meter reading will be approximately 12 db higher in the test condition than with the cable in service and therefore terminated, and 12 db should be added to the crosstalk loss as determined in subparagraph (2) above. Also, when the disturbing pair is unterminated, the normal meter reading will not be obtained at the output of the transmitting amplifier; this is unimportant since the proper oscillator output adjustment is not determined by this meter reading. The connectors should be dry and clean, when making the measurement and when in service.
(4) The nominal impedance of Telephone Terminal CF-l-( ) is about 470 ohms, but fairly sizable departures from this value occur, particularly at the higher frequencies; hence there will be some unwanted reflection effects, producing minor errors in the measured crosstalk, if the terminal is used to test other than spiral-four cable.
(5) Two Telephone Terminals CF-l-( ) could be used in a generally similar fashion to test far-end crosstalk, sending from one end at a time.
(6) In terminals provided with an OUTPUT key, by using + 10 db instead of NORMAL output where this is permissible, 10 db greater crosstalk loss can be measured. Crosstalk at other frequencies can be obtained by using an oscillator other than the test oscillator in the carrier terminal, and allowing for its sending level, set low enough not to overload the terminal; the transmitting portion of a v-f carrier telegraph channel might be used. If other test frequencies are used, the additive constant in the table in subparagraph (3) above should be adjusted, by interpolation, for the test frequency used.
Section VII. REHABILITATION OF CAPTURED LONG DISTANCE CABLE CIRCUITS
565. GENERAL.
a. Long distance cables in captured territory provide a means of establishing large numbers of long haul circuits with a minimum expenditure of material. Some sections of these cables and a substantial part of the loading ap
paratus may be damaged by the enemy and will need to be rehabilitated or replaced to make the circuits usable.
b. It is important that the cable sections rehabilitated initially be made capable of a good grade of transmission because with the
206
PAR.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 565
passage of time the circuits will have to be extended in length and will ultimately become part of the rear area communication network. This will require careful planning and engineering and personnel skilled in all phases of the work. It is essential to have cable splicers and testers trained in the technique of splicing and testing quadded cables. Rehabilitation done without skilled personnel and without sufficient regard to transmission performance is likely to prove unsatisfactory in the long run. Of course temporary expedients can be employed to establish circuits needed during the initial phase of rehabilitaton.
c. If need for rehabilitating a cable can be foreseen in advance it will be desirable to take steps to have the proper kind of cable, sleeves, loading apparatus, cable terminals, and miscellaneous material on hand for replacement purposes. This will greatly simplify rehabilitation and will give the best transmission results. The offices frequently will be destroyed by the enemy, so it is important to provide means for terminating the cable pairs in new offices. Sealed cable terminals are best for this purpose; for example, cable terminal having stock No. 5C2502 is suitable for terminating a 102 pair cable. Distributing frames, such as the one having stock No. 4E2523G, may be used also. If these are used, a short length of silk and cotton covered tip cable (par. 506) should be provided between the frame and the lead-covered cable. In many cases it will not be possible to duplicate apparatus or to anticipate requirements, especially as to the extent of damage. A search for material available locally will be necessary under these conditions. Replacement cable lengths may be found locally as it is the practice in some countries to store such cable in a safe place near the repeater stations. As a substitute for sleeves, lead sheet may be procurable and cut and formed to size.
d. Complete information on the cable and loading apparatus involved is essential. Some of this information can be obtained in advance, some may be obtained on the spot from local records or local inhabitants, and some can be determined by physical inspection and tests on the job. Important items are: the number of wires and wire sizes; whether the cable is paired, or has multiple-twin or spiral-four quads; cable lay-up and method of segregating 4-wire circuits; capacitance of the cable;
and inductance of the various types of loading coils and physical characteristics of loading apparatus. The extent of damage must also be known, including the length and locations of cable sections to be replaced, the number and locations of loading points requiring new loading apparatus, and the number and types of loading units required.
e. Care must be taken at all splices to keep the pairs and quads intact, since a split pair or phantom would probably be so susceptible to noise and crosstalk as to make the circuits useless. It is desirable also to restore the original continuity of each wire through a loading section in order to minimize the degradation in crosstalk (par. 568). It is not necessary to restore the original continuity of conductors at loading coil splices but it is important that a given pair or quad have the same loading throughout a repeater section (par. 569). As a preliminary to splicing it is necessary to know the code identification of the insulation. The paper may be colored or it may be plain and marked with printed numerals or symbols. The quads may have identifying thread binders. It is preferable to secure information in advance as to these codes from manufacturers records or from the local telephone administration. When this is not possible, the cable should be examined in the vicinity of a cable terminal and the cable coding determined by test. A spare or partially damaged cable terminal with some cable attached may serve the same purpose. If necessary, the sheath can be removed from the cable and very careful examination made of the cable layer by layer and quad by quad. To avoid displacing the wires during examination, the core should be bound at both ends of the exposed section, layer by layer, as they are uncovered and the quads released and bent back only as each is identified.
f. In Europe, cables with spiral-four construction (star quads) will be found, as well as multiple-twin quadded construction commonly used in the United States. The type of construction should be determined before splicing. In spiral-four cables the four wires are twisted together as a group so that each wire occupies a corner of the square thus formed. The wires in diagonally opposite corners of the square form a pair. It is difficult to distinguish between multiple-twin and spiral-four construction if the exposed wires have
207
PARS.
565-567
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
been disturbed. When there is doubt as to the type of construction and records are not available, a length of sheath should be removed and careful inspection made of the construction used.
g. Other outside plant considerations, such as special tools and equipment required, are covered in chapter 9.
h. A suggested organization of personnel for cable rehabilitation consists of a supervisor, two cable testers, and 8 to 10 splicing teams each consisting of a splicer and helper. Separate transportation for each tester and each splicing team is desirable.
i. Selection of suitable buildings for housing repeaters and other equipment is important for operation of the communication system. Factors to be considered in this connection are: adequacy of protection from weather, floor space in relation to future requirements, floor strength, living quarters for personnel, etc. (ch. 11).
566. FOUR-WIRE OPERATION.
a. It is advisable to plan on the operation of any repeatered circuits on a 4-wire basis. Two-wire repeatered circuits are much more subject to trouble from impedance irregularities caused by misplaced or damaged loading coils, etc. Irregularities of this nature merely increase the loss and introduce irregularities in the transmission-frequency characteristics of 4-wire circuits, whereas on 2-wire circuits they are likely to cause singing and require greatly reduced repeater gains. Non-repeatered 2-wire circuits can, of course, be used for short lengths, as limited by their loss. If damage to the cable is small, and the damaged loading coils can be replaced by coils having the same inductance, it may be feasible to operate 2-wire circuits on a repeatered basis.
b. The packaged voice-frequency repeaters (par. 518) are suitable for use on cable circuits. When these repeaters are not available, Repeater EE-99-A may be used. Repeater Tp_14_( ) is a 2-wire repeater but two of them can be used if necessary to make a 4-wire repeater. In this case, the gain controls of the unused amplifier of each of the two repeaters should be turned to the step which gives no transmission.
567. SEGREGATION FOR 4-WIRE OPERATION.
a. In 4-wire circuit operation, pairs in the
cable normally are divided into two groups, one for each direction of transmission. This is done to obtain a 10- to 20-db increase in the near-end crosstalk loss between opposite directional circuits; this is desirable because of the large crosstalk amplification involved (par. 550). Examples of American practice in segregating the 4-wire groups in multiple-twin cables are shown in figures 5-85-A, -B, and -C. These methods may be used also in some foreign cable installations.
b. Figure 5-85-A illustrates concentric segregation, in which inner layers are used for one direction of transmission and outer layers for the other direction. Quads for 2-wire circuits are used to separate oppositely bound 4-wire groups in the same layer. The 2-wire group may utilize a complete layer and may include quads in the center of the cable. Where oppositely bound 4-wire quads are in touching layers, dependence is placed on the opposite direction of stranding lay for these layers, and on splicing planned (in commercial installations) to minimize crosstalk coupling between groups.
c. Figure 5-85-B illustrates split-layer segregation, in which the oppositely bound 4-wire groups are diametrically opposite in each layer and separated by one or more quads of the 2-wire group. The 2-wire group may include the center quads. Figure 5-85-C is a special case of split-layer segregation, in which two diametrically opposite quads in each layer are used as separators; these separator quads are used for 2-wire circuits. Since figures 5-85-B and -C are idealized, the cross section of the cable will agree with the sketches at only a few points, because the stranding lay is clockwise for one layer and counterclockwise for the adjacent layer. However, considering each layer separately, the oppositely bound groups are diametrically opposite and separated by diametrically opposite quads of the 2-wire group.
d. Figure 5-85-D shows the 4-wire groups separated by a diametric shield. Figure 5-85-E shows them separated by a concentric shield (layer shield). Such shields may be found in some foreign cables.
e. In reconditioning a cable for 4-wire operation, it will be desirable to maintain the segregation between the 4-wire groups. Segregation is necessary because, unlike 2-wire circuits in the same group, there may be a
208
large number of repeater sections in tandem, all contributing to the crosstalk. Two repeater sections are 3 db worse than one, 4 sections 6 db worse, 8 sections 9 db worse, etc. Also the near-end crosstalk amplification for 4-wire circuits is usually much greater than that for 2-wire circuits. If segregation in a cable cannot be restored, the crosstalk degradation will depend on the number and location of the non segregated sections, and will approach 10 to 20 db in extreme cases of damage. The greatest benefit from segregation is obtained in cable sections close to the ends of the repeater sections because it is at these points that the greatest differences in level occur between oppositely bound pairs. Near the middle of the repeater section segregation is not so essential because the level differences are small.
f. To maintain segregation through undamaged lengths and replacing lengths, the two 4-wire groups must be identified. This may be a difficult problem. If a length extending out from a repeater station is undamaged and the 4-wire groups can be identified at the repeater station, the cable segregation can be determined by buzzer or other suitable identification tests from the office to the end of the undamaged portion. If the cable cannot be identified in this way either of the following methods can be tried: consult local records regarding color codes of quads, quad iount, size of conductors, type of 4-wire circuit loading, etc.; or inspect one or two undamaged splices within a loading section or an undamaged loading splice, since the groups may be indicated in splices. If identification is not possible, segregation through undamaged lengths can be
maintained by a quad-for-quad substitution provided at least one wire of each quad is continuous. Such substitution requires identification of the same quad at both ends of the damaged length, disconnection of this quad, and splicing a quad in the new length in its place.
g. If more than one cable is available on a route, opposite directional circuits can be placed in separate cables. Circuits employing different loading systems may be used in opposite directions provided both loading systems are satisfactory for the circuit length required.
h. If quads in a 2-wire group must be used to establish 4-wire circuits, there will be no segregation between opposite directional 4-wire quads. If the 4-wire repeaters are placed at the same location as the original 2-wire repeaters, and if the circuit lengths are restricted to the lengths normally used for 2-wire operation, crosstalk results should be satisfactory.
i. Segregation in replacement lengths can be accomplished by using one of the segregation methods illustrated in figures 5-85-A, -B, or -C or by using a separate cable for each direction.
568. CAPACITANCE UNBALANCE.
a. Side-to-side and phantom-to-side capacitance unbalances in cable quads are important sources of side-to-side and phantom-to-side crosstalk, respectively. The capacitances involved are those between each wire of one side circuit and the two wires of the other side circuit, in the same quad, and also the capacitances between each wire of the quad and all other conductors in the cable as well as the sheath. If certain conditions of equality are
209
PARS.
CHAPTER 5, VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 567-568
FOIL SHIELD -x F0IL
___ 2-WIRE —] SH'ELt>A/^X
z^Kwire/zX
lwireN Pwire+ Ewire/ 'wire4 CS\wireXx0vire /A ' Z
xZZ/Z+iX xX wire Vz
CONCENTRIC- - SPLIT LAYER SPLIT LAYER DIAMETRIC SHIELD LAYER SHIELD
LARGE CABLES® g, SMALL CABLES D E
A c
aTHE 2-WIRE GROUP MAY BE ABSENT OR A
SECOND 2-WIRE GROUP MAY BE IN THE CENTER OF THE CABLE TL 54825
Figure 5-85. Typical segregation methods for long distance cables.
PAR.
568 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
met in the values of these capacitances, the capacitance unbalances, and hence the within-quad crosstalk will be a minimum. In normal civilian cable installations, the capacitance unbalances are reduced as much as possible in order that crosstalk will not be excessive. This is usually done by measuring unbalances at one or more splices in the loading sections, selecting quads with approximately equal unbalances, and splicing these selected quads, with or without transpositions, as required to obtain minimum over-all loading section unbalances. On a few residual quads, the unbalances may not match satisfactorily and small condensers are connected between appropriate wires of the quad for further unbalance reduction. Another method, used on some cables installed by the Germans, involves splicing the cable without regard to capacitance unbalance, and applying capacitors at one point in a loading section on all quads having excess capacitance unbalances.
b. Restoration of a cable to its original crosstalk performance, requires capacitance unbalance tests and correction in each loading section affected. Since this requires special testing apparatus and techniques, and considerable time, it may not be practicable in most military situations. An alternative is to recondition the cable without capacitance unbalance testing, but to maintain the original continuity of the conductors to the greatest extent practicable. The resulting degradation in phantom-to-side crosstalk would be zero with no replacements and reach a maximum of about 20 db if the capacitance unbalance correction were upset in every loading section. If high crosstalk should develop as the 4-wire circuits are extended to longer lengths, it would be feasible to improve the crosstalk by use of within-quad balancing capacitors at the ends of reconditioned 4-wire repeater sections. This requires special techniques and equipment but by the time such a procedure is required it should be possible to make arrangements for these and plan the work so as to cause minimum circuit interruption. Methods of making such localized capacitance unbalance corrections, and measuring crosstalk coupling, are described in Section G72.225 and Section E36.105, issue 2 of Bell System Practices. A large reduction in side-to-side crosstalk (15 to 20 db) may be obtained in this way. The reduction in phantom-to-side crosstalk is
limited to 6 to 8 db by the differences in attenuation and velocity of propagation of the side and phantom circuits.
c. Loading section capacitance unbalances after rehabilitation depend upon the number of replaced sections, their lengths, their locations relative to loading coils or capacitance unbalance corrective splices, and whether or not the original continuity of the conductors has been restored. If the original continuity of the conductors has not been restored, the capacitance unbalance may be much greater than that of the replacement cables alone.
d. Approximate rms values of capacitance unbalances (mmf) of lead-covered multipletwin quadded cables are given in the following table. A comparison of the capacitance unbalance figures indicates the advantage of making test splices, when practicable, in which capacitance unbalance corrections are made.
Length Capacitance unbalance (mmf)
Phantom-to-side Side-to-side.
1,500-foot reel 75 30
6,000 feet (1,500-foot reels) with no test splices 150 60
6,000 feet with three test splices 15 15
6,000 feet with one test splice 40 30
The minimum crosstalk loss due to capacitance unbalances may be estimated from the following formulas:
Minimum crosstalk loss (db) (equal level far-end at 1,000 cycles),
Phantom-to-side = 180—20 log (4CV/N'V/|Zg| |ZP|) Side-to-side = 180-20 log (2CVN | Zs|)
Where C = appropriate rms capacitance unbalance (mmf) for a loading section.
N = number of loading sections.
| Zs | = magnitude of nominal impedance of side circuit (par. 571)
| Zp | = magnitude of nominal impedance of phantom circuit (par. 571)
Substitution in these formulas shows that the estimated minimum crosstalk losses are about 69-db phantom-to-side and 73-db side-to-side for a 50-mile section (N=44) having 3 test splices per loading section and using the 6000-88-50 loading system (par. 571). The rms
210
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 568-569
crosstalk losses may be estimated by adding 8 db to the minimum losses. Because of crosstalk in loading units, these minimum crosstalk losses might be reduced about 3 db. An additional reduction in the phantom-to-side minimum crosstalk loss will be caused by crosstalk coupling resulting from differences in the resistances of the two wires of the side circuit. Unless the wire joints at splices are properly soldered the latter reduction may be large and the crosstalk loss may be extremely variable.
e. Phantoms are not generally used on spiral-four quads because of the high crosstalk between side and phantom circuits in the same quad.
569. LOADING CONSIDERATIONS, 4-WIRE CIRCUITS.
a. When it is impossible to duplicate the loading apparatus which must be replaced, it will be necessary to use the nearest available equivalent as substitutes. Paragraph 571 discusses the loading systems likely to be encountered and lists a number of American loading units and loading coils whch can be used for replacement work. When the phantom will be used, it will generally be necessary to use phantom loading units which consist of two loading coils for the side circuits and one loading coil for the phantom. When phantoms are not involved, 88-mh loading coils from Signal Corps stocks may be used. These units or coils may be used singly, or two in series or in parallel to obtain close to the desired inductance.
b. Parallel or series connection of phantom loading units or coils increases the crosstalk contributed by the loading coils because of the increased number of coils on the circuit. In addition, phantom loading units of American manufacture are adjusted in the factory for minimum crosstalk in circuits having the impedance for which the loading is designed. Because of the change in circuit impedance when series or parallel connection is used, the side-to-phantom crosstalk will be increased and to a lesser extent the side-to-side crosstalk. With loading units in parallel or in series/ the phantom-to-side crosstalk per loading section may be as important as an rms capacitance unbalance of 30 to 50 mmf. The relation between mmf and crosstalk loss is discussed in paragraph 568d. Phantom loading units have a fixed ratio of side-to-phantom induc
tance, which may not be the same as that of the units which they replace, so it will not always be possible to duplicate both the side and phantom inductance.
c. When the inductance of a replacement coil is not the same as that of the coil replaced, an increase in attenuation generally results. If a number of such replacements must be made the penalty will be less if the replacements can be located at consecutive loading points so as to make a homogeneous section of circuit. If a number of the existing loading coil cases are removed for repair, it may be possible to relocate them so that the new cases can be grouped consecutively.
d. The introduction of loading coils of the wrong inductance at scattered points in a loaded circuit causes irregularities in the transmission-frequency characteristic of the circuit as well as excess loss. These effects increase with the amount of the inductance departure from normal, the number of such loading points in a repeater section, and the number of repeater sections affected. Irregularities in the transmission-frequency characteristics make it difficult to equalize the circuit and are undesirable from the standpoint of voice-frequency telegraph transmission and operation of telephone circuits at low net loss.
t n i i J । ।//i <3.5---------------FRACTION OF---]—|---------
LOADING COIL / /
INDUCTANCE / /
3.0----------------DEPARTURE —f—1--------J---
25----------------------------/-/-----r—■
T> / / /
M 20-------------------------- / /------I------
O ’ll
। 5-------------------J—X —!-----------------
\x>/ / /
i o — - - ~' y
0.5------------—--------------------y /------
_ ---*025______-*
-----------------
0 01 0.2 0.3 0.4 05 0.6 0.7 0.8 09 1.0
FRACTION OF CUTOFF FREQUENCY
TL 53250
Figure 5-86. Loss caused by a departure from average inductance at a single loading point.
e. Figure 5-86 gives data for estimating the approximate increase in line loss which will occur when a loading coil with an inductance excess or deficiency is inserted at a single loading point. For example, if an 88-mh coil
211
PAR.
569
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
is used in place of a 177-mh coil at one loading point of a circuit having 177-mh loading at 6,000 feet spacing, the increased loss would be 0.9 db at 2,000 cycles. This is obtained by reading the curve for a loading departure of
— 0.5 and for a fraction of the cut-off 177
frequency of = 0-7. The value of 2,900 cycles, for the cut-off frequency of 6000-177 loading, is obtained from figure 5-89. A similar use of figure 5-86 gives an excess loss of 0.2 db at 1,000 cycles, for this example.
f. Loading coils with equal inductance departures at two or more widely separated points will cause an increase in loss roughly proportional to the number of coils. Continuing the example of subparagraph e above, the effect of substituting 88 mh for 177-mh coils at five well separated points in a circuit would be in the order of 5 db at 2,000 cycles and 1 db at 1,000 cycles. This represents a considerable narrowing of the useful frequency band. If similar irregularities occurred at 10 loading points the effect would be twice as great as for 5 points, provided the 10 points were scattered over two or more repeater sections. If scattered over only one repeater section, the excess loss probably would not be as large as that estimated by this method because a considerable separation between the loading irregularities is necessary for figure 5-86 to apply. However, the transmission-frequency characteristic would tend to have large irregularities in this case, as discussed in subparagraph d above.
g. When coils having the wrong inductance are used at consecutive loading points instead of being widely scattered, the loss increase will be at a slower rate than the increase in number of coils; if the number of such points is large, the transmission loss of the complete section approaches the sum of the attenuations of the original and repaired sections plus a small (usually negligible) reflection loss at the junctions. When this condition is reached, if the replacement coils have a lower inductance than the original, the loss of the complete section will have increased; if they have a higher inductance, the loss at low and medium frequencies will have decreased but the cut-off frequency will have been lowered. This is illustrated by the results of computations made by exact methods which show that
if half of a normal repeater section were 6000-88 loaded and the other half 6000-177 loaded, the repeater section loss at 1,000 cycles would be about 1.5 db more than if the whole repeater section were 6000-177 loaded. The cut-off frequency would be that of the 6000-177 loading. A similar type of computation indicates that the substitution of 88-mh for 177-mh coils at five consecutive loading points in a 6000-177 loaded circuit would increase the loss 1.1 db at 2,000 cycles. Tnis, of course, is much less than the effect of substitution at five widely separated points, as estimated in subparagraph f above.
h. Incorrect loading section capacitance is also a cause of impedance irregularity. This may result from replacing portions of the cable with cables having different pair capacitance per mile from that of the original. Military stocks of lead-covered cable have a nominal pair capacitance of 0.062 mf and phantom capacitance of 0.102 mf per mile. The nominal capacitances per mile of commercial long distance multiple-twin quad cables are expected to lie in the range from about 0.054 to 0.62 mf for side circuits and 0.087 to 0.102 mf for phantoms. Lead-covered cable with spiral-four quads usually have a capacitance of 0.062 mf per mile for the side circuits and about three times as high for the phantom. The effect of a capacitance excess or deficiency, expressed as a fraction of normal loading section capacitance, is approximately the same as for an equal fractional excess or deficiency in loading coil inductance. This can be estimated from figure 5-86.
i. The end section of a loaded cable is the distance from the office to the first loading point in the repeater section, expressed as a fraction of the normal distance between loading points. Loaded cables are usually terminated at about 0.5 end section. Some loading systems are designed for midcoil termination, in which case there is a coil of half the normal inductance at the office and a full section of cable between the office loading coil and the next loading point. If the cable has to be rerouted, or the office relocated, it may not be feasible to restore the original end section or termination of the cable. This will not be serious in the case of four-wire operation as the principal effect will be to make it somewhat more difficult to equalize long circuits. The
212
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 569-570
effect of end sections on 2-wire circuits is discussed in paragraph 570b(6).
j. Foreign cables of the Krarup type have conductors which are continuously loaded by means of iron wire wrapped spirally around each conductor. If sections of this type of cable must be replaced, probably the only practicable expedient will be to use ordinary nonloaded lead-covered cable. This will increase the loss and introduce impedance irregularities but the effects should be tolerable for 4-wire circuit operation if the replacement lengths do not total more than about a mile per repeater section. More extensive repair would require special engineering, including consideration of applying coil loading to any long lengths of the replacement cable.
570. TWO-WIRE CIRCUITS.
a. Capacitance Unbalance. Near-end crosstalk is amplified by repeaters on either 4-wire or 2-wire circuits. On 4-wire circuits suitable near-end crosstalk performance is obtained by segregation (par. 567). On 2-wire circuits suitable near-end crosstalk performance for circuits in the same quad cannot be obtained even though the repeater gains are less and the circuits are shorter, unless the capacitance unbalances are low. Therefore, capacitance unbalances within quads carrying 2-wire circuits, if near a repeater, are very much more serious than they are in 4-wire circuits. Unbalances near the middle of a 2-wire repeater section are not so important because of the smaller level differences at such points.
b. Loading Considerations.
(1) In rehabilitating 2-wire cable circuits the loading considerations discussed in paragraph 569 apply. It is highly desirable to duplicate the original loading units or else select units having the right inductance. Selections may be made from the American loading units discussed in paragraph 571.
(2) Any deviation from uniformity in loading coil inductance or loading section capacitance will cause impedance irregularities in a loaded circuit. These irregularities will affect the balance of 2-wire repeaters used on the circuit. The effects on balance may be estimated by using figure 5-87. This figure shows the approximate return loss caused by inserting a loading coil of incorrect inductance at one loading point. If the loading point is at a distance from the repeater, the actual return loss at the repeater will be approximately
(R -J- 2A) db where R is the return loss obtained from figure 5-87, and A is the loss between the repeater and the loading irregularity. Hence, an irregularity will have the least effect on balance if it is located at the center of a repeater section. If there is more than one loading irregularity in the repeater section, the return loss at the repeater will be the combined return loss of each irregularity computed separately. The separate return losses should be converted to power ratios, added, and reconverted to db, to secure the combined return loss. The method of converting db to power ratio and vice versa is described in chapter 12. Return losses in db are considered to be negative when using chapter 12. Return loss computations should be made using the frequency at which the repeater is most likely to sing. This frequency will depend on the type of filter used in the repeater, but, in the absence of other information, a frequency of 2,500 cycles per second may be used.
30. — ( । ,
\ FRACTION OF
25 ____\------------------------LOADING COIL------------,
\ INDUCTANCE
„ k \ DEPARTURE
J> XX ..
■u 20------\X X---------------------------------------------
3 !5---------^0.25------------------------------------------
| '0------------
5---------------------- —
o’-------------------------------J-----1----
0 0.1 0 2 0 3 04 0.5 16 0.7 0.8 0.9 1.0
FRACTION OF CUTOFF FREQUENCY TL 54981
Figure 5-87. Return loss caused by a departure from average inductance at a single loading point.
(3) The procedure described in subparagraph (2) above, is illustrated in the following example. Assume that a repeatered, 2-wire, 19-gauge circuit with 6000-177 loading has an 88-mh loading coil substituted for a 177-mh coil at one loading point. Let this loading point be so located that there is a loss of 3.5 db between it and the 2-wire repeater. The loading
• • 177-88
coil inductance departure is — — — 0.5 and
the fraction of the cut-off frequency is^^ = 0.86. Figure 5-87 indicates that the return loss
of this irregularity will be 4 db at the loading point. The return loss at the repeater will be 4
+ (2 X 3.5) — 11 db. If there were another
similar loading irregularity located 6.5 db away
213
PARS.
570-571 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
from the repeater, the return loss of this second irregularity would be 4 4- (2 X 6.5) = 17 db at the repeater. The power ratios corresponding to 11 db and 17 db are 0.08 and 0.02, respectively. The sum is 0.10 which corresponds to about 10 db. This is the combined return loss of the loading irregularities at the repeater. A return loss of 10 db would be too low in the usual case, as it would permit the repeater to have only about 5-db gain. Under conditions of smaller inductance departures located further away from the repeater, computations of this sort might indicate that satisfactory repeater gains could be used.
(4) Although figure 5-87 is drawn in terms of loading coil inductance departure, it may be used to determine the effect of capacitance deviations, as described in subparagraph 569h. Such deviations will most often occur when a loading section is too long or too short. For example, if the normal loading coil spacing is 6,000 feet, a section only 4,500 feet long would have a deficiency of . AAA—= 0.25. The curve marked 0.25 in figure 5-87 would apply in this case. The geographical location of an irregularity due to a capacitance deviation may be assumed as being located at the midpoint of the affected loading section.
(5) The foregoing discussion indicates that 2-wire operation with repeaters is likely to be unsatisfactory unless the cable can be
Ratio of loading inductances .Tunction return loss (db)
O.Sfc* O..5/c» O.75fa*
0.9 31.5 29.5 24.5
0.8 25 23 19
0.7 21 19 15.5
0.6 18 16 13
0.5 15.5 13.5 11
• fc is the cut-off frequency of the section using the higher loading inductance. The reflection loss at the junction will seldom exceed 0.1 db at 1,000 cycles.
Figure 5-88. Junction return losses between two loaded circuits having different loading inductances.
restored practically to its original condition. However, if the cable is practically intact and
the replacement loading units can be grouped, 2-wire operation may be feasible with reduced repeater gains even if the inductance differs somewhat from the desired value. Figure 5-88 gives the approximate junction return losses between two electrically long sections of cable loaded at the same spacing with coils of somewhat different inductances. To get the effect on repeater balance, twice the loss between the repeater and the junction should be added.
(6) It will be necessary to readjust the building-out capacitors in the balancing networks of the repeaters to compensate for any change from the normal length of end-section (par. 569i). Some networks are designed to balance any end section above about 0.2 if the building-out capacitors are properly adjusted. Other types of networks may be designed for a particular end section. When the loading points cannot be located to give the desired loading section or end-section capacitance, it may be possible to arrange the loading so that there will be a capacitance deficiency in the sections involved. Then the equivalent of normal capacitance can be obtained by buildingout the capacitance with the proper length of building-out cable which may be connected in series or as a bridge on the main cable. Use of building-out cables for this purpose is covered in Bell System Practice, Section AB23.195.
571. LOADING SYSTEMS AND APPARATUS
a. Foreign Loading Systems. Figure 5-89 gives the loading systems which have been approved by the International Consulting Committee, Telephony (CCIF) for international circuits. These and others listed in TM 11-487 may be encountered. TM 11-487 gives a method for estimating the 1,000-cycle loss per mile with these loadings and the usual sizes of wire.
b. Loading Units. Some of the American types of loading units which can be used for repairing CCIF standard loading systems are given in figure 5-90. These units are designed for loading the two sides and the phantom of a phantom group. Except for the MF11 loading unit, they are not stocked by the Signal Corps. The units not carried in stock may be obtained on special order through Army Communications Service, specifying the number of units per loading point and the number of loading points. If necessary, two of these units may be connected in series or parallel to obtain approximately the correct load ng in-
214
PARS.
CHAPTER 5. VOICE-FREQUENCY AND CARRIER TELEPHONY OVER WIRES 571-572
Loading system* Nominal impedance (ohms) Cut-o ff frequency (cycles)
Side Phantom Side Phantom
5577-30-12 700 350 7,470 9,300
6000-44-18 800 400 5,800 7,000
6000-44-25 800 500 5,800 6,000
6562-50-20 850 450 5,430 6,830
6000-88-36 1,150 550 4,100 5,000
3000-88-36 1,600 800 5,800 7,000
6000-88-50 1,150 650 4,100 4,300
3000-88-50 1,600 950 5,800 6,000
5577-140-56 1,550 800 3,500 4,400
6000-177-63 1,600 700 2,900 3,600
6000-177-107 1,600 1,000 2,900 2,900
6562-190-70 1,600 750 2,710 3,465
6562-200-70 1,700 800 2,710 3,660
10730-65 700 3,500
“In the loading systems, the first number is the coil spacing in feet, the second is the inductance of the side circuit loading coil in millihenries, and the third, when present, is the inductance of the phantom loading coil in millihenries. TM 11-487 lists the cable capacitance normally involved with the given loading systems.
Figure 5-89. Loading systems approved by the CCIF for international circuits.
Western Electric Company type Inductance (mh) Resistance (ohms)
Side circuit Phantom
Side circuit Phantom De 1,000 cycle De 1,000 cycle
MFI 172 63 13.8 16.4 6.9 7.6
MF11 88 50 6.3 7.2 3.1 3.6
MF2 44 25 3.6 4.0 1.8 2.0
MF4 31 18 3.1 3.4 1.5 1.7
Figure 5-90. American loading units.
ductance. The increased phantom-to-side crosstalk, is discussed in paragraph 569b.
c. Nonphantom Loading Coils. It may sometimes be expedient to use nonphantom type coils (88 mh) from Signal Corps stocks in the theater to restore a nonphantom circuit to operating condition. Two coils may be connected in tandem to obtain 176 mh or two coils may be connected in parallel to obtain 44 mh. Loading Coil C-114-A (88 mh) should not be used for loading of paper-insulated cables except as a very temporary expedient because of the difficulty of making the installation moistureproof.
572. IDENTIFYING LOADED CIRCUITS.
a. General. In cable restoration work it is necessary to know the cable lay-up; 4-wire segregation method; side and phantom circuit capacitance per unit length of the cable; loading coil inductance, spacing, and pair assignments; and the identification of the loading coils in any loading coil cases which need to be inserted, either in new cases, cases severed from the cable as the result of sabotage, or cases disconnected for repair. If local records are not available giving the desired data, it will be necessary to resort to other means for acquiring this knowledge. The cable lay-up and 4-wire segregation methods may be found by inspection as discussed in paragraph 567. The loading coil spacing may be determined by linear measurement after locating two adjacent loading points. The capacitance per unit length can usually be measured. Where this is impossible, it will be necessary to assume values, such as 0.062 mf and 0.102 mf per mile, for side circuit and phantom, respectively, (p^r. 569h). The loading coil inductance and loading spacing identifies the loading system. However, on a given circuit group, the capacitance per loading section must be known if it is necessary to resort to transmission measurements in order to determine the loading coil inductance. The capacitance C per loading section equals the spacing times the capacitance per unit length.
b. Determination of Loading Coil Inductance.
(1) Several methods of determining the inductance of loading coils are given in the following paragraphs. These methods depend on the relation between the capacitance per loading section, assumed to be known, and other factors which may be determined by
215
PAR.
572
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
transmission or impedance measurements. The choice of method to use depends upon the available testing apparatus and the length of undamaged cable section.
(2) The loading coil inductance may be calculated from the capacitance per loading section and the cut-off frequency. When the
6000; 172/ 7 / 73000-887 | 3000,-22/
_ 6000r44 L/ 1 /_6000-22 T/
0.5 -- W-—------------/-------------------t---
U f / / / / A
=! 0 4 -Z ---Z—> ----jZ---1 c----------J-------
2 ^6000-88S ~S
tt rS*'— __________________________
lu 0 3 \f -------------------------------
P"" ---- --------' ---- 19 GAUGE
£ ----- ------------------------16 GAUGE
? 0.2 A-----------------------------------------
in LOSSES ARE FOR CABLE CAPACITANCE OF 0 062 MF.
o PER MILE AND TEMPERATURE OF 55° F.
-J 0.1 “VALUES ABOVE 0.7 OF THE CUT-OFF FREQUENCY ARE APPROXIMATE. ________1____1___1___1__1____1__1----1__1 1L— 123456789___________________________________10
KILOCYCLES
COIL SPACING-FEET 6000 6000 6000 3000 6000 3000
COIL .INDUCTANCE -MH. 172 88 44 88 22 22
CUT-OFF FREQUENCY-KC. 2.9 4.0 5.6 5.6 7.9 11.0
NOMINAL IMPEDANCE-OHMS 1550 1100 800 1550 550 800
TL 54966
Figure 5-91. Transmission loss of loaded cables.
undamaged section of cable is several loading sections long, the cut-off frequency may be determined approximately by measuring the loss at a number of frequencies and then assuming the cut-off frequency to be about 15 percent higher than the frequency at which the loss is 1.5 times the loss at 1,000 cycles. Figure 5-91, illustrates the shapes of typical attenuation-frequency characteristics for circuits with several loading inductances and spacings. The inductance of the loading coil can be calculated by substituting known values in the formula
L — 1
Where fc = cut-off frequency in cycles
L — loading coil inductance in henries C = loading section capacitance in farads
(3) If the section is too long to be within the range of the transmission measuring set, the inductance may be calculated from the loading section capacitance and the nominal impedance. The nominal impedance, Z, may be estimated roughly by measuring the loss caused at 1,000 cycles by bridging the circuit terminal across the output of an oscillator sending into a transmission measuring set,
both of known impedances. The bridged or nominal impedance Z can be calculated from the formula
? Zq ' 2(r-lj
where Zo is the oscillator or the measuring set impedance, (the two are here assumed to be equal) and r is the current ratio corresponding to the measured loss in db (ch. 12). The inductance can then be calculated by substituting known values in the formula.
L = Z2C
Where L = loading coil inductance in henries 0 = loading section capacitance in farads
(4) If an impedance bridge is available the loading coil inductance, L, can be determined from measured values of short-circuit impedance, Zs, and open-circuit impedance, Zo. The impedance of the circuit is measured with the far end of the line short-circuited and is repeated with the far end open, using the same frequency setting of the oscillator for both measurements. The frequency should be approximately 1,000 cycles. Best results will be obtained when the distance from each end of the section under test to the nearest loading coil is 0.5 of a loading section. Under this condition, the inductance of the loading coil in henries is equal to the product of the absolute magnitudes of the short-circuit impedance and the open-circuit impedance divided by the capacitance of the loading section in farads. This may be expressed by the formula
T ZSZO ,
L = —— henries
If the cable does not terminate with 0.5 load-x ing section at each end, the multiplier (1-|-—) should be added to the formula, where n is the number of loading coils and x is the algebraic sum of the departures from 0.5 end section at the two ends of the cable. In this case the formula becomes
L—ZsZo(i_|_X) henries C n
The actual loading coil inductance will be slightly lower than the value estimated from this formula because the estimated value includes the inductance of a loading section length of the cable. This may be estimated by assuming the inductance of the cable to be about one millihenry per mile.
216
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CHAPTER 5. VOICE FREQUENCY AND CARRIER TELEPHON\ OVER WIRES 572-573
(5) If an impedance bridge is not available and the section of cable is too short to identify the cut-off frequency, the loading coil inductance may be determined by disconnecting a loading coil case and measuring the coil inductances. A record of how coils were connected to the cable pairs should be kept so that, by tracing the circuits through the section of cable, the inductance measurements of the coils in a single loading coil case can be used to determine the loading system used on the various pairs of the cable. The inductance of a loading coil can be measured by connect-
Loading unit Auxiliary capacitor (mf) .1 pproximate resonant frequency (cycles)
Side Phantom
172-63 0.25 770 1,270
140-56 0.25 850 1,345
88-50 0.25 1,075 1,420
44-25 0.5 1,075 1,420
Figure 5-92. Loading coil identification, resonant frequencies.
ing the coil and a series capacitor as a shunt across the output of a variable-frequency oscillator sending into a transmission measuring set. The oscillator frequency is varied to determine the resonant frequency which is the frequency at which maximum loss occurs. The inductance of the coil can be calculated from the known values of the resonant frequency and the capacitance of the auxiliary capacitor. For phantom group units, the side and phan
tom inductances can be measured separately. Resonant frequencies for typical loading units are given in figure 5-92.
(6) To identify the loading coils in an isolated loading coil case, the coil inductances may be measured by means of an impedance bridge if a suitable one is available. Otherwise the method given in subparagraph (5) above, may be used.
573. TELEGRAPH OPERATION.
a. D-c telegraph circuits can be established over the simplex circuits of the cable pairs of rehabilitated cable. It is not desirable to operate U. S. Army telegraph equipment on a composited basis over cable pairs because the telegraph distortion and the telegraph thump in the telephone circuits would be excessive. Composited operation on cables will be possible if civilian equipment designed for this purpose is found intact.
b. It is possible that some foreign installations will have repeating coils permanently inserted in each pair at the splice where the cable enters the building. If these coils do not have simplex taps brought out, it will be necessary to remove the coils and provide other repeating coils with simplex taps. It is desirable to have the junction point of the cable pairs and office equipment accessible so that d-c tests can be made to locate troubles on the pairs.
c. Voice-frequency carrier telegraph systems can be applied to the telephone circuits in the cable. The number of usable telegraph channels will depend on the band width of the telephone circuits and whether the circuits are 2-wire or 4-wire, as discussed in chapter 3.
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Section I. GENERAL FACTORS
601. SCOPE.
a. This chapter covers primarily the transmission aspects of radio circuits. General background considerations are in section I. V-h-f transmission is covered in section II, which contains methods for estimating communication performance over various types of terrain and over sea water, a summary of the principles of proper v-h-f antenna siting, and information on radio relay systems. V-h-f antenna types are described in section III. H-f transmission information, including estimates of ground-wave and sky-wave communication ranges, is given in section IV. H-f antenna types and general transmission line data are covered in section V. Types of mutual interference are described and methods for estimating the likelihood of mutual interference between different radio sets in the same vicinity are discussed in section VI. Information on remote control units, which are used when the talker or the signal center is at some distance from the radio set, is found in section VII. A brief summary of the characteristics of the chief Signal Corps radio sets used for ground communication and of a number of U. S. Navy and British radio sets is in section VIII.
b. A general discussion of the fields of use of miltary radio and wire circuits is in chapter 1. While the radio propagation data given in this chapter apply both to telephone and telegraph, the information on radio telegraph systems from the telegraph point of view is covered in chapter 3, which includes, in particular, radio teletypewriter systems. Data on c-w telegraph communication ranges, however, are in section IV. Information relating to radio traffic, radio plant layout, and radio maintenance is given in chapter 11. More detailed information on Signal Corps ground radio equipment is in TM 11-487.
c. This manual does not cover v-h-f fighter control, radio direction finding, or radar. It gives only incidental information on aircraft
radio transmission, and on radio sets used in service between ground and aircraft which are also useful for ground radio communication.
602. GENERAL.
a. Selection of Equipment. Radio equipment for use by the Army is available in a wide variety of types covering nearly any situation apt to be encountered. The solution of theater radio problems involves the evaluation of a number of factors relating to radio transmission under the particular conditions involved and the selection of proper equipment through knowledge of the types and capabilities of facilities at hand or available by procurement.
b. Service Requirements and Physical Conditions. The major factors to be considered before selection of equipment can be undertaken are:
(1) Maximum distance over which communication is required.
(2) Amount of traffic to be handled.
(3) Availability of frequency assignments.
(4) Degree of reliability desired.
(5) Degree of security desired.
(6) Degree of portability desired.
(7) Time available for installation.
(8) Type of intervening terrain, that is, whether the radio path is over sea or land; whether the land is flat or mountainous, jungle or relatively open.
(<9) Type of facilities required, that is, telephone, teletypewriter, facsimile, or hand telegraph. This is influenced by other requirements, such as security and traffic load.
(10) Type of service, such as fixed ground communication to mobile stations, ground to aircraft, etc. Also, whether point-to-point only, or switchable facilities are required.
(11) Type of power supply available, for example, engine generators, commercial power, or batteries.
219
PARS.
602-603
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
c. Electrical Requirements. With the above factors known, reference to sections II to VIII of this chapter, supplemented by additional information on radio sets and associated equipment given in TM 11-487, permits the determination of the following equipment requirements :
(1) General type of facility required. Fixed plant or tactical, single-channel or multichannel equipment are available.
(2) Frequency range of set to be used. Radio sets available now or in the near future cover frequencies from about 10 kilocycles to at least 300 megacycles.
(3) Radiated power required. Radio sets for tactical use have outputs ranging from a fraction of a watt to several hundred watts. Transmitters rated from 300 watts to 40 kilowatts are available for fixed point-to-point communication.
(4) Type of antenna required. Antennas range from the small whips used on handytalkies to large rhombic and diversity antenna systems used on the powerful fixed station installations. The type is influenced by the transmission requirements and space available for proper siting.
(5) Power supply requirement. Power supplies range from dry batteries for small portable sets to gasoline or diesel engine-driven alternators or commercial power supply for the larger installations.
(6) Remote control requirements. These are influenced by antenna siting arrangements and service requirements.
603. GENERAL TYPES OF FACILITIES.
a. General types of radio facilities which are available for use include the tactical sets issued as standard equipment to the various field units, which incorporate features making them desirable for portable and mobile use; and the fixed plant installations which are made available through the Army Communications Service.1 The type best suited to the particular needs in a given situation depends largely upon the time available for installation. This may involve the use of tactical equipment as a stop-gap solution for a problem which ultimately should utilize equipment in
1 Refer to TM 11-487 which gives descriptive, technical, and logistical data for Signal Corps tactical and fixed plant radio equipment for ground use. Requests for further information on fixed plant equipment should be addressed to Office of the Chief Signal Officer, SPSLP.
the fixed plant category. On the other hand, when the need for circuits can be foreseen and planned for in advance, time may permit a better solution, involving procurement of suitable fixed plant apparatus, if needed, and the technical assistance of the Army Communications Service. Such procedure is essential in meeting theater requirements for the more permanent long distance circuits, because tactical sets of sufficient power and operating in the proper frequency bands are not available or suitable for many such purposes. For example, long-distance circuits involving the use of frequencies as low as 100 kilocycles or powers as high as 40 kilowatts are available only through the Army Communications Service.
b. In the h-f band, tactical radio sets are frequently equipped to provide either continuous-wave radiotelegraph (c-w), tone modulation2 telegraph, or voice modulation; the desired mode of operation being selected by means of control switches. The long range heavy traffic administrative installations, generally engineered by Army Communications Service, also provide for high speed Morse and radioteletype operation. Chapter 3 discusses the various types of modulation which can be used for radiotelegraph operation.
c. In the v-h-f band, most of the Signal Corps tactical radio sets are designed for voice operation only and use frequency modulation (fm). Amplitude modulation (am) is used in all radio sets equipped for voice communication with aircraft. Amplitude modulation is also used in practically all similar types of U. S. Navy and British radio equipment.
d. V-h-f multichannel radio relay systems may be used in the same manner as wire carrier circuits to form a part of the regular telephone network, provided security rules for radio are observed. Such systems have important advantages in speed of installation and in weight and bulk of equipment, and have
2 Tone modulation may be of either of two types. In the first type, which is the one described in chapter 3 as single-tone modulation, the radio carrier is modulated with an audio-frequency tone when the telegraph key is closed and is transmitted without modulation when the key is open. The second type differs from this in that when the key is open, neither the carrier nor the modulation is transmitted. The second type is the one generally furnished with tactical radio sets operating in the h-f band. The terms mew and A-2 emission which appear as modulation characteristics associated with some of the radio sets listed in section VIII, are usually equivalent to tone modulation. The terms A-l emission and A -3 emission are equivalent to cw and voice modulation, respectively. A-0 emission is steady carrier alone.
220
PARS.
603-604
CHAPTER 6. RADIO SYSTEMS
many tactical uses, such as in a rapid advance, or for spanning short island-to-island jumps. They are described in paragraph 622.
e. Means of obtaining multichannel teletypewriter operation, or simultaneous teletypewriter and voice operation (speech plus duplex) on various types of radio sets are discussed in chapter 3.
604. CHOICE OF FREQUENCY BAND.
a. General Considerations.
(I) The signal system in an active theater of operations may include several hundred radio nets and communication circuits. The operation of such a large number of radio stations without serious interference requires the highest order of supervision and control. The allocation of frequency assignments in each theater is usually controlled by a central authority with due regard for type of equipment, mode of operation, power output, and method of tactical employment. From a transmission standpoint the choice of frequency band suitable for use in a given situation depends primarily upon the distance involved, the nature of the terrain in the transmission path, and the noise and interference conditions prevailing at the receiving stations. In practice, other factors must also be considered, such as: type of message traffic to be handled, desired reliability of service, availability of equipment and frequency assignments, and the prevailing tactical situation. Because of the relatively larger number of radio sets used in the h-f band, where both ground-wave and sky-wave propagation are used, communication in this band may be subject to severe interference from both local and distant radio stations, as discussed in subparagraph b below. For this reason every effort should be made to avoid use of the h-f band whenever practicable, that is, the v-h-f band should be used for communication over short or moderate distances.
(2) For purposes of uniformity and convenience in the terminology used in designating the various bands or ranges into which the radio-frequency spectrum may be divided, the terms listed in the following table have been adopted by the Armed Forces.3 Sections II to V of this chapter conform approximately to these designations.
3 These terms are the same as those used by the Federal Communications Commission.
Frequency {me) Description A&breniaiion
0.03 to 0.3 Low frequency If
0.3 to 3 0 Medium frequency mf
3.0 to 30 High frequency hf
30 to 300 Very high frequency vhf
300 to 3,000 Ultra high frequency uhf
3,000 to 30,000 Super high frequency shf
b. Transmission Characteristics at Various Frequencies.
(1) Radio transmission between two points takes place by means of ground waves or sky waves. Sky waves are radio waves which reach the receiver after reflection from the ionosphere. Ground waves reach the receiver through the earth’s lower atmosphere. These modes of transmission and properties pertaining thereto are discussed more fully in sections II and IV.
(2) Frequencies in the 0.03- to 0.3-mc band are used for ground-wave transmission over long distances, primarily in northern latitudes, as an alternative to h-f sky-wave transmission which is subject to blackouts because of auroral disturbances prevalent at latitudes above 60° N. Frequencies from 0.1 to 3 me are used mainly for ground-wave transmission for moderately long circuits over water and for moderate to short distances over land. Frequencies from about 1 to 3 me are generally suitable for night-time sky-wave transmission over relatively short distances (0 to 200 miles) and frequencies from about 3 to 8 me are generally satisfactory for daytime use over such distances, provided antennas are used which radiate well in a nearly vertical direction. Long-distance sky-wave transmission at night generally utilizes from 3 to 12 me, while during the day 6 to 25 me is usually the preferred range. Frequencies from 3 to 30 me are also used for ground-wave transmission for relatively short distances over land or moderate distances over water. Frequencies from 30 to 300 me are used for ground-wave transmission over short distances; sky-wave transmission in this fre-frequency band is absent or sporadic. At these frequencies, transmission is not necessarily confined to line-of-sight, but may extend to
656935 O—45-
16
221
PARS.
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
somewhat greater distances because of the bending (diffraction) of waves over obstacles, and to considerably greater distances where certain meteorological conditions are favorable.
(5) In evaluating the relative performance of. radio sets utilizing the various portions of the frequency spectrum, antenna efficiency is an important item. The short antennas used on many tactical radio sets in the h-f band, in order to meet mobility requirements, are very inefficient at the lower frequencies. For example, a transmitter rated at 500 watts output may radiate as little as 5 watts at some frequencies when standard whip antennas are used. On the other hand, antennas in the v-h-f range are very efficient, that is, practically all of the rated output power is radiated. However, as discussed in section V, relatively efficient h-f antennas can sometimes be substituted for whips on tactical sets when operating conditions permit semifixed installations.
c. U.S. Army Allocation of Frequencies.
(I) The frequencies from about 1.5 to 8 me are widely used at present by all services for both short- and long-haul communication.
(2) Long-haul administrative and special service traffic via sky wave in the 100-kc to 25-mc frequency band is generally handled by Army Communications Service equipment with more elaborate antenna installations than are involved in tactical networks.
(3) Some of the principal U. S. Army tactical frequency assignments above 20 megacycles are:
20 to 27.9 me, armored forces, mechanized cavalry.
27 to 38.9 me, field artillery, tank destroyers. 27 to 40 me, air warning (temporary).
40 to 48 me, infantry.
70 to 100 me, air forces, ground forces.
100 to 156 me, ground-to-aircraft and air-craft-to-aircraft.
These assignments may not be rigorously adhered to in all cases, but should be followed whenever practicable in order to avoid interference and resulting confusion.
d. Frequency Control. One of the most important prerequisites to the successful operation of radio communication systems is the accuracy with which assigned operating frequencies are adjusted and maintained. Although
accurate control of operating frequencies of most radio sets is assured by the use of appropriate crystal control units, a considerable number of tactical ground and aircraft radio sets use self-excited oscillators which are inherently less stable than crystal-controlled oscillators. Many of these latter radio sets incorporate built-in crystal calibrators which are used in conjunction with a calibrated tuning dial to adjust the radio set to the required operating frequency. Other radio sets, however, are adjusted to frequency by means of tuning dials, the calibration of which must be frequently checked against an external frequency standard.
605. FACTORS PERTAINING TO USE OF FREQUENCY MODULATION AND AMPLITUDE MODULATION FOR TELEPHONY.
a. In this chapter no distinction is made between amplitude modulation and frequency modulation in giving v-h-f distance ranges of point-to-point radio circuits. This is because these distance ranges are based on signal-to-noise ratios for radio telephone circuits which are operating at or near the limit for the transmission of intelligible speech. At this limit, the difference between a-m and f-m communication ranges, while favoring frequency modulation, is quite small, assuming equal unmodulated transmitting powers. However, frequency modulation has the ability to reduce noise in the presence of a strong r-f signal, whereas in amplitude modulation the only improvement lies in the increased radio-frequency signal, the noise remaining constant. Hence, where received field intensities are higher than the minimum required, as at short distances or with favorable antenna siting, frequency modulation provides a substantially better signal-to-noise ratio than amplitude modulation. Furthermore, f-m transmitters are substantially lighter in weight and require less power supply than a-m transmitters having the same unmodulated power output. Accordingly, f-m sets are widely used in the v-h-f band, where sufficient frequency space is available to obtain a relatively wide swing. Frequency modulation has not as yet been used by the U. S. Army for telephone transmission in the frequency region below 20 me. However, the frequency-shift teletypewriter service provided for h-f circuits, as discussed in chapter 3, may be considered a form of narrow-band frequency modulation.
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PARS.
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CHAPTER 6. RADIO SYSTEMS
b. The characteristic of an f-m receiver which permits the stronger of two signals to take control or capture the set is advantageous in the usual case where the desired signal is the stronger. In situations where several transmitters and receivers are in close proximity, however, a receiver may be captured by .spurious transmitter’ radiations which are stronger than the desired signal. To avoid mutual interference under these circumstances requires careful selection of frequencies, as discussed in section VI.
606. RELIABILITY CONSIDERATIONS.
a. The reliability of a radio circuit is generally defined as the percentage of the total service time that communication is satisfactory. Satisfactory communication exists when the signal-to-noise ratio is sufficient to meet requirements for the type of facilities involved, that is, voice, hand telegraph, teletypewriter, etc.
b. On important routes it may be essential that the radio circuits operate satisfactorily at practically all times, that is, that performance should approach 100 percent reliability on the basis of 24-hour service. In other cases, satisfactory communication over the entire 24-hour period may not be essential, or frequent repeats may be tolerable. The problem confronting a Signal Officer is that of choos
ing specific sets which will provide the grade of service required in a given situation, or of recognizing the limitations of available equipment so that all concerned will understand the degree of reliability to be expected.
c. For reasonable distance ranges, reliability of v-h-f systems is largely determined by equipment failures rather than by transmission difficulties. H-f reliability in the groundwave range is affected largely by static, and in the case of sky-wave transmission, by the variability of the sky-wave signals. H-f reliability is also considerably affected by interference from other stations, especially at night.
d. In the event of enemy jamming or excessive interference, the use of c-w hand telegraph rather than voice or tone modulation is the more effective way to increase reliability. The advantage gained is sufficient in many cases to provide a high percentage of reliability on circuits where tone or voice modulation is practically unintelligible. Another alternative is to increase the power which is transmitted. This may be accomplished either by use of a set having higher power, the use of a more efficient antenna, or the use of an antenna which is directive and, therefore, transmits more power in the desired direction. Receiving directivity is also advantageous in improving the signal-to-noise ratio.
Section II. V-H-l
607. GENERAL.
a. V-h-f (30-300 me) radio communication of the sort which is reliable 24 hours of the day is confined to ground waves, that is, waves which travel near the earth’s surface. Only this type of propagation is considered in this section. Sky-wave transmission (via reflection from the ionosphere) sometimes occurs, particularly at frequencies near the lower end of the band, but such instances are likely to be infrequent and generally unpredictable. Since ground waves attenuate rapidly, useful v-h-f transmission is generally limited to relatively short distances unless exceptional antenna sites on high hills are available at both ends of the path. Transmission distances can be extended by means of automatic radio relay sets.
TRANSMISSION
b. The distance range and performance estimates given herein are based entirely on standard propagation. Recent experience in war theaters and elsewhere has indicated that meteorological conditions (temperature and humidity of the troposphere, that is, the lower atmosphere) sometimes give rise to what is termed guided propagation, which may have the effect of greatly extending the distance over which usable field intensities, are received. Such conditions are most frequently encountered where stations are located near the shore of an ocean or other large body of water, and may be present for either long or short periods of time. It is believed that meteorological effects are most pronounced at frequencies above 30 me, although some experience indicates a substantial influence be
223
PARS.
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
low this frequency. Sufficient information is not available on guided propagation to permit the inclusion of this factor in estimating transmission ranges or performance.
c. In this section the limitations and advantages of v-h-f transmission are reviewed first, followed by a brief summary of transmission ranges generally experienced under various field conditions (pars. 608, 609, and 610). After a brief discussion of the characteristics of v-h-f radio wave propagation over smooth and hilly terrain, computed distance-range curves for single-channel voice communication over flat land and over sea water are given to illustrate the effects of transmitter r-f output power and moderate antenna elevations on distance-range (pars. 611, 612, and 613). Generalized distancerange curves cannot be plotted for hilly or mountainous terrain, since here the particular topography of the path between stations is a controlling factor with respect to the intensity of received signals.
d. To compute distance ranges such as given above, or performance over any sort of terrain for a particular set of conditions, it is necessary to estimate the received field intensity between specific station sites and then to compare this value with the required field intensity. Minimum operating field intensities required for various types of radio circuits are given in paragraph 614. Two sets of nomograms for use in making field intensity estimates are given next. One set is for use with antennas at moderate elevations for transmission over smooth land or sea water, or in terrain where hills intervene between stations (par. 615) ; the other set applies to situations in which the antennas are sited on aircraft or on mountainsides well above the intervening terrain (par. 617). Both sets of nomograms are based on certain specified conditions regarding radiated power, antenna gain, etc.; corrections for other conditions are given in paragraph 616.
e. The important factors involved in antenna siting and in choice of polarization are summarized next, followed by a discussion of miscellaneous transmission considerations (pars. 618, 619, and 620). The section concludes with a description of methods for setting up v-h-f single-channel and multichannel radio relay systems, including a discussion of
their fields of use and their limitations (pars. 621 and 622).
608. OPERATIONAL ADVANTAGES OF VHF.
Several advantages to be gained by using the v-h-f band for communication requirements over short to moderate distances are as follows:
a. Congestion in the h-f range is relieved.
b. The general absence of sky waves permits v-h-f assignments to be duplicated in adjacent areas with less likelihood of interference, and tends to reduce the chance of interception at a distance by the enemy. However, freedom from interception cannot be safely assumed.
c. When a satisfactory v-h-f radio circuit is once established, a high percentage reliability is assured even in areas where high atmospheric static prevails.
609. FACTORS AFFECTING V-H-F TRANSMISSION.
a. V-h-f transmission, in contrast with h-f (3-30 me), is favored by a number of factors, which are:
(1) Frequencies in the v-h-f band are usually free from atmospheric static noise except during local storms.
(2) There are no seasonal or diurnal variations in the transmission path of the magnitude encountered in h-f sky-wave transmission via the ionosphere. Signals are therefore solid except when affected by changes in meteorological conditions.
(3) Quarter wavelength or half wavelength antennas in the v-h-f band are small and are much more efficient than h-f antennas of comparable physical size.
(4) Performance of v-h-f circuits may be improved substantially, except under certain conditions, by raising antennas to moderate elevations above ground. Thus, masts of a height practical for tactical work may be used to good advantage. Greater elevations, obtainable by utilizing hills for antenna sites, provide further improvement.
(5) Directional antennas for improving transmission in the desired direction are of relatively small dimensions in the upper part of the v-h-f band and directivity gains equivalent to raising the transmitting power by four times or more are not hard to attain.
(6‘) Good ground connections for the antennas are usually not essential, unlike the case for some h-f antenna types.
224
PARS.
609-610
CHAPTER 6. RADIO SYSTEMS
b. Other factors tending to counteract the advantages listed above are as follows:
(1) Shadow losses introduced by the earth’s curvature and by intervening hills are greater than with h-f radio waves.
(2) Trees or dense jungles in the vicinity of the antennas cause more loss than at lower frequencies.
(5) Fading occurs at times in the v-h-f band, especially at extended distances. Reflections from airplanes in or near the transmission path may also cause severe signal variations on occasion.
610. V-H-F TRANSMISSION RANGES GENERALLY EXPERIENCED.
a. General.
(1) The problem of determining the maximum usable communication range of a given type of radio set is complicated by the fact that performance depends not only on such factors as the r-f power output, frequency, and type of antennas used, but also on a variety of external factors. Among these are the manner in which antennas are sited with respect to elevation and proximity to hills, buildings, vegetation, and sources of electrical noise; as well as the nature of the terrain along the transmission path. Terrain characteristics are classified below as flat, jungle, mountainous, and sea water. The maximum permissible distance between two stations also depends on the type of circuit, since the minimum required field intensity is greater for multichannel than for singlechannel operation, and may also be greater when the section involved is one of several in tandem rather than a single section (par. 614d).
(2) An indication of the transmission distance ranges generally experienced with available Signal Corps v-h-f apparatus during maneuvers and in the war theaters is given below. This experience has involved mainly single-channel f-m sets operating in the 20-to 40-mc band, but theoretical considerations indicate that similar distances are to be expected from 20 to 100 me and possibly higher if suitably elevated antennas are used and if directional types are provided at the higher frequencies. The information immediately following is merely a summary to indicate roughly the distance limitations for singlechannel point-to-point operation with no in
termediate radio relay sets. Detailed methods for estimating performance for specific situations are given later, including multichannel systems and circuits using automatic radio relay sets.
b. Flat Terrain.
U) In so-called flat country (exclusive of jungles), reasonably satisfactory v-h-f single-channel radio-telephone transmission results on the average for distances of 30 to 35 miles, using 50-watt transmitters and halfwave dipole antennas centered at heights of 40 to 50 feet above the earth.4
(2) The use of antennas on masts implies fixed or semifixed installations. For mobile or portable service with vertical whip antennas near the ground, the distance range in the 20- to 40-mc band for 30-watt sets such as Radio Sets SCR-508 and SCR-608 is reduced to about 10 to 15 miles, and to about 5
Figure 6-1. Radio Set SCR-300 in walkie-talkie operation.
miles for 2-watt sets such as Radio Sets SCR-509 or SCR-510 and SCR-609 or SCR-610. Radio Set SCR-300 (0.5 watts) has a range of about 3 miles. Figures 6-1 to 6-5, inclusive, show some of these sets under various field operating conditions.
4 For tactical purposes, masts exceeding 40 feet are considered impractical although in some sases provision is made for extending the heights to 50 feet.
225
PAR.
610
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Figure 6-2. Radio Set SCR-508 installed in Tank, Medium, M3 Al (showing its two radio receivers, interphone control box, and a part of its radio transmitter).
c. Jungles. In dense humid jungles, with antennas located in and well below the top of the jungle growth, transmission with any ordinary amount of power is sometimes limited
Figure 6-3. Radio Set SCR-510 installed in Truck, Yi-ton, 4x4.
Figure 6-4. Radio Set SCR-608 in Chest CH-74 installed in Truck, Command, %-ton, 4x4.
to distances of only 1 mile or less. The range can be improved materially if the antennas are placed in open clearings 100 yards or so across or, better still, supported high enough to protrude above the jungle growth.
d. Mountainous Terrain. In mountainous country, unless measures can be taken to site antennas properly, it may be impossible to transmit more than 5 to 10 miles without intermediate radio relays even with 50-watt sets and antennas on masts. For low-powered sets with whip antennas, the range will naturally be much shorter. Such poor performance occurs if the transmitting and receiving antennas are located close to the base of high intervening hills. However, when antennas
Figure 6-5. Radio Set SCR-609 in use reporting artillery hits.
226
PARS.
610-611
CHAPTER 6. RADIO SYSTEMS
are sited favorably, satisfactory transmission in hilly country, exclusive of jungles, is common for distances of 40 to 50 miles with 50-watt sets. Under favorable conditions where line-of-sight paths can be approximated by using high mountains for antenna sites, it has been found possible to operate 50-watt sets over paths 70 miles or more in length. In other instances, using 250-watt sets and directional antennas, distances slightly over 100 miles have been covered successfully using frequencies between 30 and 40 me. Greater distance ranges than these are possible if antenna sites elevated 500 feet or more above intervening terrain are available. On such long circuits, fading, caused by changes in meteorological conditions, may present a problem.
e. Sea Water. Distance ranges over sea water may be considerably greater than over land when using frequencies in the lower part of the v-h-f band with antennas centered at normal mast heights. Limited observations indicate ranges in the order of 150 miles at 30 to 100 me, with directional antennas elevated on hills or cliffs along the seacoasts and using a power output of 250 watts. In the higher part of the v-h-f band, flat land and sea distance ranges should be generally much alike for comparable siting conditions.
50 WATTS RADIATED POWER HALF-WAVE DIPOLE ANTENNAS eo 3 CENTERED 40 FT. ABOVE THE
/X EARTH AT BOTH ENDS
70 X/X----------1---------------------------
\\\ FREQUENCY IN S MEGACYCLES
i— 60 \------f-------------------------- S
S ^\^\\250
50---\----Xj4cX----------------------------
g X 65\X
> 40------------------------------------------
5 30------------— Xx ------------------------
| 20-----------------------------------------
.Q 10---------------------^X/V.---------------
o-----------------------------------------
-1 o----------------------------------------
-20--------------------------------W—-------
250-*AW85
_30|____________________________i40-^y-30
2 5 IO 20 50 100 200
DISTANCE .IN MILES
TL54894
Figure 6-6. V-h-f propagation over smooth land.
611. PROPAGATION OF V-H-F RADIO WAVES, a. Over Smooth Earth or Water.
(1) Under the ideal condition of smooth
earth, the intensity of the transmitted signal, beyond the first mile or so, diminishes in a regular and uninterrupted manner as the distance from the transmitter is increased. Similar propagation characteristics are found in so-called flat country and over water, since here the surface is smooth enough to approach the ideal.
(2) Figure 6-6 illustrates this theoretical relationship between field intensity and distance over smooth land for either horizontal or Vertical polarization (par. 619) and 40-foot antenna elevations. (These curves also apply for sea water when using horizontal polarization.) The field intensities obtained in practice, using this power and these antenna elevations, generally will be less than shown, because of irregularities in terrain, the presence of trees, and possibly other factors which cause the actual conditions to differ from the theoretical. With allowance for these factors, it is possible to calculate the distance ranges to be expected with radio transmitters of various power outputs. Such ranges are described for smooth earth and sea water in paragraphs 612 and 613, respectively.
b. Over Irregular Terrain.
(1) Propagation characteristics over irregular terrain are in marked contrast with those for smooth earth or sea water. Here, the variation of field intensity with distance depends largely on the profile of the terrain between transmitting and receiving antennas. An increase in distance may result in either decreased or increased field intensity, depending on the particular topography involved. Substantial changes in field intensity may result
ASSUMED CONDITIONS 50 WATTS RADIATED POWER HALF-WAVE DIPOLE ANTENNAS ON 40 FT. MASTS
I 85 MC. _________
4J5JJ-1-LIJ Lil I I I I [I I I I I I I I g s ' i FIELD INTENSITY OVER
E jr +50----------4------------------------SMOOTH EARTH FOR - -
-UJ COMPARISON n
OO. ---1———Fl |\ —---------
+30--------------------A----= = _; ——----------
og + 2° PROBABLE FIELD INTENSITY OVER-+
yg tio--------PATH HAVING THE PROFILE SHOWN—----------------V —
X 0-----------BELOW ____________________L_
8=0 _|OI----------------------------------------------------y.
2500 ।------------------------------------------------------
Z 2000 ---------------------———________/X_________-___■_______
o . PROFILE OF -x
KU 1500 ---————------------TRANSMISSION —--------------
mon TRANSMITTING PATH // //////X IX.
gu. iooo — ANTENNA -------'?'//>
0 5 10 15 20 25
DISTANCE-MILES
Figure 6-7. V-h-f propagation in hilly terrain, illustration of the character of field intensity variations to be expected.
2T7
PARS.
611-612 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
from relocating stations, even without any change in the distance between them.
(2) This is illustrated by figure 6-7 which shows, in profile, an assumed transmission path over hills, together with values of field intensity likely to be received at various points along the path. This emphasizes two facts regarding transmission in hilly country; first, that the choice of antenna sites is very important, and second, that there is no satisfactory basis for calculating general distance ranges. Instead, the received field intensity may be estimated for a given site involving a path of known profile, and thus the selection of antenna sites may be based on the circuit performance estimated for various available locations. A detailed method for determining received field intensities, in such terrain, and also over smooth earth and sea water, is given in paragraphs 615 and 616, and a general summary of siting considerations is presented in paragraph 618.
612. TYPICAL V-H-F DISTANCE RANGES IN FLAT COUNTRY.
a. Distance ranges typical of operation in flat country for various antenna elevations and transmitter powers are given in figure 6-8 for general reference purposes. These calculated curves are based on operating conditions explained below and serve to illustrate the effects of changes in antenna elevation or power on distance range in fiat country. Methods for computing distance ranges for situations differing from those illustrated by the curves are given in paragraphs 615 and 616.
b. The distances indicated are those at which the estimated field intensity reaches the minimum operating values which are defined later in paragraph 614 as satisfactory for single-channel use. The curves are computed for smooth earth propagation with nominal allowances (4, 7, and 10 db for 30, 85, and 140 me) for transmission line losses and losses caused by trees and small topographical irregularities. The distances shown are in general agreement with experience.
c. For frequencies between 70 and 160 me, directional antennas commonly used have gains of the order of 6 db as compared with conventional half-wave dipole antennas, and the distance ranges shown in figure 6-8 are based on this amount of gain at each end, except as noted thereon.
d. Figure 6-8 distinguishes between vertical and horizontal polarization (par. 619) and between poor and good soil at antenna elevations and frequencies for which these factors have a significant effect on the range.5 Equal elevations are assumed for both transmitting and receiving antennas; however, for elevations above 40 feet with a frequency
Figure 6-8. Tyical v-h-f distance ranges in flat country.
below 100 me or for any elevation with higher frequencies, the ranges shown apply if the product of the two antenna elevations is unchanged. For example, the range with one antenna at 200 feet and the other at 50 feet is the same as that with both at 100 feet. 5
5 The terms poor soil and good soil as used throughout this section are defined as follows. Poor soil means soil of relatively low conductivity and dielectric constant, such as that consisting largely of rocks, gravel, sand, or coral. Good soil means soil of relatively high conductivity and dielectric constant, such as clay, loam, marsh or swamp, and alkali soil.
228
,00l I 11 Illi I IIIL^UrUJ
OQ ___ ___ I | I I_________' x ZX*______ _
TRANSMITTER S
POWER ->---- '
6°----------------------------------------------
40____■ Z _ _ ZZ--------------------------------
2O — —------- III I-
<£*tT —- ' 1(30-40 MC BAND)
o _____LU LJ I—LI i .. I ill 1.
IO 20 30 50 IOO 200 300 500
TRANSMITTING AND RECEIVING ANTENNA EFFECTIVE ELEVATION IN FEET
AT LOW ELEVATIONS-----VERTICAL POLARIZATION OVER POOR EARTH
-----VERTICAL POLARIZATION OVER GOOD EARTH -----HORIZONTAL POLARIZATION
0
1,000----/ /-------------------„------------ y 7- °o
' / -J’-'-" | <“■ 5
u r«—Di-—* _30 r _ 0 w
। pH .1— —l-P .-------- "20 10,000 J s
i ■6>00°
H 3,000i----------------------1 . I ।-----1",- 5 - 3,000 >z30- ZX
> I EXAMPLE B I ‘ 3 "<‘2,000 ' x' ’30n- " ‘° >
3 '________________.a--------1 I I |J '2 p.O^ A
2,000---------------------------------------aS V300 t 50 '5°a^ °
// A a st t -*20:
Z / k 0,1 \iO * 70 ■70'^' ’
' / — - x/ \ a so- J
1,000------/--------V-------------\ £ -80 >
\ O 90 O “30
/ / **" ^^'x - 9 0
--- X. UJ 100-J----------------------------------------------------------------------------^-0 J LIOOJ “35
lol INI 0 5 10 15 20 25
MILES
IN EXAMPLES A AND B THE ELEVATION SCALE ------------IS THE SOLUTION OF EXAMPLE A
IS ENLARGED BY ABOUT 25 TIMES, GIVING AN EXAGGERATED IMPRESSION OF THE PROFILE- ------------IS THE SOLUTION OF EXAMPLE B
O INDICATES ANTENNA SITES-
(CHART IS FOR 70-10 0 MC)
TL5489I
Figure 6-13. Example: Use of field intensity nomograms.
232
CHAPTER 6. RADIO SYSTEMS
PAR.
615
20-40 MC SCALE 5
50 WATTS RADIATED POWER
HALF-WAVE DIPOLE ANTENNAS CENTERED p+50
40 FEET ABOVE THE EARTH
-+45
- +40
- +35
- + 30
SCALE I D| MILES
p 50 -30 -20
- 10
- 5
- 3 - 2
- I
-0.5
- 03 - 0.2
- 01
Z
SCALE 4 O
z o D=TOTAL DISTANCE N OC
< 20- r3 -1
N o
at -4 z1
30 - 40- o
o Q. -5 -7 oco
O £ 50 - 60 - -10 -15 ct
70 - IdZ
X 80 - -20 T r~
h~ ti
£ 90 - Id
at UJ 100 - -30 TOC FUJ
120- -40
< -50 u z <
Id
-80 o
- 4
(X
- —5
- -10
- -15
- -20
--25
- -30
--35
TL 54918
Figure 6-14. Nomogram for estimating field intensity, 20 to 40 me.
233
SCALE 3
SCALE 2 H FEET
p 10,000
- 5,000
- 3>000
- 2,000
V 1,000
Y 500 Vsoo V200
V ioo \-50
^J-o
PAR.
615
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
70-100 MC 50 WATTS RADIATED POWER HALF-WAVE DIPOLE ANTENNAS CENTERED 40 FEET ABOVE THE EARTH
SCALE 5
- + 50
+40
- +35
+30
+25
SCALE I D| MILES
p 50 -30 -20
-10
- 5
- 3 - 2
- I
-0.5
-03 -0.2
-0.1
SCALE 4 p+20
D=TOTAL
DISTANCE Z
O
- +15
<
N
a. - +10
z <
r5
- — o
7 — Fq.
- 7 < —+5
N _J
- 0
,5"_|5
a.
2O--2o £g --5
f X
3°--30 --I0
X AC
40— H uj
-40 > < —15
50- ~
- 50 ° U Z <
< Id 60- _J <0 --20
-eo^—^
70- J -70 > --25
O
60-
o ao- Id
O
UJ 90- -90 60-------------------------------------------____________
□ O Ul CD u < 501_________________________________________________L_^J
01 02 05 I 2 5 10 20 50 100
DISTANCE IN MILES
TL 54890
Figure 6-19. Free space field intensity curve.
c. Correction for Transmitter Power: Factor P. When the transmitter power differs from the reference value of 50 watts, an appropriate correction from the table of figure 6-20 must be made.
Transmitter power (watts)
Correction factor (db)
0-5........................ Subtract 20
1 Subtract 17
2 Subtract 14
5 Subtract 10
10.......................... Subtract 7
20............x............. Subtract 4
50a................................... 0
100............................... Add 3
250............................... Add 7
500............................... Add 10
1,000.............................. Add 13
a Reference condition.
Figure 6-20. Corrections for transmitter power.
d. Corrections for Transmission Line Loss: Factor Lz.
(1) Antenna transmission lines of appreciable length introduce a significant loss, particularly at the higher frequencies of the v-h-f band. Typical losses per hundred feet for flexible coaxial cable of the type in general use are given in figure 6-21. These values should
Frequency Correction for transmission
(me) line loss (db per 100 feet)
20 to 40 ...................................Subtract 1
70 to 100...................................Subtract 2
120 to 160..................................Subtract 3
220 to. 260.................................Subtract 5
Figure 6-21. Corrections for transmission line loss.
be assumed unless other information is available relating to the specific type of line used. Some information on coaxial cables is given in figures 6-146 and 6-147; detailed informa
tion on all standard types is given in TM 11-487.
(2) A transmission line loss should always be included for the transmitting antenna, since this loss represents a reduction in radiated power. For receiving antennas, inclusion of a line loss is also necessary in the usual case when set noise, rather than external noise, is controlling.
e. Correction for Directional Antenna Gain: Factor G.
(I) Field intensities indicated on the nomograms of figures 6-14 to 6-17 are those obtained with a vertical or horizontal dipole antenna in a direction perpendicular to the antenna elements. When any other type of antenna or some other direction of propagation is involved, a correction should be made for the gain or loss of the actual antenna relative to this reference condition. For example, when an antenna having a 6 db gain in the forward direction is used at each end of a circuit and each antenna is properly oriented, the estimated field intensity should be increased by 6 -|- 6 = 12 db, assuming set noise is the controlling noise.
(2) Actually, as discussed in paragraph 614e, the received field intensity in the above example is increased only 6 db, which is obtained from the directional transmitting antenna, but at the same time the field intensity required is decreased 6 db because of the gain of the receiving antenna. Treatment of receiving antenna gain as a gain in field intensity is a matter of convenience in using the procedure given herein in conjunction with the required field intensities of figures 6-11 and 6-12.
(5) In situations where external noise or radio interference is present to such an extent that it would predominate over set noise when receiving on a nondirectional antenna, the effect of substituting a directional antenna will depend on whether or not this improves reception of the noise as well as the signal. When the noise source lies in the same direction from the receiver as the distant transmitter, a directional receiving antenna increases the received noise as well as the received signal and there is no net gain in .signal-to-noise ratio. When the external noise source is in some other direction, the improvement in signal-to-noise ratio depends on the relation of the efficiency of the antenna in the
239
PAR.
616 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
ASSUMED CONDITIONS
Example 1 Example 2
Radio Set AN/TRC-1,-3, or-4 AN/TRC-1,-3, or-4 with Amplifier AN/TRA-1
Frequency band 70-100 me 70-100 me
Rated transmitter power 50 watts 250 watts
Antenna type, gain, and polarization AS-19/TRC-1, 6-db gain, horizontal AS-19/TRC-1, 6-db gain, horizontal
Antenna effective elevation Mast height, 40 ft. Mast height, 40 ft. at one end; 90 ft. effective elevation at other end
R-f transmission line type 100 ft. flexible coax, cable at each end 100 ft. flexible coax, cable at each end
Type of operation Single channel, voice 4-channel, voice
Type of circuit Point-to-point, one radio section Point-to-point, one radio section
Profile of radio path As in example A, figure 6-13 As in example B, figure 6-131
Remarks No external noise expected. Antenna in trees at one end of circuit. No external noise expected. Antenna in clear at both ends of circuit.
CALCULATIONS FOR EXAMPLES 1 AND 2
Profile characteristics figure 6-13 Di =8, D = 20, H =2,000 Di = 10, D=22.5, H = 1,600
Reference field intensity (fig. 6-13) +4 db +5 db
Antenna elevation corrections (fig. 6-18) 0 +7
Sum a +4a + 12a
Transmitter power correction (fig. 6-20) 0 +7
R-f transmission line corrections (fig. 6-21) -4 -4
Antenna, directional gain corrections (par. 616e) + 12 + 12
Approx, tree loss correction (par. 616f) -2 0
Estimated field intensity (sum of above items) + 10 db from 1 mv/meter +27 db from 1 mv/meter
Min. required field for satisfactory (figures 6-11 and 6-12) + 15 +25
Difference (last 2 items) — 5 +2
Estimated performance from figures 6-11 and 6-12 Questionable Satisfactory
a Examine figure 6-19 before proceeding further to be assured that the free space field exceeds this value (par. 616b (4).
Figure 6-22. Sample v-h-f performance estimates.
240
PARS.
616-617
CHAPTER 6. RADIO SYSTEMS
direction of the signal to its efficiency in the direction of the noise, that is, on the horizontal directional pattern of the receiving antenna (par. 624c).
f. Correction for Loses Caused by Trees: Factor Lt.
(1) Trees in close proximity to an antenna ordinarily cause some loss in field intensity and it may be necessary to include an allowance for this in arriving at the resultant estimated field intensity. Present information merely indicates the approximate magnitude of loss to be expected.
(2) Recent measurements using antennas somewhat below treetop level in densely wooded areas ■ indicate that with both the transmitting and receiving antennas so situated, the loss when using vertical polarization is about 3 or 4 db for frequencies in the 20- to 40-mc band, and 10 db in the 70- to 100-mc band. With horizontal polarization, losses are negligible at 20 to 40 me and quite small at 70 to 100 me. Higher losses occur in the higher frequency bands. For scattered trees these losses are not as severe but are usually present in some degree. In dense humid jungles with antennas located well down in the jungle growth, losses are very high and seriously limit v-h-f transmission with either horizontal or vertical polarization.
g. Sample Performance Estimates Showing Use of Correction Factors. The upper portion of figure 6-22 states conditions assumed for two examples. The lower portion of figure 6-22 shows, step-by-step, the calculations involved in estimating performance for each of the examples. The procedure is a straightforward application of the equation given in paragraph 615b (2) for estimating field intensity. The estimated value is then compared with values in figures 6-11 and 6-12, from which the performance classification is determined as satisfactory, questionable, or unsatisfactory for the type of circuit involved.
617. V-H-F TRANSMISSION WITH ANTENNAS AT GREAT ELEVATIONS.
a. General.
(1) The foregoing information and the nomograms of figures 6-14 to 6-17 relate to v-h-f transmission with antennas at effective elevations of 500 feet or less. The corresponding distance ranges are generally limited to
less than 100 miles over smooth earth or sea water and frequently to much less than 50 miles when intervening hills are present. However, greater distance ranges are possible when one or both antennas are raised to considerable heights as on an aircraft or on mountains.
(2) General experience indicates that with antennas at great elevations the useful v-h-f communication range is approximately the line-of-sight distance (fig. 6-23) or somewhat beyond for transmitter powers of the order of 5 to 50 watts.0 Most of this experience has been obtained with antennas on aircraft. The nomograms in figures 6-24 and 6-25, which are discussed in the following subparagraphs, give field intensity data for transmission from an aircraft to a ground station and from one aircraft to another, over smooth earth or water with either horizontal or vertical polarization.
(3) Limited experience with antennas located on mountains indicates that under favorable conditions, defined in subparagraph d, below, the transmission performance is similar to what would be expected for antennas on aircraft at the same elevation above the intervening terrain. The nomograms in figures 6-24 and 6-25 can therefore be used as guides in estimating the communication possibilities of mountain-to-mountain transmission, where the mountain sites are well above the intervening terrain as in island-to-island paths, but should be used with caution until more experience indicates their degree of reliability.
(4) The nomograms in figures 6-24 and 6-25 indicate usable field intensities at distances sometimes well beyond line-of-sight. On such circuits fading becomes serious and the circuits may be inoperative part of the time (subpar, e below). Circuits should not be overextended to distances greater than indicated by the nomograms; instead, h-f facilities should be used.
6 The line-of-sight distance, Do, is defined by the following equation for standard propagation over smooth earth:
Do = V2H1 + Zlh
where Do is in miles and Hi and H2 are the antenna elevations in feet above ground at the two ends of the circuit. This equation includes the effect of a gradual change in the dielectric constant of the earth’s atmosphere which, for standard conditions, causes a refracting effect equivalent to increasing the earth’s radius by one-third.
241
PAR
617
COMMUNICATION SYSTEMS ENGINEERING
F
x* *** H\ " — —-
D 7H2
E 1 .ET - 0 - 50 - 200 - 500 - 1,000 - 2,000 - 3,000 Po=-> 1 /2 D Ml H| +V^H2 O LES - 0 - 50 - IOQ - 150 1- FE 2 .ET - 0 - 50 - 200 ‘ 500 - 1,000 - 2,000 >*3,0 00 /
- 5,000 - 7,000 ' l(\000 -200 - 250 - 300 - - 5,000 - 7,000 - 10,000
- 15,000 - 350 - 15,000
- 20,000 -400 - 20,000
- 25,000 - 30,000 • i -450 - 500 - 25,000 - 30,000
- 40,000 - 650 - 40,000
OF A lO.OOO-FOOT ELETHE OTHER END, FOR
NOTE:
THE DASHED LINE ILLUSTRATES USE OF THE CHART FOR THE CASE VATION AT ONE END OF THE PATH AND A 3,000-FOOT ELEVATION AT WHICH THE LINE-OF-SIGHT DISTANCE IS 220 MILES.
Figure 6-23. Maximum distance for line-of-sight path.
242
PAR.
CHAPTER 6. RADIO SYSTEMS 617
ELEVATION OF HIGH ANTENNA
FEET
(I) r 40,000
-30,000 -25,000 f2) 350- 300- (3) -40 or id id a Id CL db BELOW FREE SPACE
85 MC (*) 70—i 250 MC (5) -80
-20,000 60- -70
& 250- -42 — -60
Id ■.I
—J UJ 50-
- 15,000 5 cT Id 200- -44 o 03 < 40- -50 -40
— 12,000 o z "0 1 ^^^^30- -30
< 150- -46 Q -20
-10,000 -40
-10,000 \ “ 3,000 2 30- . Q ® y
- 2,000 u < ^/^30
A 1,000 *“ 500 Z 200-_44 -q ^y^20 _£Q
< i ^y^
- 15,000 IO-L|O
° I50-' 46 uj
- 20,000 / “48 u y o
✓
I00-- 50
- 52 uj
-25,000 \ Id
\ - 54 a
50-1-56
“30,000
L 40,000
TL 54938
Figure 6-25. Nomogram for estimating field intensity, both antennas at elevations exceeding 500 feet, 50 watts radiated from half-wave dipole.
oetween antennas on scale 2 determines values on scales 3, 4, and 5. The estimated field intensity at 85 me, for example, is equal to the reading on scale 3 less the value on scale 4. In a
244
similar manner, the estimated field intensity at 250 me is equal to the value on scale 3 less the reading on scale 5. The field intensity at 150 me is approximately midway between the val
PAR.
CHAPTER 6. RADIO SYSTEMS 617
ues for 85 and 250 me. When the effective elevation of the lower antenna lies between 40 and 500 feet, the field intensity obtained from the nomogram should be corrected by adding 3, 8, 13, or 22 db for elevations of 60, 100, 200, or 500 feet, respectively. These are average values, applicable to either horizontal or vertical polarization within the precision of the nomogram method. If the addition of such height-gain corrections should cause the resultant field intensity to exceed the free-space value as read on scale 3 of the nomogram on figure 6-24, the free space value should be used. Corrections for transmitter power, directional antenna gain, transmission line losses, etc., should also be made as in paragraph 616. When the effective elevation of the lower antenna exceeds 500 feet, figure 6-25 should be used, as explained in subparagraph c, below.
(2) The example indicated on figure 6-24 shows that for antenna elevations of 40 and 3,000 feet the estimated field intensity at 85 me at a distance of 100 miles is 30 —37 = 13 db above 1 microvolt per meter for 50 watts radiated power. The corresponding field intensity for 250 me is 50 —38 = 12 db. This value can be compared with the required value on figure 6-11 or 6-12 to estimate performance.
(
io 20 30 50 100 200 300 500
ANTENNA ELEVATION IN FEET
TL549I5
Figure 6-28. Gain in field intensity obtained by raising one antenna from a low elevation (10 feet).
PAR.
618 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
VERY GOOD
(I ) Z--
TO distant STATION,
VERY /
„ poor / //Xx
FAiRiX X toXxZZ/XZZ/Ai
XXXX ® I
Figure 6-29. V-h f antenna siting in hilly country.
TL 54958
of the five sites shown, and is quite probably the best available, since experience has shown that sites directly, on the summit of a hill are frequently inferior to those on the brow. Location 2 is usually preferable to any shown behind the hill. The worst choice would be location 5. Location 4 is better than 5 in spite of the fact that the antenna is farther away from the distant station because the angle through which the wave bends is reduced appreciably. Location 3 is much better than any of the others back of the hill because the antenna is located on another hill, a condition which not only reduces the angle of bend (thus coming a little closer to line-of-sight) but also increases the effective antenna elevation, thereby improving the received field intensity as indicated earlier in figure 6-18.
(3) There are some kinds of antenna sites where the signal improvements arising from increased antenna elevation given in figure 6-18 are not always applicable. Such sites include locations on the back slope of a hill, or in a narrow river valley between ridges, one of which blocks transmission, or on an extended level plain behind an intervening hill but close to its base (less than a half mile away), as in the case of location 5 of figure 6-29. All such sites are undesirable but are sometimes unavoidable. In such situations the field intensity may vary considerably from one location to another nearby, and may be stronger for antennas located on low masts than for antennas located on high masts. The best location and antenna elevation is determined by trial and error, an increase in r-f signal intensity being observed either by noting improved audio signal-to-noise ratio on reception or by observing changes in squelch
control settings or in limiter grid current (fm), when the radio receivers are provided with such facilities. The more positive indications of r-f signal change obtained by the latter methods are to be preferred, since a set may not show much audio signal-to-noise improvement in rough listening tests when the field intensity is increased by a change in location. However, the improvement may be of considerable value should interference or jamming develop.
(4) On several occasions, when using a directional antenna in mountainous terrain, it has been found that in situations where the straight-line path between stations crosses the peak of a nearby hill, best results are obtained with the antenna oriented so that it points at a small angle off to the side of the straight-line course, rather than directly towards the distant station, particularly if the off-course direction involves lower terrain such as a mountain pass. Presumably more signal energy is reflected from the sides of neighboring hills than is diffracted over the top of the obstructing hill. On the basis of this experience, it appears desirable to experiment with the aiming of directional antennas when establishing circuits over irregular terrain.
e. Sea Water. In transmitting or receiving over sea water using vertical polarization, increased antenna elevation, up to several hundred feet, is of no advantage with frequencies in the lower portion of the v-h-f band, as shown by figure 6-28. Thus, antenna sites on the beach, using low masts if desired for concealment purposes, are as good as any obtainable unless high hills are available a short distance inland. For higher frequencies, there is an advantage in raising an antenna even a
248
PARS.
CHAPTER 6. RADIO SYSTEMS ____618-620
small amount above beach level, and even small hills provide better sites. With horizontal polarization, the higher the hill or mast, the better, regardless of frequency.
619. POLARIZATION.
a. General.
(I) Transmission characteristics for horizontal and vertical polarization have been outlined in various places throughout this section, and are collected and reviewed here.
(2) For practical purposes, in the v-h-f band, radio waves transmitted from a vertical antenna are usually regarded as being vertically polarized, and those from a horizontal antenna are normally regarded as being horizontally polarized.7 Either type of polarization may be used for v-h-f transmission, but the performance will be different under certain situations. In all cases, the orientation of the receiving antenna, that is, horizontal or vertical, should be the same as that of the transmitting antenna at the distant station.
b. Advantages of Vertical Polarization. Advantageous characteristics of vertical polarization for v-h-f transmission are as follows:
(I) Simple vertical dipole or whip antennas are nondirectional in a horizontal plane. This feature is advantageous when good communication is desired in several directions from a station.
(2) Where antenna elevations are limited to 10 feet or less, as for motor vehicle applications in transmitting over land, vertical polarization results in a signal at least twice as strong in the 20- to 40-mc band as would be obtained with horizontal polarization using antennas at the same elevation. This difference is less pronounced with frequencies in the 70-to 100-mc band and is negligible when using higher frequencies.
(5) For transmission over sea water, vertical polarization is decidedly better than horizontal when antennas are below a certain elevation. This elevation is about 300 feet at 30 me, but only 50 feet at 85 me and still lower at the higher frequencies. This means that with ordinary antenna mast heights of 40 feet, vertical polarization is advantageous at frequencies less than about 100 me. At higher frequencies there is little if any difference.
(4) From limited observations it ap
7 A more technical definition of polarization is given in chapter 12.
pears that vertical polarization is less subject than horizontal to variations in received field intensity caused by reflections from aircraft flying over the transmission path. This may be of importance in locations where aircraft traffic is heavy, as at air fields.
c. Advantages of Horizontal Polarization. Advantageous characteristics of horizontal polarization are:
(1) A simple horizontal antenna pointed east and west, for example, transmits and receives best in north and south directions and performs poorly by comparison, in east and west directions. This inherent directivity is sometimes of advantage as a means of minimizing interference.
(2) Horizontal antennas are less apt to pick up man-made interference, which is ordinarily vertically polarized.
(5) Indications are that when antennas are located in fairly dense forests, horizontally polarized waves usually suffer lower losses than vertically polarized waves, especially in the higher portion of the v-h-f band. Also, standing wave effects which cause relatively large changes in the field intensity of vertically polarized waves for small changes in antenna location among trees or near the edge of a forest are not nearly so pronounced with horizontal polarization. In very dense jungles, performance is poor and probably not much affected by polarization.
620. MISCELLANEOUS TRANSMISSION CONSIDERATIONS.
a. Security.
(I) Any radio transmission is subject to enemy interception. However, several measures may be used which contribute toward making interception of signals by the enemy more difficult. These measures are also of value in reducing the possibility of causing interference with the reception of friendly signals.
(2) When received signals are well above •the required values, the transmitting antenna should be lowered in elevation and the transmitter power reduced when feasible. This will impair reception by the enemy without materially affecting performance on circuits operating with considerable transmission margin. Also, lowering the antenna may afford some degree of concealment of radio sets from enemy observation, and lessen the danger of antenna breakage during stormy weather.
249
PAR.
620
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
(5) Advantage may be taken of the shadow loss caused by hills obstructing a transmission path when it is possible to locate the transmitting station so that hills will intervene in the direction of the enemy but not in the desired path. The effectiveness of this measure in a given situation may be estimated from the charts of figures 6-14 to 6-17.
(4) The use of directional transmitting antennas ordinarily provides higher signal intensities in the forward direction than would be obtained with nondirectional types. In other directions, in back or off to the side, interception is made more difficult because the transmitted signals are relatively weak. It is sometimes practical to orient the antenna so as to obtain a very weak signal in a particular direction where transmission is unwanted, at a fairly small cost to transmission over the wanted path.
b. Noise and Interference.
(1) General. The radio communication range is inversely related to the amount of noise or radio interference at the receiving antenna location. In other words, the more noise or interference present, the shorter the distance over which satisfactory communication can be established, assuming other factors remain the same. High noise will cause errors in superimposed voice-frequency telegraph (teletypewriter) circuits; and on channels used for voice communication, it will reduce intelligibility and make the channel more difficult to use satisfactorily. Common sources of noise are industrial plants using electrical equipment, radio transmitting stations, power lines, motor ignition systems, etc. In addition to these sources, spurious radiation from associated transmitters may cause considerable interference, as discussed in section VI. Every reasonable effort should be made to select installation sites in quiet country locations, away from industrial or concentration areas and repair stations or heavily travelled highways. Remote control facilities may be used to obtain separation between the radio terminal and the signal center, which is often in a congested area. In general, the use of horizontal polarization will considerably reduce the effect of man-made interference, since usually such in
250
terference is predominantly vertically polarized. Suitable chokes or filters in power leads will reduce direct noise pick-up in the receiver from motor-generator sets or power lines. The importance of using all of the power available on a marginal circuit should not be minimized. If, because of faulty line-up, damaged transmission lines, or incorrect adjustment of antenna elements, a radio set rated at 50 watts only radiates half that amount, the resulting loss of power may cause failure of the circuit.
(2) Static Noise. Available data on the effect of atmospheric static interference on telephone transmission in the v-h-f band indicates that the problem is not serious in many parts of the world during most of the year. The worst static occurs during local thunderstorms, and causes most trouble on circuits' which are operating with only marginal field intensities. In such cases there may be instances where the message will have to be repeated.
(3) Ignition,"Teletypewriter, and Cipher Machine Noise. A fairly common type of interference is ignition interference from motor vehicles or gasoline-driven motor-generator sets. It is believed that such noise sources in military equipment in good condition will be sufficiently suppressed. In cases where shielding and suppression measures prove inadequate, the source should be physically separated from the receivers affected. Interference from the sparking of contacts in teletypewriter equipment and from cipher machines is of a similar nature.
(4) Tube and Contact Noise. Perhaps the most common source of noise is that due to poor maintenance, that is, noisy tubes and poor contacts in radio receivers. Another source of noise on radio telephone circuits is burning noise between carbon granules in a defective microphone at the radio transmitter. Unless these troubles are located and cleared, performance may be considerably impaired. Noisy tubes in the receiver input stages will cause more trouble than elsewhere in the circuit.
(5) Noise Reduction. Some further general suggestions on noise reduction are in paragraph 654.
PAR.
621
CHAPTER 6. RADIO SYSTEMS
621. SINGLE-CHANNEL AUTOMATIC AND MANUAL RADIO RELAYS TO EXTEND THE V-H-F DISTANCE RANGE.
a. General. Frequently communication at very high frequencies is required over distances greater than can be spanned by a single radio jump over the particular terrain encountered in a given situation. In such cases radio relays can be used. Several standard radio sets have been designed to provide such operation automatically, including Radio Sets AN/TRC-1 (70 to 100 me), AN/TRC-8 (230 to 250 me), and AN/CRC-3 and AN/CRC-3A (30 to 40 me).8 When any of these sets is used as a single-channel radio relay set for push-to-talk operation, the transmitter and receiver are connected together in such a way that the transmitter carrier is automatically controlled by a relay in the radio receiver which is actuated by the received signal. Several radio relay arrangements requiring no modification of these standard radio sets are described in the
RADIO TERM- AUTOMATIC RADIO TERMINAL SET RADIO INAL SET
RELAY SET
TL 54903
Figure 6-30. Two-section radio communication system for simplex operation with automatic radio relay set.
following paragraphs. Other arrangements have been improvised in the field, but such schemes usually involve set modifications or auxiliary apparatus and will not be covered here.
b. Single Automatic Radio Relay, Simplex Operation.
(2) Where only two radio sections are to be worked in tandem, a simple form of automatic radio relay may be used as shown in
8 The AN/TRC-1 consists of the basic radio components of multichannel radio sets AN/TRC-3 and AN/TRC-4, differing only in that spare transmitters, receivers, and power units are omitted and only the minimum apparatus necessary for single-channel communication is provided. Similarly, the AN/TRC-8 consists of the basic radio components of multichannel radio set AN/TRC-11 and AN/TRC-12.
figure 6-30. Such a system requires only one transmitter and one receiver (each with its own antenna and mast) at the automatic radio relay station. Because of the simultaneous operation of the transmitter and receiver at the radio relay, different frequencies are required for the two directions of transmission. The system operates in the following manner. Frequency L is assigned to the radio transmitter at each terminal and also to the receiver at the automatic radio relay. Frequency f2 is assigned to the transmitter at the automatic radio relay and to the receivers at the two radio terminals. At the radio relay set, the output of the radio receiver is connected to the input of the radio transmitter. At both terminals and also at the radio relay the transmitters are normally not radiating. When a person desires to talk from one of the terminals, he operates the push-to-talk button on his microphone which puts his radio transmitter on the air and makes his radio receiver inoperative. His speech will then be transmitted at radio frequency fT to the receiver at the automatic radio relay point, applied to the radio transmitter at that point and delivered by that transmitter at frequency f2 to the radio receiver at the distant station.
(2) The frequencies f, and f2 must be so chosen that the transmitter at the radio relay station cannot capture the receiver at that point because of spurious transmitter radiations or spurious receiver responses (sec. VI). With present sets such as Radio Relay Set AN/TRC-4 and with convenient antenna spacing, such interference is more easily avoided if U and f2 are at opposite ends of the operating frequency band. Because of the desirability of this frequency separation, individual receiving and transmitting antennas are shown for the terminals also, although a common antenna might be used if the received signals are strong enough to compensate for the fact that the single antenna cannot be adjusted for optimum performance at both fj and f2.
c. Several Radio Relay Sets in Tandem.
(7) When more than one radio relay is required, the arrangement shown in figure 6-31 may be used. Two transmitters and two receivers, each with its own antenna, are required at each radio relay point. In order to avoid interference from the transmitters of adjacent sections, which might cause the sys-
251
PAR.
621
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
RADIO TERMINALSET
AUTOMATIC RADIO RELAY SET
AUTOMATIC RADIO RELAY SET
AUTOMATIC
RADIO RELAY SET
RADIO TERMINAL SET
TL 54905
Figure 6-31. Four-section radio communication system for operation with automatic radio relay sets.
tem to lock up, different frequencies must be used in the different sections. However, subject to the distance between radio sets and their disposition within the system, operating frequencies may usually be repeated after the second section, as illustrated in figure 6-31, especially if directional antennas having good front-to-back ratios are used. Four frequencies, as shown, would therefore be sufficient for proper operation if it were not for mutual interference between transmitters and receivers at the radio relay points. With present sets, such as Radio Relay Set AN/TRC-4, it is difficult to avoid such interference unless transmitters and receivers operate in widely different portions of the 70- to 100-mc band, or are separated physically more than is usually convenient (sec. VI). In such cases six frequencies may be required, as indicated by the bracketed values on figure 6-31, where fT, f3, and f5 are at one end of the frequency band and f2, f4, and fc are at the other end. The number of sections probably can be increased beyond four without increasing the number of frequency assignments beyond six by using the sequence in this manner:
f, —f2 —fa—f4—f5 —f6 —f4 —f2, etc.
f4-f5-f6-fi-f2-f3-f4-f5, etc.
where the upper and lower series correspond with the upper and lower directions of transmission indicated in figure 6-31. The arrangement shown can be used push-to-talk and also permits full duplex operation (both directions simultaneously) ; the latter is a requirement for multichannel operation. If used for multichannel operation the radio sets must be capable of continuous operation without overheating.
(2) With this full duplex arrangement using different frequencies for the two directions of transmission, Telegraph Terminals CF-2-( ) and CF-6 can be used directly on some single-channel radio sets to provide 4 to 12 2-way voice-frequency telegraph circuits (ch. 3).
d. Combination of Automatic and Manual Radio Relays.
(1) Another method which requires less equipment is to break the circuit into two or more parts, with each part limited to two sections, and to relay the message by means of
RADIO TERMINAL SET (AT RADAR)
AUTOMATIC RADIO RELAY SET
Figure 6-32.
RADIOTERM- MANUAL RADIO TERMINAL SET RELAY INAL SET
(2 OPERATORS)
AUTOMATIC RADIO RELAY SET
RADIO TERMINAL SET (AT OPERATIONS CENTER)
TL 54904
Four-section radio communication system, one manual and two automatic radio relay sets.
252
PAR.
621
CHAPTER 6. RADIO SYSTEMS
RADIO TERMINAL SET
Cat radar)
AUTOMATIC RADIO
RELAY SET
C4lI [70 EM WRITTEN *2 MESSAGE f2 I F2 _
—* T T * T
-- R T R =2^^
RADIO TERMINAL SET CM ANU AL RELAY)
AUTOMATIC RADIO
RELAY SET
RADIOTERMINAL SET (AT OPERATIONS CENTER")
TL 54906
Figure 6-33. Four section radio communication system for light traffic, one manual and two automatic radio relay sets.
operators. For spanning a length of 100 miles over terrain permitting jumps of only 25 miles, the circuit would be broken into two parts with manual relaying at the middle point. The number of frequencies required will depend on the quantity of traffic which the circuit is required to handle.
(2) Figure 6-32 shows a 3-frequency arrangement such as might be used at an air warning system operations center for handling heavy traffic incoming from a radar. Frequencies fi and f2, also fi and f3, must be chosen to avoid capture of the radio receiver by its associated transmitter at the automatic radio relay stations (sec. VI). It is believed that most satisfactory operation would be secured by using two operators. In the direction from a radar to the operations center, one of the operators at the manual relay station can continuously receive information from the radar, while the other operator can continuously transmit to the operations center the information written down by the first operator. Thus, the manual relay operation does not impede the traffic flow although it does, introduce a small time lag. If the direction of traffic flow should reverse, a frequency f4 would have to be used, as shown in brackets in figure 6-32; otherwise interference would result at the manual relay point unless special operating procedures were used.
(.?) Figure 6-33 shows the 2-frequency arrangement for handling light traffic. Frequencies 7 and f2 must be so chosen as to avoid capture of the radio receiver by its associated transmitter at the automatic radio relay station (sec. VI). In this case the operator at the manual relay point would no longer
be able to receive and send at the same time. This arrangement, therefore, appears unsuitable for general use where speed is required, although it might be satisfactory in some emergencies. It should be noted that this method of manual relaying requires only one radio transmitter and one radio receiver at the manual point, but one operator would be able to handle the traffic without undue fatigue for only limited periods.
e. Received Field Intensities Required for Several Single-channel Radio Relay Sections in Tandem.
(7) For f-m systems, when the field intensity is close to the minimum permissible for single-channel point-to-point telephone circuits, a small increase in field intensity will produce a large increase in audio signal-to-noise ratio. For this reason and for reasons outlined in subparagraph (2) below, the increase in received field necessary for such circuits to allow for several radio relay sections, or jumps, in tandem, is generally negligible. Single-channel v-h-f radio telephone systems arp generally operated on a point-to-point basis or on a basis equivalent to this from the standpoint of required signal-to-noise ratio.
(2) When there are several jumps it is frequently the case that one of the jumps will contribute a controlling amount to the noise at the terminal. In this case, the allowance for the contribution of the other jumps is negligible, whether the transmission is amplitude modulation or frequency modulation.
(5) For amplitude-modulated systems, when a number of jumps contribute an approximately equal amount to the noise at the terminal, the required received field intensity
253
65(>9;i5 O -45---------IS
PARS.
621-622 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
at each radio receiver is increased, the amount of increase in db being 10 log N, where N is the number of jumps. The necessary increase for particular values of N is as follows:
N 2 3 4 5 6 8 10
db increase 3 5 6 7 8 9 10
622. V-H-F MULTICHANNEL SYSTEMS.
a. General.
(1) Radio systems, like wire circuits, can be designed to transmit several telephone conversations simultaneously by the addition of carrier equipment. Such radio systems must be in operation continuously rather than on a push-to-talk basis and must use different frequencies for the two directions. Telephone circuits obtained in this way may be connected to a switchboard in the same manner as wire circuits and thus form a part of the regular telephone network. Such radio systems may be used in tandem with wire circuits, with the carrier frequencies passing over both the wire and radio sections. In such cases security rules for radio rather than for wire lines must be observed by users. Such a system may be used as an adjunct to wire in order to span some difficult terrain, such as a water crossing, or it may be used as a complete unit in order to obtain long-distance trunks which are primarily radio. The discussion below relates primarily to the latter type of use.
(2) The use of 4-channel radio relay sys
tems instead of wire systems provides substantial savings in installation time and weight and bulk of equipment, including outside plant, required for a given number of communication channels. The radio relay systems have been found very advantageous for use during a rapid advance. A comparison between them and wire systems is given in TM 11-487. A general comparison between wire and radio is in chapter 1 of this manual.
b. System Using Radio Terminal Sets AN/TRC-3 and Radio Relay Sets AN/TRC-4.
(1) An available 4-channel radio relay communication system consists of Radio Terminal Sets AN/TRC-3 and Radio Relay Sets AN/TRC-4, together with Telephone Terminal Sets TC-21 and Ringer Sets TC-24 for obtaining four telephone channels, and Telegraph Terminal Sets TC-22 if it is desired to superpose voice-frequency telegraph on one or two of the telephone channels (preferably on channel 3). The system operates with frequency modulation in the frequency band 70 to 100 megacycles, with a nominal power output of 50 watts. The modulating frequencies range from about 200 to 12,000 cycles. A schematic illustration of a system is given in figure 6-34. The radio relay sets and radio terminal sets are described in TM 11-2601. Photographs of these sets are in figures 6-35 and 6-36. System line-up procedures are described in TB SIG 78.
(2) The nominal spacing between radio sets is 25 miles, but the actual spacing will depend considerably on the type of terrain, an-
f Y RR
RTK -----------~
tTRT
AUTOMATIC RELAY STATION
TERMINAL A TERMINAL B
&^TTEErXPl| S-a( [TELEPHONEiTELEGRAPHtkH
O-j- CF-? —TERMINAL / LEGEND \ TERMINAL TERMINAL ~3~°
LJ— 1 _ ' CF-1 CF-2
-------- । ------------- ~O TELEPHONE ______________________ 1-^-0 -OTELETYPEWR ITER «CS' M,Lt---------------RINGERS ।
EQUIPMENT RR RADIO RELAY SET AN/TRC-4
RC-120 rt radi° TERMINAL SET AN/TRC-3 EQUIPMENT
----—--- S-4 TELEPHONE CABLE RC-120 SPIRAL-FOUR CUP TO 5 MILES)
NOTE:
ADDITIONAL RADIO RELAY SETS MAY BE USED TO EXTEND TOTAL LENGTH OF SYSTEM.
T<- 54959
Figure 6-34. Schematic illustration of 4’channel radio relay communication system.
254
PAR.
622
CHAPTER 6. RADIO SYSTEMS
Figure 6-35. Radio Relay Set AN/TRC-4 prepared for operation in Truck, Weapons Carrier, %-ton, 4x4.
tenna siting, and method of using the circuit, as discussed earlier in this section and in following subparagraphs. A 250-watt amplifier designated as Amplifier Equipment AN/TRA-1, described in TM 11-2601, gives a nominal transmitting gain of 7 db. In general, four or more radio frequencies are required for radio relay operation, as discussed in paragraph 621c. These frequencies must be very carefully chosen to prevent mutual interference between the various radio transmitters and receivers (sec. VI). Because of the use of different operating frequencies in the two directions of transmission, four antenna sys
tems are required at each radio relay set and two at each radio terminal set.
(3) Channel 1, which is the voice channel of the spiral-four carrier system using Telephone Terminal Sets TC-21, is the only channel which is brought down to voice frequency at radio relay- points, and is therefore the only one available for use as an order wire between these points and the radio terminal sets. When channel 1 is also used as a telephone circuit connected into switchboards, routines for message priority between switchboard and order wire must be established. Channel 1 is normally not used to provide facsimile or voice-frequency telegraph circuits.
(4) In order to permit advantageous siting of radio terminal sets, provision is made for separating them from the telephone terminals by as much as five miles of spiral-four cable (Cable Assemblies CC-358-( )). In such cases, local order wire circuits between telephone and radio terminals are provided over the phantom of the spiral-four cable.
c. System Using Radio Terminal Sets AN/TRC-11 and Radio Relay Sets AN/TRC-12. Another 4-channel radio relay system consists of Radio Terminal Sets AN/TRC-11 and Radio Relay Sets AN/TRC-12, used together
Figure 6-36. Radio terminal station of 4-channel radio relay system, (showing Telephone Terminal CF 1 ( ), Telegraph Terminal CF-2-( ), and Radio Terminal Set AN/TRC-3).
255
PAR.
622
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
with Telephone Terminal Sets TC-21 and Ringer Sets TC-24 to derive the telephone channels and with Telegraph Terminal Sets TC-22 for superposed voice-frequency telegraph. This system operates with frequency modulation in the frequency band 230 to 250 megacycles with a nominal output power of 12 watts. Further details are in TM 11-618.
d. Multichannel Versus Single-channel Operation. When several radio circuits are required between two given points, multichannel operation will result in a considerable saving in required equipment and personnel, and in the number of radio frequency assignments, as compared to what would be needed for singlechannel operation. The advantage is not, however, as great as might be expected on first thought, since the percentage modulation of each channel must be substantially less than would be permissible for single-channel operation ; otherwise the total modulation resulting from signals on the different channels would exceed 100 percent, thus overloading the system and causing excessive interference from one channel into another. The required lowering of modulation level per channel, for the 4-channel systems discussed above, is of the order of 12 db. As a result of this, together with the higher noise on the top channel of a multichannel f-m system, the received field intensity must be higher for multichannel than for single-channel operation, by an amount depending on the quieting action of the f-m receiver under the particular circumstances. It is thought that on the average a 10-db increase in received field intensity, for 4-channel compared to single-channel operation, will suffice to make the signal-to-noise ratio on channel No. 4 as good as that for single-channel operation. (Channels 1 to 3 will be better than channel 4 by various amounts. Effects of imperfect equalization are considered separately in subparagraph h below.) Hence the allowable distance between relay points, and the total distance which can be satisfactorily spanned with a given number of sets, is less for 4-channel than for single-channel operation. Also a 4-channel system requires more careful maintenance than a single-channel system.
e. Received Field Intensities Needed for Multichannel Multijump Operation.
(1) With the received field intensity required for satisfactory 4-channel operation
with existing sets, it is thought that further increases in received field intensity will result in roughly equal increases in audio signal-to-noise ratio in the upper channels. With more than one relay section or jump per system, if all of N jumps have the same received field intensity, the required db increase in received field intensity for each jump is 10 log N, while if one of the jumps controls the received audio noise, which is more apt to be the case, no increase is necessary. For values of 10 log N, see paragraph 621e (3).
(2) When a trunk consists of one or more radio relay sections (jumps) in tandem with one or more wire repeater sections, each wire repeater section can be considered as the equivalent of a radio jump in finding the required received field intensity on the radio portion of the circuit.
f. Operation as Via Trunks.
(7) When radio relay systems form a part of the regular telephone network and are used as via trunks for switched telephone service, a further increase in received field intensity is necessary in order to provide an adequate speech-to-noise ratio when the trunks are operated in tandem. When the trunk in question is the end trunk in the circuit, the speech from the distant talker is attenuated by the loss of the intervening trunks. In the typical arrangement shown in the transmission plan in chapter 2, there are three 6-db trunks in tandem, and the distant talker’s speech would be lowered by the loss of two intervening trunks, or 12 db, before reaching the trunk in question. In order to compensate for this loss, the noise on this trunk must be lowered 12 db. That is, in order to provide a just tolerable ratio of received speech-to-noise on the built-up connection, the last trunk must be designed such that its noise contribution is 12 db lower than if it were not designed for use in tandem with two other trunks. In general, if the trunk is designed for use as an end trunk in tandem with other trunks whose net losses total X db, the noise requirement on the end trunk is stiffened by X db. In the above, the contribution of trunks other than the end trunk to the noise received by the listener is small and has been disregarded. To obtain a 12-db improvement in audio signal-to-noise ratio on a given multichannel radio system, the received field intensity should be increased by about 12 db. The resulting required field
256
PAR.
622
CHAPTER 6. RADIO SYSTEMS
intensities are high enough to require excellent antenna siting in order to obtain radio relay systems as long as 100 miles and capable of operating as via trunks in the regular telephone network.
(2) When v-f telegraph is used on one or two of the four telephone channels, the above requirements are not changed.
g. Interchannel Crosstalk, General. In the existing multichannel radio relay systems, the interference from one channel into another (interchannel crosstalk) is relatively high compared to that on comparable wire systems. This depends on the linearity of the system; it is approximately independent of the length of radio relay sections, but increases with the number of relay sections. Overloading of the transmitters increases the interchannel crosstalk. On this account it is very important to carry out the line-up procedures given in TB SIG 78.
h. Equalization Limitations. Another limitation of these systems is equalization of the transmission of different frequencies. If the gain in a particular channel is greater than that at the line-up frequency of 4,900 cycles (which corresponds to 1,000 cycles at voice frequency in channel 2), signals in the channel in question tend to overload the system. If the gain in a particular channel is lower than that at the line-up frequency, the gain deficiency can be made up only at the receiving end if standard arrangements are employed, and when it is made up, the noise and interchannel crosstalk are increased about as much as the received speech. Frequency characteristics of individual radio relay and radio terminal sets vary; but there is a general tendency for channel 3 to have higher gain, and channels 1 and 4 lower gain, than that at the line-up frequency. On the basis of early production models it has been estimated that channel 4 of AN/TRC-3 and -4 should not be used for more than three jumps between terminals (later models may do somewhat better than this) and that channels 1 to 3 should not be used for more than seven jumps between terminals. Comparable data on AN/TRC-11 and -12 were not available at the time when this manual was prepared.
i. Methods of Improving Equalization or Interchannel Crosstalk.
(1) The first steps to take are careful maintenance procedures: to see that the circuit
is kept carefully lined-up (per TB SIG 78 in the case of Radio Terminal Set AN/TRC-3 and Radio Relay Set AN/TRC-4) ; that adequate signal voltages are being received, through proper siting, careful adjustment and orientation of antennas, and careful alignment of individual receiver stages; and that vacuum tubes and line voltages have been carefully checked.
(2) If interchannel crosstalk is objectionably high after the above steps have been taken, and if other noise is relatively low (for example, if this noise is mainly set noise and if the received field intensity is safely above the required minimum values given in figure 6-12), then an improvement can be obtained by lowering the degree of modulation. It has been found that if the audio signals fed into the radio system are lowered in level by 5 db the interchannel crosstalk will be reduced by about 10 db, and thus the ratio of speech to interchannel crosstalk will be improved by about 5 db. In order to keep the net loss of the circuit unchanged, the audio gain at the receiving radio terminal is increased by the same amount (5db) that the audio transmitting level is lowered. This produces a 5-db increase in the noise (other than interchannel crosstalk) on the radio channel; however, if this noise was small to begin with, there is a net improvement in the circuit. Methods of lowering the audio signal level fed into the radio system are as follows. Where there is sufficient spiral-four cable between carrier terminal and radio terminal, the levels on the system may be lowered by setting the cable compensator in the transmitting radio terminal at an increased loss (that is, on a lower step). When the cable compensator is on the lowest step and still more loss is required, a balanced pad (ch. 12) may be inserted just ahead of the transmitting radio terminal.
(3) The 0 dbm mark on the panel meter on some Radio Receivers R-19/TRC-1 may be as much as 2 db in error. If this condition occurs the radio transmitters may be inadvertently overmodulated. This can be avoided by making an accurate recalibration of the panel meters.
(4) Channel 4 can be discarded if the number of jumps is too great to permit its use.
(5) With a large number of jumps, the equalization can be improved by inserting, at the relay station nearest the middle, two Telephone Terminals CF-l-( ), back to back,
257
PARS.
622-624 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
that is, with their voice-frequency sides connected together. This permits the level at the 1,000-cycle point of each telephone channel to be adjusted independently. The telephone terminals should be connected on a 4-wire basis (ch. 5) ; or if temporarily connected on a 2-wire basis they should be mounted close to each other and connected directly to each other with no bridged apparatus, and the monitoring jacks of the two Telephone Terminals CF-l-( ) should not be used, so as to prevent singing of the telephone circuits. The transmission levels should be adjusted so that each jump except the last is operating at 0-db nominal net loss and the last is operating at 6-db net loss. In some cases it may be possible to use, instead of the two Telephone Terminals CF-l-( ), a single Telephone Repeater CF-3-A; the adequacy of this expedient will depend on the transmission-frequency characteristics of the particular radio relay and ter
minal sets which happen to be included in a given system, and can be determined only by trial.
(6) Where traffic conditions warrant, it may be practicable to arrange radio relay systems so as to provide direct rather than switched connections between long-distance centrals, thus avoiding the 6-db loss in received speech volume produced by each added tandem trunk.
(Z) Where very many jumps are required, it may be practicable to employ v-f telegraph instead of speech transmission. For this purpose, Telegraph Terminal Sets TC-22 can be used directly into Radio Terminal Sets AN/TRC-3. By using two telegraph terminal sets at each radio terminal, eight 2-way telegraph channels can be used for about ten jumps. Further information on the use of carrier telegraph over radio circuits is in chapter 3.
Section Hi. V-H-F ANTENNAS
623. GENERAL.
a. Antennas for use in the v-h-f band may be classified as either directional or nondirec-tional. Nondirectional antennas transmit and receive equally well in all horizontal directions. Directional antennas transmit and receive better in some horizontal directions than in others, and are usually more efficient in the desired direction than a nondirectional antenna at the same elevation. (The word directional is used with a different meaning in the h-f band, where vertical directivity for sky waves is important.) Directional antennas which consist of multiple elements are sometimes called arrays.
b. The nondirectional types are used in situations where communication is required in a variety of compass directions. This requirement, plus mechanical advantages, is the reason for using vertical whip antennas on mobile and portable radio sets where the tactical situation is apt to involve communication in any direction. The directional types provide more efficient transmission over fixed paths.
c. Antennas are available for transmitting and receiving either horizontally or vertically polarized waves (par. 619). In areas where numerous v-h-f sets must operate with little separation between antennas, the use of ver
tical polarization on some circuits and horizontal polarization on others is one measure which may be used to reduce mutual interference. In all cases, however, antennas capable of utilizing the same type of polarization should be used at both ends of a radio circuit, or serious loss in transmission will result.
d. In this section, the advantages of directional antennas are summarized briefly before discussing specific antenna types. Descriptions of a number of the more common antenna types are then given, including some nonstandard types which might be used in an emergency. The nondirectional types are discussed in paragraphs 626 to 631, and paragraphs 632 to 636 cover the directional types. General information on v-h-f antenna dimensions follows, and the section concludes with data on r-f transmission lines, including a line which may be improvised from field wire (pars. 637 and 638). Further information on antennas and antenna coupling arrangements is available in TM 11-314 and TM 11-487.
624. ADVANTAGES OF DIRECTIONAL ANTENNAS.
a. General. For communication between fixed or semifixed installations, directional antennas may be used to increase the distance
258
PARS.
624-625
CHAPTER 6. RADIO SYSTEMS
range. Such antennas can be obtained in convenient size for the middle and upper portions of the v-h-f band.
b. Signal Gain. As transmitting antennas, the directional types radiate stronger fields in the desired direction than simple dipole antennas at the same effective elevation above the earth, and as receiving antennas they extract more energy from the passing field. These gains amount to from 6 to 10 db at each end of the circuit for some of the types illustrated in later paragraphs.
c. Signal-to-noise and Signal-to-interference Ratio.
(7) General. The gain of a directional receiving antenna provides an equivalent improvement in r-f signal-to-noise ratio when set noise is the controlling source of noise. When external random noise coming in from all directions is controlling, the use of a directional antenna may also improve the r-f signal-to-noise ratio by as much as 10 db, by rejecting noise from many directions. When radio interference exists, directional receiving antennas are of no advantage if the interfering source is in the same direction as the distant transmitter. However, large improvements in signal-to-interference are possible if the interfering source is localized in a given direction and the antenna can be oriented so that this direction corresponds with a minimum in the directional pattern.
(2) Effect of Unbalanced R-f Transmission Line. Some tactical v-h-f balanced antennas are fed through directly-connected unbalanced coaxial transmission lines. With such unbalanced connections, currents will tend to flow on the outer surface of the coaxial lines, and undesired radiation (or response) will take place. This radiation may not seriously affect the major lobes in the directional pattern of an antepna, but will tend to fill in the nulls. For example, if the antenna is horizontal and the coaxial down lead is vertical, measurements of the horizontally polarized directional pattern will probably indicate little difference from that obtained using a well balanced transmission line. The down lead, however, may be radiating relatively strong vertically polarized waves. Thus, in situations where directivity is a means utilized to reduce mutual interference between nearby sets, orientation of antennas to take advantage of expected nulls in the antenna patterns may be
ineffective, since the major coupling may be between the down leads, the radiation patterns of which are nondirectional. Also, with sets in close proximity in the same building, stray currents on the transmission lines may cause direct coupling at the sets, independent of that caused by radiation. Balancing arrangements which reduce current flow on the outer surface of the coaxial line are standard with some antenna types described below, and are recommended for use in the above situations.
d. Security. The use of a directional antenna does not guarantee security. However, directivity of a transmitting antenna is desirable, since the energy may be concentrated in a given direction, thus reducing the chances of interception.
625. TACTICAL V-H-F ANTENNAS.
a. There are a variety of v-h-f antennas whch are used both for transmitting and receiving. In many applications the antenna associated with a set is switched from receiver to transmitter on a push-to-talk basis.
O
MAST SECTIONS---r-w
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Figure 6-37. Typical whip antennas.
259
PARS.
625-627 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
b. Tactical radio sets are equipped with specific antennas for which the output circuits were designed. The use of a different antenna in an effort to improve transmission may-make matters worse, unless proper leads and coupling units are used to match the new antenna impedance. Standard antenna couplers have been provided for some sets which permit the use of antennas other than those for which the sets were designed. These arrangements are briefly discussed in connection with the antenna types involved.
626. WHIP ANTENNA.
The whip antenna illustrated in figure 6-37 is the most commonly used v-h-f antenna where the distances to be covered are rela
tively short, and where portable or mobile operation is of primary importance. Since a considerable portion of tactical radio communication comes within this category, the whip antenna finds wide application. This antenna should be used in a vertical position, and is then nondirectional. As commonly used, the antenna length may lie between quarterwave and half wavelength for frequencies in the neighborhood of 30 megacycles, and half wavelength for frequencies above about 40 megacycles. (Half-wave whips have a gain in horizontal directions, of about 2 db over a quarter-wave whip at all frequencies, but are of prohibitive size at the lower frequencies.) If a standard whip is broken, a piece of wire of equal length supported vertically may be used.
HIGH IMPEDANCE T----------\A
BALANCED CIRCUIT BALANCING3* VD SECTION \
TO SET
SCHEMATIC
>---RADIATING ELEMENT
COAXIAL TRANSMISSION LINE---
HOUSING (TO COAXIAL CABLE)
TL 5494-9
----RADIATING ELEMENT
TL 53404
Figure 6-38. Balanced half-wave dipole antenna (part of Antenna Equipment RC-81).
Figure 6-39. Antenna Mast AN-56—A supporting two Antenna Equipments RC-81.
627. HALF-WAVE DIPOLE ANTENNA.
a. The vertical half-wave dipole antenna illustrated in figure 6-38 is fed at the center with a low impedance (50 to 70 ohms) coaxial cable through a balancing section illustrated more clearly in the schematic. The balancing section is approximately one quarter wave in length shorted at the point where
260
CHAPTER 6. RADIO SYSTEMS
PAR.
627
WOODEN_> SUPPORT
TL 549 38
Figure 6-40. Improvised half-wave dipole antenna.
the flexible transmission line connects, thus presenting a high balanced impedance as seen from the dipole. Such construction minimizes current flow on the outer surface of the transmission line. This antenna is supplied as Antenna Equipment RC-81 with Radio Transmitting Equipment RC-257 operating in the 100- to 156-mc band. Figure 6-39 illustrates two such antennas mounted on Antenna Mast AN-56-A.
b. Dipole antennas may be improvised for emergency use, using materials found in the field. Such antennas are shown in figures 6-40 and 6-68. When used vertically, this antenna type should be provided with a wooden support to the feed cable (as illustrated), extended out at right angles to the antenna for a distance of a quarter wavelength or so. This
spacing is to reduce the effect of the vertical transmission cable on the radiation field of the antenna. The total length of the antenna should be adjusted to 95 percent of half wavelength for the operating frequency, but this length is not crictical of adjustment and may vary ± 5 percent without adverse effects on transmitting or receiving, provided that the transmitter will load properly. When used vertically, the antenna is nondirectional in a horizontal plane. When used horizontally, the antenna has directional characteristics, the optimum direction being at right angles to the
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Figure 6-41. Adjustable vertical coaxial antenna.
261
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PARS.
627-628 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
antenna wire on either side. The pattern width is 90 degrees at points 3 db down from maximum and 120 degrees at points 6 db down from maximum.
628. VERTICAL COAXIAL ANTENNA.
a. The type of antenna illustrated in figure 6-41 is provided in P-8212 antenna kit (Galvin Manufacturing Company nomenclature, Signal Corps stock No. 2A1640) as part of the equipment associated with Radio Sets AN/CRC-3 and AN/CRC-3A(30 to 40 me) ; similar antennas type 1509 (F. M. Link Company nomenclature, Signal Corps stock No. 2A272-3) are also used with type 1498 and 1505 radio transmitter-receivers (70 to 100 me). It is essentially a vertical half-wave dipole antenna constructed so as to provide a convenient mechancial feed arrangement by means of a 50-ohm flexible coaxial cable transmission line which runs up through the supporting staff. The skirt, when adjusted in accordance with instructions, acts as the lower half of the radiator and also minimizes current flow on the outer surface of the transmission cable. For optimum performance, this antenna requires readjustment of the whip and skirt lengths when the frequency is changed more than ± 1 percent from that for which the antenna was previously tuned; the skirt length adjustment is more critical than that of the whip. Complete instructions for these adjustments are packed with each antenna, and the elements of the P-8212 antenna kit are marked at quarter-megacycle intervals. These adjustments are approximately 95 percent of a quar-
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Figure 6-42. Coupling unit, used to match Radio Set SCR-609 transmitter output impedance to 50-ohm coaxial transmission cable.
ter wave for the whip and about 100 to 103 percent of a quarter wave for the skirt. The latter dimension is measured from the bottom of the shorting ring, and if a calibration is not available or is illegible, a cut and try procedure in the 100 to 103 percent range to obtain an optimum adjustment may be worthwhile on a marginal circuit. Although constructed for vertical operation, this antenna may be operated horizontally, at some inconvenience in mounting, if horizontal-polarization is required.
b. If this antenna is used with sets designed to operate into high impedance antennas, an impedance matching transformer should be
DIM
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Figure 6-43. Improvised vertical “J” antenna.
used between the set and the 50-ohm antenna r-f transmission line. For example, such a coupling unit is included in P-8212 antenna kit (Galvin Manufacturing Company nomenclature) for use with Radio Set SCR-609, as illustrated in figure 6-42.
262
PARS.
629-630
CHAPTER 6. RADIO SYSTEMS
629. VERTICAL “J” ANTENNA.
The nondirectional antenna illustrated in figure 6-43 consists of a vertical half-wave antenna with a quarter-wave matching stub directly connected to the lower end. This stub acts as a transformer for matching the impedance of the transmission line to the antenna. The transmission line may be an open wire line or coaxial cable. For low-impedance transmission lines, the connection for optimum impedance matching will be close to the metallic strap, and for cables of 70-ohm impedance or less it will usually be necessary to remove the strap and connect directly to the lower end of the matching stub. The location of the transmission line on the stub, the length of the stub, and the length of the half-wave radiator all require adjustment when the operating frequency is changed. The antenna illustrated in figure
Figure 6-45. Coupling unit (Terminal Box TM-217), used to match Radio Set SCR-300 transmitter output impedance to a 50-ohm coaxial transmission cable.
This antenna is nondirectional and is to be used with Radio Set SCR-300 (40 to 48 mc) in applications where elevated antennas rather than whips are especially desired, as in a jungle. It is assumed that a suitable support will be found available in the field. The antenna is fed through a 50-ohm flexible coaxial cable, and the equipment includes an impedance-matching coupling unit (Terminal Box TM-217) for connection between the set and the coaxial transmission line, as shown in figure 6-45.
Figure 6-44. Ground-plane antenna (antenna of Antenna Equipment RC-291).
6-43 is one which may be improvised. An adjustable antenna of this general type is used with Radio Set SCR-624-A.
630. GROUND-PLANE ANTENNAS.
a. The antenna illustrated in figure 6-44 consists of a quarter-wave vertical whip working against a rod structure simulating a ground plane (Antenna Equipment RC-291).
Figure 6-46. Antenna Equipment RC-292 (for use in fixed installations of Radio Sets SCR-508 and SCR-608).
263
PARS.
630-631 ELECTRICAL.COMMUNICATION SYSTEMS ENGINEERING
b. The antenna illustrated in figure 6-46 is a nondirectional vertical antenna designed for use in the 20- to 40-mc band with Radio Sets SCR-508, SCR-528, SCR-608, and SCR-628 in fixed locations where elevated antennas can be used to advantage. It is directly connected to these sets through a flexible coaxial cable and is supported on a 30-foot mast. While classified as a ground-plane antenna, radiation also takes place from the lower elements as well as the whip. The model shown is known' as Antenna Equipment RC-292; a similar antenna coded Antenna Equipment RC-296 is under development for use with Radio Set SCR-300 and will include a coupling unit (Terminal Box
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Figure 6-47. Antenna of Antenna Assembly AS-110-( )/TRC-7 (used with Radio Set AN/TRC-7).
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Figure 6-56. Horizontal directional patterns of vertical half-rhombic antenna using 50-foot mast.
poor earth or sea water, rather than good earth. It is noted that over sea water, which approaches a perfect earth, the computed patterns exhibit deep minima and prominent secondary lobes, similar to those shown for the full rhombic in figure 6-62. Over land, particularly poor soil, the computations indicate that these features tend to disappear with the half-
268
CHAPTER 6. RADIO SYSTEMS
rhombic. Portions of the patterns which are more than 25 db below the efficiency in the forward direction are omitted from figure 6-56.
g. These computed patterns assume the antenna to be terminated in characteristic impedance, about 400 ohms. In practice, the location of sharp minima and the magnitude and location of minor lobes may vary from those illustrated, and the best terminating impedance to use for maximum front-to-back ratio may be determined experimentally. When unterminated, the radiation and response in the forward direction is not materially affected, but a similar lobe in the pattern appears in the rear, with the maximum gain to the rear about 3 db less than in the forward direction. When used unterminated, it may be difficult to load the transmitter properly because of standing waves (ch. 12). Even when terminated, this antenna will not operate satisfactorily with certain sets designed to operate into a low-resistance load such as the impedance of a half-wave dipole antenna, unless steps are taken to match impedances by means of a transformer, a transforming line section, or a matching stub. Radio Sets AN/CRC-3 and -3A, for example, are equipped with the antenna coupling unit shown in figure 6-57. Among the radio sets listed in
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Radio Sets AN/CRC-3 and -3A).
TM 11-2616 (Antenna Equipment RC-63) to which the vertical half-rhombic Antenna RC-63 may be directly connected without any external matching networks are Radio Sets SCR-300, SCR-508, SCR-528, SCR-608, SCR-609, SCR-610, and SCR-628.
PARS. 633-634 •
h. Since there is less radiation or response to vertical fields broadside to these antennas, or to the rear whep terminated, proper orientations, when the antenna is used for receiving, will minimize interference from sources emitting vertically polarized waves. For example, vertical half-wave dipole transmitting antennas in the vicinity should be placed at positions falling in or near null points in the patterns of receiving rhombics.
634. FULL-RHOMBIC ANTENNAS.
a. General. The full-rhombic antenna is a diamond-shaped configuration of wires, supported in either a vertical or a horizontal position as illustrated in figures 6-58 and 6-59, respectively. Dimensions of 4 or 5 wavelengths per leg, or side, are required in order to obtain a substantial part of the signal gain and directive capabilities of this type of antenna. This requirement generally precludes the use of these antennas, for tactical applications, at frequencies below about 50 mc. A full rhombic has an impedance of 600 to 800 ohms, and should be fed by a balanced transmission line from a transmitter having a balanced output circuit, or if used as a receiving antenna should be connected through a balanced line to a balanced receiver.
b. Construction Details and General Characteristics.
(1) The dimensions and construction details for rhombics intended ultimately to be standardized for use with radio sets AN/TRC-1, -3, and -4 are shown in figures 6-58 and 6-59. The output circuit of these sets is unbalanced, and the balancing arrangement illustrated in more detail in figure 6-60 is therefore provided to feed either the horizontal or .vertical rhombic. The folded coaxial cable shown is one-half wave long at 85 mc, and provides a transformation from the 50-ohm unbalanced coaxial cable to a 200-ohm balanced output. It is used over the 70- to 100-mc band without change in dimensions. The tapered line section then provides a balanced matching section between this 200-ohm output impedance and the 600- to 800-ohm rhombic antenna impedance.
(2) The vertical rhombic shown in figure 6-58 may be expected to have gain and directivity characteristics comparable to those described in subparagraph c below, which gives general design and performance data for an
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269
PAR.
634
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
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antenna of comparable design. In this illustration, the antenna is shown supported on steel masts. Wooden masts are ordinarily to be preferred in order that induced currents in and consequent radiation from the masts will not alter the antenna pattern. There is some evidence that any metal near the apex, other than the wire itself, has a detrimental effect. No data
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(3) The horizontal full rhombic shown in figure 6-59 has leg lengths comparable to those described for the vertical but requires four short poles instead of one long and two short ones. The gain of. this antenna in the forward direction should be about 11 db for the
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HALF-WAVE COUPLING UNIT
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70 59' 53' 70' 29'
82.5 59' 48' 70' 29'
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Figure 6-59. Full horizontal rhombic antenna (for use with radio sets AN/TRC-1, -3, and -4).
270
PAR.
634
CHAPTER 6. RADIO SYSTEMS
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l5______MENT ARRAY- '_______ XX__________
COAXIAL ANT. WHIP LENGTH?!
LENGTH OF 1/4-WAVE WHIP ___/ xX
OR EACH HALF OF A HALF-WAVE DIPOLE. A
10 HALF LENGTH OF 3-ELEMENT---'*X
9-------------1--- ARRAY .DIRECTOR . --------
81____________1___I—L-__________। I
30 40 50 60 80 100 150 200 300
MEGACYCLES
TL54889
Figure 6-65. Approximate antenna dimensions versus frequency.
984
One wavelength (feet) =--------------
megacycles
The above expression is useful in rhombic antenna computations.
2,800 0.95 of one quarter-wave (inches) =-------
megacycles
This expression is the one used to determine the length of each half of a half-wave dipole, the factor 0.95 allowing approximately for end effect.
300
Frequency (megacycles) — —______— Wavelength in meters
300
Wavelength (meters) = --------------------—
Frequency in megacycles
These expressions are useful in converting from wave length to frequency, or vice versa.
c. For further information on v-h-f antenna dimensions, consult TM 11-314.
274
PAR.
638
CHAPTER 6. RADIO SYSTEMS
638. ANTENNA R-F TRANSMISSION LINES.
a. Coaxial Cables. Both tactical and fixed plant radio equipment usually include a suitable type and length of r-f transmission line with which to feed the antenna associated with the set. Losses for several types of lines are given in paragraph 676. In the v-h-f band, 50-to 70-ohm solid dielectric flexible coaxial cable having relatively low loss is ordinarily used to feed elevated antennas. If such lines are damaged and cannot be replaced, the damaged coaxial cable may be used on an emergency basis if the parts in trouble are cut out and the center wire and braid respliced, using tape (preferably rubber) as insulation. It is not necessary to retain the coaxial construction of the braid at the splice; but the two braids should be connected with a short piece of wire. Such splices introduce slight impedance irregularities and some loss, but the performance will usually be better than with other improvised feeders.
b. Losses in Field Wire. The attenuation of field wires ordinarily available is very great in the v-h-f band, as shown in figure 6-146. For example, the present type of Wire W-143 has an attenuation of 7, 18, and 25 db per 100 feet at frequencies of 30, 100, and 150 me, respectively. Wire W-110-B has still higher loss, especially when wet. In general, therefore, field wires are poor substitutes for coaxial cable and should be used as emergency r-f transmission lines only when the signals are sufficiently strong to withstand appreciable loss. The chances of successful operation with such wires are greatest in the lower part of the v-h-f band and with the line made as short as possible. It is much better to use spaced leads, as indicated below.
c. Improvised Spaced-wire Line.
(1) When coaxial cable cannot be salvaged, a spaced line such as shown in figure 6-66 may be improvised in an emergency for use with half-wave dipole or coaxial antennas. Figure 6-67 shows the constructional details and figure 6-68 shows several improvised horizontal and vertical antenna mountings, in case the standard dipole antenna as well as the coaxial cable is lost or damaged. The transmission line uses two conductors of any available type of insulated wire, separated by wood blocks (or better insulating material, if available) at about 2-foot intervals. Paired wire such as Wire W-110-B or Wire W-143 may be
used, in which case the two conductors of each pair are connected together and used as one side of the spaced line. The wire can be fastened to the blocks with staples, tape, string, or wire.
Figure 6-66. Improvised spaced line and horizontal halfwave dipole antenna.
(2) The impedance matching line sections shown are made from one pair of Wire W-110-B cut to the dimensions indicated for B in the table of figure 6-67, which are approximately quarter wavelengths for this wire. Wire W-110-B has a characteristic impedance, Zo, of about 150 ohms, which is about the correct value (Zo =v% Z2) for a quarterwave matching section between the spaced-line impedance (Zi = 400 to 500 ohms) and the impedance of a dipole (Z2 — 50 to 70 ohms). When the line is used for transmitting, the lower matching section may not be required if the transmitter will load into a 400- to 500-ohm impedance; similarly, it should not be used if the receiver has a high impedance input. When the lower matching section is used and the transmitter does not load properly, the length of the section may be altered slightly to
275
PAR.
638
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
TIE WITH STRING
fasten wire to blocks WITH STAPLES OR STRING
WOODEN BLOCKS (USE
BETTER INSULATING
MATERIAL IF AVAILABLE)
OPEN WIRE LINE MAY BE
ANY LENGTH BUT SHOULD BE NO LONGER THAN NECESSARY
WIRE W-IIO-B
SPLICE (SEE DETAIL)
B~ INCHES
15
TL54961
85
IOO 120 140
53
42j
35| 30'
261 24
20}
35
45
55
65
COAXIAL CONNECTOR (AS REQUIRED FOR EQUIPMENT)
___2800 . |N INCHES
MEGACYCLES S
Figure 6-67. Construction of improvised transmission line and antenna.
ANY TYPE OF FIELD WIRE
DETAIL of splice (SOLDER IF POSSIBLE)
FREQUENCY-MC.
provide the impedance required to permit loading.
d. Performance of Improvised Lines. Tests using AN/TRC-1 and AN/CRC-3 transmitters indicate that the impedance matching line sections need not be adjusted for each operat-
N0TE3:
I. USE STANDARD DIPOLE ANTENNA WHEN AVAILABLE.
2-USE ANTENNA POLE WHEN AVAILABLE OTHERWISE SELECT TREE OR OTHER SUITABLE SUPPORT AND PLACE ANTENNA AS HIGH AS POSSIBLE. CLEAR AWAY ANY FOLIAGE.
3.USE STANDARD INSULATORS WHEN AVAILABLE. ROPE OR STRING CAN BE USED IN PLACE OF INSULATORS WHEN NO OTHER INSULATING MATERIAL IS AVAILABLE.
4.WHEN THE TRANSMITTER IS LOCATED AT SOME DISTANCE FROM THE ANTENNA. THE TRANSMISSION LINE SHOULD BE RUN HORIZONTALLY, SUPPORTED SEVERAL FEET OFF THE GROUND.
TL 54964
Figure 6-68. Installation of improvised transmission line and antenna.
ing frequency. For example, using a 100-foot spaced line constructed with Wire W-110-B, the AN/TRC-1 transmitter could be loaded to full output at all frequencies tested in the 70- to 100-mc band with the matching sections cut to 24-inch lengths, corresponding with the 85 me value shown in figure 6-67. The radiated field with the line dry was only 3 to 6 db less than with a 100-foot length of coaxial cable. With the line wet the loss increased another 1 to 3 db. With the AN/CRC-3 transmitter, full loading was obtained over the 30- to 40-mc band with the matching sections cut to lengths corresponding to 30, 35, or 40 me. The radiated field with the line dry was 2 to 4 db less than with a 100-foot length of coaxial cable, and with the line wet the loss increased another 1 or 2 db. No tests were made with input powers exceeding 50 watts; the maximum power which the line can handle without overheating and breakdown is not known.
276
PARS.
639-641
CHAPTER 6. RADIO SYSTEMS
Section IV. H-F TRANSMISSION
639. GENERAL
a. The main factors relating to groundwave and sky-wave radio transmission in the h-f band (3 to 30 me), including information on expected performance and on general methods for making performance estimates, are given in this section.
b. Important differences in the transmission characteristics of frequencies in the h-f band, as compared with those in the v-h-f band, are described first, followed by a general introduction to the subject of sky-wave propagation and a discussion of the fields of use of ground waves and sky waves (pars. 640, 641, and 642). The importance of making the proper choice of operating frequencies for h-f sky-wave transmission is emphasized, and reference is made to published periodic predictions of frequencies suitable for sky-wave use (par. 643). Estimated ground-wave transmission distance ranges, and sky-wave performance over distances of 0 to 200 miles are given next, assuming certain reasonably typical conditions. Attention is called to published periodic predictions of h-f ground-wave and sky-wave performance for particular tactical radio sets for different theaters of operation (par. 644).
c. Subsequent paragraphs (pars. 645 to 653) deal with the general methods used in making ground-wave and sky-wave performance estimates, including much of the background data required. This information is useful when the published periodic estimates for the particular area in question are unavailable and when the conditions differ materially from those assumed herein for the typical cases referred to above. Step-by-step solutions of representative problems are given.
d. The section continues with a brief description of measures which may be taken to reduce radio noise in receiving areas, and a short discussion of long-distance sky-wave reliability (pars. 654 and 655).
640. COMPARISON OF H-F AND V-H-F TRANSMISSION.
a. In the h-f band, the presence of useful sky-wave transmission makes it possible to provide communication over distances far beyond either the h-f or v-h-f ground-wave distance ranges. These same sky-wave effects also
permit undesired signals from distant transmitters to interfere with the reception of desired h-f signals.
b. Atmospheric noise is important much of the time over a large part of the h-f band, unlike the situation in the v-h-f band where set noise is usually controlling. Ordinarily this static is due to sky-wave propagaton of the effects of storms in the tropics. During the summer months, effects propagated from storms in certain regions of the temperate zone, or nearby thunderstorms, may be controlling. In high latitudes, atmospheric static field intensities are generally low, but auroral disturbances affecting the reflecting properties of the ionosphere sometimes cause radio blackouts and force the use of high-powered 1-f sets for ground wave (par. 641d (3) ) in place of h-f sky-wave transmission.
c. The short antennas used on mobile h-f transmitters are relatively inefficient in the lower part of the h-f band where their physical length is only a small fraction of a wave length. V-h-f antennas of comparable physical size are relatively efficient.
d. Since the h-f band is usually crowded, proper assignment of frequencies is of great importance. Considerable increase in the total traffic capacity of the h-f band can be obtained by carefully coordinating the assignment of frequencies, transmitting powers, and type of propagation to the various users in a theater, giving due weight to the frequency limitations inherent in sky-wave transmission. When this is done and transmitters are maintained closely on their assigned frequencies, it has been found practicable to maintain a separation of as little as 4 kc between military radio-frequency assignments in the h-f band, when most of the channels use c-w telegraph.
641. SKY-WAVE TRANSMISSION, GENERAL.
a. Ionosphere Layers. Sky waves are waves which have been returned to the earth after being transmitted upward to one of several electrically conducting layers or regions (called the ionosphere) located from about 60 to 300 miles above the earth’s surface. Waves are returned because of refraction in the ionosphere which bends them back towards earth. The effect is similar to a reflection from the ionosphere, and is commonly referred to as such.
277
PAR.
641
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Figure 6-69 shows an ionosphere consisting of a single layer, as is generally the case at night. The layer is then known as the F2 layer, and lies about 150 to 200 miles above the earth.10 In the daytime, however, three layers generally appear, known as the E, Fl and F2 layers. The E layer is located 60 to 70 miles above the earth; the height of the Fl and F2 layers is somewhat more variable, lying in general from about 125 to 300 miles above the earth. The TT layer, which is below the F2 layer, is of minor practical importance.
SKY WAVES —\ \ \ 1
/ ''A\B \B N••«•••
§
H 3 M«n bmbbm ••••♦•< •• c
q 8 MM M^B*' >•••••• • CZJOOO
— 5 MM MM«« »•••••• I CZzAoOOOOO
q 4 ■■■■■ MBW* >•••*•« OO 300000C OOOC OOOOC OOOOOCX
= 3.5 MM ■■»•••< ••••« oooooopooo >OOOOOOOOOOC
3 B^M ■ '••• OOOC OOOC 0000600000
25 MMH »•••••« XX>O >0000 OO0
2 MM «••••> X
a ------------------------------------
a
h '-i~r 1 rn
z 8 BBMB*—1— noon
b ^^^■bbb—b********* 00000 r]~ ~-ioor>o/i
O 5 — ■.♦wiioooooH- 1 iQooo.
1 4 —BB ]•***« ***OQo]r. * looor o
a Ij3.5 bbbb ^—««»* >**M' ‘ IC 0000
2 -J 3 —B« ^■■bbbbbbbb^—••••• 1 — 000c on
/ 2. 5 ^BB* ^^^BBB— «*•••• >*00000000000 300
O 2 ■■■> M^BBB^BBBBB^B • •)>••*« *00000900000
3 ----------
Ul
5
- -----------------------------------------------
> 15
0 0 12 MSB
5 Z 10—I »*»»***
H □ 8 ——B^B* —••••> c
0 0 6 ■*—I BB*** ••>>•< OOOOC
z a£ 5 * 60000 JOOOOOC
Q 4 MBM !•••••«••• OOOOC OOOC OOOOOOOOOOO
5 3.5 ■■■»' »•••••• •• oopooo xjoocoooo«
3 •••••• » 00000000 >0
2.5 ■•••»••••*
2 !••••»••••
id ----------1-----------------------------------
Z
D
“)
Q 18 ----------
o 1211 । —***>***>< a
Z 10 ——**]***«!*< inr
2 8 ■■■BJBB^— B—B**»**«U*CO<: OOOOO1 -■inOQ.
Ct 6 BBM*»»M***< OOOOOO l~ -, 1 30003
O 5 BBBB^—i—^**B***uooooqi>o'- I l-innnjin
| 4 MBBBMBi^B B^B—^M*B****i **OOOOpOOC=z=lopOOq
Q 3.5 ■BBB^—**bb B<—******>*<>ooc=L=>ooooobc
2 3 ^^b4b^mb—bm*bb—X***>***oooioooooc ooq |
2.5 bb—«^^bbbw™^b^—*l»*******oooooooooc 2f—^—+bb—b^b»*4—*■*< |________|
3 5 10 20 30 50 100 200 300 500 1000
DISTANCE IN MILES
*ROUGHLY REPRESENTATIVE OF AVERAGE. CONDITIONS IN NORTHERN PART OF .TROPICS, 1944-45, USI NG SCR-399 SETS WITH 16-FOOT VERTICAL WHIP ANTENNAS GROUND WAVE RANGES ASSUME POOR SOIL AND LEVEL TERRAIN
ZTTJT C WCONLY CW }CROUND WAVE ooooooo' $icSnEyr CW)SKY WAVE
TL 54975
Figure 6-70. Illustration of frequency versus distance relationship for reliable communication.
the applicability of ground waves over the shorter distances and sky waves over longer distances for the particular terrain and noise conditions assumed. In the few instances where both ground-wave and sky-wave signals would be received, ground-wave signals are indicated on the figure. Both voice and c-w transmission ranges are shown in figure 6-70. In this figure and elsewhere throughout chapter 6, c-w transmission is taken to imply manual sending, with reception by ear.11 * * * * * * The use of teletypewriter on c-w circuits is covered in chapter 3.
i. The efficient use of frequencies in the h-f band in a theater requires rigid adherence to assigned frequencies. Off-frequency operation of transmitters may cause a variety of difficulties. To insure proper operation, Frequency Meter Set SCR-211, shown in figure 6-71, is widely used as a portable frequency standard for calibrating m-f and h-f radio transmitters and receivers in the field. It is also used at
Figure 6-71. Frequency Meter Set SCR-211-F.
monitoring and intercept stations for measuring the frequencies received from distant stations.
11 Ranges for tone modulation (par. 603, footnote 2)
are not specifically covered. In the type of tone modula-
tion where both carriei* and sidebands are interrupted
simultaneously, with reception by ear using a beating
oscillator in the radio receiver in the same way as for
c-w reception, the ranges will be of the same order of
magnitude as for c-w reception; in other methods of
tone modulation transmission or reception with a single modulating tone, stronger received fields will be necessary. For methods of modulation suitable for teletypewriter operation over radio see chapter 3.
280
PAR.
643
CHAPTER 6. RADIO SYSTEMS
b0°i—'———————————————————— ' . . 35 ..•...
60. ----------------------------------_4——
...................... T4.5- ...... s'
70° ------------------— —------------A—'-----— — X.------------s' s'--
x / ■ / •' —-— 5-°1-k"x <’■ . s'"
t . / / ... .....5.5 \ s' ..■ s'
a 60®-------------------1-—-/ ■/ Z'' " S'----------------
z /■" . ........ / (./ X..2.5-"
50® ---------------------------- --V---------”([ M-(-------------------------
\j Z' / ,' 6.5 s'" 70-’•' '■•. \'4i0'. _s'""
40 |\ \ ■ //a 7/ . 7\ ^35 """■-----------ZQ-'/
30® -■ \ •-----------4—4 ■ ■/:'/^~~--------------------~---------------------
""■-•3.0—______s I /' ■■75" ■ ■ • * xX"'x^/"-—— 7...
20”--'■'■■ .......-— ^ . / 777-----------F---
'-••4.. ' -j" 3.5 ./. / .•’ ■ K K — K ."X"""—
w IO® 7"—4~—’’ • ... X—--.■■.^j/7/7 . ---------------------. ■■...„r—— ——-^
O t—_ '■•■ X. S / I ■ \ s' ~ ’•• \ ’••
t o® ^>x • x-r--—^———=^—^^==—^7-7-7--)- •..
■y-' 7 v ,---
2°’ -'s'.' --7-\ •■■ \ ■■ ......------------yS'---
s' \ \ '■■. ">8.0--""s '" ■ " ' / ■••■’
30' ■ / —YA—•—y—— ( ~7^x’
40. 35 *°: / X______— • 65 •...-_____\_____i-X-^
X ■■' / A!> I —X ...... ..• / .■•'
50® X^ -.------4--------------7-------------..^S -'■.-
x ----- I s' ••■’ 5® ' A!>
f . 50 s^ s'' 55 _I "
8 —------T—.--------7-----------------”----(-------
” 7n. _ 5.5 -----60'______.^.___'-------
7o° ——L—_---—7-------—?——=~
80®-------------------------,---------------------------
QQ*I i ■ "1 1 I®' il ■■■!" ■ —*■ ' '■!' 1 1.1 1 ■— ■■! 1 1 ' 1 4 ■ ■—
00 02 04 06 08 10 12 14 16 18 20 22
LOCAL TIME TL 53232-5
Figure 6-72. Sample chart from a TB 11-499—( ) series report, showing F2 muf, in me, for transmission vertically upward; predicted for December, 1944, for the zone of longitude in which Europe lies.
643. CHOICE OF FREQUENCIES FOR SKY-WAVE TRANSMISSION.
a. A knowledge of the optimum working frequency (owf) for the conditions involved is perhaps the most useful single piece. of information required for successful sky-wave transmission. In the absence of all other data, the choice of an operating frequency at or slightly below the owf, the selection of the best available types of radio sets, and the installation of antennas suitable for sky-wave use, are the major rules to follow.
b. The owf is lower at night than in the daytime, and is lower for short than for long distances. In general it is advisable to have a day frequency and a night frequency, each adapted to the conditions in question, and to change from one frequency to the other on a definite time schedule. Every reasonable effort should be made to obtain frequencies which are satisfactory for sky-wave transmission under the particular conditions; however, if a frequency is assigned which exceeds the muf, transmission at this frequency may be practical for a part of the time, because of
the ionosphere variations described in paragraph 641.
c. At night, all frequencies in the h-f band below the muf which are radiated from a given transmitting station are returned to earth at the distant station with about equal intensities, assuming one reflection from the ionosphere and equal radiated powers. However, since atmospheric noise is higher at lower frequencies, it is always desirable to operate near the owf. For night operation over relatively short distances, the use of a frequency of half the muf will degrade the signal-tc-noise ratio by about 10 db. In the daytime, ionospheric absorption causes more loss at the lower frequencies, hence it is again desirable to operate near the owf. For daylight operation over short or moderate distances, a 10-db degradation in signal-to-noise ratio will result if the operating frequency is roughly 2 or 3 megacycles below the muf.
d. Periodic predictions of owf and muf, three months in advance, are contained in publications of the TB ll-499-( ) series, entitled Basic Radio Propagation Conditions,
281
PARS.
643-644
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
which are issued through the Adjutant General’s Office. Requests for these publications should state the month or months for which predictions are desired.
e. A rough idea of the value of the owf in several cases can be obtained by looking at the curves which form the top boundaries of the transmission charts shown in figures 6-87, 6-88, and 6-89, since these curves represent the optimum working frequencies for the conditions stated in the figure. In general, however, it is meaningless to attempt any interpolation between June and December values (such as those shown in the charts for 1944) to obtain optimum working frequencies for other months. In addition to seasonal trends, muf and owf values are subject to an 11-year cyclic variation; in 1948 or 1949 they are expected to reach a maximum, probably in the order of about twice what they were in 1944.
f. A sample muf chart from the TB 11-499- ( ) series of reports is reproduced in figure 6-72 (preceding page), to illustrate the type of information available in these reports. The muf depends on local time and on latitude; it also varies somewhat with longitude and is given separately, in the reports, for three zones of longitude. Figure 6-72 applies to the zone in which the European war theater lies and gives the values of muf for F2 layer reflection (this layer gives the highest muf at short distances) for a radio wave transmitted vertically upward. For distances up to 200 miles between ground stations,‘this type of chart can be used with little error. Approximate corrections for longer distances are given in subparagraph g below; and detailed directions for using the charts are given in the TB 11-499-( ) series reports. The particular chart reproduced in figure 6-72 shows, for example, that for the month and the zone of longitude represented, the F2 zero-distance muf at latitude 10 degrees North varies from 7.5 megacycles at noon up to 7.9 megacycles at 1600 hours and then down to 5.3 megacycles at midnight and 3.4 megacycles at 0530 hours. This variation in muf suggests the use of different day and night frequencies. In the illustration above, assuming an owf of 85 percent of the muf (par. 641b), a frequency of 5 megacycles could be used from 0800 to 1600 hours, and 2.5 megacycles could be used from 0 to 0800 and 1600 to 2400 hours for a 0 to 200-mile sky-wave circuit. In planning the as
signment of frequencies, it is wise to assign those near the owf for sky-wave use on circuits which are not expected to have much transmission margin, and to assign frequencies lower than this, where necessary, for sky-wave use on circuits which are expected to have some margin. Frequencies above the muf can be used for ground-wave transmission.
g. The muf is greater for long distances than for short distances. A rough idea of the ratio of the muf at various distances to that at zero distance is given in figure 6-73. Because of the ratios indicated, a frequency which is optimum for short-distance transmission at a given time is apt to be poor for longdistance transmission at the same time. This makes it unwise to set up a net including long-distance and short-distance paths operating at the same frequency. On this account, also, it may be necessary to change the frequencies assigned to a given organization when the circuit lengths which it uses change markedly from one military operation to the next.
Distance (miles) Approximate ratio of muf at given distance to that at zero distance
F2—layer transmission E-layer transmission
0 1.0 1.0
100 1.01 1.13
200 1.03 1.5
300 1.07 1.9
400 1.13 2.4
600 1.3 3.3
800 1.5 4.0
1,000 1.8 4.5
1,500 2.4 4.8
2,000 2.7 4.8
2,500 2.9 4.8
Figure 6-73. Approximate relations between maximum usable frequencies at various distances.
h. Further information concerning the detailed procedure for predicting suitable frequencies is in the TB 11-499-( ) series reports and in TM 11-499.
644. ESTIMATED GROUND-WAVE TRANSMISSION RANGES AND SKY-WAVE PERFORMANCE.
a. General.
(I) This paragraph contains approxi
282
PAR.
644
CHAPTER 6. RADIO SYSTEMS
mate ground-wave transmission ranges, estimated for a number of reasonably typical conditions. For sky-wave transmission, the information is given in terms of the hours during which various frequencies below the muf will provide satisfactory communication, under the conditions assumed, over distances of 0 to 200 miles. The performance data given here may be used where the actual conditions approximate those specified and where more detailed information is not available. Reference is made to similar information on predicted performance which is now available in publications issued periodically by the Office of the Chief Signal Officer, as covered in subparagraph e below.
(2) Computations of transmission ranges are in general based on estimates of the distance at which the signal-to-noise ratio is just satisfactory. While the noise actually present may be atmospheric static, local man-made radio noise, set noise, or interference from friendly or enemy transmissions, the only interferences which can be estimated in advance are static and set noise; and these, particularly static, are subject to considerable variation and are not accurately known. Moreover, the computations of received signal intensities involve estimates of propagation via a varying ionospheric path in the case of sky-wave transmission, and they also involve judgment of the characteristics of the terrain in the case of ground-wave transmission. Predictions of transmission ranges are therefore necessarily inexact. This applies both to the information given in the present paragraph and to any other similar predictions. Such predictions can, however, be a valuable guide in planning if their limitations are recognized.
(5) The distance range and performance estimates given in this paragraph are for circuits over which communication should be reliable except for a small percent of the time in the period indicated, assuming that the equipment is functioning properly and that local noise and interference from friendly or enemy transmissions are negligible. Greater ranges could be obtained if operation is required during only a portion of the time.
b. Sample Ground-wave Distance Ranges. Figure 6-74 gives estimated ground-wave distance ranges for a number of tactical radio sets with specified antennas over smooth poor earth, good earth, and sea water, and with
atmospheric noise conditions corresponding with noise grade areas 2 and 4 of figures 6-90 and 6-91. Illustrations of most of these radio sets and of a few other common tactical sets are in figures 6-75 to 6-85 inclusive. Tactical sets range from the small Radio Set SCR-536 (handie-talkie) with a rated power of 0.02 watt, to the large vehicular sets such as Radio Set SCR-399, with a rated power of 400-watts cw.
c. Limitations on Ground-wave Range Data.
(1) In the jungle, ground-wave ranges are much less than for the poor earth condition in figure 6-74. A rough approximation is that ground-wave ranges through dense jungle are of the order of one-tenth as great as over poor earth. Over sea water they are of the order of ten times as great as over poor earth.
(2) In the higher part of the h-f band, antenna siting precautions similar to those described for v-h-f (par. 618) are necessary in order to attain the estimated range. Such precautions are less important in the lower end of the h-f band.
(3) An estimate of the effect of hilly country in reducing ground-wave transmission range is shown in figure 6-86. To use this figure, obtain a profile of the proposed transmission path, draw the triangle as shown in the figure, and read the reduction factor. An example is shown for the case of Di = 10 miles, H = 2,000 feet and an operating frequency of 7 megacycles, the resulting reduction factor being 0.58. Multiply the expected ground-wave distance range, previously determined on the basis of smooth earth, by this reduction factor. If the product is greater than the actual distance between antennas, the siting is expected to be satisfactory. This shadow chart applies for distances up to about 100 miles; for greater distances the reduction in range is somewhat less than given by the chart. It is based on the assumption that the field intensity in the absence of hills would vary inversely as the square of the distance; this is a reasonable approximation for h-f transmission over land.
(4) Computed distance ranges for sea water apply when transmitting and receiving antennas are practically at the water’s edge. There is evidence that considerable losses occur if they are inland more than a few hundred feet, except in marshy terrain. If inland sites must be used, placing the antenna on the for-
283
PAR.
644 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Type of set Rated power (watts) Type of antenna Frequency (me.) Estimated ground-wave distance ranges (miles), based on atmospheric noise typical of middle latitudes a
Poor soilb Good soilb Sea water °
Voice Cw
Midmorning Midnight Midmorning Midnight Midmorning Midnight
Voice cw Voice 1 CW V oice CW Voice 1 cw Voice CW Voice cw
SCR-177-( ), SCR-188-A 75 75 Inverted L as furnished 1.5 60 125 6 14 180 300 28 65 550 750 80 250
4.5 22 55 6 16 70 125 22 | 50 380 500 200 330
12.5d 8 21 9 24 21 50 24 55 170 240 175 250
SCR-193-( ) 75 75 15' whip 1.5h 12 30 3 7 60 120 12 35 220 420 20 100
4.5 18 45 5 13 65 110 17 45 350 480 160 300
SCR-284-A 8 20 — 25' whip 3.8 13 40 3 10 45 110 12 35 300 500 90 260
5.8 9 28 4 12 28 75 12 .35 230 370 130 270
SCR-299-( ), SCR-399-( ), SCR-499-( ) 300 400 15' whip 2.0h 23 60 5 13 90 170 23 55 -100 600 100 280
4.5 30 70 8 23 85 150 30 70 420 550 240 380
8.0 16 40 11 30 45 90 30 70 280 380 240 340
12.5® 13 35 15 40 35 70 35 75 200 280 200 280
18® 20 45 25 55 45 80 50 90 180 240 200 250
Inverted® L 2.0 70 140 8 20 180 300 35 80 600 800 160 370
4.5 35 75 10 26 90 160 35 75 440 550 250 400
SCR-506 20 80 15' whip 2.Oh 10 35 2 7 45 115 9 35 220 470 22 160
4.5 13 45 4 13 45 115 13 45 300 480 120 300
SCR-694-C, AN/TRC-2 7 20 15' whip 2.Oh 8 24 2 5 35 90 7 24 170 400 14 100
3.8 1 11 35 2 8 40 100 10 30 280 470 70 225
6.5 7 23 3 12 22 60 11 35 200 340 125 250
a Noise grade 2 assumed for middle latitudes (figs. 6-90 ® Upper frequency limit of SCR-299 is and 6-91). power of SCR-399 and SCR-499 is less thar b Applies to flat or gently rolling count ry; for hilly country at frequencies above 8.0 me. see paragraph 644c. f Lower frequency limit of SCR-694-C is c Ranges for sea water assume that transmitter and re- 8 Ranges assume 65' total antenna lengl ceiver are at the water’s edge; otherwise ranges may be ma- for 4.5 me., with 20' vertical portion in each terially shortened. 11 Set noise, rather than atmospheric noise d Upper frequency limit of SCR-177 is 4.5 me. Rated controlling at receiver during midmorning ii power of SCR-188-A is less than listed value at frequencies above 4.5 me. 8.0 me. Rated the listed value 3.8 me. h for 2 me.,- 35' case. 3, assumed to be i these cases.
Figure 6-74. Estimated ground-wave distance ranges for specific radio sets (continued on opposite page).
284
PAR.
644
CHAPTER 6. RADIO SYSTEMS
Type of set Rated power (watts) Type of antenna Frequency (me.), Estimated ground wave distance ranges (miles), based on atmospheric noise typical of tropical areas*
Poor soilb Good soilb Sea water «
Voice Cw Midmorning Midnight Midmorning Midnight Midmorning Midnight
Voice cw Voice CW Voice cw Voice cw Voice cw Voice cw
SCR-177-( ), SCR-188-A 75 75 Inverted L as furnished 1.5 24 60 3 7 100 180 14 35 360 550 25 120
4.5 18 45 4 10 60 110 14 35 350 480 125 250
12.5d 9 24 7 19 24 55 20 45 175 250 160 225
SCR-193-( ) 75 75 15' whip 1.5h 11 27 2 4 55 110 4 16 200 400 5 35
4.5 14 35 3 8 50 100 11 28 320 450 95 225
SCR-284-A 8 20 25' whip 3.8 10 32 2 6 35 100 7 22 260 450 40 180
5.8 8 27 2 8 26 70 8 25 225 370 90 225
SCR-299-( ), SCR-399-( ), SCR-499-( ) • 300 400 15' whip 2.0h 22 60 3 7 85 170 12 35 400 600 35 160
4.5 23 60 5 14 70 130 17 45 400 530 160 300
8.0 17 45 8 22 45 90 23 55 300 400 200 300
12.5° 15 35 11 30 35 75 23 65 200 280 200 270
18° 14 35 16 40 35 65 35 70 170 225 170 225
Inverted8 L 2.0 35 85 4 11 120 200 20 50 470 650 75 240
4.5 27 65 6 16 80 150 20 50 400 550 180 330
SCR-506 20 80 15' whip 2.Oh 9 30 1 4 45 115 4 18 200 450 6 70
4.5 10 35 2 8 35 100 8 28 270 450 65 225
SCR-694-C, AN/TRC-2 7 20 15' whip 2.0* 8 23 1 3 35 90 3 13 160 400 4 40
3.8 8 27 2 5 30 85 6 20 240 430 30 150
6.5 7 23 2 8 20 60 7 24 200 340 85 225
• Noise grade 4 assumed for tropical areas (figs. 6-90 and 6-91).
b Applies to flat or gently rolling country; for hilly country see paragraph 644c.
0 Ranges for sea water assume that transmitter and receiver are at the water’s edge; otherwise ranges may be materially shortened.
d Upper frequency limit of SCR-177 is 4.5 me. Rated power of SCR-188-A is less than listed value at frequencies above 4.5 me.
e Upper frequency limit of SCR-299 is 8.0 me. Rated power of SCR-399 and SCR-499 is less than the listed value at frequencies above 8.0 me.
f Lower frequency limit of SCR-694-C is 3.8 me.
e Ranges assume 65' total antenna length for 2 me., 35' for 4.5 me., with 20' vertical portion in each case.
11 Set noise, rather than atmospheric noise, assumed to be controlling at receiver during midmorning in these cases.
Figure 6-74. Estimated ground-wave distance ranges for specific radio sets (continued).
656935 O—45-
•20
285
PAR.
644
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Figure 6-75. Radio Set SCR-399 installed in Truck, Cargo, 21/2-ton, 6x6.
Figure 6-76. Vehicular Radio Set SCR-193 in Truck, Command, 3/t-ton, 4x4.
Figure 6-77, Field operation of Radio Set SCR-284,
Figure 6-78. H-f radio station consisting of transmitting and receiving components of Radio Set SCR-188.
Figure 6-79. Radio Set SCR-511 in operation.
Figure 6-80. Radio Set SCR-506 installed in Truck, %-ton 4x4
286
PAR.
644
CHAPTER 6. RADIO SYSTEMS
Figure 6-84. Radio Set SCR-593 (receiver only) in use at an automatic gun site.
Figure 6-81. Radio Set SCR-399 installed in Truck, Amphibian, 21/2-ton, 6x6.
Figure 6-82. Handie-talkie Radio Set SCR-536 in operation.
Figure 6-85. Radio Set SCR-694-C installed in Truck, l/i-ton, 4x4.
Figure 6-83. Radio Set SCR-543 and Switchboard BD-72 * in operation.
ward slope of a hill will tend to compensate for such losses.
d. Sample Estimated Sky-wave Performance.
(1) Figures 6-87, 6-88, and 6-89 give estimated sky-wave performance with half-wave horizontal or nearly horizontal antennas, for several tactical radio sets for distances in the 0- to 200-mile range. With such antennas, the received sky-wave signal is roughly the same at all distances up to about 200 miles. The figures show the frequencies at which reliable
287
PAR.
644
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
\ H ^xxxx^^
Lxx x k \ x x x xx^>»J -0.9
-<-D| —► ---------------- D---------------
O UJ
0.
FREQUENCY H D|
MC FEET MILES
r-10.000 IM
* ts
- 7,000 q
- 3 ~°7 R
- 5,000 _ O
~ 4 - 4,000 50 <0
- 5 x
- 3000 _ £
___7_ 20 ___. — =0-6 *
------ 2,000 ____— —10 u
-10 ------------- X
- '.50° - 5
15 - 1,000 "0,5 I
- 700 g
- 30 “ 1 >
- 500 °
“ 05 -0'4 u
“ -400 q
- 300 - n ? <
0-2 qt
- 200 - O.| J
- 150 -0.3 S
- 100 ®
ft
- 0.25 g
- 02
TL 54893
Figure 6-86. Nomogram for determining decrease in ground-wave range over land because of shadow effect.
point-to-point sky-wave transmission is expected at these distances at various hours of the day. The top curve on each graph is a plot of the optimum working frequency. Different kinds of cross-hatching indicate conditions which are good for phone and c-w transmission or for c-w transmission only. Areas below the owf but not cross-hatched indicate regions of poor signal-to-atmospheric-noise ratio. Each figure is for a separate locality, the upper and lower graphs in each case corresponding with two general types of radio sets rated at about
20 and 400 watts, cw, respectively. The performance is indicated for two times of the year 1944, June and December. In future years up to 1948 or 1949 the values of owf will tend to increase, as noted in paragraph 643e.
(2) It is assumed that both the transmitting and receiving antennas are horizontal. The use of horizontal receiving antennas is important for sky-wave transmission at these distances in order to favor reception of the high-angle signal and to discriminate against lower-angle atmospheric static.
288
PAR.
__________________________’ CHAPTER 6. RADIO SYSTEMS________________________644
6 T~fT.... 1(1 I 6, ... ... ! |
N o T JUNE N T V DECEMBER
5 -£* 4 4-------— * 5 4 4--------------------------
° w S \\xX\Jx £* 07 co XxXz^sXzDkX
2 Z Xa V u X Kxz XX) 5X
2 2 Z>oooo ZxPhone & cw>>X
3 3----------------------------------------------------------------------
2 (x/XvXXxOXXQyyvvi^\x*vXaX 2 S?2&._____________zfi66wa99xxW(xkS53X>?>
00 04 08 12 16 20 00 00 04 08 12 16 20 00
LOCAL TIME LOCAL TIME
RADIO SETS SCR-299, SCR-399, SCR-499
HALF-WAVE HORIZONTAL ANTENNAS, 30 FEET HIGH
DISTANCE: 100 MILES (TRANSMISSION APPROXIMATELY THE SAME, 0-200 MILES) TL 54944 Figure 6-87. Sky-wave performance chart, location: Germany, 1044.
6 ---+"V JUNE 6 ? U T DECEMBER
5 > 4 5T-------------------------- 5 _ct* * ■*---jKPHONE & CvX---------
. , *5 o) oo J&-?vx Xxxxx x xxrzVS< W)Yxo t— cn oo - XX4vYA^2VkKXX \
< (£> <\j X/OQxxScy*XX?CXX vOs vio\ VPHONE&CW* iVX XX> k o 5 'v PHONE &CWXS
5 4 54------------------------------------
3 3----------------------------------------------------------------------
2 2 l2XX>XPH0NE & 5 - FVyxPHONE &
5---------Pv” /OrjUXXX/XCFGxfo X/v - $---------r\ Vv /VyyyK/vy'yC AA< XyO r
4 —------4 SC----------------------------------
2 >Oi hl r [T~n~'r| 1111' 111111 rT'i"i i ri' 11111111 . "'“ “tel—
2 so.-._____________________________________________
—r~ — —rV'Ti —-----------1~—
30. ------------XL^Cu • — z._ ^=Lx2_ —
2O.vt^'----j—V £
= ..££.4g-=r~;L_;__;_______c._K. ------—---------------— ^—^==-=
„.|-1 I I I I I I FTMI H H I I I I I I H I . I I I I I I I I I
90®E I2O’E I5O®E 180° I5O“W I2O®W 90®W 60°W 30°W 0° 30°E 60°E 90®
LONGITUDE
Figure 6-90. Noise grade areas, May through September.
TL 54975
(2) Basically, the question as to whether radio transmission in a given case is satisfactory can be answered by comparing two quantities, namely: the field intensity actually re-cieved, and the field intensity (at the radio receiver) required to over-ride atmospheric or other noise. Subparagraph b below, gives data relating to the required field intensities, assuming that certain conditions apply at the receiving end. Corrections to cover other conditions are given further on. The actual received field intensity is discussed in paragraph 646 for ground wave and in paragraph 648 for sky wave. A short-cut in ground-wave calculations can be taken in the case of certain particular noise conditions by using the information in paragraph 647, instead of that in paragraphs 645b and 646. Data given in paragraphs 649 to 652 relative to the characteristics of transmitting and receiving antennas must be used in conjunction with the other material. Examples of the use of all this material, in itemized step-by-step form, are given in paragraph 653.
b. Required Field Intensities for Various Noise Areas.
(1) Estimated values of signal required to override atmospheric noise can be obtained
from figures 6-90, 6-91, and 6-92. These figures are based on available information regarding atmospheric static, and it is expected that they will be revised when additional information becomes available. These data refer to intensities which would over-ride static perhaps 95 percent of the time. With somewhat lower received field intensities, transmission would be practicable part of the time, insofar as atmospheric static is concerned.
(2) Figures 6-90 and 6-91 show the world as divided for convenience into five static noise areas. This is done separately for the periods from May through September and from November through March. The atmospheric noise level is low in area 1 and high in area 5.
(3) Estimated values of signal field intensity required to over-ride the atmospheric noise in each of these areas are shown in figure 6-92 for various frequencies at different times of the day. These values are for voice communication; for manual cw the required field intensities are taken to be about 17 db less. The difference of 17 db makes a small allowance for conditions under which the talker does not produce full modulation of the radio transmitter.
291
PARS.
645-646
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
90’.--------------------------------------------------------------
. 2^? /fey
i {o°-----k-z M • ♦+, / nr^—H—tr +— ——-Vv + rr u ---------------
/ \ TT \~7\ ~H -
'4** \ 2 A\ r4/
30° y — L — -X 4— f —t ——-------------------/ — \ ) /-----------
40o=^^- — ---------------------------------------— — ~^ =
5 0°-----=====----------------------— |\-t- /- ■ ----------------
I *
X 60°-------------------------------------— ----------------------
| 70o = = = = = = ^__---------------------------l_^=- = -
80°-----------------------------------------— Z------------------
9 0°----------—---------------------------------------------------
90°E I2O°E I5O°E 180° I5O°W )20°W 90°W 60°W 30°W 0° 30°E 60°E 90®
longitude TL 54976
Figure 6-91. Noise grade areas, November through March.
(4) In the portions of these curves indicating low required field intensities, atmospheric static may be so low that limitations produced by other kinds of noise must be allowed for. The field intensity required to override set noise is not indicated on the curves, on account of the wide range of efficiencies of tactical antennas and receiving-set input coupling arrangements. The likelihood is that set noise will be limiting during part of the time in the lower noise grade areas, but not often in the higher noise grade areas.
(5) The data on which figure 6-92 is based were obtained by measurements of noise in short vertical receiving antennas. Receiving antenna corrections for use in sky-wave propagation computations are discussed in paragraph 652.
646. GROUND-WAVE SIGNAL FIELD INTENSITIES.
a. Transmission Over Land and Sea Water. Computed curves of ground-wave field intensity over smooth earth and sea water are given in figures 6-93, 6-94, and 6-95. Over land, the field decreases rapidly as the distance is in-
creased. At moderate or great distances, loss due to the curvature of the earth becomes important, and the rate of attenuation over land or sea becomes increasingly large. The field intensity values given in these figures are expressed in terms of power radiated from a short vertical antenna and apply with sufficient accuracy also to a vertical antenna up to a half wave long. They do not apply to the rated power of the radio set. Corrections to relate rated power to radiated power are given for vertical whip and half-wave horizontal antennas in paragraphs 650 and 651, respectively. These corrections are particularly important in the case of the short whips frequently used for h-f transmission. In the lower end of the h-f band, the radiated power from such antennas is only a small fraction of the rated transmitter power. The qualifications noted in paragraph 644c should also be borne in mind when using figures 6-93 to 6-95. Estimates of ground conductivity for particular theaters of operations are given in the publications referred to in paragraph 644e.
b. Transmission Through Jungle. The attenuation of ground waves through heavy jungle
292
PAR,
CHAPTER 6. RADIO SYSTEMS 646
40 ---—------—'—'-----1— 50 FT--—-----—T—1-----r—
NOISE GRADE 1 a XXX------------------
3 20 ------------ 2 30 ----------------------
g 04-^^ X^'20,00 £ 04__X"^
a- 10--------“ Xr~X---------i 20-----------— -------
w 10 vaW s cv_7/> \\\
o -io--------—Vn\— rn 0 ———\'x—
2 \v A < vxr>^ v—12 V \
< /XC X— 12 \ \ \ \ \ l \
_q-2o -----———YA-Vv -10-------------------ylA-
■o 08 \\ V 73 \ \ \
-30--—L-—--------------ill \ -20-------------------lllA
I 2 3 5 7 10 20 30 I 2 3 5 7 10 20 30
FREQUENCY - MC FREQUENCY - MC
50 rxxr -------1-1----1-- 6 °kK -----------1---1--1--
£ NOISE GRADE 3 NOISE GRADE 4
h 40~^xr^x J 12n—— 5 50 -----—------—
3 --00 &
30-----------------------2 40-X—---------------------
£E 04--\\X \ ----16,20
£ x_ ^^xS^x 5 00
20 --- £ 30-----X XX\sX-----------
3. x. 16 --^ /Vx \\\W ’a \
- 10 vX. s* \\\W 20—X---------------------
u xZ>A—08 Wva “ x
> — x-----------12 \\ \\\ id X ,—■—
O 0-------------------W~W > 10------- -"T— \—X---y\----
< VpH rn 07 TO 11-0 Vi
JO -10---------------------^Pr * o---------------- -P
* n * \
- 2 0------------------«>—LI _ I o------------ AJ
I 2 3 5 7 10 20 30 I 2 3 5 7 10 20 30
FREQUENCY - MC FREQUENCY - MC
70 LVX -----------1--1--
NOISE GRADE 5
Ot 60----X0 <--------------
H X. /---16,20
k «« y~ 00
2 50 —"^X---—--------------
NUMBERS ON CURVES tt
ARE LOCAL TIMES AT a? *0-------lXJ~'"^S~------
RECEIVING STATION > 07 TO II—
S 30-----------—~^x?\------
> 20-----------,-----—— \—
$ \
,0----------------------L
X> '
0J---------------------
I 2 3 5 7 10 20 30
FREQUENCY - MC
TL54692
Figure 6-92. Field intensity required to override atmospheric static in various noise grade areas, for voice transmission.
293
PARS.
646-647
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
is extremely great. The effect of this high attenuation, combined with losses due to foliage in the immediate vicinity of the antennas and with the high atmospheric noise characteristic
60 ^X5^—---------------------------
---------------
\ \\ \x XX 4'cx H x X. X W °>yXJ X__________________
XxxxXX I o______XxXxx'x—
uj XxAX \ x \\ X X \
> X X. X. X \ \ \
o ^.X X. \ X X X \ \
m CX XX XX \\ \
<-20--------------X\X X. \ XX X
A 0----------\V\\
> ^x\\?\ \ V
< -20-------------x - —\ - X—- \ \ v x
T> N. X \ \\ \ \
- 40----------------A —X- X—X3 —V-
"S 6 * 12 * * is * * * *°| 2 5 10 20 50 100 200 500 1000
DISTANCE IN MILES TL 54865
Figure 6-94. Ground-wave field intensity versus distance over good soil, 1 watt radiated, short vertical antenna.
also afford a suitable path. Another possibility is the use of long horizontal antennas, which may work even when lying on the ground (pars. 666 and 667). The use of sky-wave transmission is often the best solution. Estimates of jungle ground-wave ranges are
given in some of the published information referred to in paragraph 644e.
c. Example of Use. As an example of the use of figures 6-93 to 6-95, suppose that a certain radio circuit is observed to give just tolerable voice transmission at 20 miles over level ground on a frequency of 3 me, and that, moreover, it is observed that the signals are steady and therefore presumably ground waves. How far can the circuit be used for cw on ground-waves ? Solution: The required field intensity for cw is about 17 db less than for voice transmission (par. 645b). On figure 6-93, the distance at which the 3-mc signal intensity is 17 db weaker than it is at 20 miles is found to be 50 miles for poor soil, and for good soil (fig. 6-94) the result is about the same. Hence cw could probably be used out to 50 miles.
60----------------------------■----------------
40 0.2MC
r 1 MC
120----------------------------\x?—
| o---------------------------------\ \\ \ V
> c \ \ \ \ '
r--------------------------------------
-40-------------------------------------A---- \ \ -
-60‘--------------------------------------3—-A—1
12 5 10 20 50 100 200 500 1000
DISTANCE IN MILES T. 54866
Figure 6-95. Ground-wave field intensity versus distance over sea water, 1 watt radiated, short vertical antenna.
d. Step-by-step Procedure. Detailed procedure
is given in paragraph 653 for the use of fig-
ures 6-93 to 6-95 together with other informa-
tion in this chapter, to obtain an estimate of ground-wave performance of a particular radio set.
647. GROUND-WAVE DISTANCE RANGE VERSUS RADIATED POWER FOR SPECIFIC NOISE CONDITIONS.
a. General.
(1) Figures 6-96 to 6-101 inclusive give estimated ground-wave ranges over poor soil, good soil, and sea water, for various values of radiated power, assuming that the transmitting and receiving antennas are vertical and not exceeding a half wave in length. The ranges shown assume that the earth is smooth, hence they are subject to the qualifications
294
PAR.
CHAPTER 6. RADIO SYSTEMS 647
RADIATED POWER-WATTS I RADIATED POWER-WATTS
CURVE ~ PHONE j CW CURVE ~ PHONE CW
A________i____.02 A________I___________.02
B______IP_____0.2 B____[0_______0.2
C______100____2 C____100______2
D _____1,000__20 D 1.000 20
E' 10,000 200 . E 10,000 200
--- MIDNIGHT -----------MIDNIGHT
---MID-MORNING -----------MID-MORNING
-X- RANGE RESTRICTED AT LOW FREQUENCIES -*«--GRANGE RESTRICTED AT LOW FREQUENCIES
BY SET NOISE IF RECEIVING WHIP AS SHORT BY SET NOISE IF RECEIVING WHIP AS SHORT
AS 16 .FEET IS USED. AS 16 FEET IS USED.
20 1111'111/pn'^PffTTnw 20~ i 111hi //////ii/ir ~i 111 ii
„zzzz^z; ■ :zf^^z±zz: s:: Titzzzzz:
z,4 —------------------------------- -14--------------------aSzSH---------------
“12----4----U--------/----}--------- >12--------------------aU_±1_, XI----------
s 10 —7N—/1'-; Z 810 TxTsSk--------------
s»—iV_T"Tr.......................... s 8--------------------/ i v~vv------------
oc 6---A-q!......................... * 6 7----------------r---------------/ --
4 —fl—4
2---S A 2--
- *• **- - **• A B C D E
o 1—1 I I I 1.1 I I 11 11 ——— I I I I I I I 111 0 1 ————1—--------1 1 ————I—
2 3 4 .5 7 10 15 20 30 40 50 70 100 20 30 40 50 70 100 200 300 400 500 700 1000
USEFUL RANGE IN MILES USEFUL RANGE IN MILES
TL54968 TL54970
Figure 6-96. Ground-wave distance range over poor soil, Figure 6-98. Ground-wave distance range over sea water, noise grade 2, vertical antennas. noise grade 2, vertical antennas.
given in paragraph 644. The relation between these correspond roughly to conditions in the radiated power and the rated output power of middle latitudes and in tropical areas, respec-the radio transmitter is discussed m para- tively. These curves may be used directly for graphs 649 to 651. Separate curves are given the specific conditions to which they apply, for noise grades 2 and 4 (figs. 6-90 and 6-91); For other conditions, interpolation may be
-------------------------------- resorted to; or better, the method given in --------------------------------paragraph 646 may be used instead. The mid-
RADIATED POWER-WATTS
CURVE ~ PHONE CW ------------------------------------.
A________I______.02
B 10 0.2 -------------------
C~ 100----2-- ---------------------------- RADIATED POWER-WATTS
--5-----L000---20 CURVE —PITONE CW~
I—E- I- IO°°° 200 □ —§---------------is-dr~
---MIDNIGHT C 100 2.
---MID-MORNING D__1,000__20
rH- -»RANGE RESTRICTED AT LOW FREQUENCIES E 10,000 200
BY SET NOISE IF RECEIVING WHIP AS SHORT _ MIDNIGHT
AS 16 FEET IS USED. -MID-MORNING
20 tti-iz/i//i--------------------r
;::few:== U iw/iw hi |||=i i|iitiizz
o 1.1 I 1 ——I 1. I I---------1—1 o ——L.1..1 I .1--------------—Illi
7 10 15 20 30 40 50 70 100 200 300 1.5 2 3 5 10 20 30 50 100
USEFUL RANGE IN MILES USEFUL RANGE IN MILES
TL54969 TL5497)
Figure 6-97. Ground-wave distance range over good soil, Figure 6-99. Ground-wave distance range over poor soil, noise grade 2, vertical antennas. noise grade 4, vertical antennas.
295
PARS.
647-648 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
the radio receiver output is apt to be set noise ■ „ „ , rather than static. It is estimated that this curve---------------------------phone cw-will occur for noise grade 2, midmormng, tor
—§-------। J -----— 16-foot whips at frequencies below 4 mega-
—|-------[op------2___ cycles. This tends to reduce the range to dis-
e lo.ooo goo tances less than would be predicted for static
----midnight---------------noise alone. Such reductions in range are ---------------------------MID-MORNING i .• shown by separate branches of the daytime
I I I I I// // I// (K curves on figures 6-96 to 6-98. The branches
18 y j of these curves which do not show these re-
2 ,4 / / / 7| A ductions apply to longer antennas; for exam-
z 14___/ \A / \b / y~'\p~^E pie, at 2 me a length of about 35 feet would be
5 |0_y \/ 'J Xj required to avoid a reduction in range.
I b — ' /\ ~/\ / jX_______x______ b. Step-by-step Procedure. Detailed procedure
S _ A /B Nyc xTd- s(e \ _________is given in paragraph 653 for the use of
“ 4 _r____( ____ figures 6-96 to 6-101 together with other in-
z " formation in this chapter, to obtain an esti-
ol I I I? I | | | |L T I mate of the ground-wave performance of a
5 7 10 20 30 50 100 200 300 particular radio set.
USEFUL RANGE IN MILES
TL S4972
Figure 6-100. Ground-wave distance range over good soil, 648. SKY-WAVE SIGNAL FIELD INTENSITIES. noise grade 4, vertical antennas. a General. Sky waves are subject to fading,
and to various kinds of other variations, as night curves apply fairly well throughout the outlined above. Hence sky-wave field intensi-hours of darkness; the midmormng (not fjes are predictable only on an average basis, noon) curves represent conditions when at- Estimates of sky-wave field intensities, based mospheric static is at its lowest intensity at on information available at present, are given frequencies in the lower part of the h-f band jn paragraph.
(fig. 6-92). b. Estimated Values. Figure 6-102 shows
( 2) When atmospheric static is of low estimates of sky-wave field intensity for vari-intensity, and when only a small fraction of Ous frequencies and distances, for maximum the voltage picked up in the receiving antenna and minimum absorption in the ionosphere, is delivered to the radio receiver (as in the At night the absorption is minimum (absorp-case of a short whip), the controlling noise at fion constant K = 0), and a single curve serves __________________________________ for all the frequencies indicated. The other curves are for K = 1, which occurs when the
RADIATED POWER-WATTS
CURVE PHONE CW a
—F- io -otF- ^+30rrnri— i i I 1 i l ITT1—m
—F i,ooo -----
E 10,000 200 S O+|0=z:55-—-S; \
------------------ MIDNIGHT 05 w A —= ----------------------------------------------------------MID-MORNING----------------------------------------------0------------------------------------------------------------------------------------------''xY/'j/L “ II I IM. Hl TTTT 1 '*-------------------------------------------------------rtn\- 2 s -3°-\
i'A-------------------fcsfeis h -'wLuAaYv
z’l/aaw—~ a h7i-in—4 \ ye?
J | y /'X|ASs\\ o "8 * °5O 70 100 200 300 400 500 700 1,000 2.000
4---------A yF - / 111 DISTANCE IN MILES
? --—n —CH APPLIES TO FREQUENCIES BELOW THE M U E AND
2--- ' A B) C D E TQ UND|STURBED IONOSPHERIC CONDITIONS
ol---------------—1111-------------—1—!— fa BELOW 3MC. FIELD INTENSITIES ARE ESTIMATED
10 20 30 40 50 70 100 200 300 400 600 800 WITH LESS CERTAINTY THAN AT HIGHER FREQUENCIES
USEFUL RANGE IN MILES TL54973 TL 53203 5
Figure 6-101. Ground-wave distance range over sea water, Figure 6-102. Sky-wave field intensity versus distance be-noise grade 4, vertical antennas. tween ground stations for limiting values of K.
296
CHAPTER 6. RADIO SYSTEMS
PARS.
648-649
sun is at the zenith (directly overhead). For other cases the value of K varies as shown approximately in figure 6-103. (Monthly values of K are given in the TB 11-499 series reports.) To illustrate, figure 6-103 shows that at latitude 25° at noon in winter, K = 0.72. To estimate the received field intensity for this
figure 6-103. Typical values of K for use in conjunction with figure 6-102.
or any other fractional value of K, prorate the difference between the K = 0 and K = 1 curves on figure 6-102. For example, at 2 me and 150 miles, the received field intensity (fig. 6-102) is about 21 db above 1 microvolt per meter for K = 0, and -23 db for K = 1; 0.72 times the difference between these values is 0.72 (21 23) = about 32 db, and the received
field intensity for K = 0.72 is 21-32 = -11 db from 1 microvolt per meter.
c. Qualifications. The values of received field intensities in figure 6-102 are for 1 watt of radiated power, determined as described in paragraphs 650 to 652. The values apply to the incident, or arriving field intensities, and
not necessarily to field intensities in line with a particular antenna; hence they are subject to the receiving antenna corrections described in paragraph 652. Figure 6-102 applies only when the frequency is below the muf for the conditions in question, and a separate check must be made to see whether this condition is satisfied before using the curves. Furthermore, figure 6-102 is based on normal absorption, not including auroral absorption near the magnetic poles, or effects of sporadic-E or other variant conditions. An additional absorption effect not included in figure 6-102 occurs when the frequency in question is very close to the muf. Absorption close to the E-layer muf produces the rainbow-shaped regions of relatively poor transmission shown in some parts of figures 6-87 to 6-89 (see particularly figs. 6-87 and 6-88, June, Radio Set AN/TRC-2).
d. Effect of Path Length on K. For distances up to 2,500 miles, the value of K should be determined for the midpoint of the transmission path. For greater distances the process is more complicated, and may be handled by use of TM 11-499 Radio Propagation Handbook and the TB 11—499—( ) series reports, or by referring the problem to Communication Liaison Branch, Plans and Operations Division, Office of the Chief Signal Officer, Washington 25, D. C. TM 11-499 contains a considerable fund of additional information on sky-wave propagation.
e. Step-by-step Procedure. Detailed procedure for the use of figure 6-102, together with other information in this chapter, to obtain an estimate of sky-wave performance of a particular radio set, is given in paragraph 653.
649. DETERMINATION OF RADIATED POWER.
a*. The term radiated power has been used in the sense used in other Signal Corps publications on sky-wave transmission. This radiated power is a quantity proportional to the square of the field radiated in the desired direction by a transmitter.12 If ground-wave transmission is being used, the direction in question is that along the ground toward the distant station. If sky-wave transmission is being used, the desired direction is upward
12 In general, the radiated power as used in this and other Signal Corps publications is not the true total power radiated, but is a quantity convenient to use in transmission calculations. It includes a correction for radiation pattern of the transmitting antenna.
297
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PARS.
649-650
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
toward the ionosphere in such a direction that it will ultimately arrive at the distant receiver. In practice, the field intensity in the desired direction, for a given transmitter and antenna, may be considerably smaller than would be computed by assuming that the radiated power would be equal to the rated power of the transmitter. This is particularly true with short vertical antennas in the lower part of the h-f band. Antennas used with fixed plant h-f radio sets may be considerably more efficient, since they can be built with dimensions which are optimum for use between well defined points.
b. In order to convert rated power into radiated power it is necessary to apply a correction which is largely a function of the antenna type used. In the case of whip antennas it is convenient to consider this correction as consisting of three parts, namely; No. 1, the transfer efficiency of the combination of radio transmitter, coupling unit and antenna used, that is, the proportion of the rated transmitter power which reaches the antenna-ground circuit; No. 2, the radiation efficiency of the antenna, that is, the proportion of the power fed into the antenna-ground circuit which is actually radiated; and No. 3, the pattern efficiency, that is, a correction to take into account the fact that any antenna radiates better in some vertical directions than in others. For ground-wave transmission using short whips, correction No. 3 is 0 db when used in conjunction with figures 6-93 to 6-101. In the case of sky-wave transmission using a halfwave horizontal antenna, correction No. 1 is usually taken as negligible, and corrections Nos. 2 and 3 are combined for convenience.
650. POWER CORRECTIONS FOR WHIP ANTENNAS.
a. Transfer Efficiency. The transfer efficiency correction for a whip antenna used for transmitting varies with the radio transmitter used. For four types of tactical transmitters tested, the correction varied from -10 to -2 db at 2 to 3 megacycles, and improved with increasing frequency until it reached -4 to about 0 db at 6 to 8 megacycles. These values probably indicate the range in magnitude of correction No. 1 of paragraph 649 for tactical sets using whips. Since such information on specific sets is not generally available, this correction may be approximated by assuming
-6 db at 2 me, -2 db at 8 me, and 0 db above 10 me.
b. Radiation Efficiency. Figure 6-104 gives estimated radiation efficiency corrections for 16-foot and 4-foot whip antennas as a func-
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Figure 6-104. Radiation efficiency correction for vertical whip antennas.
tion of frequency. It is believed that the corrections for a 16-foot vertical whip will apply approximately when it is mounted on a vehicle or when used with a radio transmitter placed on the earth together with a good counterpoise, such as Counterpoises CP-12 and CP-13, or 8 radial wires about 25-feet long laid on the ground and connected together at
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THESE ARE AVERAGE CORRECTIONS FOR POOR AND GOOD SOIL.SINCE.FOR THE CONDITIONS COVERED,THE TYPE OF SOIL HAS SMALL EFFECT TL 54967
Figure 6-105. Sky-wave radiation pattern corrections for vertical whip transmitting antennas.
298
PARS.
650-651
CHAPTER 6. RADIO SYSTEMS
the ground terminal of the radio set. If the counterpoise or other good ground is not used, much greater losses may be experienced. The corrections shown in figure 6-104 correspond to correction No. 2 of paragraph 649.
c. Pattern Efficiency. Figure 6-105 gives estimated sky-wave pattern efficiency corrections for a vertical whip antenna, as a function of distance between transmitting and receiving sites. Two distance scales are given on this figure. The F2-layer distance scale is for use when sky-wave transmission occurs via the F2 layer, as will be true at night and also in the daytime unless the operating frequency is well below the maximum usable frequency.13 These curves give values for correction No. 3 of paragraph 649. In practice, the pattern efficiency can probably be improved a little (possibly 3 or 4 db) for short distance sky-wave transmission by tilting the antenna somewhat from the vertical in a direction away from the distant station (fig. 6-106-A). Further improvement might be obtained by placing the antenna on a steep slope such as the side of a mountain and erecting it perpendicular to the slope (fig. 6-106-B). Another possibility of improvement arises when the antenna is in a valley, in such a position that waves radiated sideward from the antenna reflect from the side of the valley and up to the ionosphere at such an angle as to return to earth at the distant receiver (fig. 6-106-C). For such pur-
t
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Figure 6-106. Use of whip for short distance sky-wave transmission.
13 Reports in the TB ll-499-( ) series give 2,000-km E-layer muf predictions; for other distances the E-layer muf can be obtained by multiplying the 2,000-km values by the following factors:
Distance (miles')
Factor
0 100 200 300 400
500 600 800 1000
0.21 0.24
0.310.410.51
0.61
0.70 0.84
I T
0.95
If the E-layer muf for the distance in question is above the operating frequency, use the E-layer scale on figure 6-105; otherwise use the F2-layer scale.
poses the ionosphere can be imagined as an approximately horizontal mirror at a great height. Also, a whip antenna mounted on a large unsymmetrical metal object (such as a truck with trailer) which may serve as a horizontal radiating surface raised off the ground, may have a better pattern efficiency for short distances than shown by the figure.
d. Use of Corrections.
(1) As an example of the use of the above power corrections, assume that a transmitter rated at 75 watts output is to be used on a 100-mile sky-wave circuit at a frequency of 2 megacycles, with F2-layer transmission. Assume further that a 16-foot whip is to be used and that correction No. 1, the transfer efficiency correction, amounts to -6 db for the average combination of transmitter and antenna (par. 650a). From figure 6-104, the radiation efficiehcy correction, No. 2, is -15 db; and from figure 6-105, the pattern efficiency correction, No. 3, is -12 db. The total correction to be applied to the rated power is therefore —6—15—12 = -33db, corresponding to a power ratio of 0.0005. Hence, a transmitter rated at 75 watts would in this instance yield a radiated power of only 75 X 0.0005 = 0.04 watt. This is the power to be used in estimating received sky-wave field intensity from figure 6-102.
(2) For ground waves, correction No. 3 is 0 db and the total correction is -21 db, that is, the radiated power is 75 X 0.008 = 0.6 watt. This is the power to be used in estimating received ground-wave field intensity from figures 6-93 to 6-95, or ground-wave distance range from figures 6-96 to 6-101.
e. Effect of Multiple-hop Transmission. In computing figure 6-105 one-hop transmission was assumed, that is, a single reflection from the ionosphere. At the longer distances, multiplehop transmission will often contribute materially to the received field. This is equivalent to improving the pattern efficiency; that is, equivalent to moving the long-distance values closer to 0 db (fig. 6-105).
651. POWER CORRECTIONS FOR A HALFWAVE HORIZONTAL ANTENNA.
a. Limited data indicate that with properly fed half-wave horizontal antennas the transfer efficiency correction is negligible.
b. Computed values of radiation plus pattern efficiency correction for such antennas
299
NOTE: THESE ARE AVERAGE CORRECTIONS FOR POOR AND GOOD SOIL, SINCE, FOR THE CONDITIONS COVERED, THE TYPE OF SOIL HAS SMALL EFFECT. TL 54916
Figure 6-107. Sky-wave radiation efficiency and pattern corrections for half-wave horizontal transmitting antennas.
are given in figure 6-107. The values given are for the case when the sending and receiving antennas are broadside to each other, a condition advisable for long-distance transmission. At short distances, values for the case when the antennas are end-on to each other would be approximately the same as shown. The curves indicate the effects of changing the height of the transmitting antenna, for various frequencies and transmission distances. In general, for short- or medium-distance transmission between horizontal half-wave antennas, the antennas should be not greater than about one quarter wavelength above the ground; while for longdistance transmission, heights approaching half-wave will result in increased efficiency, since a greater part of the radiation in this case is at low vertical angles.
c. At long distances, in cases where poor efficiency is shown in figure 6-107, multiple-hop transmission will tend to improve the pattern efficiency.
652. RECEIVING ANTENNA PATTERN CORRECTIONS.
a. Sky-wave signals at the receiving site arrive at various vertical angles, depending on the distance between stations. The amount of signal picked up and delivered to the receiver therefore depends on the vertical pattern of the receiving antenna, that is, its response to a signal arriving at the vertical angle or angles involved. The amount of static interference delivered to the receiver is also a function of the vertical directional pattern of the receiving antenna and the angle of arrival of the static. The signal-to-noise ratio at the
300
PARS.
651-652 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
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PARS.
652-653
CHAPTER 6. RADIO SYSTEMS
receiver input will therefore be independent of the antenna used if the signals and external noise arrive at the receiving antenna over the same sky-wave path. However, if the signal arrives at a high angle while the nope arrives at a low angle, or vice versa, the' signal-to-noise ratio at the receiver input will depend on the relative response of the antenna at the two angles.
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TL549I2
Figure 6-108. Sky-wave pattern corrections for vertical whip receiving antennas.
b. Approximate corrections to take into account the relative response of the receiving antenna to signal and to noise, for various distances of signal transmission by sky wave, are given in figure 6-108 for a short vertical an-
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TL 54966
Figure 6-109. Sky-wave pattern corrections for half-wave horizontal receiving antennas.
tenna and in figure 6-109 for a half-wave horizontal antenna. These corrections are added to the estimated incoming signal field, and the result compared with the field required to override atmospheric static as given by figure
6-92. For example, at 2 me, 100 miles, and F2-layer transmission, the receiving antenna pattern correction for a vertical whip is about —6 db and for a half-wave horizontal is about +9 db. (For information indicating when to use the F2-layer scale and when to use the E-layer scale, see paragraph 650c.)
c. With a directional receiving antenna, such as a horizontal rhombic on long-range circuits, considerable discrimination against noise is possible, especially when the direction of transmission is appreciably different from the direction of the controlling noise sources in the tropics.
653. PERFORMANCE ESTIMATES.
a. General.
(1) Step-by-step procedures for calculating ground-wave and sky-wave performance, and examples using the information in paragraphs 645 to 652, are given below.
(3) In considering whether a sky-wave calculation or a ground-wave calculation, or both, should be made in a particular problem, it may be clear from the nature of the problem which kind of transmission will predominate, and if so, only this kind need be calculated. For example, for 100-mile transmission in jungle, only sky waves need be considered; and for frequencies well above the muf, only ground waves need be considered. If there is doubt, both calculations can be made, and if either calculation indicates satisfactory transmission, the result can be considered satisfactory. A possible exception to the latter conclusion occurs when the estimated received ground-wave and sky-wave field intensities are practically equal, in which case there may be severe fading.
(3) In determining whether the groundwave computation should be made with the aid of figures 6-93 to 6-95 (ground-wave field intensity versus distance), or of figures 6-96 to 6-101 (ground-wave range versus radiated power), use the information in paragraph 647a(l).
b. Step-by-step Procedure, Using Figures 6-93 to 6-95 (Ground Wave Field Versus Distance).
(7) Find required field intensity from figures 6-90, 6-91, and 6-92 (correcting for c-w versus voice transmission when appropriate) and from any additional data, gained from experience in the particular locality, on other sources of noise or interference.
656935 0—45------21
301
PAR.
653 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
(2) If the transmission path is over earth, estimate the type of ground; good, poor, or jungle. See the information referred to in paragraph 644e. In the absence of this information, loamy, clay, marshy, or alkali soil can be considered good; rocky, sandy, or gravelly soil and coral can be considered poor.
(3) Find the rated power of the transmitter, from section VIII of this chapter or otherwise. Express in db above 1 watt (fig. 6-110).
(4) Find from paragraphs 649 and 650, or otherwise, the relation between rated and radiated power. Hence find the radiated power in db above 1 watt.
(5) Find from figures 6-93, 6-94, or 6-95 the expected field intensity at a given distance, for the particular radiated power, as described in the above example, and compare with the required field; or find the distance at which the required field intensity is reached.
(6) If the country is hilly or mountainous, make the shadow correction described in paragraph 644c.
(7) If the transmission is through dense jungle, divide the expected range for poor earth by approximately 10.
c. Example of Use. Problem: Find the estimated ground-wave c-w distance range of Radio Set SCR-193 at 2 me over sea water, using a 16-foot whip, for the month of December, in Formosa. The steps in the solution are numbered as in the preceding subparagraph.
(1) From figure 6-91 the noise grade is 2. From figure 6-92 night-time noise controls and midnight may be taken as representative, the required field at this time being 40 db above 1 microvolt per meter. This is for voice transmission ; for cw, 40-17 = 23 db is required.
(2) Not involved in this problem.
(3) Rated power is 75 watts, or about 19 db above 1 watt (fig. 6-110).
(4) Transfer efficiency correction is -6 db (par. 650a).
Radiation efficiency correction is -15 db (par. 650b).
Total transmitting corrections are -6 -15 — -21 db.
Radiated power is 19 —21 = —2 db with respect to 1 watt.
(5) Figure 6-95 gives received field intensities over sea water at various distances with 1 watt radiated power. The required field is +23 db, from step (1), with a radiated
power of 2 db below 1 watt, from step (4). This would correspond to a required field of +25 db. if 1 watt were radiated. Therefore, to find thp range in the present example, note from figure 6-95 the distance at which the field intensity for 1 watt radiated falls to +25 db. This distance is about 150 miles. (As noted previously, the sea water curves of figure 6-95 are applicable only when antennas are close'to the water’s edge.)
Watts
db above
1 watt*
1 0
2 3
4 6
5 7
7 8.5
10..............................................10
20..............................................13
30..............................................15
50.............................................. 17
80.............................................. 19
100..............................................20
200..............................................23
300..............................................25
400. . ...........................................26
500..............................................27
1,000.............................................30
10,000..............................................40
15,000..............................................42
a Other values can be obtained from information in chapter 12.
Figure 6-110. Approximate relation between watts and db above 1 watt.
d. Step-by-step Procedure for Using Figures 6-96 to 6-101 (Ground-Wave Range Versus Radiated Power).
(1) If the transmission path is over earth, estimate the type of ground; good, poor, or jungle. See the information referred to in paragraph 644e; or in the absence of this information, loamy, marshy, or swampy soil can be considered good; rocky, sandy, or gravelly soil and coral can be considered poor.
(2) Find rated power of the transmitter, from section VIII of this chapter or otherwise.
(3) Find from paragraphs 649 and 650, or otherwise, the relation, in db, between rated and radiated power. Find the corresponding power ratio, less than unity, from chapter 12, and multiply by the rated power to obtain the estimated radiated power in watts.
(4) From the appropriate one of figures 6-96 to 6-101, find the estimated range (interpolating if necessary).
302
PAR.
653
CHAPTER 6. RADIO SYSTEMS
(5) If the country is hilly or mountainous, make the shadow correction described in paragraph 644c.
(6) If transmission is through dense jungle, divide the expected range for poor earth by approximately 10.
e. Example of Use. Take the problem of subparagraph c above, and use the numbered steps of subparagraph d.
(1) Not involved in this problem.
(2) Rated power is 75 watts.
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Figure 6-119. Inverted-L antenna for use with Radio Sets SCR-177 and SCR-188.
660. SLOPING-WIRE ANTENNA.
The sloping-wire antenna illustrated in figure 6-120 is an end-fed antenna which may be strung up hurriedly between two trees, or between one tree or other support and a post driven in the ground near the radio set. When used for short- or moderate-distance sky-wave
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Figure 6-120. Sloping-wire antenna.
transmission, this antenna works best if made approximately a half wavelength at the operating frequency and sloped at a fairly low angle to the ground. The sky-wave signal transmission will be best when the sending and receiving antennas are broadside to each other, about 6 db poorer when they are end on with their high ends pointing toward each other, and intermediate when they are end on with low ends pointing toward each other. This type of antenna produces good shortdistance sky-wave transmission; it produces fair ground-wave transmission, especially in directions approximately in line with the an
tenna. The efficiency for ground-wave transmission can be increased, and directional effects reduced, by making the antenna nearly vertical. Further information on this antenna is given in paragraphs 663 and 664.
661. HALF-WAVE HORIZONTAL ANTENNAS.
a. General. The most suitable type of tactical antenna for sky-wave transmission is the horizontal half-wave antenna. Such antennas may be either center-fed or end-fed. Center-fed antennas are used preferably with a low-impedance transmitter or receiver which is balanced to ground, and with a balanced downlead or transmission line. End-fed antennas of a total length of a half wave are high impedance ; however, this impedance may be lowered in various ways (par. 663) to permit proper loading of a transmitter.
b. Use for Short-distance Transmission. These antennas when erected at heights under a quarter wavelength, radiate and receive well at the steep vertical angles involved in sky-wave transmission over distances up to at least 200 miles between stations. As receiving antennas for such use, they tend to reject atmospheric noise and interference coming from distant sources via sky waves at low angles, thus improving the signal-to-noise ratio. Experiments indicate that these advantages are shared by both end-fed and center-fed antennas, provided a proper down lead is used with the end-fed type (par. 663). At distances up to 200 miles, the orientation of the antennas is relatively unimportant as regards reception of the desired signal; hence the antennas can sometimes be oriented so as to minimize interference from distant sources.
c. Use for Long-distance Transmission. If the antenna height is increased above about a quarter wavelength, the maximum of the antenna vertical directional pattern will no longer be vertically upward but will be at some lower angle. At heights approaching one-half wavelength above ground (which are practical for the upper part of the h-f band) the pattern maximum will be at angles suited for sky-wave transmission over a distance of several hundred miles. This is indicated on figure 6-107.
d. Length of Half-wave Antenna. The length in feet of a half-wave horizontal antenna, reasonably remote from the earth or from
310
PARS.
661-662
CHAPTER 6. RADIO SYSTEMS
other structures, is approximately 468 divided by the frequency in megacycles. This is 95 percent of the free-space half wavelength. Figure 6-121 tabulates this length in feet versus operating frequency. The length of a half-wave antenna consisting of an insulated wire on or close to the ground will be from 55 to 80 percent of these values.
Frequency (megacycles)
Antenna length (feet)
2 ........................................234
3 ..’.....................................156
4 ........................................117
5 ......................................... 94
6 ......................................... 78
7 ........................................ 67
8 ......................................... 59
9 ......................................... 22
10 ......................................... 47
F .........................................468/F
Figure 6-121. Length of half-wave antenna versus frequency.
e. Standard Tactical Half-wave Antennas.
(1) Center-fed. A doublet antenna kit has been standardized for use as a transmitting antenna with Radio Sets SCR-299-( ), SCR-399-A, and SCR-499-A. This kit is described in TM 11-280 and TM 11-281 with changes thereto. It consists of the parts for the antenna, a coaxial transmission line, and coupling arrangements which are substituted for the regular tuning units and transmitter tank14 coils. A sketch of the antenna is given in figure 6-122.
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Figure 6-122. Doublet antenna for use with Radio Sets SCR-299, SCR-399, and SCR-499.
(2) End-fed. Certain tactical radio sets are arranged to end-feed an antenna of a total length of approximately a half wave. These include Radio Set SCR-694, the higher frequency unit of Radio Set AN/TRC-2, and Radio Transmitter BC-191-( ) used in Radio
14 This tank coil is the inductor in the tuned plate output circuit of the radio transmitter.
Sets SCR-177-( ), SCR-188-( ), SCR-193-( ), and AN/VRC-1. At frequencies above about 5 megacycles, somewhat better transmission can be obtained by using the arrangements described in paragraph 663 where applicable.
662. IMPROVISED CENTER-FED HALF-WAVE ANTENNAS.
a. For particular Radio Sets. In one theater, a doublet antenna, including a twisted pair down-lead, was improvised using available materials. The improvised method of connecting the antenna, and changes made in the transmitter output circuit, are shown in figure 6-123 for Radio Transmitter BC-191-( ), and in figure 6-124 for Radio Transmitter BC-610-B used in Radio Set SCR-299-( ). No change was made in the antenna circuit of the receiver used with this arrangement.
b. For Other Radio Sets. With other radio sets having transmitters capable of feeding a doublet through a transmission line of 50- to 100-ohm impedance, an improvised antenna such as described in subparagraph a above or one made from parts of the antenna kit described in paragraph 661e could be used, preferably making changes similar to those shown in figures 6-123 and 6-124 in the transmitter
—ft—■----------ft---
F7>77 \ /Tm7
\
z4?\ L * 'l ANTENNA "6.
____(_ \ SJ RELAY --I.MTCMMA ft
\y\/ 7 ''X an ’ enna g
ri ' T^XTl fl LOA da J
= : p"°"D" - ' —— -9 LOADB>cC^
COUNTERPOISE
° GROUND
° RECEIVER
PROCEDURE:
SET "ANT CIRCUIT SWITCH N"ON 3 WHICH GIVES ABOVE CIRCUIT.
SET "ANT IND TUNING M " ON O.
SET "ANT COUPLING SWITCH D" FOR PROPER LOADING OF AMPLIFIER.
REMOVE SHORTING BAR BETWEEN COUNTERPOISE AND GROUND TERMINALS.
CONNECT TRANSMISSION LINE TO TERMINALS MARKED ANTENNA AND COUNTERPOISE AS SHOWN
TL 53236-5
Figure 6-123. Revised circuit of Radio Transmitter BC-191-( ) for use with half-wave doublet
antenna.
output and receiver input circuits to isolate them from ground. If the radio set cannot be isolated from ground, an isolating transformer can be used (par. 675c (1)).
311
c. Transmission Lines. If the antenna is removed so far from the radio set that the loss in a twisted pair down-lead or transmission line would be objectionable, a spaced-pair transmission line may be used. Losses in twisted pair are given in paragraph 676, which also describes an improvised spaced-pair transmission line using Wire W-110-B. A better impedance match is obtained between antenna and spaced-pair transmission line if the improvised folded doublet described in subparagraph d below is used instead of a halfwave doublet.
d. Folded Doublet Antenna.
(1) A folded doublet may often be used to advantage with an open wire transmission
line or 200-ohm transmission cable. The input impedance-frequency characteristic of such an antenna at frequencies near half wave is broader than for a single half-wave antenna near its resonant frequency; hence moderate changes in frequency' should not require dimensional changes. The total length of a folded doublet is a multiple of a half wave, but since it is folded it requires the same space between supports as a half-wave antenna. Its directional pattern is approximately that of a center-fed half-wave antenna.
(2) Figure 6-125 shows a 2-wire folded doublet, having an impedance of about 300 ohms, used with a transmission line having a characteristic impedance of about 450 ohms.
312
I ' >
PAR.
662 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING________________
I—O £ § '-J
■ ria rfXefis-
■ w f____________g " " EZ
B+^ -f2
STANDARD CIRCUIT
/'TVAAA - - O< — — C I PAIR OR ___ ।
/_______g - 0 -IcOAXIAL/X^X
__________J 04 2 (• y'
I 2r'X' REVISED CIRCUIT \0 J
B-t- - x—y
NECESSARY REVISIONS.
THE SERIES CAPACITOR AND THE VARIABLE INDUCTANCE ARE DISCONNECTED FROM TERMINAL I.
TERMINAL 2 IS REMOVED FROM "GROUND"
THE TRANSMISSION LINE IS CONNECTED TO TERMINALS I & 2.
TL 54S50
Figure 6-124. Revised circuit of Radio Transmitter BC-610-B for use with half-wave doublet antenna.
PARS.
CHAPTER 6. RADIO SYSTEMS 662-663
SPACER U----------A--------------1 ohms, used with a transmission line of about
[] 600-ohm characteristic impedance. While it
/ I T B D —| I is preferable to keep the folded horizontal
/ I \\ wires in a horizontal plane, they can be ar-
// k INSsLpaTcers-- = ^transm'ss'on LINE \\ ranged one above the other, as illustrated. / Vrqpe \ = , rope\\ (4) These antennas are not furnished as
/ 1 XU, > standard antennas, but have been improvised
OR hthfr . successfully in the field using 080 copper or
convenient support convenient support copper-steel wire. For optimum results, they
A= ^8Q(MqFEET c=6to8inches should be used with balanced transmitter out-
A fl WFOR .064 (NO 14 B & S) WIRE put and receiver input circuits.
B=V Dll W'FOR .0 8 0 (NO. 12 B & 5) Wl RE
* l2/4"FOR.I 02 (NO. 10 B & S) WIRE
tl 54847 663 |MpROviSED END-FED HALF-WAVE
Figure 6-125. Center-fed horizontal 2-wire folded doublet ANTENNAS antenna.
a. General.
The transmission line impedance may be low- (1) Improvised end-fed half-wave hori-ered by bringing the wires closer than indi- zontal and sloping antennas for use in the cated in the figure; or a 4-wire line or 200- frequency band from 2 to 6.5 megacycles are ohm cable (par. 676) may be used for this pur- shown in figures 6-127 and 6-128, respectively, pose. As indicated, the wires are equipped with in-
(5) Figure 6-126 shows a 3-wire folded sulators which may be jumpered to give an-doublet, having an impedance of about 600 tennas which are half wavelength at 2.0, 2.5, wooden _________________ ______________wooden 3.0, 4.0, 5.0, or 6.0 megacycles. The figures also
spacer p___B -|Af. B , ■spacer indicate simple down-lead arrangements help-
B-. rfcr- *n fading the transmitters when such an-
J T T--------------4 =!-----------| l tennas are used with radio sets on the ground.
m In general, a lead-in is used which is of such
// / spacers-=_' \\ a length that the antenna-to-ground impedance
// I ^---transmission line \\ as seen from the set is of a value which per-
**/ ROPE S = 1 ROPE-^» rnits efficient feeding of the antenna by the
4 u U X transmitter. In the case illustrated, a lead-in
convenient support convenient support ranging from 26 to 47 feet is used, the length
a= EET C’Gtob'nches depending on the transmitter used and the
B=A DRroR:olo(No. 'll b&sjwire frequency of transmission, as explained below.
[7V2"for.io2Cno.io bis) wire With horizontal antennas, the excess of lead-in p. r . / j i • , 7 , - t . wire is taken up by a folded zig at the set. as
Figure 6-126. Center-fed horizontal 3-wire folded doublet . .. ... « n - °
antenna. indicated m figure 6-127. With a sloping-wire
“I —rope a b c o e
j--EJ—a3p<----------------7°-— 0=0 - ”(1 1
/I -DOWN LEAD / \
/ y---------ylNSULATORS—' \\
/ / IZ+iIC \\
/ / P0ST ROPE-^* \ \
30 MAST OR OTHER XiL^^^'SET 301 MAST OR OTHER
CONVENIENT SUPPORT ^CROWS FOOT COUNTERPOISE 8-25'TOES CONVENIENT SUPPORT LENGTH of horizontal wire FREQUENCY* EFFECTIVE JUMPER
---(MCT_____LENGTH (FT) INSULATORS
20 234 ABCDE
I*! 60 78 ---
aFREQUENCY AT WHICH WIRE IS HALF-WAVE LENGTH. TL 525QI-S Figure 6-127. Horizontal half-ivave antenna with impedance-transforming lead-in.
313
Operating frequency (me) Antenna length (feet) Approx, transmitter settings for maximum power*
PA coil Antenna coupler
Top Lead-in b
2.0 234 47 31 75
2.5 234 47 15 85
2.5 187 47 21 75
3.0 187 47 11 90
3.0 156 47 15 85
3.5 156 47 6 95
3.5 117 47 13 100
4.0 117 47 4 80
4.0 94 47 10 90
4.5 94 47 4 100
a For frequencies between those listed, approximate settings may be estimated by interpolating between values
Operating frequency (me) Antenna length (feet) Approx, transmitter settings for maximum power*
Antenna selector Antenna coupler Antenna tuning
Top Lead-in’’1
3.8 117 26 1 100 200
4.0 117 26 1 100 290
4.5 117 26 1 100 450
4.5, 94 26 1 100 290
4.95 94 26 1 100 420
5.5 94 26 1 100 490
5.5 78 26 1 100 430
5.8 78 26 1 100 480
at successive tabulated frequencies which have the same tabulated length of antenna top and lead-in.
b For horizontal antennas, lead-in length is length of down-lead plus zig] for sloping antennas, lead-in length is zig length.
used on the ground with end-fed half-wave horizontal
Figure 6-129. Approximate settings for use in loading transmitters when
or sloping antennas with lead-ins (continued on opposite page).
314
PAR.
663 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
/ r—ZIG AT RIGHT \y______t
\ ANGLES TO y V\ / 11
\SLOPING WIRE yy \
\ I
/ P0S1" B ROPE-^ ABOUT 30'
/ / / 11 A~ '
--$ /—V L— INSULATOR / H
ABOUT 4* / \ 7\z _^y
' X CROWS FOOT
COUNTERPOISE 8-25 TOES
LENGTH OF HORIZONTAL WIRE
FREQUENCY * EFFECTIVE JUMPER (M C)LENGTH (FT.) INSULATORS
2.0 234 ABCDE
2.5 187 ABCD
3.0 156 ABC
4.0 117 AB
5.0 93.5 A
_ -6.0 78 ---
FREQUENCY AT WHICH WIRE IS HALF-WAVE LENGTH. TL 53237-S
Figure 6-128. Sloping-wave antenna with impedance-transforming lead-in.
antenna, practically all the lead-in is employed (2) A similar antenna and feeding ar-in a. zig. For tactical sets operated on the rangement may be used with vehicular ground, the set ground is provided by means mounted sets by connecting the lead-in wire of a crow-foot counterpoise consisting of eight to the terminal on the mast base (remainder 25-foot wires. of mast not used), or directly to the antenna
Radio Transmitter And Receiver BC-654-A Used in
Radio Transmitter BC-653-A Used in SCR-506-A. SCR-284-A.
PAR.
663
CHAPTER 6. RADIO SYSTEMS
Radio Transmitter BC-191-E used in SCR-177-( ), SCR-188-( ), SCR-193-( ), and AN/VRC-1.
Operating frequency (me) Antenna length (feet) Tuning unit* Approx, transmitter settings for maximum power* (Antenna circuit switch “N" on position 1)
Top Lead-inb Antenna coupler “D” Antenna inductance tuning “M” Antenna capacitance tuning “0”
2.0 234 47 TU-5-A 5 36 35
2.5 234 47 TU-5-A 5 13 100
2.5 187 47 TU-5-A 5 23 100
3.0 187 47 TU-5-A 5 11 80
3.0 156 47 TU-5-A or-6-A 5 21 35
3.5 156 47 TU-6-A 5 8 50
3.5 117 47 TU-6-A 5 23 0
4.0 117 47 TU-6-A 5 9 100
4.0 117 26 TU-6-A 6 11 100
4.5 117 26 TU-6-A 6 12 0
4.5 94 26 TU-6-A or-7-A 5 17 0
4.95 94 26 TU-7-A 6 13 0
5.5 94 26 TU-7-A 5 5 100
5.5 78 26 TU-7-A 5 9 50
6.0 78 26 TU-7-A 5 6 50
6.5 78 26 TU-8-A 6 0 0
8 For frequencies between those listed, approximate settings may be estimated by interpolating between values at successive tabulated frequencies which have the same tabulated length of antenna top and lead-in.
b For horizontal antennas, lead-in length is length of down-lead plus zig; for sloping antennas, lead-in length is zig length.
’Or equivalent (TM 11-800).
Figure 6-129. Approximate settings for use in loading transmitters when used on the ground with end-fed half-wave horizontal or sloping antennas with lead-ins (continued).
post of the set if a relatively large opening in the vehicle is available. In this case, the ground terminal of the set is connected to the vehicular chassis which serves as a counterpoise.
( = TILT ANGLE TERMINATING
RESISTORS \ J—FRONT ——-"TT” END SIO£——— H POLE
SIDE POLE—L__—-------- / .
e. ef- / s'
A*' ■c^s' Sil
5/ —SIDE POLE
v --s'
REAR POLE-------------------SIDE
TAPERED DOWN LEAD----t/l y'
4-WIRE I Ss'f'f'! Lx*——GROUND LINE——\ transmission!-—MM ' y^ LINE J M^ Jy
CONNECTION y'' \ /-TAPERED DOWN
DETAIL s' \ / LEAD
4-WIRE LINE—
CONNECTION DETAIL TL 53*86
Figure 6-134. Receiving horizontal rhombic antenna.
nonreactive resistors of a few watts rated dissipation are used. The directional pattern of a receiving rhombic is similar to that of an equivalent size transmitting rhombic. For receiving rhombics, reference may be made to TM 11-2611.
319
PAR.
670 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
(2) The broad-band properties of the rhombic have permitted as many as four to six receivers, each tuned to a different frequency, to be multipled on a single antenna. The direction of each distant station should in general be close to the optimum direction of transmission for the particular rhombic. Each radio receiver should be balanced to ground. To prevent interaction between receivers, it may be necessary to use arrangements such as described in paragraph 675c.
d. Choice of Site for Rhombic Antennas.
(I) Bearings for proper alignment of rhombics, and engineering details, furnished to the field for each specific installation by Army Communications Service. However, the actual choice of an antenna site is the responsibility of the officer in the theater. Proper choice of an antenna site to take fullest advantage of existing terrain is always of importance, and especially so in the case of rhombic antennas.
(2) The best location for a rhombic is over flat, level terrain with no obstructions beneath or surrounding the antenna. It is very seldom that this ideal condition can be found in practice.
(3) The following points should be considered in the choice of a site:
(a) The antenna should be erected over flat terrain with no hill, building, or
other large object within the area of the rhombic.
(b) The terrain immediately in front of the termination end of the antenna should preferably be level and of approximately the same slope as the ground beneath the antenna, for a distance of at least i/o mile. In this case the rhombic may be mounted parallel to the ground.
(c) Where the rhombic must be located over ground where there are differences in elevation at the various pole sites, but where the terrain ahead of the antenna is level, it should be erected with the antenna wires level. Their elevation should be the average of the elevation of the four pole sites plus the recommended height above ground.
(d) Hills or large buildings (particularly metal frame structures) immediately in front of the proposed antenna site should be avoided.
(e) Isolated trees within the rhombic area will have negligible effect on the performance of the antenna. However, the antenna should not be erected over a heavily wooded area where the trees are an appreciable height compared to the rhombic. Choice of such a site is likely to result in absorption loss and in a change of directional characteristics. Data are not available on the exact magnitude of the changes in rhombic antenna characteristics over heavily wooded areas.
r-----------------------d------------------------h
X ■ LI -----H f—S 1
Z see I X zk
/ CONNECTION-^/ X. I X ' Is
/ DETAIL / / \
/ X. / X transmission line
/ / X. CONNECTION DETAIL
✓ /^Z 2-WIRE X
/ s' —TRANSMISSION X.
/ s' \ line H \
/ l\ i 45°
W F-----------------------
J ELEVATION --------LEAD=H------------4 X
LEGEND
D POLE SPACING BETWEEN CENTERS J ATTACHMENT SPACING
_LL OWE HALF UPPER ELEMENT T TIE WIRE (APPROX 45 FT)
L2 ONE HALF LOWER ELEMENT 0 30° APPROX
S INITIAL DEFLECTION (DOWN LEAD 8. LOWER ELEMENT^ HANGING FREE) H 75 FT PREFERRED
b 12 FT. PREFERRED
Figure 6-135, Double doublet receiving antenna.
TABLE 1 DOUBLE DOUBLET REC. ANTENNA DATA
TYPE BAND RANGE (NOMINAL) D J LI L2 S
(IN MEGACYCLES) (IN FEET)
A 2.5-20 130 37 60 30 3
TL 53487
320
PARS.
671-672
CHAPTER 6, RADIO SYSTEMS
671. DOUBLE DOUBLET RECEIVING ANTENNA.
a. A receiving antenna used rather widely in fixed plant is the double doublet illustrated in figure 6-135 (TM 11-2629, when published). This consists of two doublets of different lengths connected criss-cross at their center, as shown in the detail, and attached to the end of a 2-wire transmission line, preferably of about 200 ohms impedance (par. 676). One doublet is cut to a half wavelength for the lower of two operating frequencies and the other is made a half wavelength for the higher frequency. The impedance curve of such an antenna will not change as rapidly in the neighborhood of the half wavelength frequencies as does the curve for a single doublet. The antenna is therefore more of a broad band antenna than would be the case if two separate half-wave doublets were used. However, the antenna impedance has an antiresonance point intermediate between the two half-wave frequencies. The signal-to-noise ratio is, in general, not as good as if at each operating frequency a half-wave horizontal cut to that frequency were used. Maximum response in the directional pattern is broadside to the antenna.
b. Recent tests indicate that a general purpose double doublet may be constructed for use from about 2.5 to 20 me. This antenna consists of a top horizontal 4-mc half-wave element and a lower 8-mc half-wave element, both erected on poles 50 to 75 feet high. The higher poles are suitable for longer-distance transmission. Such an antenna collects signals (long-distance sky-wave) better over a wide range of frequencies than any single halfwave dipole, but not as well as a set of dipoles, each cut to half wavelength at its own operating frequency.
672. TRANSMITTING DOUBLET ANTENNA (DELTA-MATCHED).
The doublet antenna illustrated in figure 6-136 is often used with moderate powered (0.3 to 2.5 kw) transmitters over distances of 500 miles or less for point-to-point fixed station communication (TM 11-2656). For this application its use is often justified in place of the more elaborate rhombic, and it has^ advantages by virtue of its high-angle radiation properties. For transmission up to about 200 miles, the height of the antenna above ground should not exceed approximately a quarter wavelength for the operating frequency used; for long distances the height expressed as a fraction of a wavelength may with advantage be increased, but not above approximately a half wave. The transmitting doublet furnished for fixed stations consists of a single horizontal wire of approximately one-half wavelength, the exact length of which must be properly adjusted by a trial and error procedure. The power is transferred from a balanced 600-ohm transmission line to the antenna by a so-called delta-matching system. The ends of the wires of the transmission line are fanned out and attached to the antenna at equal distances from the center. The dimensions of the delta and the length of the antenna must be such as to match the line to the antenna so that standing waves on the line are minimized. The proper length of the antenna and the width of the delta at the antenna end are dependent upon height above ground, ground conditions, frequency, and the effect of metallic structures (towers, guys, etc.) in the vicinity of the antenna. In practice it has been found possible to specify the dimensions of the delta for a given frequency and height above ground so that only the
------------——- A --------------------•J.IO'-. r—B —*i
A=APPROX. .48 WAVELENGTH \ / ° \ 7x7-----------------
B=APPROX. .12 WAVELENGTH X \ / / '
C-APPROX. .15 WAVELENGTH Z \ / / \
H IS USUALLY 70 FT / \ \
DETAILED DIMENSIONS / \ / / X.
ARE GIVEN IN TM 11-2656 X \_// \
X - h \
X — - —12"
X = ♦”WIRE SIZE.W6B 8. S X.
yZ APPROX. X.
X , to STATION 'X
IF w ■ w 'X—
T . ELEVATION I
TL 53484
Figure 6-136. Delta-matched doublet antenna.
321
322
PAR. 672 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
—INSULATORS INSUL AT ORS ~j
* / 44°------------' '------------------
S ~'+a-----------( v----------:--------
•---------2 5O' TO 40 O'-----------•
PLAN
/fiT---------TT------------------------ TA 1
/ / 1 u 12-0—H COPPERWELD—1 \ \
/ / W" \ \
/ / I ---CABLE AND SEIZE \ \
/ / I EVERY TWO FEET TO \ \
/ / 1 LEAD-IN INSULATOR \
/ LIGHTNING rtf < v^-J \
/ 0AP-------fl r4\
I /—WINCH , \-----TRANSMITTER
- )» I » 1 GRADE , ~
----T z Ay
TL 53395
Figure 6-138. Crowfoot antenna.
323
PAR.
673 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
d. Wave or Beverage Antenna.
(I) A general description of this antenna is given in paragraph 665. At the lower frequencies being considered here, it becomes more important to install the antenna over high-resistivity (rocky or sandy) earth, since the wave-tilt effect which is responsible for its operation is approximately proportional to the square root of the product of frequency and soil resistivity at these frequencies. The wave antenna may be used for long-distance transmission and reception. The construction of the standard transmitting wave antenna differs from that of the receiving wave antenna, though both operate on the same basic principle of wave tilt. The receiving wave antenna generally consists of two spaced wires erected about 15 feet above ground on short telephone poles and is often made several wavelengths long, perhaps a mile or two, although for best efficiency it should not exceed about 2^/2 wavelengths. In the reception of signals on the antenna, the two wires operate in parallel with ground return. The antenna may be connected directly to the receiver or through coupling transformers and a transmission line. When operated in this fashion, the terminating resistor is placed at the end remote from the receiver and nearest the origin of the desired signal (fig. 6-139-A). It may often be necessary to locate the near end of the receiving antenna 200 feet or more from the receiving station to avoid the manmade noise which would be picked up if the end of the antenna were located at the receiver building.
(2) The receiving wave antenna is often arranged in a somewhat different manner (fig. 6-139-B). The antenna is run from the receiving site in a direction opposite to the origin of the desired signal. The received signal is built up between the wires and ground as it travels along the antenna away from the receiving site. At the far end of the antenna, a special transformer takes the signal existing between the pair and ground, converts it to a balanced-to-ground signal and feeds this signal to the pair of wires which now act as a balanced 600-ohm transmission line back to the receiver. Thus, the antenna serves as both antenna and transmission line. At the receiver end of the line, the balanced-to-ground signal is fed through a transformer and transmission line to the receiver. The terminating resistor
R is located at this coupling transformer and serves to dissipate any signal arriving from the direction opposite the desired signal. With this system, optional reception in either direction or simultaneous reception in two directions with two receivers is possible (fig. 6-139-C).
(3) At frequencies below 800 kc a properly located transmitting wave antenna should give results equivalent to a vertical antenna several hundred feet high. The transmitting wave antenna as furnished by Army Communi-
324
DIRECTION
*-------OF SIGNAL
TRAVEL
ANTENNA
RECEIVER I
O----- <"
B R + A
O----- \
/////////^^^^^
FUNDAMENTAL RECEIVING CIRCUIT
A
B <•-----DIRECTION
3701600 OHMS OF SIGNAL
I----- A TRAVEL
ANTENNA___________60°i600 °H Ms
o) I Jo ' SI Q !—►
3lk>—> । RECEIVER
ANTENNA
— R \
A RECEIVING CIRCUIT IN GENERAL USE
B
B7Q.6OO OHMS
600 OHMS:COAXIAL IMPEDANCE
antenna ZjlZZ COAXIAL LINE^
7+ y !-REC. I
I I ] ___f (EAST)
y) । A N T E N N A________________
600 OHMSICOAXIAL IMPEDANCE
I----E J |<*EST’<
SIMULTANEOUS RECEPTION FROM TWO DIRECTIONS c
TL 52505-5.
Figure 6-139. Receiving wave antenna.
PARS.
CHAPTER 6. RADIO SYSTEMS 673-675
cations Service consists of three conductors arranged in the configuration of an equilateral triangle (5 feet on a side) and erected approximately 15 feet above ground on short telephone poles. The antenna length is generally made between one and two wavelengths. For lengths greater than about 2^ wavelengths, the gain of the antenna generally decreases. Because of limitations of ground space, it is sometimes necessary to make the antenna less than one wavelength long, in which case the full gain of the antenna is not realized. The antenna is terminated at the far end (to ground) through noninductive resistors capable of dissipating approximately one-third of the transmitter power. The near end of the wave antenna may be connected to the transmitter directly or by means of a transmission line of the same impedance as the antenna. The antenna may then be operated over a wide frequency range without adjustment.
674. SPACE DIVERSITY ANTENNA SYSTEMS.
a. For long-distance sky-wave transmission, the use of a space diversity antenna system together with specially designed radio receiving equipment will provide an advantage of the order of 10 to 15 db as compared with use of a single antenna in combatting the effects of fading on teletypewriter operation. A similar but perhaps smaller advantage may be obtained for sky-wave transmission at short distances. In this system, two (or sometimes three) separate receiving antennas are connected to separate radio receivers, the outputs of which are suitably combined. Each individual antenna should be adapted to the type of transmission in question. The antennas should be separated approximately 3 wavelengths or more at the operating frequency; where space is available, 10 wavelength separation is worth while. The reason for the advantage is that under these circumstances the signals received in each antenna usually fade independently of each other.
b. When space limitations do not permit obtaining the separation referred to above, a lesser diversity advantage may be obtained by utilizing polarization diversity. This is based on the observation that the vertical and horizontal polarization components of a received sky-wave signal usually do not fade simultaneously. Thus, diversity can be obtained from two antennas, one responsive to hori
zontally polarized waves and the other to vertically polarized waves; for example, a horizontal doublet and a vertical doublet. It has been observed also that on two horizontal halfwave antennas, placed at right angles to each other, signals do not usually fade simultaneously. Such antennas may be used to obtain diversity and low noise on short-distance sky-wave transmission. Polarization diversity can also be obtained from a single horizontal halfwave doublet used together with a suitable balanced transformer with midtap (fig. 6-140).
HORIZONTAL DOUBLET ANTENNA
BALANCED DOWN-LEAD
BALANCED SHIELDED
TRANSFORMER jJLoJ WITH MID-TAP pmf □_
r2 r,
Figure 6-140. Schematic of means of obtaining polarization diversity from horizontal doublet.
The horizontal component is picked up in receiver Ri and the vertical component in receiver R2. A similar scheme can be used to obtain polarization diversity from a single rhombic antenna. The directional patterns of the antenna circuits connected to Ri and R2 will differ, whether the antenna is a doublet or a rhombic. This limits the effectiveness of these arrangements.
c. One form of radio equipment for diversity reception is illustrated in figure 6-141.
675. ANTENNA PARKS.
a. General.
(1) At locations where a large number of radio circuits terminate, such as a higher headquarters, careful layout of the numerous antennas is needed. A general plan for signal center radio equipment is discussed in chapter 11, which includes a figure (fig. 11-59) showing relative locations of a signal center and associated radio transmitters and receivers. Some general technical principles for laying out antenna parks are given below.
(2) The use of separate sites for the
325
PAR.
675
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Figure 6-141. Radio receiving station using diversity re* ception equipment (showing two Schuttig diversity mixing units and eight Radio Receivers BC-779).
transmitting antennas, the receiving antennas, and the signal center, together with suitable remote control arrangements, helps to prevent interference between transmitters and receivers (sec. VI), and reduces interference into receiving antennas from man-made radio noise arising from unsuppressed teletypewriter and ciphering equipment, d-c motors, etc. at the signal center.
(3) A reasonable rule to follow when greater separations would be impractical, is to separate transmitting and receiving antenna parks by at least one mile when the transmitter power is less than 10 kw. For higher transmitter powers the spacing should be greater. In many cases, the separation is much greater than indicated above because of local considerations (ch. 11).
(4) When it is necessary to place the receiving antennas close to the signal center in which the radio receivers are located, higher minimum received field intensities are gener
ally required, because of radio noise from the signal center itself and also from industrial sources when the signal center is in a city. Furthermore, the small space ^available in a city location may force the use of antennas which do not discriminate very well against such kinds of interference.
b. Transmitting Antenna Parks.
(1) Large transmitting antenna parks should be planned in advance to use the available space to the best advantage, provide for efficient operation, allow space for growth, reduce hazard from bombing, economize on the total number of tall poles which must be erected, and obtain reasonably short antenna r-f transmission lines.
(2) When a transmitting antenna is closely coupled to others in the vicinity, the currents induced in these antennas may be large enough to distort the radiation pattern of the transmitting antenna. Furthermore, cross modulation between transmitters may cause the radiation of spurious frequencies (par. 686). Separations of a half wavelength or more are desirable when convenient. Theater experience indicates that a separation of about a quarter wavelength between parallel half-wave transmitting antennas is reasonably adequate, provided that the antennas are tuned to materially different frequencies, that the length of one antenna is not an integral multiple of another, and that the transmitters have about the same output power ratings.
(3) The use of single-wire ground return transmission lines bunched closely together to feed several antennas will introduce coupling which will nullify any benefits obtained by proper separation of the antennas. Low-impedance end-fed ground-wave antennas may be fed by coaxial transmission lines, with the center conductor attached to the antenna down-lead and with the outer conductor connected to a crowfoot counterpoise. Balanced antennas, fed through balanced open wire lines or low-loss balanced cable pairs, are to be preferred for skywaves. For low coupling between balanced open wire r-f transmission lines, a rough rule to follow is that the minimum separation between pairs should be about eight times the spacing of the wires of a pair.
(4) One arrangement of balanced antennas which typifies layouts which have been used in the theaters is shown in figure 6-142. An arrangement which was found workable in
326
CHAPTER 6. RADIO SYSTEMS
PAR.
675
ELEVATION Q - TRANSMITTER A, B,C,D : SLOPING ANTENNAS TL 54926
Figure 6-143. Antenna park for a number of Radio Transmitters BC-610.
transmitter tuning units used (Radio Set SCR-399) were modified to use parallel resonance instead of series resonance to permit proper feeding of the antenna. For alternative methods see paragraph 663.
c. Receiving Antenna Parks.
(I) The antennas in a large receiving park can be arranged along the general lines discussed above. 'In a park close to a large headquarters, balanced antennas, balanced r-f transmission lines, and balanced receivers are desirable for sky-wave reception in order to minimize the effects of man-made noise. Unbalanced antennas required for ground-wave reception may be connected to their receivers through coaxial cable; a better method may be to use an isolating transformer at the base of the antenna, with its balanced winding connected to a balanced transmission line working into a balanced receiver. One such transformer (stock No. 2C471) is listed in TM 11-487.
(2) For optimum performance, individual antennas tuned to the operating frequency should be used with each receiver. However, where space is limited, several receivers may be multipled on a single antenna. With this arrangement, the antenna should have suitable directional and impedance characteristics over the required band of frequencies. One antenna may not be able to meet all requirements, in which case the receivers should be divided into groups with a separate antenna for each group. For example, a horizontal doublet antenna may be used for sky-wave circuits over distances up to 200 or 300 miles, while a tall vertical antenna will give better results on ground-wave reception from nearby stations. The doublet antenna may be cut to about 1.25 wavelengths for the highest frequency to be used and will work reasonably well down to frequencies at which the length is somewhat below a half wave. The vertical antenna for ground waves should not exceed about 0.65 wavelength at *Le highest frequency, and is relatively efficient down to frequencies at which the length is somewhat below quarter wave.
(3) When space permits and where their directional characteristics are suitable for the transmission paths involved, wave antennas and rhombic antennas are also suitable for use over a relatively wide frequency band with multiple receivers. Double doublet antennas may also be used. In addition, the antenna illustrated in figure 6-144 is suggested as an improvised sky-wave antenna (not supplied as standard) which has a better impedance characteristic over the 2- to 10-mc band than a single-wire doublet antenna such as described
327
1 n '''• n • n • n • r
Q S
NOTES.
O SPACE IS AVAILABLE, GREATER
V ^SEDESl‘RABLEBETWEEN RH0WBICS AND OTHER ANTENNAS j:oX%exrooVrTeenXoubletjnsert insulat°rs El transmitter house
• SUPPORTING POLE OR MAST TRANSMISSION LINES, ETC.. NOT SHOWN TL 54927
Figure 6-142. Sample transmitting antenna park.
one case for end-feeding half-wave sloping antennas from a number of Radio Transmitters BC-610 (used in Radio Set SCR-399) is shown in figure 6-143. To adjust each sloping-wire antenna to approximately half wavelength at its operating frequency, an insulator is inserted at the proper point. In some cases it may be necessary to carefully select operating frequencies for antennas separated by only 75 feet (fig. 6-143) in order to avoid excessive coupling between transmitters. Some of the
T °--------------
------0-------o B □----------------------------
______c_______a
□-------A--------
D ABOUT
--------------° 75 FEET
SUPPORTING „
WIRES —* □-------2---------1_
--------------O *- SUPPORTING A WIRES
«------ABOUT 350 FEET—----—
PLAN
B ---
T ABOUT
I 60 FEET
in subparagraph (2) above. However, such refinement in doublet antenna construction is not warranted unless external noise is low enough for set noise to become controlling with a simple doublet.
(4) When several receivers operating on different frequencies are connected to the same antenna, some reduction in the signal voltage delivered to each receiver must be expected. When receivers having balanced inputs are available, less loss will ordinarily result if these are located close together and connected in series, rather than connected in parallel. Up to four or five receivers may be connected in series in this manner before the losses exc'eed 10 to 15 db with respect to an individually tuned half-wave horizontal antenna per receiver. Unbalanced receivers must be operated in parallel, and the use of more than two or three will probably cause substantial transmission losses. These losses in signal caused by the use of several receivers on a common antenna do not necessarily degrade the audio signal-to-noise ratio; where atmospheric static or man-made noise is high, considerable loss can be tolerated before the set noise of a good receiver becomes an important factor.
(5) When several receivers are on the
same antenna, interference in a receiver may be caused by radiation from the high-frequency oscillators of the other receivers. One arrangement for reducing this effect is to use a distributing amplifier system which affords some isolation between the various receivers. A small 10-channel device of this sort, available in limited quantity through Army Communications Service, is the RCA multicoupler, model S-8853-1. It has a 200- or 600-ohm balanced input and also a 75-ohm unbalanced input. The input circuit is untuned, but with selected vacuum tubes the modulation products caused by strong undesired signals are kept to about 2 microvolts for unwanted signals up to 10 millivolts. The requirement of restricting unwanted signals to 10 millivolts may necessitate considerable separation from any transmitting antenna, especially in the case of vertical antennas and transmission over good soil.
(6) Another method, which avoids interference from modulation products, is to parallel all receivers across the common antenna after first inserting in one of the leads to each receiver a series-connected fixed inductor and variable capacitor. The reactance of the whole series circuit formed by the inductor, capacitor, receiver, and impedance toward the antenna is
328
PAR.
675 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
3' 3' 3' 3'
-----------44'---------------------------44'-----------X*
1 /=Z2Z22ZZ22Z22IZ\ /2222222222X222222Z2Z22X22\
| eg ' XU ' i‘
300" TRANSMISSION LINE
PLAN VIEW
2:8*
T+r ,___________________________________■______________________________n
5S5 4 ' _Jh4 f7—b
/ )
END VIEW SIDE VIEW
TL 54853
Figure 6-144. Eight-wire broad-band doublet receiving antenna for 2- to 8-mc band, improvised from tactical open wire pole line materials.
>
PARS.
675-676
CHAPTER 6. RADIO SYSTEMS
tuned out at the operating frequency of the particular receiver. This method reduces the loss caused by multipling, and also produces a maximum of signal voltage across the receiver. By this method, 5 to 10 receivers may be multipled without excessive loss. Standard equipment for using this method is not available, and construction of this type of equipment in the theaters should be undertaken only by skilled radio design personnel. The capacitor should be variable with a maximum capacitance of the order of lOOmmf. The tuning adjustments of the individual series circuits are not entirely independent of each other when bridged across a common antenna. Hence, after initial adjustments, or when an operating frequency is changed, the tuning should be checked over two or three times to insure optimum adjustments of all networks for the particular set of operating frequencies.
676. RADIO-FREQUENCY TRANSMISSION LINES.
a. General. When a radio set cannot be located very close to its antenna, connection is made by means of a transmission line which may be either open wire or cable. In tactical applications such a line is usually short, consisting merely of a down lead. In fixed locations where numerous sets are operated, the antenna separations are such that transmission lines back to receiver or transmitter centers may be as much as several hundred feet long.
b. Types of Lines.
(1) An open wire line consists of two or more parallel wires of the same size maintained at a fixed separation by insulating spacers at suitable intervals. An open wire line commonly used in fixed plant transmitting installations consists of a pair of 162-mil (No. 6 B&S or AWG) copper wires spaced 12 inches apart to give a characteristic impedance of 600 ohms. Another type of open wire line, frequently used in fixed plant receiving installations, is composed of four 64-mil (No. 14 B&S or AWG) copper wires arranged in the form of a 1.3-inch square, with diagonally opposite wires connected together. The characteristic impedance of this arrangement is about 200 ohms.
(2) Transmission cables are available in various forms. One variety consists of two insulated wires twisted together or paralleled and held together wth ° —‘i+herproof mate-
rial such as impregnated braid or vinyl insulation. Another type of balanced cable consists of two parallel conductors imbedded in a common insulating medium, with or without a metallic sheath. Coaxial cable, consisting of a center conductor mounted inside of and coaxial with an outer metallic tubing or metallic braid conductor and separated from it by spaced insulators or solid insulation, is also in general use.
(3) An unbalanced open wire cage is used in broadcast and low-frequency service. The construction resembles a coaxial line and, as supplied by Army Communications Service, consists of four outer conductors in the configuration of a 15-inch square connected together at each line support, and an inner conductor mounted coaxially with and insulated from the cage formed by the outer conductors. Two parallel conductors connected together are sometimes used in place of the single center wir^when a lower characteristic impedance is desired.
(4) Improvised lines using field wire are discussed in subparagraph f below.
c. Transmission Line Balance. Two-wire or 4-wire open wire lines, and twisted-pair or parallel-pair cables, are known as balanced transmission lines, because the impedance to ground of each side of the line is about the same as a result of symmetry. Coaxial cables and the open wire cage are called unbalanced lines, since the two sides of the circuit have entirely different impedances to ground because of the asymmetrical construction. For minimum transmission line radiation and attenuation while transmitting, and for minimum attenuation and noise pick-up while receiving, balanced transmission lines should operate between antennas and apparatus which are balanced to ground. The 4-wire line with diagonally opposite wires shorted together has a high degree of balance to ground if installed properly. Coaxial type lines are for use mainly between antennas and apparatus which are unbalanced to ground. (See also paragraph 624c(2) and 654d(l).
d. Characteristic Impedance and Attenuation.
(7) Open wire lines having practicable wire spacings generally range from about 200 to 800 ohms in characteristic impedance, and have, low transmission loss (attenuation). The impedance depends on the center-to-cen-
329
PAR.
676 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
ter spacing between conductors, and on the number and size of the conductors used. In
figure 6-145 the characteristic impedances of 2-wire and 4-wire open wire lines are plotted for several sizes of wire and spacings, to-
gether with the formulas from which they
were derived. ....................... ,,,,,,------T^F?0-22j no
^
A - TWO-WIRE LINE ' 's'-'s's's--- 10
I s'.' ..•''X.X'Xs' «
.'S.'. "s' ''s 's'. -—■ 6
,00---------- I g
2
2 600 Xs 1/2" 2<
O 'Z'‘XLZXXL^'''''.'^sX'^ °
N° Z^XX^XX' 4O0/,”z<>^^>z^;z?------------------------
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a 400 -------———-------------2==-:^=’:^ io
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^'^Z.s^'ZZX’ZZ'-^ZZ^""' »s*
200 ------XI —
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° .8 I 1.5 2 3 5 7 10 15 20
SPACING CS> BETWEEN WIRES -INCHES
NOTE WIRE SIZE (BAS) WIRE DIAM.CMILS)
18 20 22
40 32 25
TL 54927
4
204
6 8 10 12 14 16
162 128 102 81 64 51
Figure 6-145. Characteristic impedance of open wire balanced transmission line.
(2) For all practical purposes the loss of an open wire transmission line whose length is 100 feet or less may be neglected at frequencies in the h-f band. The r-f loss of a 2-conductor open wire line may be estimated from the following formula for copper or copper-steel wires and dry weather:
VF
a = 0.00314 ---—
d logie— where
a = loss in db per 100 feet
F — frequency in megacycles
d — diameter of conductor in inches
S = spacing of conductors in inches The loss of a 4-conductor line may correspondingly be estimated from:
Vf
a = 0.00314-----—
.. V2S d logio—-— d
where S is the side of the square and the other symbols are as above. Sample values of loss, computed from the above formulas, are included among the curves plotted on figure 6-146.
(,?) Cables, either balanced pair or coaxial, generally have characteristic impedances ranging from about 50 to 200 ohms, and the transmission loss is usually relatively high. Some data on coaxial cables, twin conductor balanced shielded cables, and a balanced uif-shielded cable are given in figure 6-147. Infor-
50 ------------1-------1--1--
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u- X X L w-143 s'
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23 5 10 15 20 30 50 100 150
FREQUENCY-MEGACYCLES
TL 54849
Figure 6-146. Attenuation of coaxial cable, balanced polyethylene cable, dry field wire, field cable, and open wire.
mation on most of these, and on other standard types of coaxial cables, is given in TM 11-487. A curve showing loss at various frequencies for two types of coaxial cable is included in figure 6-146. For balanced operation, a dual coaxial can be improvised by lash-
330
PAR.
676
CHAPTER 6. RADIO SYSTEMS
ing together two single coaxials and using the inner conductors for a transmission line and the outer conductors for a shield. This pair has the same loss as the single coaxial, but twice its impedance.
Type Description Characteristic impedance (ohms) Approximate loss at 20 me (db per 100 ft) Over-all dimensions (inches)
RG-8/U Single coaxial 52 0.8 0.4
RG-ll/U Single coaxial 75 0.8 0.4
RG-22/U Twin conductor 95“ 1.3 0.4
RG-57/U Twin conductor 95 a 1.1 0.62
RG-23/U Dual coaxial 125“ 0.6 0.7 x 0.9
Stock No. 1F4F1-4 Balanced unshielded polyethylene cable 200“ 0.35 0.6 x 0.3
“ Impedance of balanced circuit.
Figure 6-147. Characteristics of radio-frequency cables.
e. Velocity and Electrical Length. The velocity of propagation of waves along a well-insulated open wire line is nearly that of a wave in free space. In paired and coaxial cables the velocity is materially reduced. Because of these deviations from free-space velocity, the physical length corresponding to a full-wave electrical length is less than it would be in free space and may be calculated from the formula
984 V/Vo Physical length (feet) =------------.
F
In this formula F is the frequency in megacycles and V./Vo represents the ratio of actual velocity to free-space velocity; V/Vo is about 0.98 for open wire lines, and has values ranging from about 0.5 to 0.7 for various types of twisted pairs. For solid dielectric coaxial cable, the value of V/Vo is approximately 0.65, and for bead-insulated cable the value is about 0.85. All of these values are approximate, and are given to indicate that impedance matching sections, etc., may vary appreciably in physical length, depending on the type of line used.
f. Improvised R-f Transmission Lines.
(1) Field wire of the types ordinarily used for telephone purposes may be used as twisted pair r-f transmission cable in emer
gencies. The transmission loss in these wires is high, even when dry, as indicated by the curves for various field wire types in figure 6-146. At receivers, such losses between antenna and set may be tolerated in cases where external noise, rather than set noise, controls the audio signal-to-noise ratio. At transmitters, however, the losses cause equivalent decreases in radiated power, and should be avoided except in emergencies or on circuits having plenty of transmission margin. When moist, the losses of these wires may be several db greater per 100 feet than shown for dry wire. The characteristic impedances of Wire W-110-B and Wire W-143 are about 150 and 70 ohms, respectively, in either the h-f or v-h-f bands. The impedances of most other field wires are probably within that range.
(2) These field wires may be used as spaced twin pairs to form a relatively low-loss, high-impedance open wire pair, such as the 2-inch spaced portion of the line illustrated in figures 6-66 and 6-67. Lines of this type will have characteristic impedances comparable with similarly spaced open wire lines of the same general dimensions (fig. 6-145), but the losses will ordinarily be greater. However, the losses should be materially lower than shown for field wire in figure 6-146, where the field wires are used as twisted pairs. Hence spaced twin pairs are advantageous when fairly long radio-frequency transmission lines must be constructed of field wire. Impedance relations must be such as to permit satisfactory transmitter loading.
g. Impedance Relations. When a radio set is connected to an antenna through a transmission line, the impedance looking into the line at the radio set terminals (here called the load impedance for brevity) will in general not be equal to the antenna impedance, but will be modified by propagation down the line. In the special case when the antenna impedance equals the characteristic impedance of the line, the load impedance will also be equal to the antenna impedance. With low-loss lines of any impedance, the following are good approximations for the impedance relationships. If the line is a half wave in length (or a whole multiple of a half wavelength), the load impedance will equal the antenna impedance. If the line is an odd multiple of a quarter wave in length, it will act as an impedance transformer, thus: let the antenna impedance be A
331
PARS.
676-677 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
and the characteristic impedance of the line be Z; then the load impedance equals Z2/A. (In this expression,, both the magnitude and the phase of Z and A must be considered. Z is-nearly a pure resistance. Thus if A has negative reactance, Z2/A will generally have positive reactance, and vice versa.) The length of a transmission line can sometimes be chosen so as to utilize these properties. For example, if a transmitter is designed to work directly into a given antenna, but if in a particular case the antenna must be located some distance from the transmitter, it may be practicable to arrange matters so that the length of the transmission line between transmitter and antenna is a half wave, or a multiple thereof, at the operating frequency. By this means the impedance facing the transmitter is made about the same as if the transmitter were directly connected to the antenna.
677. PHANTOM ANTENNAS.
a. General. Phantom antennas (dummy or artificial antennas) are used in place of the actual antennas for routine testing of radio transmitters under normal load conditions, or when retuning a transmitter to a new operating frequency. Their use is essential in combat areas in order to avoid putting r-f carrier on the air when not sending a message.
b. Standardized Phantom Antennas.
(1) Phantom antennas have been standardized for use with several radio sets, as follows :
(a) Antenna A-27 (Phantom) ; for use with Radio Set SCR-506. (TM 11-630).
(b) Antenna A-28 (Phantom) ; for use with Radio Set SCR-300. (TM 11-242).
(c) Antenna A-29 (Phantom) ; for use with Radio Set SCR-624.
(d) Antenna A-62 (Phantom); for use with Radio Sets SCR-508 and SCR-528. (TM 11-600).
(e) Antenna A-82 (Artificial) ; for use with Radio Set SCR-536. (TM 11-311).
(/) Antenna A-83 (Phantom) ; for use with Radio Sets SCR-608 and SCR-628 (TM 11-620).
(2) Two of the above phantom antennas are illustrated in figures 6-148 and 6-149. Antennas A-27, A-62, A-82, and A-83 are adjustable and can be made to quite accurately represent the actual impedance of the antenna as installed, so that little or no retuning is
required when the transmitter is switched to the operating antenna. Antennas A-28 and A-29 contain fixed elements representing average antenna impedances, and some additional adjustments may be required when the transmitter is switched to the operating antenna.
if
bP .--------■*—■"»----- <
PHANTOM ANTENNA
FOR USE WITH
SCMTO
INSTRUCTIONS
S WITH ‘
I CMtex WITH .f
I U9T10H AKTEH** '•'”3
•sfp'. 2
Tl 549ST
Figure 6-148. Antenna A-62 (Phantom).
The use of these phantom antennas is described in the technical manuals for the respective radio sets and in TM 11-314.
c. Improvised Phantom Antennas.
(7) Phantom antennas for the h-f band can be improvised by using electric light bulbs
332
CHAPTER 6. RADIO SYSTEMS
PAR.
677
Figure 6-149. Antenna A-83 (Phantom).
of appropriate voltage ratings to produce various desired resistance loads. This type of dummy antenna is particularly useful as a substitute for a resonant antenna since such an
antenna is resistive only. However, lamp loads can also be used to provide the resistance component of nonresonant antennas, on the assumption that the reactive component of the actual antenna can be tuned out.
(2) Connections to the lamps should be made by short heavy leads soldered to the base, in order to minimize reactance which, as the frequency is increased, may otherwise cause the total impedance to differ appreciably from the calculated hot d-c resistance value. If it is necessary to use more than one lamp to produce the desired load resistance, the lamps should be arranged symmetrically and the connecting wiring should be balanced, that is, the leads to each lamp should have the same length. In the v-h-f band, lamp loads may have appreciable reactance and consequently may not produce satisfactory loading of some transmitters.
(3) Antenna resistance varies considerably with the type, ranging from 5 ohms or less for the resistive component of short whips to at least 1,500 ohms for end-fed half-wave antennas. Figure 6-150 suggests lamp combinations for various resistance loads. In each case the lamps should light to about normal brilliance; otherwise the resistance values may depart appreciably from those shown in the figure. For example, when an 80-ohm load is desired for a 50-watt transmitter, figure 6-150 indicates that two Lamps LM—28 connected in series will be suitable. If a 600-ohm load is desired for a 25-watt transmitter the nearest available lamp load is obtained from one lamp having Stock No. 6Z6815-9.
(4) Carbon resistors of the VL’-to 5-watt size may be used as phantom antennas in low power transmitters. If an r-f milliammeter is not available for current readings (power ~ a light of appropriate current rating, inserted in series with the resistor, may be used for making a rough estimate of current by observations of its brilliance as compared to normal.
656935 0-45-
-23
333
TL 54911
TL 54910
PAR.
677 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Xmtr output (watts') Characteristics and resistancea of lamp combinations suitable for loading various transmitters
0.1 No. of lamps 1, LM-74 1, LM-71
Characteristics 1.3v, 0.1a 2.0v, 0.06a
Resistance 13 ohms 33 ohms
Stock No. 6Z6756 2Z5971
0.5 No. of lamps 1, LM-50 2, par.
Characteristics 2v, 0.25a 6v, 0.04a
Resistance 8 ohms 75 ohms
Stock No. 2Z5950 2Z5877-11
2 No. of lamps 2, ser. 1, LM-27 1, LM-53
Characteristics 3.2v, 0.35a 6-8v, 0.25a 12-16v, 0.2a
Resistance 18 ohms 25 ohms 70 ohms
Stock No. 2Z5882-1 2Z5927 2Z5953
5 No. of lamps 1 1, LM-37 1 2, LM-49, ser. 1, LM-41
Characteristics 6.3v, 0.8a 13v, 0.33a 18v, 0.25a 28v, 0.1a HOv, 6w
Resistance 8 ohms 39 ohms 72 ohms 560 ohms 2020 ohms
Stock No. 2Z5878-9 2Z5937 2Z5878-6 2Z5949 2Z5941
10 No. of lamps 2, ser. 2, LM-37, par. 2, LM-38, par. 2, LM-41, par.
Characteristics 6.3v, 0.8a 13v, 0.33a 28v, 0.17a llOv, 6w
Resistance 16 ohms 20 ohms 82 ohms 1010 ohms
Stock No. 2Z5878-9 2Z5937 2Z5938 2Z5941
25 No. of lamps 1 1, LM-28 1 1
Characteristics 12v, 25w 32v, 25w 115v, 25w 230v, 25w
Resistance 6 ohms 40 ohms 528 ohms 2090 ohms
Stock No. 6Z6812-6 6Z6832-1 6Z6815-9 6Z6830-25
a The resistance values indicated in the body of the table par. indicate that the lamps are in series or parallel, respec-are those calculated for normal brilliance, with either a single tively.
lamp or combination of lamps. The abbreviations ser. and
Figure 6-150. Incandescent lamps suitable for dummy loads (continued on opposite page).
334
PARS.
677-678
CHAPTER 6. RADIO SYSTEMS
Xmtr output (watts') Characteristics and resistance* of lamp combinations suitable for loading various transmitters
50 No. of lamps 2, LM-28, par. 2, LM-28, ser. 1 1
Characteristics 32v, 25w 32v, 25w 115v, 50w 240v, 50w
Resistance 20 ohms 80 ohms 264 ohms 1150 ohms
Stock No. 6Z6832-1 6Z6832-1 6Z6815-2.1 6Z6840
100 No. of lamps 2, ser. 2, par. 1 2, ser.
Characteristics 12v, 50w 115v, lOOw 250v, lOOw 240v, 50w
Resistance 6 ohms 66 ohms 625 ohms 2300 ohms
Stock No. 6Z6812-7 6Z6815-17 6Z6850-100 6Z6840
300 No. of lamps 6, ser. 3, par. 1 3, ser. 3, ser.
Characteristics 12v, 50w 115v, lOOw 115v, 250w 115v, lOOw 250v, lOOw
Resistance 17 ohms 44 ohms 53 ohms 396 ohms 1875 ohms
Stock No. 6Z6812-7 6Z6815-17 6Z6815-4 6Z6815-17 6Z6850-100
The resistance values indicated in the body of the table par. indicate that the lamps are in series or parallel, respec-are those calculated for normal brilliance, with either a single tively.
lamp or combination of lamps. The abbreviations ser. and
Figure 6-150. Incandescent lamps suitable for dummy loads ( continued).
Section VI. MUTUAL INTERFERENCE BETWEEN RADIO SETS
678. GENERAL.
a. At key points in a military radio communications system numerous circuits terminate, necessitating the use of many transmitters and receivers in the same general locality. The selection of frequency assignments to avoid mutual interference between neighboring radio sets therefore becomes considerably more complicated than when only two or three units are involved. This is especially true when only a restricted number of frequencies are available in a given area, thus preventing free selection of frequencies.
b. The major type of interference which must be guarded against is interference in receivers from nearby transmitters. Interference in receivers caused by spurious radiations from other nearby receivers is usually not serious, but must sometimes be considered in
situations where receiving antennas are closely grouped or when several receivers are connected to a common antenna. Proper tuning of transmitters and proper lining up of receivers, as described in the technical manuals for particular radio sets, will reduce the likelihood of mutual interference. The information in this section will aid in locating the sources of such mutual interference as may occur.
c. A description of the way in which trans-mitter-to-receiver interference arises is given first, and broad measures which may be taken to reduce it are suggested (par. 679). The factors responsible for interference, including spurious transmitter outputs, spurious receiver outputs, and spurious receiver responses are discussed next (pars. 680, 681, and 682). The location of spurious responses in simple
335
PARS.
678-679
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
superheterodyne receivers and in superheterodyne receivers having two mixers are then considered in some detail (pars. 683 and 684). A discussion of additional spurious receiver responses caused by the heterodyning of two interfering signals, and additional spurious transmitter outputs caused by cross-modula-lation between two transmitters concludes the section (pars. 685 and 686).
d. Present information on the magnitudes of some factors affecting the interferenceproducing properties of various radio sets is very limited. Therefore, while it is possible to estimate reasonably well the frequencies at which interference is likely, and to draw general conclusions as to the degree of interference, it is impractical to predict accurately the seriousness of interference at specific frequencies. Wherever possible, therefore, it is wise to rehearse communication set-ups, using proposed physical layouts and frequency assignments. By this procedure, necessary changes in the initial assignments can be made before the actual operation. Experience gained in this manner should be made available to others so that frequency assignment combinations which have been found to work satisfactorily can be among the first to be tried in similar situations elsewhere. An example of this procedure is TB SIG 78 and TM 11-2601 which recommend certain frequency combinations for use with Radio Terminal Set AN/ TRC-3 and Radio Relay Set AN/TRC-4.
679. TRANSMITTER-TO-RECEIVER INTERFERENCE.
a. Transmitter-to-receiver interference is difficult to avoid in a congested area because the desired signals arriving at the receivers from distant transmitters are usually weak, and can be interfered with easily by the relatively strong signals radiated by nearby transmitters.
b. Each transmitter radiates small amounts of energy at many frequencies other than its carrier frequency; and each receiver is responsive, although very inefficiently, to signals of many frequencies other than the one to which it is tuned. In addition, signals from two transmitters of different frequencies may heterodyne in a receiver mixer tube to produce interference. These spurious radiations and responses greatly increase the number of frequencies at which interference can occur. For example, when transmitting and receiv
ing antennas are close together, interference may result not only in receivers tuned to frequencies near the strong transmitter carrier, but also in receivers tuned to frequencies corresponding with weaker spurious transmitter radiations. In addition, interference may result when the strong transmitter carrier frequency corresponds with one of the many weak spurious responses of the receiver. It is also possible for interference to occur when a spurious transmitter radiation corresponds with one of the receiver spurious responses, but serious interference of this type is not normally experienced.
c. Many of the interferences which occur with antennas closely spaced disappear when the intensities of interfering signals are reduced by separating the transmitting and receiving antennas. Such separation pays larger dividends than might be expected, because at many of the spurious response frequencies the receiver sensitivity has been found to depend on the intensity of the interfering signal. For these cases, a decrease of 20 db in the field intensity, caused by antenna separation, simultaneously reduces the receiver sensitivity to spurious response by another 20 db or more, thus rapidly eliminating many interferences.
d. Because of the advantages brought about by antenna separation, it should be emphasized that a headquarters location should be so chosen as to provide ample opportunity for separating transmitting and receiving antenna parks as much as is feasible. Such separations have been found desirable even in commercial installations which operate on fixed frequencies. Antenna separations of as much as 5 miles are not uncommon in military use for h-f sets using powers of 400 watts and above, and a spacing of 1 or 2 miles should permit reasonable flexibility in frequency assignments.15 For 50-watt sets in the v-h-f band, numerous workable assignments should be available with 14-mile antenna separation,10 provided that the transmitters and receivers operate near opposite ends of their available frequency band, thus taking full advantage of antenna tuning and r-f tuning. In most cases, a frequency dif-
15 Separation of transmitters and receivers generally requires the use of remote control equipment, such as is discussed in section VII of this chapter.
1G As noted in paragraph 678, this applies when several transmitters are involved. With a single radio relay set, it is not difficult to find combinations of frequencies permitting close proximity of transmitting and receiving antennas.
336
CHAPTER 6. RADIO SYSTEMS
PARS.
679-680
ference greater than 10 percent should prove adequate. With greater antenna spacing, the number of workable channels increases. Mutual interference can exist between sets operating in widely separated frequency bands if they are physically near each other. For example, h-f transmitters emit spurious radiations at many times the operating frequency, and these radiations may cause interference in v-h-f receivers. Also, h-f receivers frequently have spurious responses in the v-h-f band, which may permit a nearby v-h-f transmitter to cause interference.
e. When space is not provided to establish the separations between transmitting and receiving antenna parks noted in subparagraph d above, types of interference normally neglected become important. With numerous transmitting and receiving antennas separated only a few hundred feet or located very close together on a building or tower, the number of interference possibilities increases to such an extent that a solution of the frequency assignment problem becomes very difficult, if not impracticable, with the information on sets which is generally available in the field. If such a difficult situation cannot possibly be avoided, it is essential to understand the set characteristics responsible for interference in order to select initial frequency assignments which will have some prospect of proving reasonably satisfactory when operations begin. Also, when interference does occur, a knowledge of the various possible interference factors will permit a more rapid determination of the type of interference involved, thus leading to a rational rather than a trial and error solution of frequency rearrangement. The remainder of this section therefore deals with spurious set characteristics, and indicates at what frequencies spurious radiations and responses are apt to occur, including illustrations based on measurements made on several sets.
680. SPURIOUS TRANSMITTER OUTPUTS.
a. Most of the power in the r-f output of a transmitter is at the operating carrier frequency and its relatively narrow sidebands. However, a small amount of power is always present at all of the harmonics of the masteroscillator frequency. In h-f transmitters, the operating frequency is the same as this oscillator frequency or double, triple, and in some
cases, four times the oscillator frequency. In crystal controlled v-h-f equipment, the operating frequency is often many times (for example, 18, 24, or 96 times) the master-oscillator frequency, particularly in f-m transmitters where frequency modulation is derived from phase modulation. In the latter case the spurious components are spaced fairly closely and those falling near the transmission frequency tend to have the greatest magnitudes. For example, in a transmitter having a multiplication of 96, as in Radio Set AN/TRC-1, which uses frequency modulation, spurious out-f
puts occur at intervals of-~- above and below ub
the operating frequency, fopr. Figures 6-151, 6-152, and 6-153 show magnitudes, as measured in a 70-ohm load, for Radio Transmitters BC-610, BC-191-E, and T-14/TRC-1.
a °FI- 1 111 11 111 i~n
ui -----------------OPERATING FREQUENCY 2.2 MC
a -------------------------------------
a ___________________________ ________________________
* 50-rk-j-—-----------ZLZ--------------------------zzzzzz
5 --j- F-j--y----------------------------------------
S1 °° | h I I j [InnTtTTl t ffi “
I I IHI llzlilRil li*ll hl |if IM। I|e> || I? II |io| lull II12I Itt? il 0 5 10 15 20 25 30
FREQUENCY IN MEGACYCLES
« °H4-HI l-l L1JJ 111111111 11111
W ------------------OPERATING FREQUENCY 3-7MC
a --------------------
a: ___________________
5 50--------$--------------------------------------ZZZZZ
’l00zdz:ttz:ttzznz’~i_—>------------------------------t
—Lil I II III ||? I! | 13, I lA I II IP I! ||6, 1.7 J ?|
0 5 10 5 20 25 30
FREQUENCY IN MEGACYCLES
£ ZZZZZ ZZZZZZZZoa Ji* cy 7.4mc
a -------------------------------------------------III IT
a ________________________
u -------------------------------zzzzzzz
Be ---------------------------------------------------
O -------------------- v
_J o > ?--------------------
w ----------------------------------------------------
CD ____________________________
’l00zzzzzzzz--------------t-ZZ zzzzzzz!
-LI III I I 11 ‘I II 11.2| III ZZ3ZZZZZ~* 0 5 10 15 20 25 30
FREQUENCY IN MEGACYCLES
NOTES’- THE NUMBER AT PLOTTED LINES EQUALS THE FREQUENCY DIVIDED BY THE OPERATING FREQUENCY.
THE OUTPUTS SHOWN DOTTED ARE NOT PRESENT WHEN A CRYSTAL IS USED.
TL 54982
Figure 6-151. Spurious outputs of Radio Transmitter BC-610 arranged to feed a 70-ohm load. (BC-610
is a component of Radio Sets SCR-299 and SCR-399.)
337
PARS.
680-682 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
b. Since the frequencies of these spurious o, , , , , ,
outputs are different for different operating „ |~ | । M I I I I I । * 1-h-L_L
frequencies, it is apparent that the number of g frequency 7i 2mc_____________~ I | I I "III T
receiving channels which may be interfered < ----------------------------------------------
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mitting frequency will be accompanied by a m ZZZZZZZZZtZZfczn jt
series of spurious outputs, displaced in fre- 3100 ZZZZZZZZZT ZTl L------------------------
quency from any other series. l-l m II lllllllllll II I I 1 I I ,.1_L .
40 60 80 IOO 120 140
- _ _______________________________ CRYSTAL HARMONIC
K °DZ -1.1 1 I I I 1.1 I I H _1-1 1. I H I I I I..1 1 1 I I I _i i i ii i i i
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C ------------------------------------ FREQUENCY IN MEGACYCLES
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0 5 10 15 20 25 30 B______________________V E 0
FREQUENCY IN MEGACYCLES j [ T T
a zzzzzzrzzzzztaz: ZZZZZZZ±Z
XI00------------4--- -----------------------
W ZZZjl I H JoPERAtIng'FREQUENCY ^MCI 40 60 80 100 120 140
a ____________________________________ CRYSTAL HARMONIC
S ------------------------------------ —I------------------------1--1-1---1--1--1___1___I_I_
o 50 --------------------------------- 40 50 60 70 80 90 IOO 110 120 130
O ZZZZ'ZZZ ’ZZZ ZZZ~ZZZZZZZZZZZZZZZ FREQUENCY IN MEGACYCLES
d ----Z-----Z---E---?-----1------!---- TL 54877
m ____________________________________X
jjioo------------------------)________Z Figure 6-153. Spurious outputs of Radio Transmitter
---r------4--J---J 1 -J-- X-----T-14/TRC-1 measured in a 70-ohm resistive load. 0 "ii 1 a 1 |Q 15--------------------------20 W 25-30 (T-14/TRC-1 is a component of Radio Sets
FREQUENCY IN MEGACYCLES AN/TRC-1, -3, and -4.)
amples of the magnitudes and frequencies of s °| I I I I I I iTTE^jJiW these spurious receiver outputs in a 70-ohm
g ________Z!Z__________________________ dummy antenna for the Hammarlund super-
15 so ZZZZZZZ ZZZZZZZZZZZZZZZZZZZZZZZ Pro and the Hallicrafters SX-28 h-f receivers,
g ZZZZZZZZZZZZZ4ZZZZZZ5ZZZZZZZZ“ and f°r Radio Receivers BC-312 and BC-342,
d ZZZZZZZ ZZZZZ------------------------ are sh°wn i*1 figures 6-154, 6-155, and 6-156.
“ioo---------ZZZZZZZZZZZZZ ZZZZZZZZZ Figure 6-157 shows spurious receiver outputs
’ LL1..1.1 I bfl I I 1 I ar I I I I all 1 I I Ulll for a v-h-f receiver, Receiver R-19/TRC-1 of
5 frequency in megacycles 25 30 radio sets AN/TRC-1, -3, and -4. In a simple
superheterodyne receiver the local oscillator note-- the number at each plotted line is the frequency is related to the operating frequency HARMONIC OF THE CARRIER. , . . . , pool?
tl 54870 by expressions given m paragraph 683b.
Figure 6-152. Spurious outputs from Radio Transmitter
BC-191-E measured in a 70-ohm resistive load. 682. SPURIOUS RECEIVER RESPONSES.
(BS^i91j7(7 n S^ts superheterodyne receiver which is
and an/vrc-1.) tuned to receive an r-f signal of a certain fre-
quency will respond at that frequency better 681. SPURIOUS RECEIVER OUTPUTS. than at any other. However, it will also respond
Almost without exception, military receiv- inefficiently to signals at numerous other fre-ers are of the superheterodyne type. The quencies scattered over a wide band extending fundamental or harmonics of the local oscil- above and below the normal operating range lator in one receiver may reach a nearby re- of the set. The exact location of the spurious ceiver through various paths, the most impor- response frequencies is a function of receiver tant probably being by coupling between the design, and the relative efficiency or sensitivity antennas connected to the two receivers. Ex- ot the receiver at these freqencies depends on
338
PAR.
CHAPTER 6. RADIO SYSTEMS 682
< ITTT-II-I Illi ULU U .LU LU ULLCFl Ll I 11 11 111 [receiver tuned for 3.0 mcu
so-------------RECEIVER TUNED FOR 2.5 MC_ ON 3 0 TO 5 0 MC SCALF
50l I I I I I I I I I I I ON 15 TO 5-CTmC SCALE 50 ?-H 111 1171? ~ T |TT ~
___I_________________ _____________________________________
—ziz----------------- ----------------------------9________r______~
---—I—--------------- --------------------- —n---------------------
-------------------- o--------------4---------------------------
JI I..I1.I Itl.Id.I IBB „ Htill 11 III II III II IIIIflffl
° 0 5 10 15 20 25 30 S 0 5 10 15 20 25 30
o FREQUENCY IN MEGACYCLES § FREQUENCY IN MEGACYCLES
z50ZZZZZZZZZZZR-.tU I VeJr* 1 * * * IJneLi 1 FOR 's.QMCZ o
H ZZZZZZZZZZZ Pl1 III TS ?,(jTr ffw" I [T| I | | | I IT [RECEIVER tuned FOR S.omc.II
go-------tZZZZZZZZZZEZZZZZZZZZZZZZ g -------------------------ZZZZIZZZZZZZZZZEZZ
5 H4+HII lll-H-H-IH+l I H I I I H I 11 2 zzzzzzzzzzzzzzzzzzzzz-zzzzz'z-
0 5 10 15 20 25 30 - 0 -----------------------
FREQUENCY IN MEGACYCLES 2 _________________________
uj 1 LL I 1 I II I I I I IB I I I I 111 I | | I II I I I I || | t~1
2 |~|-[ l- l | | | | | | leUcLUrJ-J .1 U UJ-.kk > FREQUENCY IN MEGACYCLES 25
____________Receiver tuned for io.omc _ o
j ________________ON 5,0 TO I0 QMC SCALE _ 5
■0 ______________________________________ <
I --------------1------------------------ Ji
u 0-------------Z------------------------ |0| RECEIVER TUNED FOR ft.OMr||
------------------------------j----------- 50-------------------_ON5.O TO sZqmC SCALE Z 1 L 0 5 * * 10 15 20 25 30 zzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
FREQUENCY IN MEGACYCLES ---------------------------
TL 54 874 „---------------------------------------
0--------------------------------------
Figure 6-154. Spurious r-f outputs from a Hammarlund ---------------------------
super-pro receiver (equivalent to BC-779) measured I q $ * ‘2^ ^51 30
across 70-ohm resistance connected across ■ FREQUENCY IN MEGACYCLES
the antenna terminals. TL 53201-S
r Figure 6-156. Spurious r-f outputs from Radio Receivers
I" । | | | | | | | |~|rf(~TiiKicr. cntTinurl BC-312 and BC-342 measured across 70-ohm resistance
ON apTP^QMC SCALEMC connected across the antenna terminals. (One or both
_____Y--I T I I H T Tl I ~ °f these receivers are components of Radio Sets ____________________________________________________________________________________________ZT____________________________________________ SCR177 B, SCR-188-A, SCR-193-( ), _______________________________________________S____________________________________________--_ SCR-209, SCR-210, SCR-245, SCR-299, 0______________________________________________________________________________________________ZZZZ2 ZZZ ZZ ZZZIZZZL- SCR-399, SCR-499, and
----------------Z ZZZZZtZZZZZZZZZ AN/VRC-l.) i—1——111 —lb 1 1 111____________________________________1 1 1 1 1 111 1 1 r 1 1 1 1 1 111 1 1
20 5 10 15 20 25 30 . ...........
§ FREQUENCY IN MEGACYCLES ' \ ___RECE I VER "TUNED TO 7l.'3 MC I]
| 50-------------. CRYSTAL^ 762QKC ~
o w --------------zr___________
s -s___________~____________ZE___________
o i -I-----EEz-----------------
? I | || || [RECEIVER TUNED FOR 5-8 MCU 2 0-----------------f----------ZLZj__1______f
t- 50------>l_.. ON 3.0 TQ 5.6 MC SCALE ~ Z Z —-T — ZLZIZ______________________L_ZL.
_i __________________Z_ZZZZZ"Ti l ~r“ 2 Is| | I 6lI I I >11 I I ell I I r| I I IiqI I lull I12I ibiI
o ________________________ z 40 50 60 70 80 90 100
g ________________o_______JZZZZZZiZZZZZ “ frequency in megacycles
cl _______________ " nr h
---------------zxzzrzzzzzxzx:
1 111111 III 11.11 III 1111 Ilf 11111111 l-H g
w 0 5 10 15 20 25 30 2
> FREQUENCY IN MEGACYCLES S
< i4iti rri
< -Z_______——zzzzzzzzlzzzzzzzzzzz
-I I I I I I U-LlgjRECEIVER TUNED FOR lO-OMCll -----------r - j F-------f-
50---------------JbN 5.8 TO iZbMC SCALE _ ’ -J----->-------------------
ZZZZZZZZZZ"ZZZZZZZZZZZ---------------- L °2E'____________1_5_JZ-ZmznzznzzuzzziaT
I----------- 50 60 70 80 9 100 110
0___ZZZZZZZZZZZZZZZ---'------!-'-- frequency in megacycles
-------------------------------------- NOTE: NUMBER AT EACH PLOTTED LINE INDICATE THE
1 1 ‘ 1 । । । 111 1 I I 1 !■ 1 1 I I...L 1, I,.1.1-CRYSTAL HARMONIC
< 0 5 10 15 20 25 30 TL 54876
FREQUENCY IN MEGACYCLES Figure 6-157. Spurious r-f outputs from Receiver
v- ire a - i _ R-19/TRC-1 measured across 70-ohm resist-
r igure 6-155. Spurious r-f outputs from a Hallicrafters SX—28 ance connected across the antenna terminals.
receiver measured across 70-ohm resistance connected (R-19/TRC-1 is a component of radio
across the antenna terminals. sets AN/TRC-1, -3, and -4.)
339
PAR.
682________________ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING_______________________
such factors as the antenna selectivity, the
r-f selectivity, the degree of filtering in the °|X1'| I [I I I II, I I I III I I I I I I 11 heterodyning oscillator output circuit, and, in ZZZZZi--------------a widVfrequfnc^^angf
numerous cases, on the intensity of the inter- K --------
fering signal at the spurious response fre- £ -----------------4--------------------
quency. £ ------ZIZ---ZZZZZZZZZZZZZZ
u ---------I--------------------------------
0 IOO------|c — —---------------------------__
om.TTTlTI 11 I I I 11 i 1'1" 11 i i 11 i ii-i i.| f 111 I Ml 11 11 li I 111 I j 111 I |i| EEE ________________________ RESPONSES OVER A-----------------< ° 5 10 15 20 25 30 ____________________________________________________________________________________________WIDE FREQUENCY RANGE 2______________________________________________________________________FREQUENCY IN MEGACYCLES ____________________________________________________________________________________________ o 550 * *ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ 5 n
E ----------------------X---------------------------------: 2 m I I 11 I I-l-l Illi pm I i i i I I 11 I I 11
< ------------------------------------------------------ u ---------- RESPONSES NEAR
o -------------------------------------------------------- 2 --------operating frequency
O|00------0.-----4---------------------------------------- 5 --------------------------
? ------L-------------f--------------------------------- o -------------------------------
5 I I 111 I I I lllnl I I I I fl I I I InM I I I fl III ° -X------------------------
a O 5 10 15 20 25 30 A -------------------------
£ FREQUENCY IN MEGACYCLES ‘D ---------------------------"
I °i |.| 11 1111111111 rrnini 1111 im
J ______________________ RESPONSES NEAR 1-^lfflTII I Yi U I ?mlJI? ILJlft, UI ILI
C FREQUENCY IN MEGACYCLES frequency in megacycles
TL 54872 TL iA”'
Figure 6-161. Responses of Receiver R-19/TRC-1 tuned for Figure 6-159. Response of a Hammarlund super-pro receiver, 71.2 me (crystal frequency = 7.620 me). (R-19/TRC-1
tuned to 5.0 me on the 2.5- to 5.0-mc scale. is a component of radio sets AN/TRC-1, -3, and -4.)
340
PAR.
683
CHAPTER 6. RADIO SYSTEMS
683. LOCATION OF SPURIOUS RESPONSE FREQUENCIES IN A SIMPLE SUPERHETERODYNE RECEIVER.
a. General. The following steps first review the normal operation of a simple superheterodyne receiver, and then indicate the various manners in which the set may respond to-frequencies other than the desired signal frequency. Formulas and rules are given for locating the more important spurious response frequencies in each case. The same principles can be extended to apply to double conversion superheterodyne receivers, as outlined in paragraph 684.
b. Normal Response. For normal response, the incoming signal at the operating frequency, f0Pr, is selected by antenna tuning, amplified in the tuned r-f stages and then combined with a heterodyning frequency fnet in the mixer stage. The value of fhet is adjusted so that the difference frequency (beat frequency) from the mixer tube is equal to ft/, the frequency to which the i-f (intermediate-frequency) amplifier stages are tuned. In some sets fopr — fhet = fir, and in others fhet— fopr — fi/. After passing through the i-f amplifier, ft/ is applied to the final detector of an a-m receiver or to the first limiter grid of an f-m receiver, as the case may be.
c. Spurious Responses, General. The receiver, although tuned to fopr, will also respond to frequencies other than fopr when, by some combination of circumstances, a frequency of fi/is produced in sufficient magnitude at the output of the mixer stage, or in the i-f stages. Any radio frequency at which such a spurious receiver response occurs is referred to in what follows by the symbol fresp. The symbol f// refers to any frequency falling in the i-f pass band. If such a spurious signal reaches the limiter grid in an f-m receiver or final detector in an a-m receiver with an amplitude comparable with the desired signal, serious interference to voice or teletypewriter transmission will generally result. However, in c-w reception by ear, substantially more interference can be tolerated by skilled operators.
d. I-f Response. Signals within the i-f pass band may be picked up directly in receivers having insufficient shielding or insufficient r-f selectivity. The latter is an important factor when the operating frequency is within 20 percent of the intermediate frequency, which is generally possible in sets designed for use in the 1-f or m-f band. In such cases it is ordinarily specified that the receiver
should be at least 80 db less sensitive to an interference at ft/applied to the receiver input terminals than to a signal at its operating frequency.
e. Image Response. The most commonly recognized spurious receiver response is at the so-called image frequency. It is caused by the fact that there are two values of incoming frequency which will beat with fhet to produce ft/; one of these frequencies is above fhet by ft/ and the other is below fha by ft/. For sets designed such that fopr—fhet = ftf, the image response frequency is
fresp = fopr — 2fi/ and for sets where fhet—fopr = ft/,
it is fresp — fopr + 2ft/
As noted above, the symbol fresp is used here and throughout to designate any of the response frequencies, of which the image is but one example. The antenna and r-f amplifier circuits are tuned to amplify fopr. Such circuits are therefore detuned with respect to the image frequency, so that a signal at this frequency is considerably reduced in magnitude before reaching the mixer grid, thus reducing the receiver sensitivity at this image frequency. The amount of such reduction depends on set design.
f. Response at Submultiples of the Operating Frequency, fopr. A series of spurious receiver responses can also occur at frequencies of fopr,
fopr, fopr, .... fopr, where nr/=l, 2, 3,........etc.
3 4 nr/
When such frequencies are applied to the r-f stages, the r-f amplifier output will include small amounts of energy at their harmonics, because of nonlinear characteristics in the r-f stages. One of these harmonics will equal fopr, which will mix with f^z to produce ft/ in the receiver output, and this signal will proceed through the i-f and other stages in the same manner as the desired signal. The frequencies, fresp at which such spurious responses can occur are as follows;
r fopr
I resp---
nr/
Ordinarily, when fr/ exceeds 5, the magnitude of the response at the corresponding value of fresp is so weak that it can be neglected. This is because such frequencies are sufficiently removed from the operating frequency to be well attenuated by
341
PARS.
683-684
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
antenna and r-f tuning, and also because higher harmonies produced in the r-f stages by nonlinear action are weaker. Also, responses involving values of nr/ equal to 2 or more are of the type noted in paragraph 679c which are rapidly eliminated by increased separation between transmitting and receiving antennas.
g. Responses Due to Harmonics of the Heterodyning Frequency, fhet. Another receiver characteristic which is responsible for numerous responses at frequencies other than topr is that the heterodyning frequency is not usually a pure frequency, ihet, but includes harmonics of ihet such as 2fae«, 3fto .... Dhet, ihet where nt,et= 1,2,3, etc. Such harmonics will beat with certain incoming frequencies, fresp, to produce ft/ in the output of the mixer. This occurs when
Tibet ihet— fresp —f if, OT fresp — Ilhel thel = tif, that is, when
iresp = Tlhet fhet ± fif
The sensitivity of the receiver at the spurious frequencies caused by harmonics of ihet is less than the sensitivity at the operating frequency because the voltage applied to the grid of the mixer at the desired heterodyning frequency, ihet, is large compared to that of its harmonics, n^f^. The magnitudes of these harmonics become progressively smaller for greater values of n^. Values of Duet above about 4 therefore usually need not be considered.
h. Response Due to Harmonics of Base Frequency, fo,c. When the desired heterodyning frequency, ihet, is obtained by using a particular harmonic of a lower base frequency, iosc, (for example, the frequency of the crystal oscillator), as is common in v-h-f sets, ihet may be defined as Noscfosc, where Nose is the particular harmonic of fosc chosen for amplification before application to the mixer grid. Other harmonics of fosc also get through to the mixer grid in varying degrees. Any harmonic of fosc is here designated nose, whereas the capital letter Nose refers to the one used in the normal response. These harmonics will beat with certain incoming frequencies in the mixer to produce it/. The frequencies at which such spurious responses can occur are as follows:
iresp — nose fosc±ft/
The more important values of iresp are: those which result from values of nose corresponding to multiples Nose up to about 4; and those values of fresp which have a frequency between about one-
half the operating frequency and twice the operating frequency, resulting from other values of nose.
. i. Responses Due to R-f Harmonics in Combination with Harmonics of the Heterodyning Frequency or of the Base Frequency. As mentioned in subparagraph f above, harmonics of any incoming signal are produced in the r-f amplifier stages. These harmonics of an incoming signal, combined with values of n^fto or nosefose, produce numerous responses, the most important of which are those for which iresp is within ±5 or ±10 percent of fopr. The frequencies at which these responses occur are
. Tlhetihel tif
I resp =----zt----
Hr/ Hr/
. UoSC ZTkT C \ f(/
OT I resp =-—— (JN oset osc) ±---
nr/N osc Tlrf
These expressions are the same as those in subparagraphs g and h above except for the nr/ in the denominator. This type of action in the receiver is responsible for a large number of spurious responses which occur near the operating frequency, fopr (figs. 6-158, 6-159, and 6-160). Such responses occur
, Tlhet when — nr/
2,3, , . ,234
- and also values near unity, such as up 2 3 3 4 5
or nose takes on vaiues equal to Ilr/N osc
19
to, say —, where inet is higher than i0Pr, or values
3 4 5 20 ,
-, o’ 7’ UP say, —, where ihet is lower than f0Pr.
a o nt .ly
These responses are usually so dense within a range near fopr and extending as much as ±10 percent from fopr, that it is very difficult to operate nearby transmitters in that range without causing interference. The likelihood of interference at these frequencies disappears very rapidly as the transmitting antennas are moved further away.
684. LOCATION OF RESPONSES IN A SUPERHETERODYNE RECEIVER HAVING TWO MIXERS.
a. The location of spurious response frequencies in a receiver which has two heterodyning stages (as in the v-h-f Radio Receiver R-19/TRC-1 of Radio Set AN/TRC-1) can be obtained by applying the methods given in paragraph 683 in two steps.
b. In step 1, the portion of the receiver following the input to the first i-f amplifier is assumed to contribute no spurious responses, and computations of response frequencies for the first half of
342
PARS.
684-686
CHAPTER 6. RADIO SYSTEMS
the set are made as in paragraph 683. The intermediate frequency used for this computation is the actual first or high intermediate frequency, and its heterodyning frequency is the first heterodyning frequency, f»ea (or, if derived from a base frequency, nOsci fosci).
c. In step 2, the chief additional responses resulting from the second half of the set can be computed using the first form of the equation of paragraph 683i and including the case where m/=l. The intermediate frequency used for this computation is the second or low intermediate frequency of the receiver. The heterodyning frequency to use is ftei+fto2 for receivers where f»ezi is less than the operating frequency, fopr, and is Lezi — Le/2 in the case where fsezi is greater than fopr; where fhen and f«2 are the first and second heterodyning frequencies in the actual receiver. These responses, together with those computed in step 1, give an essentially complete picture of the more important spurious responses of the actual receiver.
d. While the process of producing spurious responses in a receiver with two heterodyning stages is more complicated than in the simple superheterodyne, experience has indicated that the number of important responses may be no greater. As in the simple superheterodyne, it is impractical to determine accurately the relative importance of specific spurious response frequencies without complete knowledge of the circuit characteristics of the particular receiver involved.
685. SPURIOUS RECEIVER RESPONSES DUE TO HETERODYNING OF TWO R-F FREQUENCIES.
a. When signals of different frequencies arrive at a receiver input from two local transmitters, one of the frequencies will act as a heterodyning frequency for the other in the mixer stage. If the two frequencies, or their harmonics produced in the r-f stages and in the mixer, differ by fv, interference will be possible. As a further example, interference may also arise if the sum or difference of two r-f frequencies, or of a combination of their harmonics, corresponds with the operating frequency or an important spurious response frequency. Nonlinearity of the first r-f tube is usually the cause of this latter type of effect.
b. These effects can be serious especially when one or both of the two interfering frequencies are
near the operating frequency, fopr. For frequencies substantially different from fopr, the attenuation due to r-f selectivity will reduce the magnitudes arriving at the mixer grid or at the first amplifier grid. This considerably reduces the interfering effect, since the magnitude of the interfering signal at frequency fvat the mixer output has been found proportional to the product of the r-f input values, so that a reduction of 10 db in magnitude at both frequencies, for example, reduces the interference by 20 db. Separation of transmitting and receiving antennas or taking advantage of minima in directional patterns, is therefore an effective way of reducing this type of interference.
686. SPURIOUS TRANSMITTER OUTPUT CAUSED BY CROSS-MODULATION BETWEEN TWO TRANSMITTERS.
a. When the antennas (or r-f feed lines) of two transmitters are located near each other, an appreciable r-f voltage from one transmitter may be impressed across the output tank circuit of the other. Because of nonlinear phenomena in the final amplifier circuit, this induced r-f voltage causes the generation and radiation of spurious signals at other than the operating frequency at either transmitter. For example, if one transmitter operating at 100 me has impressed across its output tank circuit a voltage at 90 me from a nearby transmitter, a signal at 110 me will be formed in the output circuit of the first transmitter which will be radiated after being attenuated by the tank, antenna coupling, and antenna tuning. Other spurious signals will be generated similarly at 80, 120, 70, 130 me etc., in the order of their strengths, but these will be of importance only in extreme cases. A difference frequency of 100 — 90 = 10 me will also be generated. In this example, interference with a nearby h-f receiver operating at 10 me may be caused, as well as interference with v-h-f receivers at several frequencies.
b. Interference of this type should not prove serious if receiving antennas are well separated from transmitting antennas. In the event they are not, the interference may be reduced by: increasing separation between transmitting antennas; reorienting the antennas of transmitters which are reacting upon each other so as to take advantage of minima in the directional patterns; and avoiding or removing any condition where two adjacent transmitting antennas are tuned for the same or nearly the same operating frequency.
343
PAR.
687
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Section VII. REMOTE CONTROL OF TACTICAL RADIO SETS
687. GENERAL DESCRIPTION OF REMOTE CONTROL EQUIPMENTS.
a. Introduction.
(1) Remote control equipments are devices for providing means whereby a radio set can be used for voice transmission or for c-w telegraph by an operator located at a point remote from the set. The principal purposes of such equipments are to provide push-to-talk control of a radio set over wire lines connected between the set and the remote operator, and to provide means for satisfactory voice transmission over these wire lines, particularly from the remote point to the radio transmitter. The push-to-talk control feature inherently provides the necessary c-w control of the transmitter for hand telegraph speeds.
(2) The components of some of these equipments include one unit which is located at the radio set and another unit which is located at the remote point. Some equipments contain arrangements for ringing and for intercommunicating over the wire lines between the remote operator and personnel at the radio set. The lengths of the connecting wire lines over which remote control and voice transmission are satisfactory vary from 1 to 10 miles, depending on the types of control units, wire, and radio sets.
(3) This section outlines the advantages of remote control equipments, discusses the principal operating features, and indicates the factors which limit the distances over which remote control and satisfactory voice transmission are feasible (pars. 687 to 690 inclusive) . Remote control equipments are included as components of some radio sets. Others may be procured as separate units and can be used with a number of different radio sets. Some of the more common remote control equipments are described briefly in paragraph 691. Arrangements for improvising remote controls are discussed in paragraph 692.
b. Operating Advantages. The principal advantages which can be realized from the use of remote control equipments are:
(1) In combat areas, a radio operator can be in a foxhole, dugout, or other location sheltered from enemy action, while his radio set and antenna are at a more exposed site suitable for satisfactory radio transmission.
(2) A speaker can be at a telephone in quarters while talking on a radio net over a field wire extension from the radio station.
(3) The locating of radio sets by an enemy radio direction finder or by aerial observation does not disclose the location of the headquarters.
(4) Time consumed by messengers traveling between headquarters and radio sets at widely dispersed points can be eliminated by locating the operators in a radio control central adjacent to the headquarters, thus expediting the handling of messages.
(5) Radio transmitters can be separated from radio receivers by distances of mile, or more to reduce mutual interference (sec. VI).
(6) In hilly country, radio sets can be located at high points from which the best radio transmission is obtained, particularly with radio sets operating in the v-h-f band, while the radio operators are at more convenient and sheltered points.
(7) A group of radio operators can be located together in a remote control central adjacent to a message center, thus minimizing personnel requirements and improving efficiency by adequate supervision.
(S) Air warning operation centers can be established reasonably remote from associated radio sets, with numerous radio channels to observers, airplanes, and other points involved in the control of operations.
c. Technical Functions.
(1) Push-to-talk control is the chief technical function of most remote control equipment. This consists principally of causing the radio transmitter to radiate only while the push-to-talk switch is pressed; but under many conditions it includes simultaneous disabling of the associated receiver. When the push-to-talk switch is released, the control equipment will cause the radio set to revert to receiving. Another push-to-talk function of some remote control equipments is to connect a 2-wire line from a remote telephone to the radio transmitter while the push-to-talk switch is pressed, and to transfer this line back to the receiver when this switch is released.
344
PARS.
__________________________CHAPTER 6. RADIO SYSTEMS_____________________687-689
(2) Various other operating features in addition to those associated with the push-to-talk switch are provided in some types of remote control equipment, among which are the following:
(a) C-w telegraph, by means of a key at a remote point.
(&) Intercommunication and ringing between a radio operator at a remote point and an attendant at the radio set.
(c) Audio amplification to provide adequate modulation of radio transmitters over long lengths of wire.
(d) On-off control of the radio set power supply.
(e) Remote selection of any one of several predetemined radio carrier frequencies.
688. RADIO SYSTEMS WITH REMOTE CONTROL EQUIPMENT.
a. The most common radio systems in which remote control equipments offer advantages are single-frequency radio nets which operate on a push-to-talk basis. Each of these nets contains at least two radio sets but may contain as many as a dozen or more. The principal reasons for push-to-talk control in such a net are:
(I) To reduce power consumption in the radio transmitters during idle periods, particularly with battery-operated sets.
(2) To permit the use of only one frequency per net and thus minimize the number of different radio frequencies required, particularly in areas with large numbers of different nets.
(
RM-I2-C ) TL 53414
Figure 6-164. Remote Control Equipment RC-47-( ).
It can be used with various other radio sets listed in figure 6-162. The principal components of this equipment are Control Unit RM-53
Figure 6-165. Remote Control Equipment RC-261.
which is located at the transmitter and Remote Control Unit RM-52 which is located at a remote point. These units are interconnected by a single pair of field wire which can have a length up to about 2 miles if Wire W-110-B is used. Dry batteries are employed for microphone battery supply and push-to-talk control.
e. Remote Control Unit RM-39-( ). This equipment (TM 11-2667) which is part of Remote Control Equipment RC-289 is shown in figure 6-166. It provides push-to-talk control or c-w telegraph operation over a 2-wire line from a remote telephone to a radio set in combination with intercommunicating and ringing features like those of Remote Control Unit RM-29-( ) (subpar, f below). Dry bat-
350
CHAPTER 6. RADIO SYSTEMS
PARS.
691-692
TL 53416
Figure 6-166. Remote Control Unit RM-39-f ), part of Remote Control Equipment RC-289.
teries are used for the operation of this equipment. The remote telephone is equipped with a telegraph key which is used for push-to-talk control or c-w telegraph operation (par. 689b(4)).
f. Remote Control Unit RM-29-( ). This equipment (TM 11-308) which is part of Remote Control Equipment RC-290 is shown in figure 6-167. This unit is located at the radio set and a Telephone EE-8-( ) is located at a remote point. Only local push-to-talk control
Figure 6-167. Remote Control Unit RM-29 -A, part of Remote Control Equipment RC-290.
at the radio set is possible with this unit (par. 689a). It includes facilities for intercommunicating and ringing over a 2-wire line between the telephone at the remote point and an attendant at the control unit.
g. Operations Center AN/TTQ-1. The uses of the radio channel control circuits of the Operations Center AN/TTQ-1 on connections to a variety of different types or radio sets are described in a Supplement to TM 11-438 dated 3 October 1944.
692. IMPROVISED REMOTE CONTROL ARRANGEMENTS.
a. Improvised remote control arrangements can sometimes be assembled for use where regular remote control equipment is not available. Some radio sets can be remotely controlled merely by extending the circuits from the microphone and head phone jacks over field wires to handset or head and chest set at the remote point. For such an extension, special adapters assembled from spare cords, plugs, jacks, binding posts, etc., may be desirable as shown in figure 6-168-A. The operations over such simple remote control facilities will not be satisfactory unless the push-to-talk control range of the radio set (par. 689b (3)) will accommodate the resistance in the field wire, and the audio transmission conditions discussed in paragraph 690 are satisfactory. The transmission loss with these facilities is derived from the sum of the three following losses:
(7) Attenuation loss in the field wire.
(2) Loss in microphone output caused by the reduction in battery supply current through the microphone.
(3) Reflection losses at each end of the field wire.
b. If the d-c push-to-talk control range is exceeded by the simple arrangements described in subparagraph a above, using the required length of Wire W-110-B, one or more of the following steps may be considered to provide satisfactory push-to-talk operation.
(1) Reduce the resistance in the push-to-talk control circuit by connecting two or more pairs of Wire W-110-B in multiple or by providing wire of larger gauge such as Wire W-143. If the control wires are also to be used for voice transmission from the remote point, connect the extra wires as described in subparagraph c(l) below.
351
HAND
GENERATOR—
TL 53420
p—HAND GENERATOR
TRANSMITTER MICROPHONE JACK BINDING BINDING INPUT I
JK-33-A POSTS FIELD WIRE POSTS PLUG TRANSMITTER
f. '_____________________________________ 6 PL-68
------------------f_____________________________ I ------------------------------------O ---------------------------------------------------------------------------------------y--------------------------------------------------------------------------------------—-_( _______________111 Id » ■> O._o_T-MICROPHONE PHONE Q a-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|_iRECEIVER _
1. CAPACITOR RECEIVER
T ABOUT 2M.F o------pi JK-34-A------------------------------------------------------------0----O-—a—(L 55 „
jack 5 *io -----------Q
ADAPTER5 AT --- IMPROVISED PJACK
REMOTE POINT ApX0TESETT -------------
FOUR-WIRE CONTROL WITHOUT RELAYb,h’J radio set^
TRANSMITTER MICROPHONE JACK »- BINDING INPUT
JK-33-A POSTS FIELD WIRE POSTS PLUG
fi -----------o—-------------—4------------ ----------S_____^L-68
M'C H A-^>--------5:____________________________________/ ■<’
JACK ---------------------------------rV----°—r
PHONE f]JK’34’A I 4 k=rrr > RECEIVER
PHONE H a---„-------o P{C | OUTPUT
JL capacitor F^'1' if plug
I------------ J ABOUT 2 ME_______ 8 LI 9 Plu_“5
IM PROVISE D ? 1----------------------------9-----°—‘—o
ADAPTER AT 3 ________________£________।---
remote point ---'--- y IMPROVISED ADAPTER WITH
FOUR-WIRE CONTROL WITH RELAY*1’3 RELAY AT RADI° SET B TRANSMITTER MICROPHONE BINDING INPUT
BINDING POSTS PLUG
JACK POSTS ____________A_____ PL-6B
JK-33-A j ------------<5----°—I
Mjc ^v- ° __________FIELD WIRE_______—---------- _p____________
JK-34-A 1 CAPACITOR --»F)__1,1^_ I
PHONE ll^ $ ABOUT 2M E ______PLUG
I............ p3 E~7 g___________RL~55
IMPROVISED ~ 10
ADAPTER AT „ . „ . _ 1T[—|-Q— 1--°—
REMOTE POINT ABOUT 2MF (IMPROVISED ADAPTER WITH
-----—--------------------------, abuui dwr-----1 RELAY AT RADIO SET
TWO-WIRE CONTROL WITH RELAYh,k C
transmitter MICROPHONE BINDING INPUT
,.ru POSTS PLUG
JK-33-A BINDING ------------O-----68
MIC f| V—°2^FIELD WIRE-r— —| °
— CAPACITOR JACK =FAB0UT 2M.F __f Fl i.i e RECEIVER
JK-34-A OUTPUT
PHONE [1 a „___________1LINE ------PLUG
| SWBD I—
IMPROVISED ADAPTER TELEG q> c ABOUT 2M F I IMPROVISED ADAPTER WITH
WITH IMPE^IA^ICE^^ATO-IING § 6SWBD ---ABOUT 2ME-------1 RELAY AT RADIO SET
COIL AT REMOTE POINT । inf^ T REPEATING COIL C-lfelf
TWO-WIRE CONTROL WITH RELAY AND IMPEDANCE MATCHING COILh,k TALKING BATTERY SUPPLIED FROM RADIO SET END D
^PROVIDE BATTERY IF NEEDED TO INCREASE CURRENT TO RE- e THE VOLTAGE OF THE BATTERY REQUIRED SHOULD BE AP-MOTE MICROPHONE AND INCREASE OPERATING RANGE OF PROXIMATELY 0.06 TIMES THE SUM OF THE RESISTANCE OF S0 THAT THE ftELAY WINDING, PLUS THE LOOP RESISTANCE OF IT WILL NOT OPPOSE THE BATTERY IN THE RADIO SET. a PAIR OF FIELD WIRE ,PLUS 100 OHMS.
kTHIS ARRANGEMENT SHOULD NOT BE USED IF THE POWER f REPEATING COIL C-I6I SHOULD BE CONNECTED SERIES 5J'i’ctLYcI2-IM C°yTR0L RELAY IN THE RADIO SET IS AIDING BY STRAPPING THE TWO BINDING POSTS ADJA-
NOISY. SEE PAR. 692 CENT TO ONE OF THE LONG SIDES OF THE BASE.
CTHIS RELAY SHOULD BE OF A TYPE WHICH OPERATES ON LESS THAN 0 5 AMPERE AND LESS THAN 50 VOLTS AND HAS A RESISTANCE OF LESS THAN 500 OHMS. dTHE RESISTANCE OF THE RELAY WINDING IN C OR D SHOULD BE MORE THAN 200 OHMS AND IN F MORE THAN 500 OHMS IN ORDER THAT THE TRANSMISSION LOSS CAUSED BY IT WILL NOT BE EXCESSIVE. DO NOT USE RELAY WITH NON-
“DUCTIVE SHUNT. TL 54987
Figure 6-168. Improvised 352
352
transmitter mumur MICROPHONE JACK INPUT
JK-33-A BINDING REPEATING COIL POSTS PLUG
। v--o POSTS C-I6I g______ PL-b6
M'C A -----------i---|,|,---oLINE FIELD WIRE — j-. 0—°
4 5 VOLT d x5WBD_____________________________________________ § n
BATTERY 3 7TELEGRAPH KEY °
0X 0-WBD o
EE-8-( ) LI LINE " 8
SWBD^ 7\
S £__1tELEG 0-------- | RECEIVER
£d<_ —Illi OUTPUT
WITH L2 SWSI/ I [0J g PLUG
HANDSET ------------------------'X O------------0--T 9 PL-55
SCREW SWITCH LINE *------°--------0—I n
SHOULD BE TURNED T Tri rroAPH kfyTI ।---------------1 -
WAY BETWEEN I J-47 ---------------------1|--------XT IMPROVISED ADAPTER
CLOCKWISE STOP----1 L0 ---------------------^7.-------1 WITH REL AY AND COIL
ANO COUNTER- X------? riOArmo AT R^DI° SET
CLOCKWISE STOP I aS^FT
IN ORDER TO 1 LB ABOUT 2M.E
REMOVE THE D-C (§) t BAT-
BRIDGES CB y o---------1
TELEPHONE EE~8-( )
AT REMOTE POINT C
TWO-WIRE CONTROL WITH RELAY, COIL.AND TELEPHONE EE-8-( )h> r TALKING BATTERY SUPPLIED LOCALLY
MICROPHONE SWITCH
T~17 _ (push-to-talk) r00r transmitter cord miC
I 0 4 g CORD MIC <0 n CD-494 PLUG
-J. 5°-76-A PLUG SWITCH W -----------A'r^N ° f) Wnr£E°~nL~t8
□ ) =p I 7 WHITE PL-68 -p--O---1 l—o—-----_____o______RED „—_ZZZ°
| /_______________RED ° । o S? ? (J BLACK,,—|-
10____________________BLACKO |- 0—j,— PHONE
CcaA<\'JPr Xx ~— ---------plug
1 1 ___________________WHITE . WHITE^ PL-55
HS-30-( I "I £ rnRn PHONE BLACK 0 [) BLACK0ZT0
256 OHMS \Z G?RD4 PLUG °---U------
■CP LU 0/4 pL-55
p ■ q o—L_o HANDSET H-22/U AND HANDSET H-23/UJ,nj_|
MICROPHONE AND HEADSET G
RECEIVER ,o..,c..,TT1-o RECEIVER
r-CH 7RAN0'TTER CORD MIC [-On TRANSMITTER^^ MIC
OHMS SWITCH H zCD’494 PLUG ohm’s SWITCH W CtT-494 PLUG
0 5 ----■> 1 ,/ GREEN nWHITE ^PL-68 OHMS [~[ . / GREEN - WHITE. PL~68
e—? TH-----------....reP.O1—<> 0-4 L0Z RED o RED Q—O
0 1 Hblaci< I- 0 [ I) BLACK0=~
a 4^ »—I
PHONE PHONE
PLUG PLUG
_____________WHITE WHITE^ PL-55__________________________________WHITE WHITE. PL-55 _____________________________________________________________________________________ Z. BLACK BLACl{ 0° ~ ° . BLACK 0 Q BLACK jzzO
HANDSET TS-I3-C )J J HANDSET TS-l5-( )J K
a5Y SH°ULD BE ONLY SUFFI- HANDSET H-22/U (RECEIVER IMPEDANCE-3500 OHMS)
CIENT TO OPERATE THE RELAY. MODIFICATION OF TS-I3-O.
b WHERE APPARATUS SHOWN IS NOT AVAILABLE USE EQUIV- HANDSET H-23/U (RECEIVER IMPEDANCE -256 OHMS)
ALENT APPARATUS. MODIFICATION OF TS-I5-A AND TS-I5-C.
: SEE MWO SIG-24 AND MWO SIG-25.
J MODIFY HANDSETS J AND K IN ACCORDANCE WITH H WHEN REQUIRED TO OPERATE WITH B. SAME MODIFICA- "IF THIS KEY IS NOT PROVIDED, PUSH-TO-TALK CONTROL TION IS REQUIRED WITH A EXCEPT WHERE A OPERATES CAN BE ACCOMPLISHED BY PUSHING IN ON THE CRANK
WITH RADIO SETS WHICH OPERATE NORMALLY WITH OF THE HAND GENERATOR IN THE TELEPHONE. THIS
HANDSETS J AND K. HANDSET TS-I5-B CANNOT BE ADDS ABOUT 400 OHMS TO THE SIGNALING CIRCUIT,
MODIFIED. AND MAY REQUIRE ADDITIONAL VOLTAGE AT g.
kWHEN INTERFERENCE FROM OTHER LINES (POWER OR COMMUNICATION) IS EXPECTED, USE F. THIS ARRANGEMENT CAN ALSO BE OPERATED WITH THE IMPROVISED ADAPTER SHOWN AT THE REMOTE POINT IN C,D, AND E, INSTEAD OF THE TELEPHONE EE-B'OSHOWN IN F. IF THIS IS DONE APPLY NOTE e TO THE BATTERY IN F, INSTEAD OF NOTE g, WHEN OPERATING WITH C OR D- TL 54988
arrangements for remote control of radio sets.
353
PARS.
692-693 ___ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
(2) Connect a battery in series with the push-to-talk control circuit to increase the current as shown optional in figure 6-168-A.
(3) Provide a more sensitive electromagnetic relay at the radio set as shown in figures 6-168-B and -C.
c. If adequate modulating volume at the radio transmitter is not obtained with the simple arrangement described in subparagraph a above, consider one or more of the following steps:
(1) Reduce the transmission loss in the voice circuit to the transmitter by providing wire of lower loss per mile, such as Wire W-143, or by providing two pairs of field wire instead of only one pair, short the wires of each pair at the ends and space the pairs about 8 inches apart on insulators, as described for open wire lines with twin pairs in chapter 5. Such a voice circuit with Wire W-110-B will have a loss of about 0.5 db per mile which is about 1/5 that of a single pair. If it is not practical to place the wires on insulators, keep them off the ground by tying them to trees, because the loss with two pairs on the ground in wet conditions would probably be no less than that of a single pair. If tied to trees, the pairs should retain a separation of 8 inches or more, and should not be in frequent contact with wet foliage.
(2) Increase the battery supply current through the microphone by one of the following procedures: connect a battery in series with the microphone as shown in figure 6-168-A; increase the potential of the battery shown in figures 6-168-C and 6-168-D; or provide the local talking battery arrangement shown in figure 6-168-E or figure 6-168-F.
(3) Reduce the reflection loss between the microphone and the field wire (par. 690f) by matching impedances through a repeating coil. A circuit for this purpose with an external battery at the radio set end is shown in
figure 6-168-D. A local battery circuit is shown in figure 6-168-E. The Telephone EE-8-( ) connected as shown in figure 6-168-F can also be used.
d. Figures 6-168-A and 6-168-B cover 4-wire remote control arrangements. The arrangement in figure 6-168-A is merely an extension circuit which can provide additional battery for the microphone and the operation of the control relay in the radio set if required. With this 4-wire control arrangement, noise from the signaling power supply will be introduced in the microphone circuit because of the resistance of the wire which is common to the push-to-talk, microphone, and receiver circuits. The amount of noise introduced .in the radio transmitter will depend upon the noise in the signaling power supply and the resistance of the common wire. The arrangement in figure 6-168-B is an extension circuit with a sensitive relay, and is mainly used with radio sets which have control relays which operate on high current or which control the radio transmitter and receiver by means of the vacuum tube filament circuit. It does not, however, provide for increasing the current through the microphone. The noise difficulties mentioned above are not experienced with this arrangement.
e. Noise or crosstalk may be encountered in the use of figures 6-168-A to 6-168-E inclusive, if the wire line is close to a power line or another communication circuit. This is because one side of the wire line is grounded at the radio set. Figure 6-168-F greatly reduces the noise and crosstalk by using a coil at the radio set end which insulates the grounded radio set from the wire line. Other nongrounded arrangements can be improvised by using the improvised adapter at the radio set end in figure 6-168-F, with the improvised adapter at the remote point in figures 6-168-C to 6-168-E inclusive.
Section VIII. RADIO SET TECHNICAL AND DESCRIPTIVE INFORMATION
693. RADIO SETS.
a. General. Figures 6-169 to 6-175, inclusive, list a number of U. S. Army, U. S. Navy, and British radio sets with pertinent data on electrical characteristics. Pictures of some of these radio sets are shown in sections II and
IV. For more complete information on tactical sets for ground use, and on fixed plant radio equipment, reference should be made to TM 11-487 or to technical manuals indicated for the specific sets. (The text of this paragraph is continued on page 379.)
354
Type F requency range (me) Rated xmtr output (watts) Type emission Type mod Frequency control Remarks
SCR-177-A xmtr, 0.4 to 0.8 & 1.5 to 4.5 revr, 0.4 to 1.0 & 1.5 to 4.5 75 cw am mo Limited Standard; ground, transportable; for tactical field units; crowfoot antenna (0.4 to 0.8 me) and X-wave inverted L antenna with counterpoise (1.5 to 4.5 me). Replaced by SCR-177-B.
tone
voice
SCR-177-B xmtr, 0.4 to 0.8 & 1.5 to 4.5 revrs, 0.15 to 1.5 & 1.5 to 18.0 75 cw am mo Ground, transportable; for tactical field units and ground-to-air communication; two receivers. Crowfoot antenna (0.4 to 0.8 me) and X-wave inverted L antenna with counterpoise (1.5 to 4.5 me). Transported by vehicle or cargo aircraft. TM 11-232.
tone
voice
SCR-188 xmtr, 1.5 to 12.5 revr, 0.4 to 13.0 75 cw am mo Limited Standard; ground, transportable; for ground-to-ground or ground-to-air communication. X- or X-wave inverted L antenna with counterpoise. TM 11-233. Replaced by SCR-188-A.
tone
voice
SCR-188-A xmtr, 1.5 to 12.5 revr, 1.5 to 18.0 75 cw am mo Ground, transportable; for semifixed use; arranged for remote control; X- or X-wave inverted L antenna with counterpoise. Transported by vehicle or cargo plane. TM-11-233.
tone
voice
SCR-193-( ) xmtr, 1.5 to 6.2 revr, 1.5 to 18.0 75 cw am , mb Vehicular; for communication between stationary or moving vehicles equipped with 50-amp. generator and 12-volt 180 amp. hr. battery. 15-ft. whip. TM 11-273.
tone
voice
SCR-197 xmtr, 1.5 to 18.0 3 revrs, 1.5 to 18.0 1 revr, 0.54 to 44.0 400 cw am mo or xtal Limited Standard; ground, mobile; high power radio station installed in truck and trailer for operation from stationary position. 45-ft. vertical antenna for transmitting and 15-ft. whip for receiving. TM 11-241. Replaced by SCR-399.
100 tone
100 voice
SCR-203 xmtr, 2.2 to 3.06 revr, 2.1 to 3.1 7.5 cw am mo Limited Standard; pack; mounts on Phillips pack saddle for animal pack transportation and operation. 25-ft. whip. TM 11-239. Replaced by SCR-245.
tone
voice
SCR-209 xmtr, 2.2 to 2.6 revr, 1.5 to 18.0 8.5 cw am mo Limited Standard; vehicular; used in combat and scout cars. 15-ft. whip. Replaced by SCR-508 and SCR-528.
7.5 tone
7.5 voice
SCR-210 revr, 1.5 to 18.0 — cw am Manual tuning Limited Standard; vehicular; receiver only of SCR-245, 15-ft. whip. TM 11-272. Replaced by SCR-538.
tone
voice
Figure 6-169. Tactical radio sets for ground use (continued on following page).
355
Type Frequency range (me) Rated xmtr output “ (waWs) Type emission Type mod Frequency control Remarks
SCR-245 xmtr, 2.0 to 5.25 revr, 1.5 to 18.0 10 cw am mo or xtal Limited Standard; vehicular; for communicating between stationary or moving vehicles. 15-ft. whip. TM 11-272. Replaced in Armored Force by SCR-508 and SCR-528. Radio Sets SCR-245-A, -B, -C, -E, -F, -H, -K, -L, -M, -MX, -N, and -NX are obsolete.
tone
voice
SCR-284-A 3.8 to 5.8 20/6.5 cw am mo (xtal cal.) Limited Standard; ground, transportable; vehicular or pack; arranged for remote control. 25-ft. whip with counterpoise for field operation or 15-ft. whip for vehicular operation. TM 11-275. Replaced by SCR-694.
8/2 voice
SCR-288-A xmtr, 3.5 to 6.3 revr, 2.3 to 6.5 4 cw am mo Limited Standard; ground; transportable or pack; temporary replacement for SCR-131, SCR-161, and SCR-171. 35-ft. horizontal end-fed wire and counterpoise. TM 11-250. Replaced by SCR-284-A.
voice
SCR-293 20.0 to 27.9 25 or 0.5 voice fm xtal Limited Standard; vehicular; installed in tanks and scout cars. High or low power by switch control. 9-ft. whip. Replaced by SCR-508 and SCR-528.
SCR-294 revr, 20.0 to 27.9 — voice fm xtal Limited Standard; vehicular; receiver only of SCR-293. 9-ft. whip. Replaced by SCR-538.
SCR-298-C 30 to 40 35 voice fm xtal Vehicular; commercial police set, used by umpire personnel. 6-ft. whip.
SCR-299 xmtr, 2.0 to 8.0 (299-F 2.0 to 12.0) 2 revrs, 1.5 to 18.0 400 cw am mo or xtal Limited Standard; ground, mobile; high power radio station for operation from stationary or moving position. Frequency Conversion Kit MC-509 gives transmitter coverage down to 1 me. MC-516 gives coverage to 12 me; MC-517 to 18 me. 15-ft. whip or half-wave doublet antenna. TM 11-280. Replaced by SCR-399.
300 voice
SCR-300 40 to 48 0.5 voice fm mo (xtal. cal.) Pack; walkie-talkie for back-pack or on-ground operation for short range communication. Half-wave whip or 3-ft. end-loaded whip. TM 11-242.
SCR-399 xmtr, 2.0 to 18.0 2 revrs, 1.5 to 18.0 400 cw am mo or xtal Ground, mobile; high power radio station installed in Shelter HO-17 which may be mounted on a 2X ton 6x6 truck; for operation from stationary or moving position. Frequency Conversion Kit MC-509 gives transmitter coverage down to 1 me. (Conversion Kit MC-543 is available for use with Radio Transmitter BC-610 to provide high-power, high-speed telegraph operation. Kit includes a 2 kw. power amplifier, with power supply, for use in frequency range of 1.0 to 18.0 me.) 15-ft. whip or half-wave doublet antenna. TM 11-281.
300 voice
SCR-499 xmtr, 2.0 to 18.0 2 revrs, 1.5 to 18.0 400 cw am mo or xtal Air transportable; high power radio station similar to SCR-399 except arranged for transportation by air. Frequency Conversion Kit MC-509 gives transmitter coverage down to 1 me. 15-ft. whip or half-wave doublet antenna. TM 11-281.
300 voice
a When two values of power are shown separated by a slant bar (/), the higher value in general applies to ground, transportable, and vehicular operation; the lower value to pack operation.
Figure 6-169. Tactical radio sets for around use (continued on onnosite oase).
356
JL
Type Frequency range (me) Rated xmtr output (watts) Type emission Type mod Frequency control Remarks
SCR-506 xmtr, 2.0 to 4.5 revr, 2.0 to 6.0 80 cw am mo (xtal cal.) Vehicular; installed in tanks, amphibian cars and personnel carriers for communication to airplanes or base stations. Five preset channels. 15-ft. whip. TM 11-630.
20 voice
SCR-508 * 20.0 to 27.9 30 voice fm xtal Vehicular; installed in tanks, armored cars, scout cars, and trucks. Two receivers; interphone amplifier; ten preset channels; 9-ft. whip. TM 11-600.
SCR-509 20.0 to 27.9 1.8 voice fm xtal Pack; operates on dry batteries from stationary position, two preset channels. 8-ft. whip. TM 11-605.
SCR-510 20.0 to 27.9 1.8 voice fm xtal Pack and vehicular; same as SCR-509 with vibrator plate supply and components for vehicular use. 6- or 8-ft. whip. TM 11-605.
SCR-511 2.0 to 6.0 0.75 voice am xtal Pack and vehicular; installed in vehicle or carried as guidon by man on horseback or as one-man load. 11-ft. whip. TM 11-245.
SCR-528 20.0 to 27.9 30 voice fm xtal Vehicular; same as SCR-508 less one receiver. 9-ft whip. TM 11-600.
SCR-536 3.5 to 6.0 0.02 voice am xtal Pack; light-weight, self-contained very short range Handie-talkie. 3-ft. whip. TM 11-235.
SCR-538 revr, 20.0 to 27.9 — voice fm xtal Vehicular; receiver only of SCR-528 plus interphone amplifier. Ten preset channels. 9-ft. whip. TM 11-600.
SCR-543 1.68 to 4.45 45 voice am xtal Ground, transportable and vehicular. Six preset channels. 15-ft. whip. TM 11-625. SCR-543-A, -B, and -C (voice only) are Limited Standard.
cw
SCR-578 xmtr, 0.5 only 5 tone am mo Substitute Standard; air transportable; hand powered sea rescue transmitter. May be dropped from aircraft. 300-ft. sloping wire antenna. See AAF Technical Order AN 08-10-94.
SCR-593 revr, 2.0 to 6.0 — voice am mo Pack and vehicular; receiver only; for alert or warning messages. Four preset channels. 7-ft. whip. TM 11-859.
SCR-608 27.0 to 38.9 30 voice fm xtal Vehicular; has two receivers; similar to SCR-508 except frequency; used in armored cars, half-tracks and trucks. Ten preset channels. 9-ft. whip. TM 11-620.
SCR-609 27.0 to 38.9 2 voice fm xtal Substitute Standard; pack; dry battery set similar to SCR-509 except frequency. Two preset channels. 13-ft. whip. TM 11-615.
SCR-610 27.0 to 38.9 2 voice fm xtal Substitute Standard; pack and vehicular; same as SCR-609 plus vibrator plate supply and components for vehicular use. 9 or 13-ft. whip. TM 11-615.
Figure 6-169. Tactical radio sets for ground use (continued on following page).
357
Type Frequency range (me) Rated xmtr outputa (watts) Type emission Type mod Frequency control Remarks
SCR-619 27.0 to 38.9 1.5 voice fm xtal Pack and vehicular; light weight, similar in function to SCR-609 and SCR-610. Two preset channels. 4X, 9- or 12-ft. whip. TM 11-619.
SCR-624 100 to 156 8 voice am xtal Air transportable; similar to SCR-522 and SCR-542 air-borne sets except arranged for ground use. Four preset channels. Vertical half-wave J antenna on 50-ft. mast. See AAF Technical Order AN 08-10-185.
SCR-628 27.0 to 38.9 30 voice fm xtal Vehicular; same as SCR-608 less one receiver. Ten preset channels. 9-ft. whip. TM 11-620.
SCR-694-AW 3.8 to 6.0 25/15 cw am mo or xtal Pack; ground, transportable and vehicular. Limited production. 15-ft. whip or half-wave sloping wire antenna. Lower values of power than those indicated may be obtained by switch control.
7/5 voice
SCR-694-C 3.8 to 6.5 20/10 cw am mo or xtal Pack; ground, transportable and vehicular. Used by parachute, airborne, and mountain troops and in amphibious operations. Repla ement for SCR-284-A. 15-ft. whip and counterpoise or half-wave sloping wire antenna. Lower values of power than those indicated may be obtained by switch control. TM 11-230C.
7/5 tone
7/5 voice
SCR-808 27.0 to 38.9 35 or 2 voice fm mo (xtal cal.) Vehicular; has two receivers; equipped with interphone amplifier. Four preset channels. High or low power by switch control. 6- or 9-ft. whip. TM 11-601.
SCR-828 27.0 to 38.9 35 or 2 voice fm mo (.xtal cal.) Vehicular; same as SCR-808 less one receiver. Four preset channels. High or low power by switch control. 6- or 9-ft. whip. TM 11-601.
AN/CRC-3 30 to 40 50 voice fm xtal Limited Standard; air transportable; commercial police set modified for air warning service. Transmitter employs a frequency multiplication of 32 times crystal frequency. (AN/CRC-3A is similar except employs an 8 times frequency multiplication). Vertical half-rhombic or coaxial half-wave dipole on 50-ft. mast.
AN/MRC-1 xmtr, (incl. ampl.) 2.0 to 13.0 2,000 cw am mo or xtal Ground, mobile; provides facilities for high power, high-speed automatic c-w transmission and reception employing Boehme equipment in addition to the normal functions of Radio Set SCR-399. The radio transmitter power amplifier and one radio receiver are housed in the transmitting Shelter HO-17, with three radio receivers and the Boehme equipment housed in the operating Shelter HO-17 or HO-27. Requires three 2J4-ton, 6x6, cargo trucks for transportation. 15-ft. whip or half-wave doublet antenna. TM 11-602 and TM 11-281. Also see Chapter 3.
xmtr, (less ampl.) 2.0 to 18.0 400 cw
300 voice
revrs, 1.5 to 18.0
“ When two values of power are shown separated by a slant bar (/), the higher value in general applies to ground, transportable, and vehicular operation; the lower value to pack operation.
Figure 6-169. Tactical radio sets for ground use (continued on opposite page).
358
Type Frequency range (me) Rated xmtr output» (watts) Type emission Type mod Frequency control Remarks
AN/MRC-2 xmtr, 2.0 to 18.0 revrs, 1.5 to 18.0 2,000 (incl. ampl.) cw & special am mo or xtal Ground, mobile; under development; to provide a high-power, single-channel radio-teletype system using carrier-shift keying and dual space-diversity reception in addition to the normal facilities of Radio Set SCR-399. Equipment to be housed in three Shelters HO-17 or HO-27. Frequency range of 2 kw power amplifier is 1.0 to 18.0 me. Frequency Conversion Kit MC-509 gives transmitter coverage down to 1.0 me. Half-wave doublet antenna. Also see chapter 3.
400 (less (ampl.) cw
300 (less ampl.) voice
AN/TRA-1 70 to 100 250 — — — Ground, transportable; amplifier equipment for use with AN/TRC-1, -3 or -4. Three element directional array on 40-ft. mast. TM 11-2601.
AN/TRC-1 70 to 100 50 or 10 voice fm xtal Ground, transportable; for single channel, or multichannel operation with spiral-four carrier terminal equipment. High or low power by switch control. Three element directional array on 40-ft. mast. TM 11-2601.
AN/TRC-2 2.0 to 3.4 and 3.8 to 6.5 20/10 cw am mo or xtal Ground, transportable and pack; two receiver-transmitters for use by isolated units. Quarter-wave inverted L antenna with counterpoise or half-wave antenna without counterpoise. Lower values of power than those indicated may be obtained by switch control. TM 11-2603.
7/5 tone
7/5 voice
AN/TRC-3 70 to 100 50 or 10 voice fm xtal Ground, transportable; radio terminal set similar to AN/TRC-1 except has sufficient equipment to insure continuous service. High or low power by switch control. Three element directional array on 40-ft. mast. TM 11-2601.
AN/TRC-4 70 to 100 50 or 10 voice fm xtal Ground, transportable; radio relay set similar to AN /TRC-1 except has sufficient equipment to insure continuous service as a repeater station. High or low power by switch control. Three element directional array on 40-ft. mast. TM 11-2601.
AN/TRC-7 100 to 156 0.5 voice am xtal Pack and ground, transportable; light-weight v-h-f communication set, transportable by a 4-man team. Two preset channels. Quarter-wave whip, or vertical broad-band antenna on 30-ft. mast. TM 11-617.
AN/TRC-8 230 to 250 12 voice fm mo (temp, compensated) Ground, transportable; for single channel, or multichannel operation with spiral-four carrier terminal equipment. Half-wave dipole and 90° corner reflector on 40-ft. mast. TM 11-618.
AN/TRC-11 230 to 250 12 voice fm mo (temp. compensated) Ground, transportable; radio terminal set similar to AN/TRC-8 except has sufficient equipment to insure continuous service. Half-wave dipole and 90° corner reflector on 40-ft. mast. TM 11-618.
8 When two values of power are shown separated by a slant bar (/), the higher value in general applies to ground, transportable, and vehicular operation; the lower value to pack operation.
Figure 6-169. Tactical radio sets for ground use (continued on following page).
359
Type Frequency range (me) Rated xmtr output (watts) Type emission Type mod Frequency control Remarks
AN/TRC-12 230 to 250 12 voice fm mo (temp. compensated) Ground, transportable; radio relay set similar to AN/TRC-8 except has sufficient equipment to insure continuous service as a repeater station. Half-wave dipole and 90° corner reflector on 40-ft. mast. TM 11-618.
AN/VRC-1 h-f units xmtr, 3.0 to 6.2 revr, 1.5 to 18.0 75 cw am mo Ground, mobile; combines SCR-542 airborne set, with SCR-193; mounted in a y~ton 4x4 truck; for ground-to-air and ground-to-ground h-f and v-h-f communication. V-h-f set has four preset channels. 15-ft. whip as h-f antenna. 3-ft. whip as v-h-f antenna. TM 11-277.
tone
voice
v-h-f units 100 to 156 6 voice am xtal
AN/VRC-3 40 to 48 0.5 voice fm mo (xtal cal.) Substitute Standard; vehicular; similar to SCR-300 except arranged for installation in light and medium tanks. 3- or 6-ft. whip. TM 11-637.
AN/VRC-5 20.0 to 27.9 30 voice fm xtal Vehicular; same as SCR-528 except for mounting arrangement. Transmitter and receiver are in separate mountings. For use in twin 40 mm. gun carriage. Ten preset channels.
RC-256 revr, 100 to 156 — cw am manual tuning (xtal cal.) Ground, transportable; receiving equipment RC-256 and transmitting equipment RC-257 are used together as a single channel radio link terminal station in conjunction with other v-h-f equipment. A waterproof shelter is required to house the combined equipment. Balanced vertical half-wave dipole on 90-ft. mast. See AAF Technical Order AN 08-10-227.
tone
voice
RC-257 xmtr, 100 to 156 50 tone am xtal
voice
Figure 6-169. Tactical radio sets for ground use (continued).
Type* Frequency range (me) Rated xmtr output (watts) Type emission Frequency control Preset channels Power source Remarks
SCR-183 xmfr, 2.5 to 7.7 revr, 0.2 to 0.4 & 2.5 to 7.7 3.5 cw mo none 14v, de Limited Standard; command set for 2-way plane-to-plane and plane-to-ground communication. Receiver is not arranged for c-w reception. Same as SCR-283 except for operating voltage. TM 11-200.
tone
voice
SCR-187 xmtr, 0.4 to 12.5 revr, 1.5 to 18.0 75 cw mo none 14v, de Limited Standard; liaison set for 2-way plane-to-plane and plane-to-grourid communication. Same as SCR-287 except for operating voltage and transmitter tuning units supplied.
tone
voice
8 All sets are amplitude modulated.
Figure 6-170. Airborne radio equipment (continued on opposite page).
360
Type* Frequency range (me) Rated xmtr output (watts) Type emission Frequency control Preset channels Power source Remarks
SCR-274-N xmtrs, 3.0 to 9.1 revrs, 0.19 to 0.55 & 3.0 to 9.1 36 cw ino (xtal cal.) 1 (per xmtr.) 28v, de Command set for 2-way plane-to-plane and plane-to-control tower communication. Frequency range shown is covered by four transmitters and three receivers, not necessarily all used in one installation.
12 tone
voice
SCR-283 xmtr, 2.5 to 7.7 revr, 0.2 to 0.4 & 2.5 to 7.7 3.5 cw mo none 28v, de Limited Standard; command set for 2-way plane-to-plane and plane-to-ground communication. Receiver is not arranged for c-w reception. Same as SCR-183 except for operating voltage. TM 11-200.
tone
voice
SCR-287 xmtr, 0.35 to 0.65 & 1.5 to 12.5 revr, 0.2 to 0.5 & 1.5 to 18.0 75 cw mo none 28v, de Limited Standard; liaison set for 2-way plane-to-plane and plane-to-ground communication. Same as SCR-187 except for operating voltage and transmitter tuning units supplied.
tone
voice
SCR-522 100 to 156 6 voice xtal 4 28v, de For 2-way plane-to-plane and plane-to-ground communication. Same as SCR-542 except for operating voltage. TM 11-509.
SCR-542 100 to 156 6 voice xtal 4 14v, de For 2-way plane-to-plane and plane-to-ground communication. Same as SCR-522 except for operating voltage. TM 11-509.
AN/ARC-3 100 to 156 6 voice xtal 8 28v, de For 2-way plane-to-plane and plane-to-ground communication. Automatic tuning of transmitter and receiver upon insertion of crystal.
AN/ARC-9 (Bendix RTA-1B) 2.5 to 13.0 50 voice xtal 10 28v, de or 14v, de For 2-way plane-to-plane and plane-to-ground communication.
AN/ARR-11 0.2 to 0.5 & 1.-5 to 18.0 . — cw — none 28v, de Receiver only. Manual tuning, six bands. Used with AN/ART-13 as a replacement for SCR-287.
tone
voice
AN/ART-13 0.2 to 1.5 & 2.0 to 18.1 100/50 cw mo (xtal cal.) 11 28v, de Transmitter only. Same as Navy Model ATC. One preset channel is between 0.2 to 1.5 me and ten are between 2.0 to 18.1 me. Half power is automatically obtained upon reaching an elevation of approx. 25,000 feet. Used with AN/ARR-11 as a replacement for SCR-287.
tone
voice
■ All sets are amplitude modulated.
Figure 6-170. Airborne radio equipment (continued).
361
Type • Radio components b Rated xmtr output (watts) Aux power supply 0 Approx total weight d (lbs.) Remarks
SCR-561 none — 1 PE-99 10,500 Control set used as an operations block of Control Net System SCS-2; provides the necessary control equipment for simultaneous operational control of up to four aircraft squadrons, for ground control of interceptor pursuit operations.
SCR-562 6 xmtrs, BC-640 (1 spare) 50 2 K-63 40,000 Mobile transmitting station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2; provides five independent channels. Uses half-wave dipoles on 90-foot steel mast.
SCR-563 6 rcvrs, BC-639 (1 spare) — 1 K-63 27,000 Mobile receiving station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2. Provides five independent channels. Uses half-wave dipoles on 90-foot steel mast.
SCR-564 2 rcvrs, BC-639 (1 spare) — 1 PE-99 25,000 Sector homing D/F station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2. By utilizing a sector transmitter the D/F operator homes the aircraft by the talk down method. Uses Adcock D/F antenna with sensing facilities.
SCR-565 2 rcvrs, BC-639 (1 spare) — 1 PE-99 25,000 Fixed D/F fixer station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2. Two or more of these sets are used for determining azimuth bearing of aircraft equipped with transmitters in the 100-to 156-mc band. Uses Adcock D/F antenna with sensing facilities.
SCR-566 rcvr, (1 ea.) BC-639 BC-624 .1 xmtr, BC-625 — 1 K-63 13,500 Mobile D/F station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2. Used as a homing and D/F Station for planes having 100- to 156-mc. radio equipment. Uses Adcock D/F antenna with sensing facilities.
8
a All radio sets operate with amplitude modulation in the 100- to 156-mc. band.
b The following table gives the characteristics of the component parts of these radio sets.
Component Characteristics of components
Type emission Frequency control Preset channe ls
xmtr, BC-625 voice xtal 4
xmtr, BC-640 voice, tone xtal 1
rcvr, BC-624 voice, tone xtal 4
rcvr, BC-639 cw, tone, voice Manual tuning (xtal cal, with assoc. Frequency Meter BC-638). none
c K-63 is a one-ton cargo trailer containing 1 Power Unit PE-99 which provides up to 7.5 kw. of three plase 120-v., 60-cycle ac. The Power Unit PE-99 has recently been replaced on new equipments by Power Unit PE-197 which provides up to 5 kw. of single phase 120-v., 60-cycle ac.
d Total weight includes vehicles, antennas, masts, and shelters.
Figure 6-171. V-h-f fighter control equipment (continued on opposite page).
362
Type • Radio components b Rated xmtr output (watts) Aux power supply c Approx total weight d (Z&s.) Remarks
SCR-567 2 xmtrs, BC-640 50 1 K-63 17,000 Mobile forward relay station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2. Provides two independent transmitting and receiving channels for extending the range of SCR-562 and SCR-563. Uses halfwave dipoles on 50-foot steel mast.
2 rcvrs, BC-639 — 1 K-63 16,500
SCR-572 none — 1 K-63 20,000 Mobile control set used as an operations block of Control Net System SCS-3. Provides the necessary control equipment for simultaneous operational control of up to two aircraft squadrons, for ground control of interceptor pursuit operations.
SCR-573 2 xmtrs, BC-640 50 1 K-63 15,000 Mobile two channel transmitting station for ground control of interceptor pursuit operations. Part of Control Net System SCS-3. Uses half-wave dipoles on 75-foot plywood mast.
SCR-574 2 rcvrs, BC-639 — 1 K-63 14,500 Mobile two channel receiving station for ground control of interceptor pursuit operations. Part of Control Net System SCS-3. Uses half-wave dipoles on 75-foot plywood mast.
SCR-575 rcvrs, 2 BC-639 (1 spare) 1 BC-624 xmtr, 1 BC-625 — 1 K-63 14,000 Mobile D/F station used either as a fixer or homer station for ground control of interceptor pursuit operations. Part of Control Net System SCS-3. For obtaining bearings on aircraft having 100 to 156 me radio equipment. Uses Adcock D/F antenna with sensing facilities.
—
8
SCR-632 6 xmtrs, BC-640 (1 spare) 50 2 PE-99 22,600 Fixed transmitting station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2. Provides five independent channels. Uses half-wave dipoles on 90-foot steel mast.
SCR-633 6 rcvrs, BC-639 (1 spare) — 1 PE-99 18,300 Fixed receiving station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2. Provides five independent channels. Uses half-wave dipoles on 90-foot steel mast.
“ All radio sets operate with amplitude modulation in the 100- to 156-mc. band.
b The following table gives the characteristics of the component parts of these radio sets.
Component Characteristics of components
Type emission Frequency control Preset channels
xmtr, BC-625 voice xtal 4
xmtr, BC-640 voice, tone xtal 1
revr, BC-624 voice, tone xtal 4
revr, BC-639 cw, tone, voice Manual tuning (xtal cal, with assoc. Frequency Meter BC-638). none
c K-63 is a one-ton cargo trailer containing 1 Power Unit PE-99 which provides up to 7.5 kw. of three plase 120-v., 60-cycle ac. The Power Unit PE-99 has recently been replaced on new equipments by Power Unit PE-197 which provides up to 5 kw. of single phase 120-v., 60-cycle ac.
d Total weight includes vehicles, antennas, masts, and shelters.
Figure 6-171. V-h-f fighter control equipment (continued on following page).
363
Type • Radio components b Rated xmtr output (watts) Aux power supply c Approx total weight d (lbs.) Remarks
SCR-634 1 revr, BC-639 — 1 PE-214 1,035 Air transportable, field operated D/F station used primarily with similar units as a fixer D/F station or, with the addition of Radio Set SCR-624, as a homer D/F station. Uses Adcock D/F antenna with sensing facilities.
SCR-637 2 xmtrs, BC-640 50 1 PE-99 5,830 Fixed forward relay station for ground control of interceptor pursuit operations. Part of Control Net System SCS-2. Provides two independent transmitting and receiving channels for extending the range of SCR-562 and SCR-563. Uses half-wave dipoles on 50-foot steel mast.
2 revrs, BC-639 — 1 PE-99 5,330
SCR-642 none — 1 PE-99 4,000 Fixed control set used as an operations block of Control Net System SCS-3. Provides the necessary control equipment for simultaneous operational control of up to two aircraft squadrons for ground control of interceptor pursuit operations.
SCR-643 2 xmtrs, BC-640 50 1 PE-99 5,800 Fixed two channel transmitting station for ground control of interceptor pursuit operations. Part of Control Net System SCS-3. Uses half-wave dipoles on 90-foot steel mast.
SCR-644 \ 2 revrs, BC-639 — 1 PE-99 5,300 Fixed 2-channel receiving station for ground control of interceptor pursuit operations. Part of Control Net System SCS-3. Uses half-wave dipoles on 90-foot steel mast.
SCR-645 revrs, 2 BC-639 (1 spare) 1 BC-624 xmtr, 1 BC-625 — 1 PE-99 25,000 Fixed D/F station used either as a fixer or homer station for ground control of interceptor pursuit operations. Part of Control Net System SCS-3. For obtaining bearings on aircraft having 100-to 156-mc. radio equipment. Uses Adcock D/F antenna with sensing facilities.
8
AN/CRC-2 revrs, 6 BC-639 1 BC-624 xmtr, 1 BC-625 — 4 PE-214 2,670 Air transportable airdrome fighter control system. s'
8
a All radio sets operate with amplitude modulation in the 100- to 156-mc. band.
b The following table gives the characteristics of the component parts of these radio sets.
Component Characteristics of components
Type emission Frequency control Preset channels
xmtr, BC-625 voice xtal 4
xmtr, BC-640 voice, tone xtal 1
revr, BC-624 voice, tone xtal 4
revr, BC-639 cw, tone, voice Manual tuning (xtal cal, with assoc. Frequency Meter BC-638). none
c K-63 is a one-ton cargo trailer containing 1 Power Unit PE-99 which provides up to 7.5 kw. of three plase 120-v., 60-cycle ac. The Power Unit PE-99 has recently been replaced on new equipments by Power Unit PE-197 which provides up to 5 kw. of single phase 120-v., 60-cycle ac.
d Total weight includes vehicles, antennas, masts, and shelters.
Figure 6-171. V-h-f tighter control equipment (continued).
364
TRANSMITTING EQUIPMENT
Type Frequency range (me) Rated xmtr output (kw) Type emission Frequency control Remarks
BC-339-( ) 4.0 to 26.5 1 Al and Special mo or xtal For telegraph or teletype operation. Switch selection of master oscillator or any one of six crystal frequencies. TM 11-836.
BC-365-( ) 0.15 to 0.55 0.35 Al mo Includes remote control unit; manual frequency change. Also used as exciter for Bunnell 6 kw amplifier. TM 11-828.
BC-447-( ) 2.0 to 8.0 and 4.0 to 13.4 0.3 Al mo or xtal Includes remote control unit. Two preset channels-May be modified for teletype operation using external exciter. TM 11-827.
SCR-281 1.7 to 2.75 0.025 A3 xtal Transmitter and receiver for use, primarily on coastal and harbor vessels. Four preset channels. TM 11-244.
10-KW Transmitting Equipment 4.0 to 26.5 10 Al and Special mo or xtal Includes Power Amplifier BC-340, Transmitter BC-339 (exciter), Rectifier RA-22, Water Cooling Unit RU-2 and expansion tank. TM 11-801.
Bunnell 6 KW (amplifier) 0.15 to 0.55 6 Al — Includes power amplifier, rectifier and antenna tuning house. Used as amplifier for Transmitter BC-365. TM 11-1055.
Press Wireless PW-15-( ) 4.0 to 21.0 15 Al and Special xtal For telegraph or teletype operation. Manual selection, of any one of six crystals. TM 11-821 (when pub-fished).
Press Wireless PW-40-( ) 4.0 to 21.0 40 Al and Special mo or xtal For telegraph or teletype operation. Frequently used as a linear amplifier for single side-band transmitter D-156000. TM 11-835 (when published).
Press Wireless PW-981-( ) 2.5 to 26.0 2.5 Al ahd Special mo or xtal For telegraph or teletype operation. Manual frequency selection of master oscillator, one of five crystals or teletype exciter. TM 11-834.
Western Electric Company D-156000 4.5 to 22.0 2 Special xtal Part of entire terminal for single-sideband radio telephone system which includes receiver D-99945 and v-f carrier telegraph equipment. TM 11-832 (when, published).
Figure 6-172. Equipment commonly used by command radio, Army Communications Service, (continued on following page).
656935 0—45——25
365
RECEIVING EQUIPMENT
Type Frequency range (me) Type output Type emission received Frequency control Remarks
AN/FRR-3A 2.4 to 23.0 dual bal. 600 ohm Special xtal Used as radio-teletype receiving station. Balanced input. Five preset channels. Tuning range may be extended to 26 me if desired. Requires one Radio Teletype Terminal Equipment AN/FGC-1. See chapter 3. TM 11-872A.
BC-779-( ) 0.1 to 0.4 and 2.5 to 20.0 8w. 600 or 8,000 ohm grounded Al, A2 and A3 manual tuning Three of these receivers used with each Schuttig Diversity equipment. Also used as manual receiving station. Balanced input. Similar to Hammarlund super-pro receiver. TM 11-866.
BC-794-( ) 1.25 to 40.0 8w. 600 or 8,000 ohm grounded Al, A2 and A3 manual tuning Same as BC-779 except for frequency coverage. Balanced input. Similar to Hammarlund super-pro receiver. TM 11-866.
Schuttig Diversity (Mixing unit only) — 6m w. bal. 600 ohm Al manual (af only) Used as receiving station for high speed tape circuit. Requires three BC-779 or three BC-794 receivers and power supplies. TM 11-2515.
Western Electric Company D-99945 4.5 to 22.0 60mw bal. 600 ohm Special xtal Single-sideband triple detection receiver. Unbalanced input. Used with transmitter D-156000 and v-f carrier telegraph equipment. TM 11-884 (when published).
Figure 6-172. Equipment commonly used by Command Radio, Army Communications Service ( continued).
TRANSMITTING EQUIPMENT
Type Frequency range (me) Xmtr output (watts) Type emission Frequency control Remarks
BC-315 2.0 to 18.1 400 Al, A2 and A3 xtal Point-to-point and ground-to-air. Dial selection of ten preset channel frequencies. No longer procured.
BC-325-( ) 1.5 to 18.0 400 Al mo or xtal Point-to-point and ground-to-air. Switch selection of master oscillator or any one of five crystal frequencies. No longer procured.
100 A2, A3
BC-339-( ) 4.0 to 26.5 1,000 Al mo or xtal Point-to-point. Switch selection of master oscillator or any one of six crystal frequencies. Also used as exciter for Power Amplifier BC-340. TM 11-836.
BC-340-( ) (amplifier) 4.0 to 26.5 10,000 Al — Point-to-point. Provides approx. 10 db increase in power output when used with Transmitter BC-339. TM 11-801.
BC-365-( ) 0.15 to 0.55 350 Al mo Point-to-point. Manual frequency change. TM 11-828.
BC-401-( ) 2.0 to 18.1 400 Al, A2 and A3 xtal Point-to-point and ground-to-air. Dial selection of ten preset channel frequencies. No longer procured.
Figure 6-173. Equipment commonly used by Airways Section, Army Communications Service, (continued on opposite page).
366
TRANSMITTING EQUIPMENT
Type Frequency range (me) Xmtr output (watts) Type emission Frequency control Remarks
BC-460-( ) 2.0 to 18.0 250 Al mo or xtal Point-to-point and ground-to-air. Dial selection of ten preset charfnel frequencies. Late models are the same as Navy TDO transmitter and are master oscillator controlled only. TM 11-812.
200 A2, A3
BC-610 2.0 to 18.0 400 Al mo or xtal Point-to-point and ground-to-air. Also used as transmitter of SCR-299, SCR-399, and SCR-499. TM 11-813.
300 A3
BC-642 4.0 to 20.0 3,000 Al, A3 xtal Point-to-point. Dial selection of ten preset channel frequencies. No longer procured.
BC-1100-( ) 1.5 to 10.0 75 Al xtal Point-to-point and ground-to-air. May be remotely controlled. Four preset channels. Part of Radio Transmitter Equipment RC-263. TM 11-816.
50 A3
RC-52-( ) 1.5 to 7.0 300 Al, A2 and A3 xtal Point-to-point and air warning. May be remotely controlled. Two preset channels.
T-4/FRC 2.0 to 18.0 400 Al, A2 and A3 mo or xtal Point-to-point and ground-to-air. May be used in conjunction with Transmitter T-5/FRC for extended frequency coverage. TM 11-820.
T-5/FRC 0.15 to 0.55 600 Al, A2 and A3 mo or xtal Point-to-point and homing. May be used in conjunction with Transmitter T-4/FRC for extended frequency coverage. TM 11-820.
Aircraft Accessories Corp. 500B 0.275 to 0.4 and 1.6 to 10.0 1,000 Al, A2 and A3 xtal Point-to-point, ground-to-air and airport control. Includes RF unit, modulator and power supply in one cabinet. Two preset channels.
Federal FT-300 2.0 to 20.0 3,000 Al, A3 xtal Point-to-point. Eight transmitters are normally used per rectifier and modulator. Dial selection of desired channel.
Pan Amer. Airways 12-ACX-2 1.6 to 24.0 1,200 Al, A3 xtal Point-to-point. Push button selection of either of two preset channel frequencies.
Pan Amer. Airways. 12-GLX-2 0.26 to 1.75 1,200 Al xtal Point-to-point and homing. Dial selection of either of two preset channel frequencies.
750 A2, A3
Pan Amer. Airways RFA-50 5.0 to 24.0 5,000 Al, A2 and A3 — Point-to-point. Used as amplifier for Pan American Airways 12-ACX-2 transmitter. No longer procured.
Press Wireless PW-10LF 0.11to0.14 10,000 Al mo Point-to-point and radio teletype.
Temco 250-GSC 2.0 to 16.0 200 Al, A2 and A3 mo or xtal Point-to-point and ground-to-air. Switch selection of master-oscillator or any one of four crystal frequencies.
Temco 1000-AG-CW 2.0 to 16.0 1,000 Al xtal Point-to-point and ground-to-air. Six preset channels. No longer procured.
Figure 6-173. Equipment commonly used by Airways Section, Army Communications Service (continued on following page).
367
TRANSMITTING EQUIPMENT
Type Frequency range (mc) Xmtr output (watts) Type emission Frequency control Remarks
Western Electric Company D-151249 (Pan Amer. Airways 4WTFA) 1.6 to 13.2 350 Al xtal Point-to-point and ground-to-air. Relay selection of either of two preset channel frequencies. No longer procured.
100 A3
Wilcox 96A 2.0 to 12.0 2,500 Al, A3 xtal Point-to-point and radio-teletype. Eight transmitters are normally used per rectifier. No longer procured. TM 11-2671 (when published).
Wilcox 96C and 96C-3 2.0 to 20.0 3,000 Al, A2 and A3 xtal Point-to-point and radio-teletype. Four transmitters are normally used per rectifier. TM 11-803 (TM 11-2671 when published).
Wilcox 96-200A or B 0.195 to 0.525 2,000 Al, A2 and A3 mo or xtal Point-to-point and homing. Wilcox 96-200A no longer procured. TM 11-802.
COMBINED TRANSMITTING AND RECEIVING EQUIPMENT
Type Frequency range (mc) Rated xmtr output (watts) Type emission Type mod. Frequency control Remarks
Collins 18-Q 1.5 to 12.0 25 cw am mo or xtal Transmitter and receiver. Point-to-point and ground-to-air. Switch selection of five crystal frequencies. Same as Navy Model TCS.
10 voice
Jefferson Travis 350A 1.5 to 12.0 50 cw am mo or xtal Transmitter-receiver equipment for fixed mobile communication. Switch selection of four crystal frequencies.
40 voice
Link 25-FMTR 30 to 40 25 voice fm xtal Commercial police car equipment for providing 2-way mobile communication. Similar to SCR-298.
Link 35-FMTR 30 to 40 35 voice fm xtal Commercial police car equipment for providing 2-way mobile communication. Similar to SCR-298-C.
Link 50 UFS 30 to 40 50 voice fm xtal Self contained transmitter, receiver and power supply. For fixed control station in mobile net.
Link 1498 70 to 100 50 voice fm xtal Self contained transmitter, receiver and power supply. For providing radio telephone communication when essentially line-of-sight operation is possible.
Link 1505 70 to 100 250 voice fm xtal Self contained transmitter, receiver and power supply. Similar to Link 1498 except provides approx. 7-db greater power output.
Figure 6-173. Equipment commonly used by Airways Section, Army Communications Service (continued on opposite page).
368
COMBINED TRANSMITTING AND RECEIVING EQUIPMENT
Type Frequency range (me) Rated xmtr output (watts) Type emission Type mod Frequency control Remarks
AN/TRC-13 (Motorola FMTR-50 BW) 30 to 40 50 voice fm xtal Commercial police type of transmitting and receiving equipment for fixed control station in mobile net. Transmitter and receiver each have built-in power supply.
AN/VRC-2 (Motorola FMTR-25 VM or FMTR-30 DW) 30 to 40 25 voice fm xtal Commercial police car type of equipment for providing 2-way mobile communication. Separate transmitter and receiver, each with built-in power supply. TM 11-607 (when published).
AN/VRC-4 xmtr, 1.7 to 8.7 revr, 0.19 to 0.51 & 1.7 to 8.7 25 cw voice am mo or xtal Transmitting and receiving equipment for crash truck use. Switch selection of master-oscillator (4.0 to 7.0 me) or any one of four crystal frequencies. In addition, receiver is tuneable from 0.19 to 0.51 me. TM 11-829.
RECEIVING EQUIPMENT
Type Frequency range (me) Type output Type emission received Frequency control Remarks
AN/FRR-3A (Press Wireless diversity) 2.4 to 23.0 into AN/FGC-1 Al, A2, A3 & Special xtal Point-to-point and radio-teletype. Balanced input. Five preset channels. Tuning range may be extended to 26 me if desired. Used with Radio Teletype Terminal Unit AN/FGC-1. TM 11-872A.
AN/GRR-2 (Hallicrafters SX-28) 0.55 to 42 speaker or headset, 500 or 5,000 ohms Al, A2 & A3 manual tuning Point-to-point and ground-to-air. Balanced input. Table mode|. Built-in power supply. Separate loud speaker. TM 11-874.
AN/GRR-3 (National NC-100-ASC) 0.2 to 0.4 & 1.5 to 30 speaker or headset Al, A2 & A3 manual tuning Point-to-point and ground-to-air. Balanced input. Table model. Built-in power supply. Separate loud speaker.
Federal 128-AY 0.015 to 0.65 speaker or headset Al, A2 & A3 manual tuning Marine or fixed station service. Unbalanced input. Table model. Built-in power supply. TM 11-858.
Hallicrafters S-22-R 0.11 to 1.5 & 1.7 to 18.0 built-in speaker, or headset Al, A2 & A3 manual tuning Marine or fixed station service. Unbalanced input. Table model. Built-in power supply.
Hallicrafters S-27 27 to 145 speaker or headset, 500 or 5,000 ohms Al, A2, A3 & FM manual tuning Airport control and air warning. Balanced input. Table model. Built-in power supply.
Hallicrafters S-29 0.54 to 30.5 built-in speaker, or headset Al, A2 & 43 manual tuning Highly portable for miscellaneous monitoring. Uses built-in telescoping whip antenna.
Figure 6-173. Equipment commonly used by Airways Section, Army Communications Service (continued on following page).
369
RECEIVING EQUIPMENT
Type Frequency range (me) Type output Type emission received Frequency control Remarks
Hallicrafters S-36 27.8 to 143 speaker or headset, 500 or 5,000 ohms Al, A2, A3 & FM manual tuning Airport control and air warning. Similar to Hallicrafters S-27 receiver except treated for tropical use. Balanced input. Table model. Built-in power supply.
Hammarlund SP-110-LX (super pro) (BC-779-( )) 0.1 to 0.4 & 2.5 to 20 speaker or headset, 600 or 8,000 ohms Al, A2 & A3 manual tuning Airport control, point-to-point and ground-to-air. Balanced input. Modified table model. Separate power supply. Operates on 25-cycle supply or batteries. TM 11-866.
Hammerlund SP-210-LX (super pro) (BC-779-( )) 0.1 to 0.4 & 2.5 to 20 speaker or headset, 600 or 8,000 ohms Al, A2 & A3 manual tuning Airport control, point-to-point and ground-to-air. Balanced input. Rack mounting. Separate power supply. Operates on 60-cycle supply or batteries. TM 11-866.
National HRO 1.7 to 30 speaker or headset Al, A2 & A3 manual tuning Point-to-point and ground-to-air. Balanced input. Table mounting. Separate power supply. Uses plug-in coils which are inserted as a unit.
Wilcox CW3 1.15 to 25.5 speaker or headset Al xtal Point-to-point and ground-to-air. Balanced input. Rack mounting. Uses plug-in coils. Eight CW3 receivers in a prewired rack, are available as Wilcox 113A Receiver Bay. TM 11-853 (when published).
Wilcox 4 CW3-D 2.0 to 26 into AN/FGC-1 Special, Al xtal For radio-teletype service. Balanced input. Used with Radio Teletype Terminal Unit AN/FGC-1 (see chapter 3). Four preset channels. The 4 CW3-D is an assembly of four CW3-D units in a single cabinet. TM 11-2204.
Wilcox F3 1.9 to 16.5 speaker or headset A2, A3 xtal Point-to-point and ground-to-air. Airport control. Balanced input. Rack mounting. TM 11-853 (when published).
Figure 6-173. Equipment commonly used by Airways Section, Army Communications Service, (continued).
370
TACTICAL EQUIPMENT.
Type*, b Frequency range (me) Rated xmtr output (watts) Type emission Frequency control Remarks
MM 2 xmtrs, 0.35 to 1.0 & 3.0 to 18.1 2 revrs, 0.2 to 2.0 & 2.0 to 20.0 100 cw mo Portable transmitting and receiving equipment composed of model TBW transmitting equipment and model RBM receiving equipment. Intended, primarily, for use in establishing an advance base radio station.
25 tone
25 voice
MU MV MW MX MAB 2.3 to 2.8 2. 8 to 3.3 3.3 to 3.9 3.9 to 4.6 2.3 to 4.6 0.2 voice xtal Light weight battery operated, two-way communication set for use by paratroopers. This series was originally designated MP but was later redesignated MU, MV, MW, and MX according to the frequency range. The MAB covers the frequency range of the series.
RBM, -1 to —3 0.20 to 2.0 & 2.0 to 20.0 — cw manual tuning Semiportable receiving equipment intended for use where transportation over wet and rough country is to be expected. Includes two superheterodyne receivers; normally used with semiportable transmitting equipment model TBW.
tone
voice
RBQ 132 to 156 — voice xtal Single frequency, superheterodyne shore receiver used with model TDG transmitter and 42A1 carrier telegraph system as a receiving terminal of a point-to-point v-h-f link.
tone
RBZ 2.0 to 5.8 — tone manual tuning Light weight, battery operated personal receiver for shore use. Superheterodyne receiver carried on operator’s chest in canvas holder; uses steel helmet as an antenna.
RCK 115 to 156 — voice xtal Receiver for use on aircraft carriers and at shore stations for communication between aircraft and ship and shore stations. Selection of four operating frequencies by means of switch plus ganged tuning of r-f circuits. Designed to reduce radiation from oscillator.
TBS-3 60 to 80 50 voice Transmitting and receiving equipment for installation on surface craft or submarine for intercommunication between task forces, convoy vessels and others.
50 tone
TBW, -1 0.35 to 1.0 & 3.0 to 18.1 100 cw mo Portable transmitting equipment; two transmitters; intended, primarily, for use in establishing an advance base station. Commonly used with receiving equipment model RBM and when so used is known as Navy model MM portable transmitting and receiving equipment.
25 tone
25 voice
TBX, -1 to -3 xmtr, 2.0 to 4.525 revr, 2.0 to 8.0 9 cw mo or xtal For ship and shore communication. Major units are supplied with canvas pack carrying cases. Transmitter operates from hand-driven generator and receiver from battery pack.
3 voice
TBY, -1, -2 28 to 80 0.5 voice mo (xtal cal.) Pack transmitting and receiving equipment intended primarily for use by Marines. May be operated by one man either in the field or while being transported.
tone
a All sets are amplitude modulated.
b Many of these radio sets may be used as substitutes for the tactical radio sets for ground use in figure 6-169.
Figure 6-174. U. S. Navy radio equipment
(continued on following page).
371
TACTICAL EQUIPMENT
Type-, b Frequency range (me) Rated xmtr output (watts') Type emission Frequency control Remarks
TCS, -1 to —5 1.5 to 12.0 25 cw mo or xtal Semiportable equipment designed according to commercial standards. Used extensively on patrol and landing craft, reconnaissance vehicles, and for similar purposes. Switch selection of any one of four crystal controlled frequencies in each of the three bands.
15 voice
TCY 0.5 only 5 tone mo Portable emergency lifeboat transmitter for use, primarily, by inexperienced personnel.
TDG 132 to 156 12 voice xtal Transmitting equipment used with model RBQ receiver and 42A1 carrier telegraph system as a transmitting terminal of a point-to-point v-h-f circuit.
AIRBORNE EQUIPMENT
Type- Frequency range (me) Rated xmtr output (watts) Type emission Frequency control Preset channels Power source Remarks
AN/ARC-1 100 to 156 6 voice xtal 10 28v, de For 2-way plane-to-plane and plane-to-ground communication. Nine main channels are provided plus one guard channel which may be simultaneously monitored.
AN/ARC-4 140 to 144 6 voice xtal 4 28v, de For 2-way plane-to-plane and plane-to-ground communication. Three main channels are provided plus one guard channel on 140.58 me which may be simultaneously monitored.
AN/ARC-4X (Western Electric Company 233A) 140 to 144 6 voice xtal 4 28v, de or 14v, de Same as AN/ARC-4 except may be operated on 14 or 28v, de.
AN/ARC-5 (ATA/ARA) l-f, m-f, & h-f units xmtrs, 0.5 to 9.1 revrs, 0.19 to 9.1 36 cw mo (xtal cal.) 1 (per xmtr.) 28v, de For 2-way m-f, h-f, and v-h-f communication. The frequency range shown for the l-f, m-f, and h-f components is covered by eight transmitters and five receivers and the v-h-f range by one transmitter and one receiver which mount in the same rack with the l-f, m-f, and h-f components. Transmitters and receivers are usually installed in groups of two or three. (The ATA/ARA is similar but does not include v-h-f units and covers only the transmitting range of 2.1 to 9.1 me, using five transmitters similar to those used with SCR-274-N. ATA/ARA— VHF consists of the v-h-f transmitting and receiving components only.)
12 tone
voice
v-h-f units 100 to 156 6 voice xtal 4 28v, de
a All sets are amplitude modulated.
b Many of these radio sets may be used as substitutes for the tactical radio sets for ground use in figure 6-169.
Figure 6-174. U. S. Navy radio equipment
(continued on opposite page).
372
AIRBORNE EQUIPMENT
Type “ Frequency range (me) Rated xmtr output (watts) Type emission Frequency control Preset channels Power source Remarks
AR-10A (Harvey Wells) 0.195 to 10.0 — cw manual tuning & xtal 12 14v, de Commercial receiving equipment. Has dual audio output and may be remotely controlled. Manual tuning range 0.195 to 8.0 me.
tone
voice
ATB/ARB xmtr, 2.3 to 9.05 revr, 0.195 to 9.05 55 cw mo 2 28v, de This equipment includes a single transmitter and a 4-band receiver. Installed in a wide variety of aircraft.
35 tone
voice
ATC (AN/ART-13) 0.20 to 1.5 & 2.0 to 18.1 90 cw mo 11 28v, de Transmitting equipment for aircraft use; selection of one manual tuning channel between 0.2 and 1.5 me and selection of ten preset channels between 2.0 and 18.1 me. Used with model ARA, ARB, and RAX-1 receivers. (Superseded by in improved version, that is, transmitter AN/ART-13, used by the AAF with Receiver AN/ARR-11 as a replacement for SCR-287.)
tone
voice
AVR-7H (Radio Corp, of America) 0.195 to 0.42 0.495 to 1.4 & 2.3 to 6. 7 cw manual tuning & xtal 2 14v, de Commercial receiving equipment which provides two crystal controlled channels or continuous tuning over the entire range.
tone
voice
AVT-12B (Radio Corp, of America) 2.6 to 6.5 30 cw xtal 4 14v, de Commercial transmitting equipment for aircraft use. Used with Receiver AVR-7H.
voice
AVT-23 (Radio Corp, of America) 3.0 to 12.5 15 cw xtal 4 28v, de or 14v, de Commercial transmitting equipment for aircraft use. Used with Receiver AVR-7H.
voice
GF/RU xmtr, 3.0 to 4.525 & 6.0 to 9.05 revr, 0.195 to 13.575 15 cw mo none 28v, de or 14v, de This equipment consists of one transmitter and one receiver each using plugin coils. Similar to Radio Sets SCR-183 and SCR-283. Transmitter GF-11 and Receiver RU-16 operate on 14v, de; GF-12 and RU-17 operate on 28v, de.
tone
voice
GO-9 0.30 to 0.60 & 3.0 to 18.1 100 cw mo none 120v. 600/800 cycle ac & 28v. or 14v, de Intended for installation in Navy patrol, land or seaplanes. Consists of a 1-f transmitter and a h-f transmitter either of which may be operated from the common rectifier unit. Commonly used with receiving equipment model RAX-1.
70 tone
a All sets are amplitude modulated.
Figure 6-174. U. S. Navy radio equipment (continued on following page).
373
AIRBORNE EQUIPMENT
Type* Frequency range (me) Rated, xmtr output (watts) Type emission Frequency control Preset channels Power source Remarks
RA-1 (Bendix) 0.15 to 1.5 & 1.8 to 15.0 — cw manual tuning none 28v, de or 14v, de Commercial multiband receiving equipment. May be locally or remotely operated.
tone
voice
RA-10 (Bendix) 0.15 to 1.1 & 2.0 to 10.0 — cw manual tuning — 28v, de or 14v, de Commercial multiband receiving equipment. Remotely controlled only.
tone
voice
RAX-1 0.20 to 27.0 — cw manual tuning 1 (per revr) 28v, de Receiving equipment used in the larger airplanes. The frequency range shown is covered by three multiband receivers.
tone
voice
RTA-1B (Bendix) 0.25 to 13.0 50 voice xtal 10 14v, de Commercial transmitting and receiving equipment. May be remotely or locally operated.
TA-2 (Bendix) 0.3 to 0.6 & 30 cw xtal 8 28v, de Remotely operated commercial transmitting equipment. (Model TA-2G covers only 2.9 to 15.0 me; model TA-2J covers both frequency ranges shown.)
20 tone
voice
2.9 to 15.0 100 cw
75 tone
voice
TA-6 (Bendix) 2.8 to 12.0 4 cw xtal 2 28v, de or 14v, de Commercial transmitting equipment. May be remotely or locally operated.
voice
TA-12 (Bendix) 0.3 to 0.6 & 3.0 to 1.20 35 cw mo 4 28v, de Commercial transmitting equipment. May be remotely or locally controlled. (Frequency range shown is that covered by model TA-12C. Other models may cover different frequency ranges.)
tone
voice
29A (Western Electric Company) 0.2 to 15.0 — cw xtal 10 14v, de Commercial receiving equipment. Provides dual audio outputs.
tone
voice
8 All sets are amplitude modulated.
Figure 6-174. U. S. Navy radio equipment (continued).
374
BRITISH ARMY COMBINED TRANSMITTER AND RECEIVER
Type Frequency range (mc) Xmtr output (watts) Type emission • Remarks
1 4.2 to 6.8 0.5 cw, voice Infantry Brigade and Royal Artillery set.
5 L.P. 2.4 to 20 500 cw, tone, voice Medium to long range transmitter for fixed stations. Mo or crystal control.
5 H.P. 0.2 to 0.6 & 3.0 to 20 2,000 cw, tone, voice Long range transmitter for fixed stations. Mo or crystal control.
9 1.875 to 9.0 10 cw, tone, voice Medium range set for Armored Fighting Vehicle use and Divisional communication. Mo control.
11 L.P. 4.2 to 7.5 1.5 cw, voice Infantry, mobile Brigade and Royal Artillery Regiment set. Mo control.
11 H.P. 4.2 to 7.5 7 cw, voice Same use as 11 L.P. and for mechanized cavalry, some Armored Fighting Vehicles and Divisional communication.
12 L.P. 1.2 to 17.5 25 cw Transportable Division-Corps set. Mo or crystal control.
6 tone, voice
12 H.P. 1.2 to 17.5 300 cw, tone, voice Division and Corps high power set. Mo or crystal control.
17 (MK II) 44.0 to 61.0 0.5 voice Searchlight control transceiver for use between searchlight section headquarters and details.
18 (MK I, II & HI) 6.0 to 9.0 0.5 cw, voice Infantry Battalion to Company man-pack set.
18 M. 2.0 to 5.0 0.5 cw, voice Same as 18 set except lower frequency. For special uses and Naval Forward Observation Officer parties.
Collins 18 M. 2.0 to 16.0 15 cw Special; not in general use. Mo or crystal control.
5 voice
19 (MKI) 2.5 to 6.25 & 230 to 255 10 cw, tone, voice Armored Fighting Vehicle set for communication between tanks.
19 (MK II & III) 2.0 to 8.0 & 230 to 255 10 cw, tone, voice Same as 19 MK I except frequency range. Mo control.
21 4.2 to 7.5 & 19.0 to 31.0 2 cw, tone, voice Royal Artillery Regiment set to replace 11 L.P. set. Mo control.
22 2.0 to 8.0 3 cw, tone, voice Divisional and Regimental set. May be used as vehicular, man-pack (3-man load), or as ground set.
23 1.2 to 15.0 250 cw, tone, voice Long range mobile set.
26 85.0 to 95.0 65 voice Multichannel point-to-point transmitter. Six duplex channels using group modulation of transmitter.
Figure 6-175. Principal British radio sets (continued on following page).
375
BRITISH ARMY COMBINED TRANSMITTER AND RECEIVER.
Type Frequency range (me) Xmtr output (watts) Type emission Remarks •
33 1.2 to 17.5 250 60 CW tone, voice Long range line of communication set. Normally carried in 3-ton 4x4 vehicle but can be set up as a ground station. Mo or crystal control.
34 157 & 230 to 255 voice Tentative characteristics; dual channel, crystal controlled FM set for local use at headquarters.
36 10 to 60 25 cw, tone, voice AA gun control set. Capable of modulation at carrier frequencies required by Apparatus Carrier Telephone 1 + 1.
37 370 to 380 0.5 voice, tone Special; set is in a telephone handset, batteries in a belt.
38 (MK I, II & III) 7.3 to 8.8 0.5 voice Light infantry man-pack set. Mo control.
0-43 2 to 12 300 cw, voice Canadian version of the 33 set.
46 3.6 to 4.3 5.0 to 6.0 6.4 to 7.6 7.9 to 9.1 1 voice, tone Commando and paratroop set for combined operations and jungle warfare. Crystal controlled and has three preset channels (in same band).
48 5.9 to 9.1 0.5 cw, voice Infantry Battalion and R.A. Regiment short range communication man-pack set. Has built-in crystal calibrator.
53 1.2 to 17.5 250 cw, tone, voice Provisional data; long range set for Division and Corps communication. An improvement of the 12 H.P. set.
57 85 to 95 7 voice V-h-f point-to-point set for duplex telephony using crystal control of transmitter and receiver.
681’ 1.7 to 3.0 0.75 cw, voice Used by Airborne troops and combined operations. Is modified form of 18 set. Transmitter can be crystal controlled.
68Q, 68R 3.0 to 5.2 0.75 cw, voice 68Q is similar to 68P set except has no prov’sion for crystal control. 68R is similar to 68Q set except has provision for crystal control.
76A 2.0 to 12.0 4 cw Provisional data; for airborne troops and jungle warfare. Modified Naval type 5G set. Crystal control only.
761’, 76Q 2.0 to 12.0 20 cw Provisional data; for airborne troops, jungle warfare and combined operations. Crystal control only. 76P operates on 12 v, de. 76Q operates on 100 to 250 volts, 50-cycle ac power pack.
Gohlen Arrow 2.5 to 17.5 1,000 Transportable, for point-to-point communication.
AD67 0.272, 0.545 1.5 to 20 75 Transportable, for point-to-point communication.
Figure 6-175. Principal British radio sets
(continued on opposite page).
376
R.A.F. COMBINED TRANSMITTER AND RECEIVER
Type Frequency range (me) Xmtr output (watts) Type emission Remarks
TR-9B 4.3 to 6.0 voice For 2-way fighter aircraft communication.
TR-9D 4.3 to 6.6 3 For single-seater aircraft or ground communication.
TR-9F 4.3 to 6.6 voice For multi-seater aircraft.
TR 1091 1.222 to 1.539 & 2.0 to 3.409 cw, tone, voice Airborne transmitter-receiver.
TR 1133B 100 to 120 2 voice, tone Airborne v-h-f voice transmitter-receiver with facility for tone operation for special circumstances.
TR 1143 100 to 124 5 voice, tone Airborne voics communication wi h tone operation on special frequency.
TR 1150 60 0.4 voice Portable 2-way Balloon Command communication.
TR 1304 3.0 to 10.0 3 voice Remote controlled aircraft transmitter.
5 2.3 to 2.8 & 4.0 to 7.0 15 voics Portable ground station transmitter-receiver.
19 (MK II) 2.0 to 8.0 10 cw, tone, voice Airborne transmitter-receiver used in fighter reconnaissance.
R.A.F. TRANSMITTING EQUIPMENT
Type Frequency range (me) Xmtr output (watts) Type emission Remarks »
T1083 0.136 to 0.50 & 3.0 to 15.0 30 cw, tone, voice Airborne transmitter; used in conjunction with receiver R1082.
T1087 1.5 to 20.0 400 cw Ground station.
100 tone, voice
T1090 0.545 to 0.857 & 1.222 to 6.667 40 cw, tone, voice Mobile ground station.
T1115 0.142 to 20.0 cw, tone, voice General purpose aircraft transmitter; used in conjunction with receiver R1116.
T1131 99 to 126 50 voice, tone V-h-f ground station transmitter.
T1154 0.20 to 0.50 & 3.0 to 10.0 40 cw, voice Aircraft or ground station transmitter; used in conjunction with receiver R1155.
T1190 1.5 to 15.0 350 cw, voice Ground station transmitter.
T1204 2.5 to 5.7 cw Point-to-point ground station.
T1223 2.5 to 5.7 cw Same as transmitter T1204 except operates on 12V battery.
Figure 6-175. Principal British radio sets (continued on following page).
377
R.A.F. TRANSMITTING EQUIPMENT
Type Frequency range (me) Xmtr output (watts) Type emission Remarks
TA-2J 0.30 to 0.60 & 30 CW Remote controlled aircraft transmitter. Provides eight crystal controlled channels. (Bendix.)
20 tone, voice
2.9 to 15.0 100 cw
75 tone, voice
TA-12B 0.30 to 0.60 & 3.0 to 7.0 35 ' cw, tone, voice Aircraft transmitter with four preset channels which may be remotely or locally controlled. (Bendix.)
TA-12C 0.30 to 0.60 & 3.0 to 12.0 35 cw, tone, voice Aircraft transmitter with four preset channels which may be remotely or locally controlled' (Bendix.)
SWB 8 4 to 23 or 3 to 22.2 3,500 cw Fixed service ground transmitter. Also used by the Royal Navy. Mo control.
R.A.F. RECEIVING EQUIPMENT
T(/pc Frequency range (me) Type emission received Remarks
R1082 0.111 to 15.0 cw, tone, voice Airborne receiver.
R1084 0.12 to 20.0 cw, tone, voice Ground station receiver. Normally used in conjunction with transmitter T1087.
R1100 1.2 to 1.5 & 2.0 to 3.0 cw, tone, voice Portable field receiver for operation under tropical conditions.
R1129 2.0 to 30.0 cw Ground station receiver working into tape recording device.
R1132A 100 to 124 voice Ground station receiver for v-h-f or for direction finding. Unmodulated carrier used for D/F.
R1155B 0.075 to 1.5 cw, tone, voice Airborne for communication and direction finding.
R1224 1.5 to 7.0 cw Used with transmitters T1204 and T1223.
RA-1B 0.15 to 1.5 & 1.8 to 15.0 cw, tone, voice Manual tuning, multi-band aircraft receiver which may be remotely or locally operated. (Bendix.)
RA-1J 0.15 to 1.5 & 2.5 to 20.0 cw, tone, voice Airborne communication and direction finding receiver similar to RA-1B except for frequency. (Bendix.)
RA-10DA 0.15 to 1.1 & 2.0 to 10.0 cw, tone, voice Remote controlled, manual tuning, multiband aircraft receiver. Operates on 14v, de. (Bendix.)
RA-10DB 0.15 to 1.1 & 2.0 to 10.0 cw, tone, voice Remote controlled, manual tuning, multiband receiver for airborne and mobile service. Operates on 28v, de. (Bendix.)
Figure 6-175. Principal British radio sets (continued on opposite page).
378
PAR.
693
CHAPTER 6. RADIO SYSTEMS
ROYAL NAVY SHORE EQUIPMENT
Type Frequency range (me) Xmtr output (watts) Type emission Remarks
65 3.0 to 20.0 15 Fixed service in assault stages.
T1190 1.5 to 15.0 800 Transmitter for fixed service.
52 ERT 0.90 to 13.5 15 Port wave.
G.P. Sets (R.A.F.) 1.5 to 15.0 15 Port wave.
SWB 8 4 to 23 or 3 to 22.2 3,500 CW Fixed service ground transmitter. Also used by the R.A.F. Mo control.
Figure 6-175. Principal British radio sets (continued).
b. Frequency Range Chart. A frequency range chart covering tactical radio sets for ground use, both amplitude modulated and frequency modulated radio sets, is shown in figure 6-176.
c. Set Maintenance. TM 11-310 Schematic Diagrams for Maintenance of Ground Radio Communication Sets, contains a condensation of information for maintenance. It is presented as a supplement to the information given in the various technical manuals of the TM 11- series for particular sets. The manual is in loose-leaf form, so that additional sheets or reissues of old sheets can be added. Changes,, which are issued at frequent intervals, include additional listings. This publication contains reference data on radio symbols, electrical units, special abbreviations, resistor and capacitor color codes and includes a vacuum tube cross-reference guide.
d. Batteries. SB 11-6 Dry Battery Supply Data, furnishes information on the dry batteries required for operation of all equipment maintained by the Signal Corps. This type of information is needed for a variety of purposes, among which are the determination of batteries to be shipped with initial issues of equipments and to be requisitioned by commanders, and the calculation of over-all and short-time battery requirements for planning purposes, both in the field and at procurement levels.
e. Vacuum Tubes. SB 11-17 Electron Tube Supply Data, contains in part I a listing of equipments which contain electron tubes, showing the tube complement and the spare tube factors for each. Part II consists of a listing of tubes, showing the equipments in which each tube is used.
379
FREQUENCY COVERAGE OF AMPLITUDE MODULATED TACTICAL RADIO SETS FOR GROUND USE
FREQUENCY IN MEGACYCLES
.15 .2 .3 .4 .5 .6 .7.8.91 2 3 4 5 6 7 8 9 10 20 30 40 50 607080100 200
' . I ■ I i I ■ I . I 1111_______________________i_____I____i I i I ■ I i I ■ l.J—I-------------i-----1----1--1—i I i I iJ—i I » 1--------------•-----1
SCR-'3lT^6Kn4.36
’•’‘■±2$—SCR-I*.
4 37 | /I 5 I
SCR-.7I---- 4.37^5.1
2.64^ |3.04
2.64 3 04
! C-I44-A ,0-145-4, । C-I47-A ,^C-I4B-A ■
0 4 P 10 '. 8 a 5
1 TU-5-A 1 TU-b-A 1
0151 -L-gscR-iTTBl-^------------- ■■ ------1 18 0
1 TU- 5 -A 1 TU-b-A *
2 .4 |i -1| 3 ■ 7
_ . WSCR-I7»5 i7<)M , ,
.4 3.
. C-I44-A C - 14 5 - Ai C-I46-A, C-I47-A , C-I48-A , C-149-A, C-I50-A.C-I51-A.C I52-A,
1 1 J T—L| I1
I 7 U-A A - 5 1 TU-AA-6 । TV-AA-7 'TU-AAS11U AA-117UAAI0
' 51 I- - I ~1'® °
' TU-5-A 1 TU-b-A 1 TU-7-AlTU-»-Al7U-7-Al7UI0A_____
I 51 ■ n I ISO
SCR- 193 ----------------------------J
1 -4
' T U- 5-A 1 TU-6-A ' _______________
27 7 L—RF^T-J52 2
27 7 /JL-L;--S C R -19 5
52.S| zH656
52.8 HI 65.6
0 54 | SCR-197
' •51 jJ.N/m-.U ■ 118 0 '0 0 0 Lan/vrc-J 1380
3.0 b. 2 100.0 I 5 b. 0
1 T U - b 'TU^7'
FREQUENCY COVERAGE OF FREQUENCY MODULATED TACTICAL RADIO SETS FOR GROUND USE
FREQUENCY IN MEGACYCLES
10 20 30 40 50 60 70 80 90 100
I----------------------1--------------1 . i —------1_______I_______I_____I_____I____i I i I i I i I i I
2............0.0 |r ..... -71 2 7.9
20 0 hgc^R^so^so^sj^^IIW 2 7
20 0 I SCR-294 &, 538 | 2 7. 9
3 0.0 I r ■■ —। ] 40.0
, rx /> MSCR-2 9 8. AN/CRC-3W 7 ?
3 0.0 _______
71 4 8 0
SCR - b08 , b09,bl0,bl9, b2 8, 80 8 & 82 8 v . . hpCR-iOQ^AN/VRC-^M
_____ \ 4 0 0 4 5.0
2 7.0 | । -X---1 138.9
FREQUENCY IN MEGACYCLES (contd.) 2 7 - 0 ■■ELMMJHHi 3 8
100 200 300 7» 'n Lffi^*C-l,AN/*raC-3.AN/'TRC-4hJ1 °‘
i______________________i______________i i________i 70 0 •o<
2 30 L— J 2 50
2 30 ■^■■1 2 50
NOTES: - AN/TRC-8
*■ L——J RECEIVER AN^TRC-12 C. WHEN COIL SETS OR TUNING UNITS ARE EMPLOYED THEIR RANGES ARE
■I TRANSMITTER INDICATED ABOVE AND BELOW THE RECEIVER AND TRANSMITTER BLOCKS
RESPECTIVELY.
B. THE NUMERALS SHOWN AT THE EXTREMES OF THE BLOCKS REPRESENT TL 53445
THE FREQUENCY COVERAGE OF THE RESPECTIVE UNITS.
Figure 6-176. Frequency coverage chart.
656935 0-45-
26
381
CHAPTER 7
POWER
Section I. POWER SUPPLIES
701. GENERAL.
Among the several sources of power supply which can be considered are commercial power, dry batteries, storage batteries, engine-driven generators, rectifiers, etc. Each type has certain advantages and certain limitations. Depending upon the application involved, they may be used individually or in combinations.
702. COMMERCIAL POWER.
a. Types. Commercial power throughout the world consists of both a-c and d-c supplies, either or both of which may be found in some localities. A wide range of frequencies and voltages will be encountered. From recent surveys made, frequencies anywhere from 20 to 76 cycles are known to exist, and a-c voltages from 100 to 260 nominal, will accompany them. To design communication equipment which could be universally operated on such widely differing commercial power supplies is obviously not economical. In view of this, most a-c operated signal equipment has been designed to operate on power services of 50-60 cycles with nominal voltages of 115 and 230 having variations of plus or minus 10 percent.
Where commercial frequencies fall outside of these limits it is usually easiest to use one or more engine-alternator sets of the types discussed in paragraph 710. Where the frequency is 50-60 cycles but the service voltage is outside the limits of 115 or 230 plus or minus 10 percent, transformers with multitap primary windings should be used (par. 705). Commercial power is often subject to unforeseen interruptions beyond immediate control. In view of this, it should be augmented by the use of one or more engine generators for standby purposes at important installations. D-c commercial power is not so readily adaptable to communication equipment except possibly in the case of some telegraph equipment such as motors of teletypewriters, etc., which have been arranged to operate from either de or ac. The reliability of d-c commercial power is usually no better than that of a-c commercial power.
b. Power Services Throughout World. Information concerning the prevailing electrical frequencies, voltages, etc. of commercial power supplies of cities and countries throughout the world may be obtained from TM 11-487.
Section II.
703. DRY BATTERIES.
a. General. Dry batteries are especially adapted for use where small amounts of power are needed and portability is required. They are capable of furnishing high output per unit of weight or volume under suitable conditions of use and they will continue to provide service under many adverse conditions. However, serious impairment or failure may result under various conditions that may be encountered.
BATTERIES
b. Aging. Dry batteries, whether on open circuit or under discharge, deteriorate in serviceability because of internal losses. The rate of deterioration varies with the size and type of cell and with temperature and humidity. In general, the smaller the size of cell the shorter will be its shelf life. High temperatures greatly decrease shelf life and low tern peratures increase it.
c. Refrigeration. Since the keeping qualities of batteries are aided by low temperatures,
383
PARS.
703-704 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
refrigeration should be used wherever possible during storage and shipment, and until the batteries are issued for service. Number 6 dry cells such as Battery BA-23 kept in cold storage for 12 months at 34° F have shown full capacity on subsequent test. Small size cells will be benefited, also, but not to the same extent. Storing batteries under these favorable conditions reduces the frequency of replacements, thus conserving shipping space.
d. Effect of Temperature on Capacity. The output obtainable from a dry battery is greater at a high temperature than at normal (70° F) temperature, provided the time of use does not extend over such a long period that the shelf loss is greater than the gain due to the increased chemical activity of the cell. At low temperatures the activity of the cell is decreased and a point may be reached where the cell is unable to deliver any current. The temperature at which this condition occurs depends on the size and type of cell and the load resistance. Except for grid service or very light current drains, dry batteries should be considered inoperative when frozen (—10° F or below). Batteries subjected to low temperatures are not permanently affected even though frozen, but are restored to full capability if their internal temperature is brought back to normal.
e. Excessive Severity of Service. High current drains reduce the battery voltage rapidly, and relatively short life and small output are obtained. The situation is improved by reducing the current drain, by providing more time for recuperation, and by operating to a low cut-off voltage per cell. Thus, for a load requiring a minimum of 4.5 volts, five cells in series will have a cut-off of 0.9 volt per cell as against 1.125 volt for four cells in series and the output will be considerably increased. If the drain is heavy, using two sets of cells in parallel will more than double the output and using two batteries alternately in place of a single battery continuously will also result in increased energy output per cell.
f. Voltage Regulation.
(1) The initial voltage of new dry cells is dependent upon the load and for ordinary loads is approximately 1.5 volts. Dry cells reaching the theaters will have lost some of their useful life, and their initial voltage under normal load may be approximately 1.4 volts.
(2) For grid service (practically no load) or very light drain services the initial voltage may be as high as 1.55 to 1.60 volts and a high cut-off voltage, 1.3 to 1.4 volts per cell, should be used to insure reliability of operation and to guard against sudden failure of the battery. In such cases the service life will approach the shelf life of the battery.
(3) As the severity of the load is increased the initial voltage will be reduced and a progressively lower cut-off voltage is required in order to avoid sacrificing battery output. For ordinary loads, it is desirable to be 'able to use the battery to a cut-off voltage of 0.9 to 1.1 volts per cell, in which case the average voltage will be about 1.2 to 1.25 volts per cell. Close voltage regulation (where required) can sometimes be accomplished by using a rheostat or by adding extra cells in series as the battery voltage drops off in service.
g. High Humidity. High humidity conditions such as are encountered in the tropics may have a very serious effect upon dry batteries by subjecting them to low continuous drains because of current leakage from cell to cell or across battery terminals. This may be caused by the condensation of moisture upon, or the absorption of moisture by, the battery jackets or assembly materials or the wetting of the packing materials in contact with the batteries. In order to reduce trouble of this nature, special precautions are taken in the manufacture and packing of batteries to be shipped, stored, or used in tropical countries.
h. References. Detailed information concerning dry batteries, their size and terminal arrangements, may be obtained from TM 11-487. Information on their construction, properties, performance, care, and testing will be found in Changes No. 1 to TM 11-430 and TB 11-430-1. Information concerning the quantities of dry batteries required for the operation of equipment is given in SB 11-6. Shelf life and similar information is given in SB 11-30.
704. LEAD STORAGE BATTERIES.
a. General. Storage batteries covered by this manual are largely used as portable sources of moderate amounts of power for the operation of electrical signal communication equipment, and for gasoline and diesel engine starting. They are generally of the automotive or aircraft types, having a compact rugged con
384
PAR.
704
CHAPTER 7. POWER
struction well suited to combat service. The high specific gravity (1,300 to 1,350) electrolyte serves to give maximum capacity in minimum space and good low temperature characteristics.
b. General Properties. Storage batteries are usually contained in moulded hard-rubber cases of three or six cells, or in separate hard rubber or plastic jars assembled into wooden trays, three or six cells per tray. The aircraft types, such as Battery BB-53, have a nonspill construction. Storage batteries are usually shipped in a dry condition, with the electrolyte in separate containers. Premature deterioration from self-discharge and sulphation are prevented by this means. Normally, they are filled with 1.285 (at 80° F) specific gravity electrolyte and charged as required. After discharge from use or long standing, they can be recharged from a source of d-c power such as a rectifier or d-c generator. The discharge and recharge cycle can be repeated; the number of times the cycle can be repeated depending upon such factors as temperature, thickness of plates, type of separators, rate of discharge, and rate of charge.
c. Factors Affecting Capacity and Life. The ampere-hour capacity of a storage battery is affected by temperature, being greater for high temperatures and less for low temperatures. Battery capacities at different temperatures are also affected to some extent by the battery construction used, but will usually come within the following limits:
Temp. °F Percent of capacity at 80°F and 20-hour rate
100.............................105-110
80................................ 100
0.............................. 50-65
—40................................. 20-25
The rate at which current is drawn from a battery on discharge influences the output obtainable at any given temperature. At high currents the voltage will fall at a more rapid rate, and at low currents at a less rapid rate, with the result that less ampere-hours will be obtained from a battery at the higher rate. The life of a battery is shortened if operated
for considerable periods at cell temperatures over 110° F. The life of a battery is also shortened if other than distilled water is added to the cells, or charging is prolonged for too long a time and at high rates which cause high cell temperatures and excessive gassing. Permitting a battery to stand in a partially or completely discharged condition for a long period (over one week at 80° F.) of time also tends to shorten its life.
d. Discharge While Idle. A storage battery loses capacity while standing idle and, if it is not used sufficiently to completely discharge it within two months, it should be given a freshening charge. The rate of discharge of batteries while standing idle is negligible at low temperatures but increases rapidly as the temperature increases, and if exposed to tropical conditions it may result in a complete discharge in less than one month.
e. Voltage Regulation. The voltage characteristic of a storage battery is relatively flat, that is, the voltage falls off at a slow rate throughout discharge. For example, the voltage of a fully charged battery at normal load is about 2 volts per cell and averages about 1.95 volts per cell for most of the discharge period. At the end of discharge the voltage falls rapidly, and no advantage is gained by allowing the voltage to fall below the cut-off voltage of 1.75 volts per cell. After discharge the battery should be charged at current rates designated for the particular battery used (TM 11-487). An example of the approximate voltages at which the battery should be recharged (cut-off voltage), is given in percentages of the 20-hour discharge rate, in the following table.
Percent of 20-hour discharge rate Cut-off voltage (80°F)
200..............................1.70
100..............................1.75
50..............................1.77
5.............................1.81
f. References. Details of storage battery construction and other pertinent data are given in TM 11-430, and descriptive matter on the various types which are available is given in TM 11-487.
385
PARS.
705-706
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Section III. POWER EQUIPMENT
705. TRANSFORMERS.
a. Rectifiers and other a-c operated devices for communication systems are generally designed to operate from a source of alternating current of 115/230 volts ±10 percent at 50-60 cycles. Numerous power services have other operating voltages and it will be necessary to transform these operating voltages to the above mentioned values. For this purpose a line of single-phase air-cooled transformers is available.
b. The multitap transformers used in fixed plant and listed below are single-phase transformers designed for operation on 50-60 cycle current. These transformers may be connected to step up or to step down single-phase voltages or they may be banked to handle 3-phase voltages.
c. In general, the primary or input winding of all TF type transformers consists of four separate coils. In some cases each of these
9o IOq IIq °I2 °l3l °I4 °I5 16° I7d 18°
O* 07
_O .O -O o
2 4 6 8
o I 150
2o 0 3 Ho ,, 018
I4o
4o o5 IOO---------ol7
_ 130 6o 07 90 016
TERMINAL BOARD IN
GE.CO TR ANSRDRMERS UP TO AND INCLUDING I0KVA.
TERMINAL BOARDIN GE. CO. TRANSFORMERS ABOVE 10 KVA
012 186140 I/ A9A13A16 015
DIAGRAM OF WINDING TERMINALS 10AND 17 ARE NOT CONNECTED TO THE TRANSFORMER WINDING. THEY ARE CONNECTED TOGETHER UNDER THE TERMINAL BOARD AND ARE USED WHEN TERMINALS 9-11 OR 16 8c IB ARE TO BE CONNECTED WITH LINKS
PRIMARY INPUT CONNECTIONS SECONDARY CONNECTIONS
LINES ON 1 8c 8 120 V- 2 WIRE LINESON 12 8c 15 240/120 V-3WIRE LINES-ON 12-17'-15
V CONNECT CONNECT CONNECT
108 1 TO 3 TO 5 TO 7 AND 2T04 TO 6 TO 8 9 TO 12 fit II TO 15 9 TO 10 TO II
120 12 TO 13 8c 14 TO 15 10 TO 13 TO 14
132 12 TO 16 8t 15 TO 18 16 TO 17 TO 18
216 1 TO 3 2 TO 4 TO 5 TO 7 8t 6 TO 8 9 TO 12 8c II TO 15 9 TO 10 TO 11
240 12 TO 13 8c 14 TO 15 10 TO 13 TO 14
264 12 TO 16 8t 15 TO 18 16 TO 17 TO 18
432 2 TO 3 4 TO 5 6 TO 7 9 TO 12 8c 1 1 TO 15 9 TO 10 TO II
480 12 TO 13 8t 14 TO 15 10 TO 13 TO 14
528 12 TO 16 8c 15 TO 18 16 TO 17 TO 18
TL 54982
CONNECTION INFORMATION FOR GENERAL ELECTRIC COMRANY
TYPES: TF_5_A
Figure 7-1. Terminal arrangements for Transformers TF-5-A, TF-7-A, TF-9-A, and TF-10-A (General Electric Company).
coils are tapped to carry 120 volts, 120 volts plus 10'percent and 120 volts minus 10 percent. By connecting these four windings in series, parallel, and series-parallel, voltages from 108 to 528 can be transformed to 120 volts, 240 volts, or 120/240 volts. The secondary or output of all these transformers have two windings. These windings may be connected in series for 240 volts, 2- or 3-wire, and in parallel for 120 volts, 2-wire. TF type transformers are equipped with solderless lugs on both the primary and secondary terminals. These transformers are air cooled and should be installed in a location that will allow ventilation and protection from the weather. An example of the terminal arrangements of Transformers TF-5-A, TF-7-A, TF-9-A, and TF-10-A is shown in figure 7-1.
d. When TF type transformers are used to supply single-phase loads from 3-phase circuits, care should be exercised to avoid overloading one or more of the phase legs of the circuit or appreciable unbalancing the phase loads.
e. The capacity of these transformers is as follows:
Type transformer Capacity kva
TF- 5-( ) ............................... 1.5
TF- 6-( ) ............................... 3.0
TF- 7-( ) ............................. 7.5
TF- 8-( ) .............................. 15.0
TF- 9-( ) .............................. 37.5
TF-10-( ) .............................. 75.0
f. Figure 7-2 shows diagrams of various connections of a load to a primary source of 3-phase power through single or banks of TF type transformers.
706. RECTIFIERS.
a. General Types. Rectifiers, as well as power packs which primarily include some form of rectifier, may be classified in three types, namely: tube, dry disc, and vibrator. Available equipments of these types are given in TM 11-487.
b. Application. Examples of applications of rectifiers are: the charging of lead-storage batteries while connected to a telephone load; the routine charging of lead-storage batteries in series or in series-parallel groups where no telephone load is involved; and the direct supply of power to a specific type of equipment, no lead-storage batteries being involved. In
386
PARS.
706-707
CHAPTER 7. POWER
connection with the use of such rectifiers for telephone loads, it is necessary to insure that the rectifier output is satisfactory for use on a talking circuit. Filter coils for this purpose are furnished with the rectifiers and mounted within them or furnished separately for external mounting. Where a quiet supply is not required, the use of the filter coil may be dispensed with, especially in the case of separately furnished coils where this can readily be done.
c. Tube Type. Tube type rectifiers are supplied in half-wave and full-wave designs. Some are arranged for operation on 115 volts ac, some for 230 volts, while others are arranged for both 115 and 230 volts, 50 and 60 cycles. Tube type rectifiers of the tungar type are available for d-c loads between 2 and 12 amperes, and up to 75 volts. They may be operated in parallel as required to supply larger loads. When used for a telephone load, care should be taken to see that the proper filtering coil is furnished, either as a part of the particular rectifier chosen for the application or separately. Regulated types such as Rectifier RA-43-( ) are available to obtain higher d-c voltages than can be obtained from the tungar type. Regulated tube rectifiers are also used to provide the very-high voltages required for radio transmitters.
d. Dry Disc Type. Dry disc type rectifiers are either of the copper oxide or selenium disc type. They consist essentially of a transformer and varistor unit (copper oxide or selenium) with associated fuses, resistors, filter coils, etc., mounted as a completely assembled unit for mounting on a wall, table, relay rack, shelf, etc. They are usually designed for more or less specific applications and are primarily for smaller outputs than the tube type rectifiers. Like the tube type rectifiers, they are also arranged for operation on a-c supply voltages of 115 and/or 230, 50-60 cycles. In selecting a dry disc type of rectifier for a particular application, the characteristics of the selenium type are such that it has a decided advantage over the copper oxide type where high temperatures are to be encountered, and therefore should be used in preference to the copper oxide type in such instances.
e. Vibrator Type. Most of the vibrator type rectifiers fall in the class known as power packs. Their design is practically always specific to a particular application. Their outputs
are necessarily small because of the nature of and limitations inherent in the vibrator elements. High currents through vibrator contacts tend to shorten their life, making frequent replacements necessary. Usually the vibrator type of rectifier is associated directly with a particular radio set or similar equipment. Consequently, their outputs have to meet such specific conditions of voltage and currents that they are rarely adaptable to other applications.
707. POWER PANELS.
a. General. Generally, for the smaller equipments at least, power panels associated with the control of generators, ringing units, rectifiers, small engine sets, etc., are an integral part of the particular equipment, so that no separate power panel for mounting their control equipment is ordinarily required. However, there are a few power panels furnished as separate units such as those for: telephone central office sets, larger engine-alternator sets, automatic engine power transfer, and synchronizing two or more alternators.
b. Telephone Central Office Power Panels. In the case of the large commercial type telephone central office sets, such as for dial equipments, the power panel mounts as a separate piece of equipment, with the apparatus mounted thereon for the control of generators, rectifiers, batteries, and ringing machines. In the case of the larger tactical telephone central office sets, such as the TC-1, a power panel having similar control functions is provided; in these cases the ringing equipment is mounted on the same panel. Panel BD-90 is a typical example of this.
c. Engine-alternator Power Panels. In the case of power panels for standard engine alternator sets (PE-( ) types) the control equipment for the smaller sets is usually mounted on a power panel directly on the set itself as an integral part of it. In the case of the larger sets, a separate power control panel is furnished.
d. Power Transfer Panel CN-22/F.
(1) General Description. Power Transfer Panel CN-22/F, obtainable with special engineering through Army Communications Service, is an automatic switching arrangement designed to maintain an uninterrupted a-c power supply! for the operation of Signal Corps communication equipment. It requires
387
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
- X X
------ ----------------prVAdv______________________________________________________________ 3 PHASE PRIMARY _ 4WIRE
——----------------------J , .... -------------PRIMARY
_____________ ___ _________________________________ NEUTRAL
juuJ LwJ Llusl] FjmJ jiw jluJ
'm+rwr|||jwri| 'wqjrmllpw
_________ __ 3 ,----------------3 PHASE ————————-----------------------------------------------------4 WIRE ---------------4 WIRE
-120/240 V. . - 120/240V
------------- * -------- SECONDARY '---------------------- SECONDARY
------------ ) -------------- . J
DELTA DELTA FOR LIGHT 8e POWER Y- DELTA FOR LIGHT 8c POWER
------------------------------------------------- X ■------------------------------------------------T -_________ DELTA
PRIMARY J J PR,MARY
Lj.QQ.JJO.., JjQJ./ IlJOL
p+Y+r |pmr
------------------------J-sicOVNDARY j_----ZZZ SECONDARY*
SINGLE TRANSFORMER FOR LIGHTING OPEN DELTA FOR POWER x, . --- — 3 PHASE x
_4 WI R E ______
—— -----------------------PRIMARY _______________________.DELTA
NEUTRAL PRIMARY
LwjJ JUUL JUuJ r JJjJ "Lqjll
Pppn fPPp pmq I'l'i
—x........................... , j _3 RHASE _____________________________________________________________11-----3 PR*|E , , - "120/240V
__________________________ -120/208 YY______________________________________ SECONDARY —SECONDARY___________________________________________________>
* * X
Y-Y FOR LIGHT 8c POWER NO-ff.---OPEN DELTA FOR LIGHT &: POWER
CONNECT SECONDARY OF EACH TRANSFORMER FOR 120V. TL 54983
Figure 7-2. Power line
388
CHAPTER 7. POWER
___________________________•x DMAC.F DELTA _ 4 WlRE PRIMARY
■--------------------------PRIMARY ____________________________
____ ______________ NEUTRAL J
jhhJ" jwJ jiLJi i
| |pw^ jw
| . ——'> 24o v delta
SECONDARY —*——— --------------L SEC0NDARY
Y DELTA FOR POWER DELTA DELTA FOR POWER
3 PHASE ---------------------------->
PRIMARY -----„ __________________ 3 PHASE
---------------------------J 4 WIRE
—f——-------------------- "PRIMARY
* 1 -----—_________NEUTRAL
Lw i i U i i LmJ r"^zrfn gH [pH |£pfq Irmwffi
' ' h _________________,__________3 PHASE
___________ 3 PHASE •——-------------4 WIRE
4 WIRE _____ . ■ _______ “I20/240V.
___________________ 120/208 Y V.___SECONDARY SECONDARY _________________________________________
" —
NOT^=" DELTA Y FOR LICHT & POWER CONNECT SECONDARY OF EACH TRANSFORMER FOR 120V. Y DELTA WITH ONE UNIT MISSING
*£ T-F~f-----------
J 5
<1 ? ।
.FRONT SIDE MECHANISM
VIEW VIEW tl 54769 ■
Figure 8-22. Merk Fallwaehler Selector
417
BRUSHES•
BRUSH
CARRIAGE-
PARS.
827-829 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
It provides full dial service and uses telephone equipment of the conventional dial type.
b. This type of system can be immediately identified by the appearance of the selector. In size it varies from less than 100 lines to about 6,000 lines.
TL 54770
Figure 8-23. Frame of Merk Fallwaehler dial system equipment.
c. This system will be found in the former Italian colonies, chiefly in North Africa. They will also be found in PBXs in Germany, especially in government buildings. It is not definitely known whether this system was exported to other countries from Germany, but it may possibly have been exported to Japan since the start of the war. This equipment, as far as is known, has been made only by The Telefonbau u. Normalzeit A.G. of Frankfort-am-Main, Germany.
828. DEMIAUTOMATIC SYSTEM (D SYSTEM).
a. With this system the subscriber receives a combination of dial and manual service. The subscriber dials the central office prefix digits of the called number and the dial equipment then connects him to a manual B operator in the terminating central office. He passes the four numerical digits of the number to this operator, who completes the call by plugging into the line multiple jack. This system uses a dial telephone at the station which is in most cases equipped with a message register and a special dial with added contacts which are essential for correct central office operation, as noted in paragraph 813b.
b. The demiautomatic system is used as an intermediate step in converting from manual to dial service. The originating central office equipment is of the standard rotary power-driven dial system type with a complement of line finders, registers, and originating selectors using the switches shown in figures 8-10, 8-11, and 8-12. The terminating central office equipment is a call distribution, automatic listening, and automatic ringing B manual switchboard. When this equipment is ultimately converted to a full rotary system, the B board is replaced with the standard terminating switches for that system.
c. This system can be identified by the type of switch used, plus the fact that a manual B board is also used.
d. The demiautomatic system was known before the war to have been used only in Copenhagen, Denmark. It might now logically be found also as a temporary replacement arrangement for bombed out offices in other cities. The Copenhagen equipment was mostly assembled in the Copenhagen plant of the International Standard Electric Corporation and has uniform features throughout.
829. SEMIAUTOMATIC DIAL SYSTEMS (AUTOMANUAL SYSTEM)
a. As far as the subscribers are concerned these dial systems provide manual service. The subscriber places a call by lifting the receiver and is automatically connected to an idle operator in the same building with the dial equipment by call distribution equipment. The operator then dials the desired number or sets it up on a key set, and the dial equipment completes the call for the subscriber. The station equipment consists of a conventional common battery telephone.
418
—RELAYS
- BRUSH CARRIAGES
“SELECTORS
-COMMON CONTROL AND RESTORAL MECHANISM
PARS.
829-831
CHAPTER 8. FOREIGN CIVIL CENTRAL OFFICES
b. The manual switchboard positions associated with this equipment are usually of the cordless type with about 50 sets of supervisory lamps and keys on each position, each set corresponding to a connection handled by the operator. In some cases these keys and lamps are not used, and only a dial or key set and a few master keys are used on each position. The switching equipment generally uses step-by-step switches or rotary switches either power-driven or magnetically operated, but all of the types of switches previously shown have been used in this system. This switching equipment has also been built on the all-relay principle.
c. The identifying features of this system are:
(I) Dial switching equipment of some type is used.
(2) Calls are handled by an operator in the same building.
(3) Dials are not used at the telephone.
d. This system is used in sizes from several hundred to several thousand lines scattered mostly in Europe except Germany. The total use is small. This equipment has been made by numerous manufacturers. Practically every one of the jobs of this type differs from the other insofar as features and equipment is concerned, but the interconnecting problems are generally only those mentioned in paragraph 8171. In addition it will generally be difficult to segregate calls from Signal Corps and civilian lines so that they can be handled by different operators. This is due to the fact that calls from subscribers are automatically routed to idle operators in rotation in order to equalize the load.
830. ALL-RELAY DIAL SYSTEM.
a. This equipment which provides full dial service, consists mainly of small cabinets or frames of relays which perform the switching functions. Conventional dial telephones are used. Very small jobs, like those shown in figure 8-24, are often mounted on walls, inside or outside of buildings or on standards or poles. The batteries and charging equipments are sometimes mounted separately. Sometimes these systems are operated from a power supply without batteries, the system then being out of order during power failures.
b. This system can be identified by the fact that the switching equipment consists of re
lays plus the fact that dials are used at the stations. The latter fact distinguishes the system from remote control and semiautomatic systems using relays for switching.
c. All-relay dial systems are occasionally used in foreign practice in sizes of several hundred lines, but the usual sizes range from about 10 lines to 100 lines. Some of these systems have been made by all major suppliers of dial equipment. These systems are found more frequently in Europe than elsewhere. While there is considerable detailed variation in these systems, these differences do not affect interconnection problems as much as the inherent limitations of this type (par. 817m).
tl 5477 i
Figure 8-24. Typical small all-relay dial system.
831. MAGNETO REMOTE CONTROL DIAL SYSTEM.
a. With this system the service is magneto manual as far as subscribers are concerned. Subscribers call the operator by means of the magneto which causes the dial equipment at the central office to connect the line to an operator in a distant manual office over a control trunk. The operator dials the called number back over the control trunk which causes the switching equipment to complete the call and release the control trunk. At the end of the call the calling party rings-off which causes the switches to release. The stations use conventional magneto sets with local batteries for talking.
419
PARS.
831-832
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Figure 8-25. Swedish crossbar switch.
TL 54772
b. The distant manual office associated with the remote control dial office may be of any type. The switching equipment of this system may consist of relays only, of step-by-step switches, or of magnetically operated rotary switches depending on the manufacturer and the size of the office. In each case the office takes on the characteristic appearance of the full dial system using the same type of switching equipment.
c. It should be noted that with this system it would not be practicable to segregate calls from Signal Corps and civilian lines so that they could be handled by different operators.
d. This type of office may be identified by the use of magneto sets at the stations and the absence of any manual switchboard in the immediate vicinity of the switching equipment. In sizes these offices range from about 10 lines to 200 lines.
e. The small amount of this equipment in use is scattered throughout all countries except Germany. Some of this equipment has been made by all manufacturers of dial equipment but most systems will be found to have been made by the following companies and their affiliates: Automatic Electric Company, Chicago; Automatic Telephone Manufacturing Company, England; Siemens-Halske, Berlin. (The last named company has made these systems for export only.)
832. COMMON BATTERY REMOTE CONTROL DIAL SYSTEM.
a. This system provides common battery manual service as far as the customers are
concerned. Subscribers call the operator by lifting the receiver, which causes the dial equipment to connect the calling line to a distant manual office over a control trunk. The operator dials the called number back over the control trunk which causes the switches in the dial office to complete the connection and release the control trunk. When the calling party hangs up at the end of the call the switching equipment releases. The station equipment is a conventional common battery telephone without a dial.
b. The remote manual office serving as a control center may be of any type. The switching equipment consists of relays for small offices and usually of step-by-step or magnetically driven rotary switches in the larger offices.
c. With this system it would not be practicable to segregate calls from Signal Corps and civilian lines so that they could be handled by different operators.
d. This type of office may be identified by the fact that the stations are of the common battery types and that there is no nearby manual switchboard associated with the dial equipment. Equipment of this type may be used in offices which serve from 50 to 200 lines.
e. This system is not extensively used anywhere but is apt to be found in almost all countries except Germany. Some of this equipment has been made by all dial system manufacturers but most of it by the following companies and their affiliates: Automatic Electric Company, Chicago; Automatic Telephone Manufacturing Company, England; Siemens-Halske, Berlin (export trade only). The dif
420
CHAPTER 8. FOREIGN CIVIL CENTRAL OFFICES 832-833
ferent varieties all present about the same interconnection problems (par. 817o). However, Siemens-Halske jobs seem to make more general use of high-resistance transmitter battery supply circuits than other systems.
833. SWEDISH CROSSBAR SYSTEMS.
a. This system which provides full dial service uses the crossbar switch shown in figure 8-25 as line finders, selectors, and connectors. Conventional dial telephones are used except where special features are required. All switches except the line finders follow dial pulses in performing the selecting functions,
in contrast to the American crossbar practice of using common control.
b. The crossbar switch provides a ready identification of this system.
c. Swedish crossbar systems have, as far as is known, been used only in Sweden. This equipment was originally made only by the Swedish government in its own factories, but may now also be made by the L. M. Ericsson Company of Stockholm, Sweden. A large number of small rural offices with capacities of 20, 50, and 90 lines have been installed and in addition some large capacity offices have been installed in cities.
421
Type of plant Approx, weight and ship space* for 25 miles Estimated man-days b for constructing 25 miles
Short tons Cu. ft.
Long range field Wire W-143 and Cable Assembly CC-358-( ) (.Spiral-four).
Wire W-143 Aerial construction—150' span Erecting pole line and cable, 1 pair Erecting cable on existing pole line 46 5.2 2,700 230 258 110
Ground surface-construction,d 1 pair 4.8 210 31
Buried0 construction,d 1 pair 4.8 210 76
2 pairs 9.6 420 98
Cable Assembly CC-358-( ) Aerial construction—150' span Erecting pole line and one cable 52 3,100 258
Erecting one cable on existing pole line 11.5 630 110
Ground surface construction d 11 610 46
Buried0 construction,d 1 cable 11 610 71
2 cables 22 1,220 105
Open wire.
Tactical open wire line—150' Span 1 Pair—4" x 4" lumber supports 4 Pair—4" x 4" lumber supports 8 Pair—round poles—22' class 9 54 72 179 3,100 3,900 8,800 283 365 625
Tactical open wire line—200' span
1 Pair—round poles—20' class 9 100 5,100 290
4 Pair—round poles—20' class 9 111 5,500 363
8 Pair—round poles—22' class 9 146 7,100 528
Fixed plant open wire line—150' span
4 Pair—round poles—30' class 7 (average) 254 12,700 538
8 Pair—round poles—30' class 7 297 14,300 733
Lead-covered cable. e
Aerialf—150' span (51 pr. 19 ga. CNB)h 334 15,000 625
Buried8 (51 pr. 19 ga. CNBh jute protected) 132 5,100 1,300
a The material lists given in the respective manuals were used as a basis for determining approximate weight and ship space figures. In the case of Wire W-143, estimates are based on material requirements and construction methods similar to those given in TM 11-369 for Cable Assembly CC-358-( ). A material surplus of 25 percent is included.
b Assumes commercial crews and conditions including 8-hour day. Work time variations with locality can be expected. The hours required to build a pole line vary with the kind of soil encountered and with climatic conditions. For example, if holes must be dug in rock or if the ground is frozen, blasting will be required which will slow the work. Swamp land also will cause the work to take longer. Digging holes in frozen swamp land may be expedited by means of the Blast Driven Earth Rod (expected to be available soon), which is used to drive a small hole into which a charge of PRIM ACORD is placed and then exploded to spring the hole to the desired diameter. The estimates assume that the work is done in mild weather and that ordinary earth digging is encountered. Hand digging in frozen ground will
add about 50 per cent to the time and in rock it will double the time estimate. If tree trimming is required this will take 25 to 50 man-hours per mile.
c Assumes use of Plow LC-61.
d Does not include material or time for constructing overhead crossings. If highways or roads are crossed aerially an allowance may be made for each overhead crossing (of the type described in TM 11-369) as follows: poles and accessory hardware, 350 lbs., 10.5 cu. ft.; construction time, 0.65 man-days.
e Does not include splicing time; this usually takes from 20 to 25 man-days per mile.
f Provision is not made in materials list for terminals, drop wire, protectors, and terminating equipment. Job includes erecting pole line, placing strand and cable.
E Only time and material required for delivery and burying of cable are included. In the burying operation a plow and automotive equipment are required.
h Western Electric Company designation for 19 gauge cable with capacitance of 0.084 mf per pair mile.
Figure 9-1. Weight, space, and construction time.
422
CHAPTER 9
OUTSIDE PLANT
Section I. INTRODUCTION
901. INTRODUCTION.
This chapter covers important features of outside plant engineering. Section II gives the general considerations of importance in planning wire facilities, in surveying routes, in assembling materials, and in organizing construction work so as to make efficient use of personnel and equipment. Section III discusses the various types of wire plant, their physical
characteristics, and methods of installation. Particular reference is made to the attention which should be paid to storm loading, and the sags and spacings of aerial wires. In sections IV and V notes are given on aspects of recovery and rehabilitation of communication lines in occupied territory. In section VI tentative information on the construction of lines suited to jungle use is set forth.
Section II.
902. GENERAL.
a. Early decision is required as to the traffic facilities needed and the type of plant to be used. Only when these decisions have been reached can a survey of the line route be carried out, a list compiled of the needed material and equipment, and arrangements made for their supply. Factors to consider from the standpoint of traffic and of transmission are outlined in chapter 11 and in chapter 5 respectively. In selecting the type of line, the following should be taken into account:
(-0 Time available for construction.
(2) Terrain and weather conditions.
(3) Length of line.
(4) Number and types of circuits.
(5) Availability of material and manpower.
(6) Availability of civil plant.
(7) Expected permanence of line (tactical or fixed plant).
(8) Future growth.
b. If, after a consideration of these factors, the use of aerial wire or cable lines is indicated, construction plans should take into account such factors as expected storm loadings, importance of line, and weight of wire or cable to be used. Information concerning construc-
PLANNING
tion of aerial lines is given in section III of this chapter. Typical problems in TM 11-487, give the relative material requirements for obtaining various circuit facilities, together with weights, volumes, and ship tons. A brief summary of this information is given in figure 9-1. Further information on the construction of open wire lines is given in TM 11-368 and TM 11-2253. In tactical situations, if enough circuits for two crossarms are required, consideration should be given to building singlecrossarm lines over different routes to improve the likelihood of good continuity of service.
903. SURVEYING AND STAKING LINE.
a. A tentative selection of the route is usually made by reference to topographical maps, aerial photographs, or a preliminary survey. When the type of line and general route have been selected, the route should be covered by a survey party and the line staked. The care with which this work should be carried out is dependent upon the type and importance of the line. In the case of pole lines, the procedure should be followed that is outlined in TM 11-368, TM 11-369, or TM 11-2253, that is, span lengths should be measured, each pole staked, and notations made of the location of cross-
423
PARS.
903-905
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
TL-50521
Figure 9-2. Typical line survey notes.
SPAN POLE POLE TR£NS
OSTANCE NO LENGTH GUYS NOTES
39+7? PIO 20'
37+57 P19 20’
35+97 ph 20’ ~B~
33+93 PI7 20'
32403 » p'6
3003 Y PIS W K
27*33 W P14 25' 22M
25+73 PI3 25' 2,2M
23*93 [9D P|2 20' C
--------2U5------------------
21*77 pn 1Q.
19*77 ^0 p|Q 2,Q'
17*97 *90 P9 20' A
15+77 ^0 P7 25' 21M
13*97 *VQ P7 '25' ll/vT^.
11+93 P6 20’ B
9 *73 ^-0 P5 20'
7 i44 P4 10'
5*97 P3 20' A
4 nVr P1 10
11*95 PI 20'
0*00 PO 20’ 6/V\ "
ings of all types, as well as changes in the type of line caused by conditions of terrain, etc.
b. It is important to avoid exposing aerial lines to electrical or physical hazards. If feasible, stay at least % mile away from paralleling power lines, highways, and railroads. The detailed information gathered (fig. 9-2) should contemplate the necessity for compiling a list of needed material and information which will aid in its subsequent distribution.
904. MATERIAL CONSIDERATIONS.
Assistance in compiling a list of the materials required to construct various lengths of different types of line can be had by referring to the examples given in TM 11-487 and also to similar lists in TM 11-368 and TM 11-2253. The line materials should be distributed along the route where they will be ready for use by the construction forces.
905. ORGANIZING CONSTRUCTION.
The type and number of crews which should be organized to carry out the construction is dependent upon the available manpower and equipment, such as line construction trucks, pole hole diggers, plows, tools, etc., which are set forth in TM 11-487, TM 11-368, TM 11-2253, and TM 11-369. The latter three manuals outline typical crews for carrying out the respective types of construction whether pole line, ground surface, or buried. The main objective is to form crews of the proper size and experience to carry out the work in an orderly and logical sequence. For instance in building pole lines, in addition to a survey crew, there might be a crew to carry out each of the following functions: deliver materials, dig pole and anchor holes, equip and set poles, place anchors and guys, and install wire.
424
PARS.
CHAPTER 9. OUTSIDE PLANT 906-908
Section III. CONSTRUCTION
906. STORM LOADING.
a. In the United States, aerial communication lines are designed to withstand three type of storm loading (see storm map in TM 11-368), namely:
(7) Light loading: a wind pressure perpendicular to the line, of 12 pounds per square foot (about 70 mph, indicated) on the projected area of wires at a minimum temperature of 30° F.
(2) Medium loading: a wind pressure perpendicular to the line, of 8 pounds per square foot (about 60 mph, indicated) on the projected area of wires covered with 14 inch radial thickness of ice at a minimum temperature of 15° F.
(3) Heavy loading: a wind pressure perpendicular to the line of 8 pounds per square foot on the projected area of w’ires covered with 1/2 inch radial thickness of ice at a minimum temperature of 0° F.
b. Under conditions of severe exposure to high winds and ice, a still heavier type of construction may . be warranted as indicated in TM 11-368.
c. European and Asiatic Countries have somewhat different storm loading requirements. In some foreign countries lines are designed to withstand three classes of loading and in others, two. In general, the heavy loading requirements result in about the same strength of line whether in Europe, Asia, or in the United States. In selecting the type of line for a given area where ice and temperature conditions are not known, an attempt should be made in advance of occupancy to obtain this information from communication or electric light agencies familiar with the countries involved. Where this cannot be done a general rule to follow is to use heavy loading construction in latitudes higher than 40°, medium loading between latitudes 30° and 40° and light loading in latitudes under 30°. There are exceptions to this rule. For instance, even in latitudes under 30° there are locations having elevations where ice and temperature conditions would indicate the advisability of using heavy loading area construction.
907. SELECTION OF POLES.
a. As discussed in paragraph 912d and in TM 11-368, 4 x 4 square poles or class 9 round
poles are used in the construction of tactical aerial lines. To meet the more extensive needs of the fixed plant, data are given in figure 9-3 which will provide the necessary information required to select poles for various types of lines in different storm loading areas. The weight and circumference, 6 feet from the butt of various classes of round poles, are given in TM 11-487. The length of poles may be estimated from the information given in the notes accompanying figure 9-3.
b. Round poles are classified in such a manner that a pole of a specified class will support a given load regardless of the length of the pole. In other words, longer poles have a larger ground circumference than shorter poles of the same class.
c. If native poles are used they should be classed on the basis of the length and the circumference 6 feet from the butt as described in TM 11-487. They should also be given a preservation treatment as described in paragraph 925b.
908. CONDUCTOR SAGS AND WIRE SPACINGS.
a. The sag and the tension in a suspended member such as wire or field cable are related, and these will change with temperature and with external loads of ice or wind. To provide a line which will operate with a minimum of service interruptions and require a minimum of maintenance, it is advisable to select installation sags and tensions which will prevent subsequent stress of the suspended member beyond the elastic limit when it is subjected to low temperatures and a recognized degree of storm loading (note a of figs. 9-9 and 9-14, note b of fig. 9-19, and par. 906).
b. The nominal span may be 150 to 200 feet depending upon the degree of loading anticipated or the urgency for facilities. The shorter span provides a line of greater strength than the longer one, other factors being equal. Recommended span lengths for use in the various loading areas are given in TM 11-368, TM 11-369, and TM 11-2253. Figure 9-4 shows the relations of individual span lengths, sag, wire size, tension, and temperature for a nominal span of 150 feet. Figure 9-5 provides the same information for a nominal span of 200 feet. Since it is desirable to have all wires on the same line as well as the same crossarm at
425
PAR.
908
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Number of wires on line* Class of pole c’ for various loading area and span length
Heavy Medium Light
150 ft. 200 ft. 150 ft. 200 ft. 150 ft. 200 ft.
1-8 9 7 9 9 9 9
9-16 7 6 9 9 9 9
17-24 5 4 7 7 9 9
25-32 4 3 7 6 9 9
33-40 4 2 6 5 9 9
8 The number of wires is the sum of the following wire equivalents of all of the attachments which the line is ultimately to support:
Attachment TJ'i're equivalents for carious loading area
Heavy Medium Light
Bare open wire 109 or 104, per wire 1 1 1
Bare open wire 128, 134, or larger, per wire 1.5 1.5 1.3
Covered paired wire, per pair, or covered single wire, per wire 1.5 1.5 2.5
Rubber-covered cable, per cable 2 2.5 5
Wire messenger (stranded), all sizes 2 2.5 5
Lead-covered cable up to diameter, per cable (not including messenger) 3 4.5 10
Lead-covered cable from \ y to l1^" diameter, per cable (not including messenger) 4 6 17
Lead-covered cable greater than l1^" diameter, per cable (not including messenger) 5 8 25
b In the preparation of this table shielding of one wire by another has been taken into account, as is the custom, for heavy and medium loading. Where the number of wires exceeds 10, only 2/3 of the actual number of wires are considered to offer wind resistance, provided that the resulting number is not less than 10.
c In determining the length of pole required, make allowances for the following:
(I) The depth the pole is to be set in the ground.
(2) The distance from the top of the pole to the wires on the top crossarm (about 4 inches).
(3) The number of crossarms (spaced 3 feet apart).
(4) The sag of the wires or cable.
(5) The clearance required between the wires and the ground at the middle of the span, normally 14 feet, (18 feet at highways and 27 feet at railroads).
d At dead-ends and at corners having a pull of more than 20 feet (interior corner angle less than 158°), use poles of a lower class number. At a corner having a pull of more than 50 feet (interior corner angle less than 122°), divide the corner equally between two poles of lower class number (TM 11-368 or TM 11-2253).
Figure 9-3. Recommended sizes of treated poles for cerial lines (American standard)-
about the same sag because of the possibility of swinging wire contacts, appearance, etc., sag tables are based on the sag requirements for the "weakest conductor. Figures 9-4 and 9-5 should be used when the lowest tensile
strength conductors are either 104 copper or 080 copper-steel. Figure 9-6 provides similar data where the weakest wire to be used is 104 copper-steel. Therefore the sags given in this latter table for the same lengths of span and
426
PAR.
908
CHAPTER 9. OUTSIDE PLANT
Span length (feet) Conductor Sag and tension at various temperatures
0°F. 30°F. 60°F. 90°F.
Sag (inches) T ension (pounds) Sag (inches) Tension (pounds) Sag (inches) Tension (pounds) Sag (inches) Tension (pounds)
100 080 C-S 2% 125 2% 100 3% 75 5 55
104 C-S 2% 230 2% 185 3% 140 5 100
104 CU 2% 230 2% 185 3% 140 5 100
109 GS 2% 225 2% 180 3% 135 5 95
125 080 C-S 3% 125 4% 100 5% 75 8 55
104 C-S 3% 230 4% 185 5% 140 8 100
104 CU 3% 230 4% 185 5% 140 8 100
109 GS 3% 225 4% 180 5% 135 8 95
150 080 C-S 4% 125 6 100 8 75 11% 55
104 C-S 4% 230 6 185 8 140 11% 100
104 CU 4% 230 6 185 8 140 11% 100
109 GS 4% 225 6 180 8 135 11% 95
175 080 C-S 6% 125 8% 100 11 75 15% 55
104 C-S 6% 230 8% 185 11 140 15% 100
104 CU 6% 230 8% 185 11 140 15% 100
109 GS 6% 225 8% 180 11 135 15% 95
200 080 C-S 8% 125 10% 100 14% 75 20% 55
104 C-S 8% 230 10% 185 14% ' 140 20% 100
104 CU 8Y2 230 10% 185 14% 140 20% 100
109 GS 8% 225 10% 180 14% 135 20% 95
225 080 C-S 10% 125 13% 100 18 75 25% 55
104 C-S 10% 230 13% 185 18 140 25% 100
104 CU 10% 230 13% 185 18 140 25% 100
109 GS 10% 225 13% 180 18 135 25% 95
Figure 9-4. Sags and tensions for lines supporting conductors with strength of 104 copper or greater and 150-foot nominal span.
427
PAR.
908 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Span length (feet) Conductor Sag and tension at various temperatures
0°F. 30°F. 60°F. 90°F.
Sag (inches) Tension (pounds) Sag (inches) T ension (pounds) Sag (inches) Tension (pounds) Sag (inches) Tension (pounds)
100 080 C-S 200 1^ 175 ' 1% 150 2A 125
104 C-S ik 365 1A 320 1% 280 2A 230
104 CU 1^ 365 1A 320 1% 280 2A 230
109 GS ik 355 1A 310 1% 270 2A 220
150 080 C-S 3 200 SA 175 4 150 5 125
104 C-S 3 365 SA 320 4 280 5 230
104 CU 3 365 SA 320 4 280 5 230
109 GS 3 355 SA 310 4 270 5 220
200 . 080 C-S 5A 200 6 175 7 150 8M 125
104 C-S 5H 365 6 320 7 280 8% 230
104 CU 5H 365 6 320 7 280 8A 230
109 GS 355 6 310 7 270 SA 220
250 080 C-S 8A 200 9% 175 11 150 ISA 125
104 C-S 8A 365 9% 320 11 280 ISA 230
104 CU 8A 365 9A 320 11 280 ISA 230
109 GS 8A 355 9% 310 11 270 ISA 220
300 080 C-S W 200 14 175 16 150 19A 125
104 C-S 12H 365 14 320 16 280 19A 230
104 CU 12 A 365 14 320 16 280 19 A 230
109 GS W 355 14 310 16 270 19A 220
Figure 9-5. Sags and tensions for lines supporting conductors with strength of 104 copper or greater and 200-foot nominal span.
temperature, are less than those given in the other tables for bare wires. Similar data for field wires and spiral-four cable are given in figures 9-15 and 9-18. Sag and tension data are given for a range of temperatures. If data are required for other temperatures they may be approximated by interpolation or extrapolation.
c. Sag information for span lengths and conductors other than those covered in subpara
graph b above can be obtained by interpolation in figures 9-4 to 9-6. In addition there are rough rules which can be used. For instance, when placing a conductor aerially in a span of moderate length in a heavy loading area, it should be tensioned at not more than about 1/5 of its breaking strength at an average temperature, say 60° F. In light loading areas, this tension might be increased to 14, of the breaking strength. Where feasible, less tension
428
PARS.
908-909
______CHAPTER 9. OUTSIDE PLANT
Span length (feet) Sag {inches') at various temperatures
0°F. S0°F. 60°F. 90°F.
100 W2 2^ 3 4
125 2H 3^ 4 5^
150 4 5 6 8
175 V/2 6^ 8 11
200 7 sy2 10^ 14
Figure 9-6. Sags for lines supporting conductors with strength of 104 C-S or greater.
should be used since some conductors will stretch more than others. A simple expression can be used to determine the sag equivalent to any tension. This is as follows: d = wL2/8T, where d = sag in feet, w — weight of suspended wire in pounds per foot, L = span length in feet, and T = tension in pounds.
d. The preferred method of sagging wires is through the use of Scale LC—64, which indicates the tension at the pulling end (TM 11-368). Initially the tension at the scale should be carried slightly above the correct value so as to achieve the desired sag in the spans remote from the tensioning apparatus. The tension can then be slacked off until the correct value of sag is obtained in the spans at the pulling end.
e. Sag may be measured by actual sighting, using a sag gauge, or by the more convenient oscillation method (TM 11-368, TM 11-369, and TM 11-2253). This latter method makes use of the relationship between the sag and the time required for a wave set up in a wire at one support to travel to the other support and back. This relationship is d = 1.006 (t/n)2, where d — sag in feet, t — time in seconds for n returns of the wave. This relationship is independent of span length. The wave is usually set up by striking the wire with the side of the hand near one support. Where sags are small, 10 returns of the wave can easily be counted. Where sags are large, greater accuracy can be obtained by swinging the whole span of wire in a direction transverse to the line as a pendulum, and determining the time required for the wire to swing through a complete cycle, over and back, a given number of times. The same relationship holds as in the former method. A stop watch is
helpful in obtaining accurate results. A curve giving the above relationship between sag and time for 10 swings of the span of wire or returns of the wave is given in figure 9-7.
f. One of the factors which has to be taken into account in engineering open wire lines is swinging wire contacts. The wires should be spaced and sagged so that such contacts will not take place at wind velocities which frequently occur. The nomogram in figure 9-8 gives the relationship between sag, wire spacing, span length, and threshold wind velocity1. In the average location it is sufficient to engineer for threshold velocities of around 40 miles per hour at average temperatures.
4Oi—-----------------------------------------
_ METHOD /
STRIKE THE CONDUCTOR A /
36— BLOW CLOSE TO ONE SUP-_________________J—
PORT AND SIMULTANEOUSLY /
— START A STOP-WATCH. STR IK-------------/—
ING THE WIRE CAUSES A /
32— WAVE TO TRAVEL FROM THE-----------Z----
_ NEAR SUPPORT TO THE FAR i
one, Where it will be -------------1----
28— REFLECTED. AT THE TENTH_____________Z__
RETURN OF THE WAVE STOP /
J — THE WATCH AND READ THE------------/_______
X TIME. THE SAG CAN THEN /
0 24— BE READ DIRECTLY FROM-----------Z-------
2 THE CURVE. /
1-------———r—————---------------— /-----------
£20-------------------------------y-----------
S-------------------------------/_____________L_
o 16----------------------------U-------------
S--------------------------y------------------
12----------------------/____________________
8------------------Z------------------------
4------------y~----------------------------
o ——i* —________________________________
0 2 4 6 8 10 12 14 16 18
TIME FOR TENTH RETURN OF WAVE - SECONDS
TL 54836
Figure 9-7. Oscillation method of measuring sag.
909. RUBBER-COVERED WIRES, GENERAL
a. Rubber-covered conductors are provided either as a twisted pair, a parallel pair, a spiral-four quad, or a 5- or 10-pair cable (pars. 910 and 911). They can be installed rapidly by simply paying out on the surface of the ground from a reel mounted on a truck, from a hand-drawn reel cart, or from reels carried by one or two men, depending upon weight.
1 The threshold wind velocity is the instantaneous velocity at which the wires of a pair begin to contact. The instantaneous wind velocity has been found by experiment to be about 1.4 times the U. S. Weather Bureau 5-minute average velocity.
656935 o—45-
-29
429
PAR.
909
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
T4
--5 ""6 KEY D
R L
s, i_U-
- - 8 -L —------------------
w
--I0 £
z given: ___
- SPACING, SPAN LENGTH, AND SAG. w w TO FIND VELOCITY:
--I5 ? FIRST LOCATE POINT ON LINE (R) § determined by straight line (J)
u. THROUGH GIVEN VALUES OF SPACING
° AND SPAN LENGTH ON LINES (S)
--209 AND (L)
£ A STRAIGHT LINE (2) FROM THIS POINT ON LINE (R) TO THE GIVEN VALUE OF __ SAG ON LINE (D) WILL INDICATE THE
25 VELOCITY SOUGHT AT ITS INTERSECTION
WITH THE LINE(V)
--30
--35
--40 45 TL 54953
260
t—I—
O
co r- «*> w cm
BOOH U3d S31IIN Nl A1ID013A ONIM
Figure 9-8. Wind velocity (threshold) perpendicular to the line at which wires of a pair begin to contact.
CJ © <0 xr CO
S3HDNI Nl DNIDVdS 3BIM IVlNOZldOH
430
PARS.
909-910
CHAPTER 9. OUTSIDE PLANT
In such cases it is usually necessary to make special provision against injury to wires from motor vehicles, artillery, tanks, or maneuvering troops. This is especially true at road crossings where these wires should either be buried or elevated on poles or trees. Buried or elevated construction is required at railroad crossings. Where exposure to injury is general throughout the route of the wire, it is usually advantageous to either bury cable or support it on poles or trees throughout its length. Surveys for buried construction should contemplate the possibility of interference from bulldozers which may be used in road building. The installation features vary somewhat with the type of wire or cable, as discussed below.
b. Information on captured enemy field wires is given in TB Sig E-15.
910. SINGLE PAIR WIRES.
a. General. The physical characteristics of the rubber-covered wires described in the following subparagraphs are given in figure 9-9 and their electrical characteristics are given in chapter 5.
b. Wires W-130, W-130-A, W-130-C, WD-3/TT (Assault wire). These wires, when furnished in i/i-mil^ lengths on Reel DR-8, weigh 9 pounds and can be carried by one man using Reel Equipment CE-11 which includes a sound-powered telephone and thus permits easy communication back to the command post as he advances. When furnished in 2-mile lengths on Reel DR—4 it can be carried by two men using Axle RL-27-( ) (fig. 9-10). Wire W-130-( ) is- furnished also in i/>-mile lengths on Reel DR-8. Because transmission over assault wires is affected by moisture, its performance is improved somew’hat when supported off the ground on trees or bushos. Methods of splicing and handling this wire are covered in FM 24-20.
c. Wire W—110—B (Field wire).
(1) This wire is the most widely used and generally available. It is now insulated with synthetic rubber instead of rubber. When supplied in 2,400-foot lengths on Reel DR-4, it can be carried on Axle RL-27- ( ) by two men as it is payed out. Either Reel DR-4, or Reel DR—5 which carries one mile of this wire, can be mounted on a hand-drawn Reel Cart RL-16 or on Reel Unit RL-31-( ). Reel DR-5 may be mounted on Reel Unit RL-
26- ( ) which is a power-driven unit that can be used either for paying out or reeling up (fig. 9-11). When this wire is used as an insert in an open wire line, it is preferable to install one Wire W-110-B (two conductors) for each open wire and to maintain, if possible, the same spacing between the sides of the circuit as used for the open wire. While this wire may occasionally have to be buried at highway and railroad crossings it is not suitable for extensive buried installations. The practices relative to the use, installation, and maintenance of Wire W-110-B are covered in FM 24-20.
(2) In commercial practice it is recognized that in construction work, good appearance and good workmanship are closely related. The appearance factor has its justification in army practice but there are conditions where its influence might be carried too far. One instance is the tendency to bunch and lash together in the form of a cable considerable numbers of Wire W—110—B or other types of field wire in approaches to switching centrals. It is obvious that during humid or wet weather conditions, such construction provides a cellular structure which invites and retains moisture, causing troubles associated with low insulation resistance that might not develop if each pair were suspended individually. In addition, individual suspension will improve transmission in wet weather and make it easier to locate trouble should it occur. The preferred method is to place crossarms and attach pairs to insulators in the manner of bare wire. Where this is not feasible a method reported as used with success in one theater uses slots for the wires in a crossarm or wooden member at suitable intervals with the support mounted either horizontally or vertically as indicated -in figure 9-12. A latch or keeper spanning two adjacent slots and secured by a thumbnut is useful to hold the wires in position. Another method shown in figure 9-12 and used in another theater, uses a horizontal crossarm with slots but no keepers. A corner pole using this type of construction is shown in figure 9-13.
d. Wire W-143 (Long range tactical wire).
(1) This wire is furnished on Reel DR-5 which can be mounted on Reel Unit RL-31 or Reel Unit RL-26-( ) as in the case of Wire W-110-B and payed out or reeled up in the same manner. It can be installed similarly on the ground or aerially, and in addition can
431
PAR.
910
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Description Twisted pair; each rubber covered; no braid; one 0.010-inch copper and six 0.0095-inch steel strands per conductor; nonstabilized. Classified, sub- stitute standard as of 7-44. Twisted pair same as W-130 except that vinylite insulation is used; nonstabilized. Classified, standard as of 7-44. Twisted pair same as W-130 except that polyethylene insulation is used; nonstabilized. Classified, standard as of 7-44. Same as W-130 except with braid on each conductor. Classified, substitute standard as of 7-44. Twisted pair; each rubber and braid covered; three 0.0135-inch copper and four 0.013-inch steel strands per conductor; nonstabilized. Parallel pair; rubber covered; stabilizing carbon-saturated paper around pair; over-all braid; seven 0.0226-inch copper strands per conductor; stabil- ized. TB SIG 101. Twisted pair; each rubber and braid covered; 14 ga. (0.064 inch) hard-drawn copper; nonstabilized. Parallel pair; rubber; cotton braid; weatherproofed; 17 ga. (0.045 inch) tinned copper-steel or bronze; nonstabilized. Same as W-108 except 18.ga. (0.040 inch). its per mile or per reel of product. abilized wire has transmission characteristics which vary between wet eather. ry splices, which may be a point of weakness, are indicated by red arkings on insulation on wire manufactured since late in 1943. nsulated wires.
pounds)0 Per mile (without reels) o 00 00 co co to 120 240 320 170 158
T 3 ,C5> 4 Per reel (wire plus reel) O <*) Coil 10 DR-7 2,640 or DR-15 1,000 DR-7 1,000 Coil 12 DR-15 1,320 Coil 100
Breaking load* (pounds') 425 425 750 500 500 500
Approximate major Nomenclature dimension of cross-secti< n _____ (inches) Cable Stub 0.50 CC-344 Cable Assembly 0.50 CC-345 Cable Assembly 0.70 CC-355 or CC-355-A Cable Stub 0.42 CC-356 Cable Assembly 0.42 CC-358-( ) Cable Assembly 0.42 CC-368 Coil C-114-A
435
PAR.
911
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
A. Sags and tensions without messengers
Span length (feet) Conductor Sag and tensions at various temperatures
0°F 30°F 60°F 90°F 120°F
Sag (inches) Tension (pounds) Sag (inches) Tension (pounds) Sag (inches) Tension (pounds) Sag (inches) Tension (pounds) Sag (inches) Tension (pounds)
100 CC-358-( ) 12 135 12H 130 13 125 14 120 w 105
W-50 12 75 12^ 70 13 70 14 65 14F6 60
W-110-B 12 30 W 30 13 30 14 25 14^ 20
125 CC-358-( ) 19 135 • 20 130 21 125 22 120 23 105
W-50 19 75 20 70 21 70 22 65 23 60
W-110-B 19 30 20 30 21 30 22 25 23 20
150 CC-358-( )8 27 135 28 130 30 125 31 120 32 105
W-50 27 75 28 70 30 70 31 65 32 60
W-110-B 27 30 28 30 30 30 31 25 32 20
175 W-50 37 75 39 70 40 70 42 65 44 60
W-110-B 37 30 39 30 40 30 42 25 44 20
B. Sags for messenger supporting Cable Assembly CC-358-( )
Span length (feet) Sag (inches) at various temperatures
In strand with cable attached In strand with no cable attached
30°F 120°F 30°F 60° F 120°F
200 9 12 3^ 4M 5
300 24 32^ 10M 12 15^
400 53 68M 31 36 44^
500 103 127 70 75 90
8 Where span lengths exceed 150 feet and ice is not expected to be a factor spiral-four cable should be supported by messenger having minimum sags shown in B above (TB
11-369-1). In areas where ice and sleet might be experienced, messenger should be used and installation made in accordance with figure 9-18.
Figure 9-15. Sags and tensions for field wires and spiral-four cable.
then the ends of the tie joined in a square knot over the messenger. The spacing of the ties should be about 6 feet. The cable and messenger should be tied together on the ground, then raised into position and the messenger only tens_oned. An alternative method of supporting the cable from the messenger, re
ported as used successfully in one theater, is to make wire hangers which are somewhat similar to the commercial type of cable suspension ring. The method of making these hangers is shown in figure 9-16. Experience has shown that unless the cable is installed with some slack, conductor breakage may re-
436
Messenger wire Span length (feet) Sag and tension at various temperatures in strand with cable attached »
0°F 30°F 60°F
Sag (inches) Tension (pounds) Saff (inches) Tension (pounds) Sag (inches) Tension (pounds)
WS-3/U 100 1A 1,625 1% 1,535 2 1,415
150 4 1,455 4A 1,370 5 1,245
200 9 1,245 10 1,135 11 1,025
W-113 200 8% 2,300 10% 1,950 12 1,645
300 29A 1,525 34% 1,300 40% 1,120
400 78 1,030 85% 940 92% 870
a Sags for nonsleet areas are given in figure 9-15.
Figure 9-18. Sags and tensions for messengers used in supporting spiral-four cable in snow and ice areas.
437
PAR.
_____________________________CHAPTER 9. OUTSIDE PLANT 9U
suit from shell concussions. Suspended spiral- culty can be overcome in cable of early manu-four cable of relatively early manufacture has facture by supporting it with messenger as under some conditions been found to stretch described above. Representative aerial con-noticeably with time. Cable which is over-ten- struction features of spiral-four cable are sioned is apt to stretch similarly. This diffi- shown in figure 9-17.
(3) Where ice or sleet conditions are fit tight in base-i ___ f___ expected to be severe and strength is the pn-
mary requisite, even in spans as short as 100 p—1 ‘—| feet a messenger support should be used for
। z | spiral-four cable. Wire WS-3/U should be
r dx___n_____ used for span lengths up to 200 feet and Wire
F V h7 y W-115 for span lengths from 200 to 400 feet.
, Figure 9-18 indicates the recommended string-
~ ing sags for each of these messenger wires | J with cable attached. When Wire W-115 is
ni« XX______used to support the cable the methods outlined
r- r------- in TM 11-363 should be used, except that the
'-Izt------ LI------1 l_L
SIDE VIEW F*—
FRONT VIEW TERMINATING . DEPOT INTERMEDIATE -FIELD REPAIR SPLICE
MAKE OF WOOD OR METAL Ci. amp - : REPAIR SPIRAL SUPPORT -terminating grip
DIMENSIONS ARE APPROXIMATE. 1
CUT WIRE
O FORM,NG O BL/ I 1 ! J IbJw
■ I I Kill
PLACE ON MESSENGER fcjwl I f M I 1
FORM ON JIG IN AND CABLE IN THIS EaV I 1J ■M /
THIS MANNER MANNER
HANGER MATERIAL SHOULD BE SOFT OR ~ connector ' «
ANNEALED WIRE, PREFERABLY OF SAME WEMO-lSTSwu TL 53>43
MATERIAL AS MESSENGER.
54839 Figure 9-17. Spiral-four aerial construction using
Figure 9-16. Jig for making spiral-four cable hangers. Cable Assembly CC-358-( ).
PARS.
911-912
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
messenger and cable should be assembled on the ground, using Wire W-110-B as described in subparagraph (2) above. When Wire WS-3/U is used, these same methods apply with the following exceptions:
(a) Since no standard suspension clamps can be used for Wire WS-3/U, it is recommended that Hubbard No. 7401 one-bolt guy clamp (stock No. 5B3448) or equal be used. The messenger should be placed in the top groove of the clamp and if necessary a piece of strand may be placed in the bottom groove to insure a firm grip on the messenger.
(5) The method of dead-ending this messenger, outlined in TM 11-369 for long span construction, may be used as an alternate to the method outlined in TM 11-363, except that a Hubbard No. 7402 2-bolt guy clamp (stock No. 5B3402) or equal should be substituted for Clamp PF-61.
(c) Since it is not safe to use cable Car LC-41-A on Wire WS-3/U, it will be necessary to use a ladder such as Ladder LC-15.
(4) If buried, this cable can be installed at any depth from 6 to 18 inches by means of cable Plow LC-61 towed by a 21/2-ton 6x6 cargo truck carrying the reel. The plow, carrying the reel, can be towed by winch line across streams or other places where the truck cannot travel. Where speed in establishing communications is vital, the cable can first be installed on the ground surface and later picked up by the plow and buried without interrupting service. If Plow LC-61 is not available a bulldozer or ditching machine can be used to make a trench in which the cable can be buried. Under favorable conditions, this cable can be laid on the ground, tested and connected at the rate of about 3 miles per hour, including the work of burying or elevating at road crossings.
(5) The connectors on each end of this cable may become corroded or fouled with mud, fungus or other foreign matter to such an extent that poor or high resistance contacts will result. It is important to guard against these conditions and make sure the connectors are clean and dry before they are connected. In some of the early installations of spiral-four cable trouble was experienced in wet weather due to connector defects including leakage around the bolts, and it was found necessary in some cases to tape the connector after coupling. If such conditions are encountered and
exposures are severe, the method of taping covered in TB SIG 67 should be followed.
c. Cable Assembly CC-345 and Cable Assembly CC-355. These 5- and 10-pair field cable assemblies use Cable WC-534 and Cable WC-535 respectively (fig. 9-14 and TM 11-371). They may be installed much the same as Cable Assembly CC-358-( ) except, that if supplied on 19-inch x 36-inch wooden reels, the reels must be mounted on a bar (Axle LC-31) in the truck or on the cable reel jacks (Jack LC-13). Experience in some theaters indicates that the plugs should be cleaned and dried before connecting, and then taped to exclude moisture in all cases. In any event, when these cable assemblies are placed underground the connectors should not be buried. However, if they are buried they should be carefully taped in the manner described in TB SIG 67. When placed aerially spans should be limited, in general, to about 100 feet, with a sag of not less than 2 feet. Cable WC-534 and Cable WC-535 are also available in various lengths without connectors.
912. OPEN WIRE LINES.
a. General. The design of open wire lines adopted by the Signal Corps has been very much simplified as compared to commercial systems. It is still necessary, however, to vary the line structures to a limited extent in order to care for such factors as economy of shipping space, speed of erection, ground clearances, swinging wire contacts, availability of materials, terrain, and storm loading. These factors explain the need for having available a lighter type of construction for tactical use (TM 11-368) than for fixed plant application (TM 11-2253).
b. Crossarms. An 8-pin crossarm (PF-92-A), 3Ci, x 414 x 88 inches, is standard for use in both the tactical and fixed plants. It can be converted into two 4-pin crossarms by one saw cut. In general, no more than two 8-pin crossarms will be carried over one route. The wire capacity of a line will be therefore, usually either 4 wires, 8 wires, or 16 wires. Occasionally, where only one pair of wires is required, they may be supported on wooden pole brackets instead of a crossarm.
c. Insulators. For tactical construction two types of insulator satisfy practically all requirements. A double-groove insulator (IN-128, sometimes called TW) is used for provid-
438
PAR.
912
CHAPTER 9. OUTSIDE PLANT
Name or material* Type No. Nominal diameter (inches) Breaking load (pounds)b Weight per mile (pounds) Remarks
080 C-S W-153 0.080 770 94 Conductivity 40% of copper wire
104 C-S 0.104 1,170 159 Conductivity 40% of copper wire
128 C-S 0.128 1,650 240 Conductivity 40% of copper wire
104 C-S 0.104 1,275 159 Conductivity 40% of copper wire
128 C-S 0.128 1,800 240 Conductivity 30% of copper wire
080 Copper 0.080 330 102 Hard drawn
104 Copper W-74 0.104 530 173 Hard drawn
128 Copper 0.128 820 262 Hard drawn
165 Copper 0.165 1,325 435 Hard drawn
109 GS W-145 0.109 790 170 High strength
083 GI W-76 0.083 250 99
109 GI 0.109 425 170
134 GI 0.134 645 359
Wire Messenger WS-3/U ''16 2,400 410 2.2M GS wire with 7-0.065 inch strands
Wire Messenger W-115 54 6,000 1,190 6M, GS wire with 7-0.109 inch strands
Wire Messenger W-90 y8 11,500 1,425 10M, GS wire with 7-0.120 inch strands
Wire Messenger W-116 % 18,000 2,060 16M, GS wire with 7-0.144 inch strands
B C-S=Copper-Steel, GI=Galvanized Iron, GS= of the breaking load. Galvanized Steel. ® Commonly used designation for nominal breaking bThe elastic limit is equal to approximately 55 percent strength; M equals 1,000 pounds.
Figure 9-19. Physical data for bare wires and wire messengers.
ing a rolling type of transposition and for dead-ending from opposite directions. A single-groove insulator (IN-15) which is lighter in weight than the double-groove insulator meets all other requirements. On the longer open wire lines in the fixed plant, D.P. (double petticoat) insulators are used instead of Insulator IN-15 (TM 11-2253).
d. Tactical Construction; Wires, Poles, and Spans.
(1) For tactical construction the wire used is 080 copper-steel. However, if wire is obtained from the supplies of Allied Nations or from locally manufactured stocks in foreign countries it might be copper or bronze.
The physical properties of bare line wires an given in figure 9-19. Single-crossarm open wire lines may use 20-foot sawed 4x4 poles, or 20-foot class 9 round poles. Pole classes are explained in TM 11-487.
(2) Where poles cannot be quickly set in the ground because of soil conditions a guyed X-frame made of 20-foot 2 x 4’s may be used. Lines carrying two crossarms require 22-foot round poles. The above poles provide 14-foot ground clearance for the wires on cross country leads. At highway crossings an 18-foot clearance is usually provided by using an extra crossarm as a vertical extension fixture carrying the regular crossarm (TM 11-368). Lo-
439
PARS.
912-913
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
MULTI-AIRLINE (BRITISH)
THIS SECTION OF MAL SHOULD BE REMOVED //Z'
AS SECTIONS OF TOWL ARE COMPLETED. / ///
/ Z/ PARALLEL
//// ROUTES
////*—TEMPORARY
TACTICAL OPEN WIRE LINE (AMERICAN)
Figure 9-20. Replacement of temporary by permanent construction.
TL 54860
cally cut timber may be used where it is available. Nominal span lengths are as follows: in light storm loading areas, spans of 150 feet are used with 4x4 supports, and 200 feet with round poles; in medium or heavy storm loading areas only the latter of these arrangements is used. There is also a tactical construction called extra heavy, which uses class 9 round poles with nominal 150-foot spans and additional guying. The planning, construction, and maintenance of tactical open wire lines are covered in TM 11-368.
e. Fixed Plant Construction; Wires, Poles, and Spans. Fixed plant lines may be of several types. They may be commercial lines that have been taken over for Signal Corps use, American or Allied tactical lines, or they may be newly constructed to meet fixed plant needs. For those lines in the latter category the span length should average 150 or 200 feet depending upon storm loading requirements. The wire should be 104 copper-steel and the poles should conform to the requirements set forth in paragraph 907. As repairs or replacements are required in inferior lines taken over by the fixed plant, it should be the aim to use materials which will bring the line structure into conformity with fixed plant standards. Additional information on the planning, construction, and maintenance of fixed plant open wire lines is set forth in TM 11-2253.
f. Guying. The extent and strength of the guying required increases with the degree of storm loading. The application of proper guying is a very important feature of aerial line
construction. Unless guying is adequate and anchors properly placed, the line will not be dependable.
g. Two-by-four Supports. A preliminary issue of TM 11-368 described a type of rapid open wire construction (RPL) in which 4x4 poles fabricated from short lengths of 2 x 4’s were permitted. Field experience has shown that this type of pole is unsatisfactory and its use has been discontinued. While fabrication of 4x4 supports from full length 2 x 4’s is permitted, solid 4x4 supports are preferred.
h. Decay and Termites. With the temperature and moisture conditions prevailing in tropical climates, untreated timber will be destroyed in a few months either by decay or termite attack. In proceeding from torrid to more temperate climates the rate of deterioration from these causes becomes progressively less, and termites disappear at about the middle of the temperate zones, at which points the hours per year favoring decay are also quite limited. To protect against these hazards and to insure a physical life permitting reuse of pole timbers, the crossarms , 2 x 4’s, 4 x 4’s, and round poles furnished for pole lines are treated either with creosote or a preservative salt (par 925b).
913. BRITISH MULTI-AIRLINE (MAL).
a. The British MAL is a lightweight! tactical open wire line which offers as its principal advantages economy in transportation and speed of installation. It is usually used as temporary construction and should be replaced
440
PARS.
913-915
CHAPTER 9. OUTSIDE PLANT
as soon as possible by tactical open wire or fixed plant. The material for four-wire construction weighs about one short ton per mile.
b. The line is supported by 16-foot tapered wood poles with a 21/^ inch maximum diameter. Poles made of steel and of a telescoping design are sometimes used. The poles are set about 18 inches in the ground and normally spaced at 115-foot intervals, with double pole construction, H fixtures, every 8th span. Each pole is guyed with stranded iron wire attached above the crossarm and anchored to stakes driven in the ground. There are two types of crossarms. The 2-pin type is 15 inches long and the 4-pin type 33 inches. Each is ll/2 x iy2 inches in cross-section and is attached to the pole by clamps. The insulators are of a 2-piece design. The bottom piece with a slot for the wire is cast on a J shaped pin. The second piece is a cap which screws on to the bottom piece, securing the line wire after it has been given a wire serving and placed in the slot of the bottom section.
c. The wires, which are usually 70 pounds per mile cadmium copper, although 40 pounds bronze or 60 pounds iron may be used, are generally placed on two crossarms in the figuration of a 12-inch square. No transpositions are used with the 2-pin crossarm unless there is exposure to power. In this case the wires are rotated 90 degrees in each span. When the wires are placed on a 4-pin crossarm they are point transposed by dead-ending each wire in opposite directions on two insulators carried on double J type pins. Thus, it will be seen that most all of the MAL line equipment differs in design from that of the Signal Corps.
d. The MAL is useful in temporarily bridging gaps when rehabilitating open wire lines. It is useful also, when available, to extend American open wire tactical lines in emergencies. When constructing such an extension it should be built adjacent to the route the tactical line is to take so that the tactical line can be cut into service by sections, as they are completed. This type of construction is shown in figure 9-20.
e. The material for the Signal Corps tactical line weighs about twice as much per mile as the MAL and requires longer to construct, but these lines are superior to the MAL in strength, stability, and endurance. The American facility nearest to the MAL, with regard
to the number of circuits which can be speedily obtained, is spiral-four cable. Experience indicates that where this cable can be suspended from trees or existing supports, with sufficient ground clearance without messenger, it can be installed at twice the speed of the MAL, and the material weighs about half that of the MAL.
914. COMPARISON OF WIRE SIZES.
Figure 9-21 gives a comparison of American, British, and French wire sizes used in telephone circuits.
915. LEAD-COVERED CABLES.
a. General.
(1) The use of lead-covered cables is confined generally to the fixed plant. The types of cables usually stocked by the Signal Corps are given in TM 11-487. They may be installed aerially, buried, or pulled into underground ducts, but are not suited to ground surface construction. When used aerially they are suspended on a supporting steel strand which must be previously installed in a substantial manner on a well guyed pole line.
(2) A list of associated suspension materials arranged according to the weight of the cable is given in figure 9-22. An example is given in TM 11-487 of the materials required to build a 100-mile aerial cable line. Some information on weights and volumes of materials along with time figures for constructing a 25-mile length are given in figure 9-1.
(3) When buried in the ground it is the usual practice to have the cable supplied with a covering of asphalt, paper, and jute to prevent sheath corrosion, although for service periods up to approximately three years this feature could ordinarily be dispensed with. Where jute covering does not provide sufficient protection, gopher-proof, or single tape armored cable should be used. Construction practices used in the installation of paper insulated lead sheath cables are covered in TM 11-363. For extensive buried installations, large cable laying plows can be used to advantage, and hand trenching can be facilitated by using cable Plow LC-61 as a rooter. Small lead sheath cables with corrosion protection up to about one inch over-all diameter can be buried by means of Plow PL-61. The installation of Army cable in underground ducts is seldom warranted unless the duct system is already available.
441
PARS.
915-916
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
D ia meter * (inches) American wires gauge b British wires pounds per conductor mile French wires diameter (millimeters)
0.224 — 800 —
0.197 — — 5.00
0.194 — 600 —
0.177 — — 4.50
0.165 No. 8 BWG — —
0.162 No. 6 AWG — —
0.158 — 400 —
0.157 — — 4.00
0.138 — — 3.50
0.137 — 300 —
0.128 No. 10 NBS — —
0.118 — — 3.00
0.112 — 200 —
0.109 No. 12 BWG — —
0.104 No. 12 NBS — —
0.102 No. 10 AWG •— —
0.098 — — 2.50
0.097 — 150 —
0.080 No. 14 NBS — —
0.079 — 100 2.00
0.072 No. 13 AWG — —
0.066 — 70 —
0.059 — — 1.50
0.055 — — 1.40
0.051 No. 16 AWG — 1.30
0.050 — 40 —
0.047 — — 1.20
0.043 -- — 1.10
0.039 — — 1.00
0.036 No. 19 AWG — —
0.033 — 20 0.90
0.032 — — 0.80
0.028 — 12^ —
0.025 No. 22 AWG 10 —■
0.024 — 9M 0.60
0.020 No. 24 AWG ey2 —
0.016 No 26 AWG —
a One millimeter is 0.03937 inch.
b American cable conductors are designated by Gauge (AWG, American Wire Gauge; the same as B&S, Brown and Sharp Gauge). American open wire conductors used by the Signal Corps are designated by diameter in thousandths of an inch, or sometimes by gauge. BWG is Birmingham Wire Gauge. NBS is New British Standard Wire Gauge. Blank spaces indicate wire sizes not generally used.
Figure 9-21. Wire sizes; American, British, and French.
b. Splicing. Splicing paper insulated cable requires men specially trained for the work. Likewise, specially trained men are needed for testing and fault locating.
c. Terminals.
(7) Cable terminals for use outdoors are generally of the sealed chamber type. They are provided with stub cables, the conductors of which are connected to binding posts projecting through a face plate. The conductors of the terminal stub are spliced to the main cable conductors.
(2) Where a distributing frame is used, as at centrals, it is usual to splice the paper-insulated cables to short lengths of textile-insulated lead-covered cables. The other ends of the textile-insulated wires are stripped of their cable sheaths and laced into forms with the individual wires terminated so as to match the spacing of the protector mounting lugs on which they are terminated.
(3) For terminating small cables (up to 51 pairs) there are available indoor type sealed chamber terminals having facilities for electric protection equipment equivalent to that ordinarily used in centrals. These terminals are illustrated in TM 11-487.
d. Loading Coils. The loading coils used for loading lead-covered cables are usually potted in welded-steel or lead-sleeve cases. The loading coil cases which are available, together with their mounting hardware are given in TM 11-487.
e. Transportation. Transportation _of lead-covered cable requires special equipment because of the weight of the reeled cable and of loading coil cases. For instance 1,500 feet of 51-pair 19 gauge cable weighs about 2,200 pounds. The reel on which this cable is shipped weighs about 500 pounds. In handling this heavy material Trailer K-37 and trucks equipped with derricks and power winches are needed (fig. 9-23).
916. SUBMARINE CABLES.
a. Spiral-four Cable. In the tactical plant. Cable Assembly CC-358-( ) (spiral-four), and Cable Assembly CC-345 (5-pair) and Cable Assembly CC-355 (10-pair) are suitable for use as submarine cables in depths of water at least up to 1Z> mile, and will probably be satisfactory for somewhat greater depths. Life expectancies of the order of one year are considered reasonable. The transmission prop-
442
PAR.
916
CHAPTER 9. OUTSIDE PLANT
Type and size of supporting messenger, b Size of cable rings (inches) Guying Size and Stock No. of serial cable support
Weight (pounds per foot) Diameter (inches) Type and size of guy messenger Size of eye bolt and eye nut (inches)
2.24 or less 1^6 or less W-115 6M) 1 x/2, for strand (PF-63) W-90 (%", 10M) % No. 2 (National) 5B17842
2.25 to 4.99 1J4 to 2 W-90 (%", 10M) 2^2, for strand (PF-69) W-116 (%", 16M) 1 No. 3 (National) 5B17843
5.00 or over 2 or over W-116 (%", 16M) 3)4, for strand W. E. Co. type D (stock No. 5B9481) W-116 « (%", 16M) 1 No. 4 (National) 5B17844
aThe following are the approximate sizes and weights of various gauges of cable:
Gauge* No. of pairs Approx, diam. (inches) Approx, weight (pounds per foot) Gauge No. of pairs Approx, diam. (inches) Approx, weight (pounds per foot)
19 51 1 F/2 22 152 134 2
19 76 2 22 404 1% 4)4
19 202 1% 4)4 22 909 2% &/z
19 455 2% 8)4 * All 19 gauge cables are Western Electric Company CNB ype, (0.084 mf per pair mile).
b Based on an average span length of 150 feet.
cIn terminating messenger Wire W-116 use two 3-bolt guy Clamps FT-56; one clamp is sufficient for terminating messenger Wire W-115 or W-90.
Figure 9-22. Aerial lead-covered cable placement data.
Figure 9-23. Laying lead-covered cable.
443
PAR.
916
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
erties of such cables, when properly laid, will be about the same as those obtained when the cables are used normally. The method of installing these cables as set forth in TB SIG 67 is abstracted here.
b. Splicing.
(I) Underwater splices in rubber- or plastic-covered cables should be avoided whenever feasible in short submarine cables. Except in the case of the spiral-four cable which is supplied with loading coil connectors, standard (vulcanized) splices should be used whenever possible. For underwater use the insulation of spiral-four cable connectors should be reinforced by means of rubber cement, DR or rubber tape, and friction tape as set forth in TB SIG 67.
(2) If it becomes necessary to.utilize expedient cable splices, rubber cement should be used when applying the insulation to the joint. Conductor splices in 5- and 10-pair cable made without the use of copper splicing sleeves, and all expedient splices in spiral-four cable, should be relieved of stress by means of a tension bridge. (TM 11-369).
c. Cable Laying Methods.
(1) Tactical submarine cable may be laid by means of suitable boats or amphibious vehicles directly from reels, or it may first be unreeled and coiled in the form of a figure eight on the deck. This will permit it to be payed out without twisting. It is advantageous to use a method which permits, in-so far as possible, the making of all splices and preliminary tests before the actual laying starts.
(2) One of the most satisfactory methods of laying is to use Truck, Amphibian, 21/2 ton, 6x6 (Duck). Four or five miles of prespliced tactical cable can be stowed in the form of a figure eight in this truck. The cable should be laid on the floor of the cockpit so that the cross point of the figure eight is at the center, with one loop extending forward and the other aft. The cable should be payed out over the stern. A suitable device for guiding the cable over the stern is an empty reel mounted in Reel Unit RL-31-( ), erected on the after deck.
(*------ STAY ROD OR
\ SHORT EYEBOLT
SPIKE AND BRACE X /< II \\\\\
POLE TO IMPROVISE X
SWAMP FOOTING WHEN „ X . ' '' '" r
REQUIRED. * X '4-X a STEEL---
V X STRAP ---
V V * X ---- c- 1 BUCKET or
„ X DISCARDED GASOLINE
X can
N0TE:
v X ib"min head CUY SHOWN, same method
Io MIN. MAy be appl|ed for S|DE GUY, QiirKrr oi . ^r-r.______________________OR FOR TWO -OR FOUR-WAY
BUCKET PLACED -------**\ V) STORM GUYS
INVERTED & EMPTY \Vj? GUT5‘
TL 54901
Figure 9-24. Guying through mucky or spongy ground.
d. As a substitute for treated wood poles, iron or steel poles have been used in some cases where they are available. This is not, however, a Signal Corps stock item.
e. Where the ground is quite spongy and mucky, it will be necessary to provide proper swamp footings as covered in TAI 11-368, to prevent the pole from sinking. Extra guying will also be required in this type of ground.
/—FIELD WIRE OR / EQUIVALENT ( ----SQUARE KNOT
forestry INSUL AT ORS
a"t n / ' --CLOVE HITCH
i Ju OR SQUARE
KNOT
ABOUT 12"
I ----WIRE WS-I/TS, W-I30-A
I OR EQUIVALENT
' / A Y\\ * > *
V / \ * *
v v \ x y
V V V
TL 5489S
Figure 9-25. Tree slung construction using single support.
One suggested method of guying, where ordinary guy stakes or anchors will not hold satisfactorily, is to use an inverted ordinary GI bucket as shown in figure 9-24.
f. When crossing ravines it is undesirable to place poles at the bottom, especially where the ground is soft and spongy, since the wire pull may be sufficient during the rainy season to lift the pole out of the hole. Poles placed in river beds may be washed out during high water. Where such locations are unavoidable it may prove desirable to place a log crib filled with stones or earth around the pole and to anchor the pole to the crib.
926. TREE-SLUNG CONSTRUCTION.
a. Several methods may be followed to construct lines with trees as supports. Spaced insulated wires which are fastened to the trees by slings of one form or another may be used. This has been called tree slung construction. One form of this construction is shown in figure 9-25. Each line conductor is supported by forestry type insulators (Graybar Electric Company No. 6651 or equivalent) which are tied to the trees with scrap wire. It is contemplated that only insulators and line wire will be taken into the jungle. The forestry type insulator is preferred because if is a split type and does not have to be strung on the wire in advance. If this type is not available, Insulator IN-75 or equivalent may be substituted.
b. In dense jungle where the line cannot be kept free from foliage, it will generally be necessary to use insulated wire such as Wire
448
PAR.
926
CHAPTER 9. OUTSIDE PLANT
WS-l/TS (single wire similar in construction to Wire W-110-B), Wire W-130-A, or other jungle type wire which may be available. If Wire W-130-A is used it should be used as spaced pairs (ch. 5).
soy*"
—AVOID THIS HOOKUP
•
AyOS
-Ao4
LEGEND r°2
—►DENOTES PULL ON WIRE
O DENOTES TREE
Zl
TL 5 4897
Figure 9-26. Layout of tree slung route.
c. One object of the above type of construction is to prevent shorts or high leakage between tip and ring of a single pair from causing circuit troubles. Another object is to increase the transmission range beyond that obtainable with a single pair. Where paired wire such as Wire W-130-A is used in place of a single field wire it should be spliced as if it were to be used as two single conductors.
d. Where it is necessary to use the construction shown in figure 9-25, supporting trees should be selected along the general direction of the desired route and chosen as illustrated in figure 9-26 so that there will always be a pull on the wire away from the tree to avoid abrasion at the point of support. The distance between supporting trees should preferably be no greater than 100 feet but may vary plus or minus 10 feet.
TIE TO TREE OR SUPPORT --FIELD WIRE OR
y / EQUIVALENT
/—CLOVE HITCH
BASKET WEAVE X, 1
TIE-FIELD WIRE-1 XL --------SPLIT FORESTRY
I fINSULATOR
/ X' WIRE WS-l/TS,
/ X W-I30-A OR
CLOVE HITCH -J X EQUIVALENT \ TIE WIRE ONLY X
'—SQUARE KNOT \
TIE TO
OTHER INSULATOR
TL 54900
Figure 9-27. Tying line wires at fixed points.
e. The line wires are allowed to slip freely through the insulators except at the ends and at intermediate points about every 1,000 feet where they are fixed or tied to the insulator. The wire is allowed to slip through the insulators in order to minimize wire breakage from fallen tree branches. In case the wire breaks, the loose ends generally will not run through more than one insulator. The sag should be great enough to permit the wire to be pulled to the ground as determined by test; this test should be made close to one of the supporting trees and not at the mid-point of the span. A method of tying the line wire to the insulator at the fixed point is shown in figure 9-27. It is arranged so that the tie wire can not make contact with the line wire and thereby cause grounds or shorts in the line.
f. The line route or signal trail should be as far as possible from the side of the main trail or road and, if a crossover is necessary, clearance should be 15 feet or more. Fixed supports on each side of the crossing are desirable.
449
PARS.
926-927
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
V-----SHORT PITCH -------7
\ BASKET WEAVE TIE /
\ USE 2 LENGTHS OF /
\ FIELD WIRE /
square — clove hitch
rxNQi \\\Wz^r A-////
NOTE:
STRAND OF TIE WIRE ON THE INSIDE OF ONE CROSS AND ON THE OUTSIDE OF THE NEXT CROSS.
TL 54099
Figure 9-28. Weave tie supporting a straight section of wire.
g. It may prove desirable to guy the trees which serve as fixed supports, particularly where the trees sway substantially. Line wire will be used for guys attached to anchors, stakes or to the base of suitably located trees.
h. If there is noise from external interference, it may be possible to reduce it somewhat by making transposition at the 1,000-foot intermediate tie points (subpar, e above), or at the end of each wire coil or reel.
927. USE OF INSULATED WIRE IN JUNGLES.
a. The objections to bunching pairs of insulated wires as noted in paragraph 910c (2),
are particularly important in the jungle on account of the rapid deterioration of the insulation. Paired wire may be supported aerially by tying it to trees with short lengths of the same wire, leaving sufficient slack to take care of tree sway. The method of tying field wires, using the weave tie, is described in TB SIG 121. Figure 9-28 shows a line drawing and a photograph of the weave tie supporting a straight section of wire.
b. When the individual pairs have deteriorated so that excessive leakage between wires of a pair appears, it may be feasible to use two pairs in place of one, making each pair a single line conductor, and thus extend the life of the wire line although obtaining fewer circuits.
c. Insulated wire should not be buried nor laid on the ground in jungles unless extremely short life is satisfactory, since the insulation deteriorates rapidly due to ground contact and attack by insects.
d. It may be possible to bypass dense jungle areas in cases where waterways or ocean shores can be used for the line route. In this case Wire W-110-B can be used as a submarine circuit. All splices should be waterproofed as discussed in paragraph 916b. Life expectancy may vary from a few days to several months depending upon the amount of movement caused by the water and the character of the water bottom. It is sometimes advantageous to use the expedient of laying spiral-four cable or Wire W-143 under water along stream beds or off shore to avoid dense growth. Spiral-four cable should have a longer life under water than Wire W-110-B.
450
CHAPTER 10
ELECTRICAL PROTECTION
1001. PURPOSE OF PROTECTION.
Protection is provided for communication apparatus and cables to avoid damage from excessive voltages and currents which may be impressed on communication lines by lightning or by accidental contact with or induction from power lines. Protectors also minimize hazard to personnel.
1002. EXTENT REQUIRED.
a. In general, protective devices are supplied as an integral part of tactical equipment. At the front it is unlikely that power lines will be energized; hence, for small-capacity equipment, protection is primarily against lightning. Larger-capacity equipment, normally used close to the front, is also protected against power line faults, since such equipment is also used farther to the rear in areas where power lines are energized.
b. Where protection is not an integral part of the equipment, provision should be made to install it unless there are no working power lines in the locality and thunderstorms are infrequent for the period and locality in question. In considering the need for protection against power line faults, it should be borne in mind that such faults are apt to develop in areas subject to bombing or other enemy action.
c. Protective equipment available for use on electrical communication systems is described in TM 11-487.
1003. PROTECTORS.
Three types of protective devices are used, namely, voltage limiting gaps, fuses, and heat coils. A protector is a combination of one or more of these devices in a suitable mounting. These protective devices are illustrated in figure 10-1.
a. Protective Gaps. The voltage-limiting device is usually a small air-gap between two
conducting blocks called protector blocks. One protector block is connected to the line and the other to ground. An excessive voltage on the line breaks down the gap; hence the voltage across the apparatus cannot exceed the breakdown voltage of the gap. Protector blocks used with communication equipment generally
HEAT COIL TL 53177
SNEAK CURRENT FUSE
TL 54840
L_____________________4—f
LINE FUSE TL 53172
PROTECTOR BLOCKS
TL 53168
Figure 10-1. Typical protector blocks, fuses, and heat coil.
have a gap of 0.003 to 0.004 inch, with a breakdown of 350 to 500 volts peak. Sufficient protection for cables is obtained with a gap of approximately 0.006 inch with a breakdown of about 700 volts peak.
451
PARS.
1003-1005
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
b. Line Fuses. Fuses are placed in the line ahead of protector blocks to limit the current which may result from an accidental contact between power and communication conductors. These fuses usually have a 5 to 7 ampere rating and are capable of interrupting 2,500 volts at 200 to 300 amperes. Fuses having a lower rating (1 to 3 amperes) are sometimes used on small switchboards, to insure blowing when the ground resistance is relatively high.
c. Sneak Current Protection. Accidental contact with power circuits may result in a voltage too small to break down the protector blocks. The current resulting from such contacts, while not large (commonly called sneak current) may, if long continued, overheat apparatus. To prevent this, a low-capacity fuse or heat coil is inserted between the protector blocks and the equipment. Sneak-current protection is generally required on local circuits at switchboards, but usually is not placed in long distance circuits nor at telephones since the equipment used makes it unlikely that overheating will occur. For large switchboard installations, heat coils, which ground the line when operated, are used. Where there are only a few lines, low-capacity fuses which open the circuit are used. Ordinarily these heat coils and fuses are rated at 0.35 ampere.
1004. PROTECTION OF SWITCHBOARD EQUIPMENT.
a. Tactical Switchboards. The protection required for small tactical switchboards is generally furnished as an integral part of the equipment. When such swithchboards are put in service, it is necessary, for the protection to function properly, to connect the ground post to a suitable ground (par. 1011).
b. Other Switchboards. Where protection is not included as an integral part, separate mountings must be provided. At large switchboard locations, a multiple mounting, designed for protector blocks and heat coils only, is generally used, a separate mounting being used for fuses if required. For smaller switchboards, a multiple mounting suitable for installing protector blocks, fuses, and sneakcurrent protection is used. A typical switchboard protector is shown in figure 10-2. Unless circuits are entirely in underground lead-
covered cables in well built-up areas, protector blocks should always be used at switchboards, since cables and rubber-covered conductors, even when buried, may be subjected to excessive lightning potentials. Fuses may be omitted at switchboards where the circuits are in lead-covered cable if not less than 6 feet of the cable, between any power exposure and the equipment, is made up of conductors not larger than 24 gauge. Such small conductors will limit the current to such an extent that fuses are not necessary. Fuses may also be omitted where communication circuits are entirely in rubber-covered wires even where exposed to contact with power circuits. Experience has shown under this condition that a sustained contact with power circuits is unlikely.
Figure 10-2. Switchboard protector.
1005. PROTECTION OF TELEPHONES.
a. Portable Telephones. Portable telephones are ordinarily not provided with protection, largely because it is difficult to apply it and to provide suitable grounds. The hazard is small, since the circuits are usually not exposed to power contact and when not too long, they receive a measure of protection from the protector in the switchboard to which they are connected.
b. Fixed Telephones. Except in well built-up areas where circuits are entirely in underground lead cable, or where circuits from switchboards to telephones do not extend outside of a building, fixed telephones should be provided with fuses and protector blocks. In general, an individual protector is used for each
452
TL534.9I
PARS.
CHAPTER 10. ELECTRICAL PROTECTION 1005-1007
pair of wires. If it is necessary to locate pro- 1007. ILLUSTRATIVE EXAMPLES, tectors outside, they should be guarded against The application of the protection principles the weather by a suitable housing. A typical discussed above is illustrated in figures 10-4, protector used at fixed telephones is shown in 10.5 anj 10-6. figure 10-3. SMALL swbd. small swbd .
k ___ OR OR
WffMU-UllllI...... ... .Ji III 11,11 y repeater station repeater station
| I FIELD WIRE OR I |
X > ---H-------SPIRAt-F9VR crA6U£-I-—|
A* & r / 4 4 ;
1 EQPT. EQPT.I
FRffife'■1 grd.- I । I [—~* CRD.|
JEresgl I kwR.**-1 I I r-”pwR.|
|GRD* -*T4J I | U2l“ GRO*I
1-----X--J L““------1
/ it'tl 53493 i Figure 10-4. Protection when there is no open wire
* ■ ' 1 between equipment.
i J TL53ISI _________
43-----------| ।---—--------
. । FICLD WIR£ PORTABLE
Figure 10-3. Telephone protector. 1 I । telephone
1006. LOCATION OF PROTECTORS FOR [ I
SWITCHBOARDS AND TELEPHONES. trunk (note 1 ’ „ e
TRUNK y-fJ-T , I FIELD WIRE PORTABLE
The best location for protectors varies with open wireor|^£-~ J,, i telephone
the type of plant and local conditions. Unless wire. 1 T T I _________
protectors are an integral part of equipment, • •
they should be located at an accessible point • । ^SE omitted ir
as near as practicable to the entrance of the I U-- । trunk is mainly in
wires into a building. They should not be in- ।___j_ ^3 covered
stalled in damp locations nor near easily ignit- switchb'oard”
ible materials. Figure 10-5. Protection for portable switchboard.
,CK1TD., cable term, box
CENTRAL OFFICE UNDER- AND LINE FUSES
I---------1 GROUND_____jSEE NOTE I)
I CABLE II---V EXPOSED AERIAL CABLE
1----——---[-*- -H------------------------
i—-....................................................... I —।
I EQPT LT~I I-cr''"-'° | ' —
| GRD " I ■f~~.. ■ ~ | °~\-o | —tSHEATH
! GRD M/ 11 SHEATH—I (T I I SHEATH ♦ F SHEATH-4 I F' k----1
1------’--1 ।----1 I ---------4 CABLE
PROTECTOR BOND BETWEEN AERIAL I /--------------T----"V-TERMINALS
BLOCKSAND AND UNDERGROUND CABLE. <“1 rH| (-F — - Hj
HEAT COILS /V-------------I_____________I I_________I
BuIS'lNo! I ’"“"p1 r4- -h ~ RUBBER COVtStB
/f -U/ j ijflof I I? ।
'----------r--I—------------1 NECTED TO I__________I
TELEPHONE ThJE Vusr* CABLE SHEATH FIXED TELEPHONE
CENTRAL OFFICE TEULIN£° E PROTECTOR L Tn f^fi^J'Snh LINE FUSE ANtX
I---------1 FUSE AND BLOCKSAND PROTECTOR PROTECTOR
EXPOSED AERIAL PROTECTOR SNEAK CURRENT BLOCKS BLOCKS
j CAB»-E BLOCKS FUSE ’
............. 5
/ £==3 I «I| I II. 1------------1
/ j I ' SHEATH ---* SWITCHBOARD TRUNK
/ 1 LINE FUSE, PROTECTOR
1-•/------1 BLOCKS AND SNEAK
L LINE FUSE. (SEE NOTE l) NOTE I. CURRENT FUSE.
PROTECTOR BLOCKS AND FUSES MAY BE OM,TTEO ,F BETWEEN THE EXPOSURE
HEAT con « AND THE TERMINAL THERE IS A SECTION OF 24
• '-L>IL5. GAUGE OR SMALLER CABLE AT LEAST SFEET IN
LENGTH. TL 53492
Figure 10-6. Protection for an extensive communication system.
453
PARS.
1008-1009
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
1008. PROTECTOR DRAINAGE.
Operation of protectors by lightning may cause false operation of carrier telegraph equipment due to metallic-circuit voltage set up by lack of symmetry in the discharges through the protective gaps. This trouble may be largely reduced by replacing the ordinary protectors with protector drainage. This drainage consists essentially of a well-balanced 2-winding coil with each winding connected in series with protector blocks to ground. This coil equalizes the discharges through the gaps. A typical equipment and schematic circuit of protector drainage are shown in figures 10-7 and 10-8. Protector
Figure 10-7. Office type protector drainage assembly.
drainage is in general supplied with both the packaged and portable types of carrier telephone line transmission equipment. The drainage has been physically located with the equipment. Where lead-covered paper-insulated entrance cable is used, protector drainage may be required at the junction of open wire and
entrance cable in situations where lightning is prevalent enough near the entrance cable to cause serious effects on carrier telegraph.
1009. PROTECTION OF CABLES.
a. Protection of Lead-covered Cables at Aerial Wire Junctions.
(1) To protect lead-covered cables against lightning, aerial wires (open wire, field wire, spiral-four) over mile long and connected to cable conductors should be equipped with protector blocks at their junction with the cable. If, on this basis, one or more cable circuits require protection, all other wires connected to the same terminal, regardless of their length, should also be provided with protector blocks, to avoid excessive potential between cable conductors. Unless the length of one or more open wire circuits at a particular terminal is over mile, no protection is required at that terminal.
(2) At the junction of aerial wire and cable, the protectors may be an integral part of the cable terminal; however, a more common method is to use a separate mounting suitable for attachment to a pole or crossarm similar to’that shown in figure 10-9.
(3) Protectors installed at the junction of cable and aerial wires should have the grounding terminal connected to the cable sheath. Where an aerial cable is small, especially where the soil resistivity is high and lightning is severe it is desirable to install a ground on the cable sheath at the open wire junction. Such a ground should have as low a resistance as can be practically obtained (par. 1011).
CENTRAL OFFICE CENTRAL OFFICE
■;®1 • ran । ai ।
T TOLL CZI opEN WIRE □ TOLL
J ENTRANCE LINE I ENTRANCE
& CABLE d CABLE _ 3.
to /rib l= — ---p urL, fl lUTiud bcbyx to
swBa“ J ab i nr-----° t D ’SWBD
rl to P/ Ty
[--Si____' |~ ~|a? —Is.J
-----2---—IjU ------
a-CARBON PROTECTOR BLOCKS,3 MILS SEPARATION b-CARBON PROTECTOR BLOCKS, 6 MILS SEPARATION d= DRAINAGE COIL
TL 534»ft
Figure 10-8. Protector drainage.
454
CHAPTER 10. ELECTRICAL PROTECTION
PARS.
1009-1011
b. Protection of Lead-covered Long-distance Cables. For aerial or buried lead-covered longdistance cable, most of the lightning damage is due to direct strokes to the cable sheath. Such strokes may give rise to excessive voltage between the sheath and the cable conductors, particularly when the cable is of small size and the earth resistivity is high. Smallsize paper insulated cable provided with extra insulation between the conductors and the sheath may be used in such areas to reduce the likelihood of these voltages causing conductor failures.
Figure 10-9. Cable protector.
c. Junction of Open Wire with Field Wire or Spiral-four Cable. No protection is ordinarily placed at the junction of open wire with field wire or spiral-four cable, since the likelihood of failure, in general, is small. However, in areas where lightning storms are frequent and buried spiral-four cable is inserted in an open wire line, as for example at a railroad crossing, it may be desirable to place protection (0.006-inch gap) at the junctions of the open wire and spiral-four cable (ch. 5). An effective ground can be obtained by installing a bare wire (No. 14 or larger) with the buried cable. The same considerations apply to buried field wire inserts in an open wire line.
1010. PROTECTION AT RADIO STATIONS.
a. Portable Equipment. No protection is required for portable radio equipment since with the short antennas used, the hazard from lightning is slight.
b. Fixed Stations.
(7) Stations using short antennas, as a rule need no special protection, for the same reasons as in the case of portable stations.
Where protection is desired, as in exposed locations with frequent lightning storms, it may be provided as described below.
(2) Protection methods for large stations depend on the type of antenna and associated transmission line used. Tall radiating masts insulated from ground should be provided with a gap (horn or sphere type) across the base insulator. In severe lightning localities, wooden poles used as antenna supports should be protected against shattering, as described in paragraph 1012a. Where a single antenna lead-in wire or an open wire transmission line is used, protective gaps suited to the equipment to be protected should be installed between such conductors and the station ground, or the buried grid (network of ground wires) at or near the station. Where a coaxial transmission line is used, the outer coaxial conductor should be connected to the station ground and also grounded at the base of the pole or tower to the buried grid, if available, otherwise to a driven ground. If the coaxial cable extends up a steel tower, it should be bonded to the tower both at the top and bottom.
(3) Where coupling equipment is placed at the junction of coaxial line and antenna, sphere gaps or equivalent (usually furnished with the equipment) are placed between the antenna terminals of the equipment and the coaxial outer conductor. Equipment installed in series with antenna conductors, such as the resistor placed in the far end of a rhombic antenna, should have a protective gap (generally a horn gap) bridged across it.
(4) As discussed in paragraph 1011b, all grounding connections at the station, including the buried grid, if any, should be made to a common ground bus.
1011. GROUNDING.
a. Grounding Connections.
(1) Every reasonable effort should be made to get low-resistance grounding connections. Under emergency conditions, it may be necessary to use a very rudimentary connection, such as a bayonet plunged into the earth. Under other conditions, a very extensive system may be warranted, such as the grounding grid for a high-power radio transmitter.
(2) Water pipes, gas pipes, or other extensive underground metallic structures should
455
TL53I87
PARS.
1011-1012
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
be utilized where available; otherwise driven grounds or buried wires should be used.
(3) Driven grounds are made by driving one or more ground rods (preferably at least 5-feet long and inch in diameter) in the earth. The grounding resistance of a ground rod may be anywhere from a few ohms to several thousand ohms, depending on the resistivity of the earth and the depth to which it is driven. High grounding resistance is found in sandy or rocky ground, and very dry or frozen ground. The grounding resistance may be reduced by using rods connected in parallel, or by applying a salt solution, or both. Salt treatment may be applied by pouring a solution of about 5 pounds of rock salt into the ground at each rod. With high-resistivity earth, this may reduce the grounding resistance by as much as 10 to 1. A ground rod should be driven into the earth for all or most of its length when practicable. Several 5-foot rods in parallel will give lower resistances than a single long rod, except where a conducting layer is reached below a high-resistance layer of some depth or the soil is deeply frozen. Sometimes a depression in the ground, which collects moisture, can be chosen for grounding. Rods should be spaced at least 6 to 10 feet apart to be effective in reducing the resistance when connected in parallel. For ordinary conditions one rod is used at individual telephones or small switchboards, and 3 to Iff rods at larger switchboards.
(4) Where it is difficult to drive rods, and where space permits, an effective low-frequency ground can often be obtained by burying a bare wire in a shallow trench for a few hundred feet. If more than one trench is used, the trenches should preferably be at right angles or at a separation of not less than 10 feet.
(5) The length of the ground lead used for carrier telephone systems should be as short as practicable, to keep its reactance low. b. Common Grounding. Grounds may be required at a particular location for more than one purpose, such as protection of communication equipment, a-c power supply ground, cable ground, and equipment ground. For protection reasons, it is best to connect all grounds to a common bus, particularly where lightning is prevalent. This will prevent excessive potential differences when one of the
grounds is carrying large currents, as may happen in a lightning storm. Such potential differences, unless avoided, may cause insulation failures and hazard to personnel. For a similar reason it is advantageous from the protection standpoint to interconnect grounds of different communication systems installed at one point. In some cases where the resistance of the ground is high, it may be necessary to use separate equipment grounds to avoid transmission difficulties; however, wherever practicable a single low-resistance ground should be used, and the ground lead should be as short and direct as practicable.
c. Grounding of Lead Cable Sheath. Sheaths of lead cables should ordinarily be grounded where they terminate at switchboards. Sheaths of underground and aerial cables should be bonded, where both are used. Sheaths of aerial cables should be electrically continuous from end to end, to prevent large differences of potential, which would otherwise occur at sheath discontinuities during lightning storms.
1012. SPECIAL APPLICATIONS OF PROTECTION.
Some of the more common situations occasionally arising and requiring special protection are briefly discussed in this paragraph.
a. Protection of Poles.
(1) Shattering by lightning of wooden poles in a wire or aerial cable line can be largely avoided, where necessary, by running a wire (for example, 104 copper or 109 iron wire) from the top of the pole to a short distance below ground. If new poles are being placed, such wires can be stapled on for the entire length. For the protection of linemen, it is frequently desirable to avoid having a ground at the top of the pole. For this purpose a gap about a foot long may be left in the wire approximately 7 feet above the ground.
(2) The scheme just described cannot ordinarily be employed where wooden poles are used as antenna masts, since it may interfere with radio communication. For such cases, a series of short gaps may be placed in the wire at intervals not exceeding a quarter wavelength.
b. Protection of Equipment Inserted in Open Wire Lines. Equipment such as repeating coils, portable repeaters, and short sections of spiral-four cable installed in open wire lines is vulnerable to lightning if not protected. The prin
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CHAPTER 10. ELECTRICAL PROTECTION 1012-1013
ciple of protecting such equipment is shown in figure 10-10. It is important that the protection applied to the lines in both directions be connected to a common ground. The resistance of the ground in this case is not important.
(.PROTECTOR-)
BLOCKS
Portable REPEATER OR SHORT SECTION OF spiral-four CABLE
T
OPEN
WIRE
REPEATING ________ COIL
"1 S i
open r i open
W!RE PROTECTOR L 1 PROTECTOR WIRE
। , BLOCKS° | | y BLOCKS |
TL53497
Figure 10-10. Protection of equipment in open wire lines.
1013. EARTH RESISTIVITY.
In the above discussion, earth resistivity is mentioned a number of times. Special test apparatus is required to obtain an accurate measurement of earth resistivity. An approximate estimate can be obtained by driving two ground rods 5 feet apart and 5 feet into the earth whose resistivity is desired, and measuring the resistance between the two rods with Test Set 1-49 or equivalent. The average of the two readings obtained by reversing the leads to the test set should be used. The resistance between rods, in ohms, about equals the earth resistivity in meter-ohms at the spot tested. Resistivities may be rated as follows: low, up to 100 meter-ohms; medium, around 300 meter-ohms; high, 1,000 meter-ohms and up. The above method of obtaining a rough approximation of earth resistivity should not be confused with the measurement of the resistance of a grounding connection. Information on the measurement of grounding connection resistance is given in TM 11-2008 and TM 11-755 (when published).
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Section I. INTRODUCTION
1101. GENERAL.
This chapter outlines the technical functions of the organization that is to engineer, install, operate, and maintain a communication system, and supplies certain of the necessary basic engineering data required. Information is included for telephone and telegraph (wire and radio) traffic engineering, and for estimating man-hours and time intervals required to install wire system offices. Desirable records, routines, and maintenance practices are suggested. Information relative to the procedure to be followed in the planning of a telephone system, together with the engineering of switchboard installations and wire telephone lines, is given in chapters 2, 5, and 9. Telegraph system engineering is covered in chapter 3, and radio in chapter 6.
1102. THEATER EXPERIENCE.
In planning a communication system it is necessary to estimate the number of calls and the duration of the average call expected to be originated by the telephones and teletypewriters. It is also desirable to know the call-carrying capacity of switchboard positions and of wire and radio telegraph and telephone channels or trunk groups, and the construction and installation time intervals. Experience from the theaters of operation should be valuable on many of these technical details in plans for a new communication system. The material herein reflects information which has become available from the theaters.
1103. PLANNING A COMMUNICATION SYSTEM.
a. Three Stages. Provision of a communication system usually involves planning at three distinct stages: long range and procurement planning to insure delivery of proper quantities and types of materials at the proper time; detailed project planning for specific facili
ties ; and day to day planning for growth, rearrangements, and repair of major damage.
b. Coordination in Planning. The numbers of trunks and local circuits are a traffic problem. The type of switchboard to be selected for a particular situation requires both traffic study and a knowledge of equipment features and limitations. Selection of the types of facilities needed for circuits involves, among other considerations, a knowledge of transmission, signaling, and construction. Wire and radio facilities must be effectively integrated. These examples are sufficient to illustrate that complete coordination of the work by all groups concerned is essential to the proper execution of each project.
c. Long Range and Procurement Planning.
(1) This planning must allow 3 to 6 months or more for delivery of materials.
(2) The estimated requirements as to the quantity, type, and geographical location of speech and telegraph facilities including radio, of all ground, air, naval, and service forces should be obtained at the earliest possible date to insure adequacy of supplies and efficiency in combining requirements in common user groups, location of long distance centrals and the larger signal centers, and maximum utilization of civil plant. Consideration should be given to the return of some civil circuits for essential civil needs. Later requirements for American military government may need to be considered and decision made as to whether such requirements shall be allowed for initially in order to minimize future work.
(2) The communication system layout should show the location of all centrals and signal centers. The number and calling rate of the local telephones and teletypewriters to be served by each central must be estimated. The number of switchboard positions can then be
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1103-1105 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
determined. The average holding time per call must be estimated. The number of trunks to other centrals can then be determined. Procurement lists of material and equipment for the entire system can then be prepared.
(4) A communication plan requires forecasts for major users, such as:
Theater headquarters:
Operational and administrative. Joint and combined control and liaison.
Ground forces:
Operational and administrative. Air forces:
Operational and administrative. Aircraft warning.
Weather.
Communications zone: Administrative.
Base, intermediate, and advance sections.
Transportation and utilities control.
Governmental and civil agencies.
(5) Intelligence reports may indicate the location of civil telephone lines, cables, radio equipment, central offices, or repeater stations in the area of the proposed operation. If not, highways and railroad routes may be presumed as possible line routes, although these are frequently not the best military routes, on account of liability to physical damage and electrical interference. Using the possible routes as a basis, the wire circuit requirements can be consolidated on a circuit diagram indicating circuit concentrations between various points. An analysis of the circuit length and concentration will result in the selection of a type of construction and the formulation of a general transmission plan.
The existing civil facilities, if known, may have a major bearing on the plan.
(6) Communications planned 3 to 6 months or more in advance of use may not be built exactly as planned, but the planning aids in assuring materials adequate for the job, however built, and provides a transmission plan as a guide in the type and grade of facility to be provided. Consideration should be given in the over-all plan for the possible use of tactical construction as part of fixed plant after its use in the tactical phase.
d. Detailed Project Planning.
(1) This planning is required when the specific need for facilities arises. The materials needed can then be ordered from the available stocks, for construction or installation, operation, and maintenance. The projects will be individual, such as a telephone or telegraph central for a particular location or an open wire pole line, a spiral-four cable between two definite points, radio relay systems, etc.
(2) Typical problems illustrating this type of planning and ordering are given in TM 11-487.
e. Day to Day Planning. This planning which is for unpredictable work such as growth, changes, and damage repair will be more accurate than the long range planning or the detailed project planning because it can be based on known results or situations, such as counts of traffic, service observations, or inspections. The reasons for changes include: the move of a headquarters from one place to another; change in the volume of traffic from time to time, growing in the early stages and possibly declining in the later stages of an operation; the shift of a highway which will require moving a pole line; and shell or bomb damage, etc.
Section II. TECHNICAL FUNCTIONS
1104. GENERAL.
a. This section covers the technical functions of an organization for planning, constructing, operating, and maintaining a communications system. These functions are tabulated in figure 11-1 but the form of organization is not indicated.
b. The division of functions for a theater
communications system is broadly by staff and field categories. Those responsible for staff planning will rely upon the staff engineering people for estimates, advice, and consultation.
1105. FUNCTIONS.
a. Staff Functions. Radio, wire, and traffic engineering in general are staff functions be-
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CHAPTER 11. TECHNICAL ADMINISTRATION
------------------THEATER COMMUNICATIONS COORDINATION -
( NORMALLY CARRIED OUT ON THEATER HEADQUARTERS LEVEL)
,-------------------STAFF ENGINEERING-------------------------
/-STAFF PLANNING--
RADIO WIRE TRAFFIC-RADIO & WIRE CLERICAL
PROJECT PLANNING PROJECT PLANNING ESTIMATES OF INITIAL RECORDS LONG RANGE PLANS
FREQUENCY ASSIGNMENT CALL SIGN ASSIGNMENT CIRCUIT ASSIGNMENT -MAJOR CIRCUITS STANDARDIZATION OF OPERATING AND MAINTENANCE PRACTICES CONSULTATION WITH STAFF AND FIELD ORGANIZATIONS STANDARDIZATION OF TELEPHONE & TELEGRAPH MAINTENANCE PRACTICES CIRCUIT ASSIGNMENT TELEPHONE DIRECTORY NAME ASSIGNMENT CONSULTATION WITH STAFF AND FIELD ORGANIZATIONS THEATER REQUIREMENTS STANDARDIZATION OF OPERATING PRACTICES-TELEPHONE & TELEGRAPH CONSULTATION WITH STAFF AND FIELD ORGANIZATIONS STATISTICS & RECORDS OFFICE ROUTINES DRAFTING DUPLICATING (MIMEOGRAPHING & BLUEPRINTING) AND PROCUREMENT
--------COORDINATION
(NORMALLY CARRIED OUT ON
FOR COMMUNICATIONS ZONE------------
COMMUNICATIONS ZONE HEADQUARTERS LEVEL)
,-----------FIELD COORDINATION FOR TYPICAL AREA
(SUBDIVISION OF BASE SECTION)
------------RADIO-------------- /----------WIRE-------
PLANT
SITING INSTALLATION MAINTENANCE SUPPLY CURRENT
ENGINEERING RECORDS
TRAFFIC
OPERATING
CIRCUIT ASSIGNMENT
LOCAL CIRCUITS
CURRENT ENGINEERING
RECORDS
TRAFFIC
LINE CONSTRUCTION INSTALLATION MAINTENANCE SUPPLY CURRENT
ENGINEERING RECORDS
OPERATION DIRECTORIES INFORMATION
SERVICE
SERVICE OBSERVING
CURRENT
ENGINEERING
RECORDS
TL 54978
Figure 11-1. Technical functions for theater communications systems.
cause the work must be started well in advance of construction and installation. Centralization of engineering functions generally leads to the most effective coordination of the requirements of the several branches of the Armed Forces. Efficient use of personnel and facilities also results. A subdivision between wire and radio functions at a fairly high level may be necessary because of specialized personnel, but close coordination of these two functions is necessary. Close coordination also is essential with civil authorities in the use of civil plant to supplement existing military plant. Engineering, traffic, and plant matters may be involved. A communication organization requires routine clerical work and also special records such as circuit diagrams, equipment records, service observing data, directories, trouble records, etc. which are mentioned in various sections of this chapter.
b. Field Functions. A communication system may have sufficient plant remote from headquarters to warrant the establishment of sub
divisions of base sections for effective administration. These field subdivisions are called areas in this chapter. When field functions are divided among areas, even the plant around headquarters may be operated as an area. Coordination of these areas from headquarters is desirable. The area functions include traffic management, plant work, and some aspects of engineering. Plant functions are field functions because they begin with the establishment of the first telephone or telegraph facilities. They continue in the extension of plant and in maintenance after the plant is placed. It is impracticable to supervise the plant work for a large system from one central location. Traffic management is largely a field function. As with plant work, it is impracticable to supervise telephone central operations from one central location.
c. Circuit Control. When long distance circuits pass through several test stations or test offices, which may lie in several areas, experience has demonstrated the necessity for a definite rule for the delegation of control au
656935 0—45------31
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1105-1107 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
thority.1 This is necessary for the orderly control of procedures such as the allocation of repeater gains and the reassignment of circuits under emergency conditions. A simple and clearly understood rule is desirable. A
rule which has been successfully utilized is that a circuit which terminates at an intermediate point on a long distance route will be controlled- by the terminal nearest theater headquarters.
Section III. TELEPHONE TRAFFIC MANAGEMENT
1106. TELEPHONE CENTRAL WORK.
a. General. Telephone traffic management is concerned chiefly with supervising the operation of telephone centrals and related work such as information service, trouble report handling, directory, and service observing work. The activities include: personnel work; operator training; standardization of methods of handling various types of calls and related operations; determination of operating force and switchboard requirements; service observations and study of operating practices to see that efficient use is made of existing facilities; position load adjustment; record work of various kinds; etc. Reference may be made to TM 11-462, FM 24-20, and FM 24-75.
b. Written Practices. Written practices are desirable for some of the traffic functions. Items to be covered should include operating technique and phraseology for handling the several types of calls. These may be calls to distant or local points, switched calls, complaints, information calls, and trouble reports. The instructions may vary somewhat for different types of switchboards. Operating technique includes proper rotation of calls between cords, ringing intervals, monitoring, handling delayed calls, conference calls, routing of calls, etc. Directions should be provided for making traffic-load counts (peg counts), holding-time records, and service observations. Directory
1 The importance of establishing a control point in European international telephony was recognized at the Budapest plenary meeting of the CCIF (International Consultative Committee on Telephony) in September 1934 at which the following rule was recommended: “One of the stations through which a circuit passes is responsible for satisfactory transmission on that circuit. This station is called the control station; it is chosen by agreement between the technical departments of the Administration and operating companies involved. Unless otherwise arranged between the technical departments interested, the control station will be one of the terminal stations of the circuit.”
preparation, distribution, and maintenance should be prescribed.
1107. TELEPHONE CENTRAL MANAGEMENT.
a. General. Operation of telephone centrals requires an adequate and well-trained force, good traffic load distribution between switchboard positions, suitable switchboard equipment location, correct marking of trunks and lines, and careful clerical work.
b. Duties of Officer in Charge. Each central requires local supervision and the officer in charge should have rank commensurate with the size of the central. He should exercise general supervision and be responsible for operation as a whole; interpret and apply directives ; select and train personnel, and provide them with necessary operating instructions, materials, and equipment; establish operatorforce schedules and coordinate shifts; see that security features are properly observed; make analyses of traffic conditions with a view to effecting improvement; adjust complaints and procedure difficulties; assign equipment locations in the switchboards; supervise the preparation of directories; and provide the necessary traffic diagrams and bulletins.
' c. Duties of Chief Operator. A chief operator is required to supervise each central to see that proper and prompt service is given. Assignment of operators to positions, supervision of information service, etc., are additional responsibilities. At long distance switchboards it is essential to watch the progress of traffic and to post delay information for the guidance of operators when trunk group trouble or congestion occurs. The chief operator should supervise the activities of personnel on duty in his shift; carry out instructions with.particular reference to moving traffic rapidly and accurately, preserving security and dealing effectively with delays, difficulties, and emer-
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CHAPTER 11, TECHNICAL ADMINISTRATION
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Figure 11-2, Diagram of telephone traffic routes.
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
POINT
ACRE (NAVY) ADSEC AH ALBIS ALENCON AMIEN ANGERS ANTWERP ARMOR ATTIC AVRANCHES BARF LE UR BAYEUI BOMBAY BRANVILLE BREST
BRITISH EMBASSY BRUSH BRYANSTON SQ. BRUSSELS CADET CAEN CARENTAN CEDAR CENTURY CENTURY CHANNE
FIRST ROUTE
ALTERNATE ROUTS
PARIS-CHERBOURG BRUSSELS PARIS-MARSEILLES PARIS-CHARTRES PARIS-LE MANS BRUSSELS PARIS-LE MANS BRUSSELS
EAGLE MAIN-CONQUER PARIS-LE MANS PARIS-RENNES PARIS-CHERBOURG PARIS GANGWAY PARIS-CHERBOURG PARIS-LE MANS PARIS PARIS-LE MANS DIRECT DIRECT FINAL
LONDON-CHERBOURG
PARIS
FINAL-MARSEILLES
PARIS-LE MANS-CHARTRES
PARIS-ORLEANS-LE MANS PARIS
PAR IS-ORLEANS-LE MANS PARIS GANGWAY-EAGLE TAC-PARIS-ORLEANS-LE PARIS-CHERBO LONDON-C GOODGE ST GANGWAY
(LONDON)
TL 54935
Figure 11-3. Telephone route bulletin.
gencies; and keep the officer in charge informed of any unusual developments. A large switchboard may require section or subsection supervisors with duties similar to those of the chief operator in relation to the operators under his direction. Supervisors also may be required for the evening and night shifts to take charge of the central, with responsibilities similar to those of the chief operator as to the moving of traffic during their shifts. Such supervisors should report to the chief operator.
d. Operator Attitude. The successful working of a central depends upon the operators. Prompt answers and completions, courtesy, and strict observance of instructions are important. Instructions are necessary as a guide but in addition common sense, secrecy, tact, and discretion on the part of the operator are required.
e. Trunk Designation Strip Marking. Clearly marked designation strips with a minimum of abbreviations are important for good switchboard operation. The difference between via and terminal grade long distance trunks necessitates marking their designation strips so that operators can distinguish between them where both grades exist between two centrals. One method is to use the initial V, placed on the designation strip after the group name in the case of via trunks, and the letter T in the case of terminal trunks.
f. Traffic Diagrams. Either traffic diagrams or route bulletins, or both, should be provided for every central, located where they will be readily accessible to operators, to indicate how to
reach other centrals. This is particularly necessary when the distant central is reached through another central or has an alternate route. At tactical switchboards, route information is by diagram as illustrated in FM 24-20 and TM 11-462. At fixed plant switchboards, if space is available, diagrams can be posted on or above the face of the switchboard positions with one diagram for every two operating positions. A diagram of traffic routes for a large fixed plant network is illustrated in figure 11-2. For such networks the routing is complex, and it is impractical for operators to use traffic diagrams for all calls. The best arrangement for such situations is to provide route bulletins in ring binders, with the names of centrals and routings arranged in alphabetical order as shown in figure 11-3. These binders can be kept at information positions which can be reached over special lines by all of the operators at the switchboard. In this case, the traffic diagrams located at the operator’s positions would cover only nearby points, direct points, and most frequently called points.
Percent of busiest
Hour hour traffic
2400-0700........................... a
0700-0800 ......................... 40
0800-0900 ......................... 70
0900-1000 ......................... 95
1000-1100..........................100
1100-1200 ......................... 80
1200-1300 ......................... 50
1300-1400 ......................... 75
1400-1500..........................100
1500-1600 ......................... 90
1600-1700 ......................... 90
1700-1800 ......................... 90
1800-1900 ......................... 60
1900-2000 ......................... 50
2000-2100 ......................... 40
2100-2200....«..................... 40
2200-2300 ......................... 25
2300-2400 ......................... 25
a For the night assignment, a single row of 10 or less positions will require one operator, but a second is desirable for relief and safety. Larger numbers of positions or double lines of positions will require more.
Figure 11-4. Typical telephone switchboard traffic distribution by hours.
g. Traffic Distribution by Hours. Where no data are available from the specific central or a comparable one, the information shown in
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CHAPTER 11. TECHNICAL ADMINISTRATION
figure 11-4 which is typical of military field conditions, may be used to estimate the number of calls in the various hours. It is important, however, to secure actual data as soon as the switchboard is working.
h. Operating Personnel Requirements. The number of positions in the switchboard lineup usually determines the number of operators on duty at the switchboard during the busiest hour of the day. Since the traffic in most of the other hours is less than that in the busy hour, the operating force can be reduced during those hours in relation to the calls handled. The number of operators required for each hour may be read from figures 11-10, Illi, and 11-12 depending upon which table applies. When the number of operators required for each hour has been determined a schedule of assignments should be drawn up to cover the actual operating requirements, supervisory requirements, meal hours, and periodic relief periods. In general, the total number of operators on the force will be from 2.0 to 2.5 times the number of operators required in the busy hour.
i. Position Load Balance. The load on a switchboard should be distributed so that the traffic flow from each switchboard position will be approximately equal. The number of line lamps allowed per line may not always permit lamps in all the appearances of the line multiple. This, in general, will not become a problem in military switchboards of a type which permit five lamps per line except for switchboards of more than 10 positions. At the Western Electric Company No. 12 switchboard, which is limited to one line lamp per line (two may be used but this limits the lamp brilliancy), the lamps should be distributed so that each position has approximately the same number. Lamps generally should be placed as fully equipped strips of twenty because it is difficult to keep a record of scattered lamps.
j. Line Priority Marking. The traffic on a switchboard may result in periods of overload for which it may be desirable to have distinctive marking on lines that should be given priority. This can be done by use of colored lamp caps on the lines that must have priority service. Another method is to insert color disks made from transparent material such as theatrical gelatin sheets inside the lamp caps, or to slip over the switchboard lamp half of a colored gelatin medicine capsule. Color ap
plied to lamp caps inside or outside, or to switchboard lamps is not entirely successful because it is difficult to obtain uniform colors on a group of lamps by this method. Coloreu designation cards can be used on lines equipped with designation strips.
k. Operating Room Quieting. The room noise usually prevailing in an operating room, and especially the noise near the operators’ heads, should be kept as low as practicable, in order to minimize transmission impairment, and provide more pleasing working conditions, both of which will tend to improve service. Noise in operating rooms results from voice sounds and from many local sources such as footsteps, bells and buzzers, clocks, cord plugs and weights, dials, fans, keys, and miscellaneous room equipment such as typewriters, chairs, doors, windows, etc. In some cases outside noise, such as street noise, is an important factor. The noise may not rise to an objectionable value in centrals of a few positions of switchboard but may be high enough to require treatment in large centrals. Remedial measures include: removal of typewriters and adding machines to other quarters; local maintenance treatment of squeaky chairs and door hinges, curtains that flap in a draft, noisy fans, and windows that rattle; fastening of linoleum to the cord well panels to deaden the sound of cord weights striking them; and elimination of unnecessary travel in or through the operating room.
1108. TELEPHONE SWITCHBOARD OPERATION.
a. General. Military switchboards are of various types as described in chapter 2 and in TM 11-487. Operating practices differ for the different types. For example, strictly local switchboards use practices that differ in many respects from the practices required at strictly long distance switchboards. It probably will be necessary to use variations to meet local conditions in some cases.
b. Local Switchboard Operation. Cord pairs should be used in rotation until all have been used. It is usual to work from left to right. Disconnected cords will not be used until reached again in rotation. Cords should be picked up by the plug shell. When idle, an operator should hold the plug of the next cord to be used, with listening key open, waiting for a call except, of course, during light traffic hours. Signals within reach, in front and to
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right and left should be answered in order of appearance. If a signal exists in a position that the operator cannot answer promptly, an adjacent idle operator should be signaled by hand to take the call. Correct action on disconnect signals is important. One-lamp disconnects usually indicate need for challenge before disconnecting, but tivo-lamp disconnects do not. It is desirable to monitor and challenge on magneto-line to magneto-line calls before disconnecting because many magneto line users fail to give the operator a ringoff signal.
c. Long Distance Switchboard Operation. Cord rotation from left to right is suggested as at local boards. A rear cord should be held in the hand while the operator is idle, with the listening key open on this cord pair. Answers on calls from a local telephone should be by the words long distance. Incoming calls from distant places should be answered by giving the name of the central. Service users should be informed of the progress of calls at reasonable intervals. Monitoring is required frequently to assist in call completion. The called number need be repeated by the operator only if in doubt. On calls delayed because of no circuit or called party busy the operator should ask for the user’s name and telephone number and the calling party should be told that the call will be recorded and completed later. The details should be entered on a ticket described in subparagraph e below, which entry should include filing time. These tickets should be passed along the board to one operator whose duty is to handle them, if the operating practices requires this method of completing. Delayed calls should be completed in the order of filing unless they are urgent (FM 24-20). The originating long distance office is responsible for all calls. At an intermediate point where through calls are switched, no ticket is required on through calls that are not delayed because of trunks busy beyond the switching point. However, on through calls that are delayed at an intermediate point because of no circuit beyond, a call order ticket also described in subparagraph g below, should be made at the intermediate point. No information calls should be handled by a long distance.operator, but should be referred either to a supervisor at centrals large enough to have them, to a special position, or to a special desk in the switchboard room. At small centrals they can be referred to the chief operator.
d. Combined Local and Long Distance Switchboard Operation. Operation of combined local and long distance switchboards requires use of the practices of both local and long distance switchboards. The local switchboard practices are used for handling local calls and the long distance switchboard practices are used for handling long distance calls. These are the practices that are given in subparagraphs b and c above.
e. Delayed Call Tickets. Tickets are required to be written by the operator at long distance and at combined local and long distance switchboards, only on calls delayed because of no circuit or called party busy. Figure 11-5 shows a suggested form of delayed call ticket. An operator at the long distance switchboard should initiate the subsequent attempts to complete the call. The service user should initiate subsequent attempts to complete local calls or calls to nearby centrals which do not require use of long distance trunks, when the first attempt finds no circuit or called party busy.
f. Delayed Call Recording Desk. One or more local telephone lines may be installed on a nearby desk to which long distance operators can connect calls for delayed call recording during periods of peak traffic or at other times, such as circuit interruptions, when it is desirable to relieve operators of as much work as practicable. The person assigned to answer these telephones can also inform telephone users of posted delays, maintain delayed call tickets in proper order, and distribute tickets to switchboard operators for completion. This work should revert to the regular operator when the load falls off.
g. Call Order Ticket. Call order tickets may be used for certain types of delayed calls. For example, when a call which is switched through an intermediate central encounters a delay in reaching a circuit to the distant point, it may be desirable for the intermediate operator, particularly on congested groups, to write a call order ticket and call back the originating operator when a circuit becomes available. Figure 11-5 shows a suggested form of call order ticket. Such calls should be completed in the order of filing time.
h. Urgent Calls. The operator may be called upon to handle calls which have been given the precedence of urgent by proper authority. Such calls may originate on loops at the operator’s switchboard or may come in on trunks. If the
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called party is busy, or if all trunks to the called switchboard are busy, an existing call may be interrupted.
i. Order of Attention to Signals. All signals should be answered in the order of their appearance. Occasionally signals of different kinds will appear at the same time, and it will be necessary for the operator to decide which signal should be answered first. In such cases, the following order of precedence should govern : first, flashing supervisory signal, because the operator of the position is the only operator who can answer it; second, incoming trunk signal in order to obtain maximum trunk efficiency ; third, line signal; and fourth, one-lamp disconnect signal, because one party may desire additional service. Two-lamp disconnect signals require no answer and the cords should be pulled down as promptly as possible as an overlap operation so that lines and equipment will be available for use on other calls. An exception to these rules is in the case of priority lines on which the signals should, of course, receive precedence over the other signals.
j. Phraseology. The phrases and practices contained in FM 24-20 and FM 24-75 are to be used where applicable. To avoid confusion both to the users and to operators, it is necessary that common practices be used throughout a communication system. Military courtesy applies in the operation of all centrals.
k. Special Services.
(I) Information Calls. Information calls for telephone numbers not listed in directories can be handled by either of two practical methods at local switchboards. If the volume of calls is small, a card with listings in alphabetical order can be mounted between each two operators on the face of the switchboard or key-shelf. For larger volumes, two interposition trunks should be provided to a table which should always be occupied, and where the record should be kept. The two trunks should be multipled before all operators. This table can also handle trouble reports. It is not practicable to attempt information service at a separate long distance switchboard because of the difficulty of maintaining directories of the many centrals involved. It is better to put the calls through to the called central where the desired information can be obtained.
(2) Trouble Reports. Trouble reports
CALL ORDER
DATE_________________
FILING_TIME__________
PRIORITY
------------FROM
CENTRAL.__
TEL. NO.
NAME
POSITION
-------------TO
CENTRAL _
TEL._N0.___
NAME
TIME COMPLETED
OPERATOR
DATE_________________________
FROM____________________
CENTRAL _____________________
NO. _________________________
NAME_________________________
TO______________________
CENTRAL _____________________
NO. _________________________
NAME_________________________
FILING TIME _________________
COMPLETION TIME _____________
DISCONNECTION TIME __________
PRIORITY ____________________
OPERATOR ____________________
TL 54879
Figure 11-5. Call order and delayed call tickets.
can be taken by the operator or passed to the chief operator at small centrals, and also at large centrals in the hours of light traffic when the volume of trouble is not great. The trouble reports can be recorded on trouble tickets shown in figure 11-6. These can be delivered to the wire chief who can maintain the line record cards of figure 11-46 on which he can record the trouble report, the nature of the trouble found, and the time it is cleared. The trouble tickets do not need to be retained. When the volume is too great for this method, the calls can be passed over interposition trunks which terminate at a table which is occupied by a repair service clerk as discussed in paragraph 1162.
( 1 't'
i—Frf—1 I u
| | X —NAA -----------f 1
! ! x ______ pbx ; । ----------------1
: : — c^T--------------' ; ;
NO 551B PBX TYPE CENTRAL fa
. . ----------------------------------- COMMON) DISTANT COMMON
i I ,_______Q__, , BATTERY BATTERY CENTRAL
TELEPHONE} j 1 (£1 ] '_________
-t-aaa—r-°—A n<>-Z_ j-L-pFI A—o- f—i ] i । jf
*—TU WIT U
: x-----cx---------/ to yrr U—--------------------------
1 1 CIRCUIT 3E ~
II ZE I I
I I \ - / I ।
I ।_______________________'-- PBX TRUNK-z| । ।
NO. 551B (X-66O7O) PBX TYPE CENTRAL B
TL 54880
Figure 11-9. Battery supply circuit to a local loop when connected to a common battery trunk.
PAR.
1114
CHAPTER 11. TECHNICAL ADMINISTRATION
Total busiest-hour traffic (originating, inward, and through calls) Positions required Number of telephones which can be served by combined local and long distance switchboards
At two orig. calls per telephone in the busiest hour At three orig calls per telephone in the busiest hour
1-100 1 1-28 1-18
100-265 2 28-73 18-49
265-440 3 73-121 49-81
440-600 4 121-165 81-110
600-765 5 165-210 110-140
765-920 6 210-253 140-168
920-1,070 7 253-294 168-196
1,070-1,225 8 294-337 196-224
1,225-1,375 9 337-378 224-252
1,375-1,530 10 378-420 252-280
Total busiest-hour traffic (originating, inward, and through calls) Positions required Number of telephones which can be served by combined loca I and long distance switchboards
At two orig. calls per telephone in the busiest hour At three orig. calls per telephone in the busiest hour
1,530-1,685 11 420-463 280-309
1,685-1,835 12 463-504 309-336
1,835-1,990 13 504-547 336-364
1,990-2,140 14 547-588 364-392
2,140-2,295 15 588-630 392-420
2,295-2,450 16 630-673 420-449
2,450-2,600 17 673-714 449-476
2,600-2,755 18 714-757 476-505
2,755-2,905 19 757-798 505-532
2,905-3,060 20 798-841 532-560
This table is based on the following assumptions:
1. The number of telephones served is 1.5 times the number of loops connected to the switchboard.
2. Each operator handles all types of calls.
3. The number of calls per operator in the busiest hour depends on the number in the team on duty. The number of calls per operator per hour is:
1 operator 100 calls per operator hour
2 operators 133 calls per operator hour
3 operators 147 calls per operator hour
4 operators 150 calls per operator hour
5 or more operators 153 calls per operator hour
4. The distribution of traffic is as given in paragraph
1112b but the table permits variations as indicated below:
Local calls..................40% to 20%
Outward trunk calls..........20% to 30%
Inward and through
(switched) calls..........40% to 50%
Total...................100% 100%
5. The switchboard face layout permits every operator to reach every local line and trunk. Additional positions (end positions) may be required to assure this.
6. Tickets are to be written on delayed long distance calls only.
Figure 11-10. Position requirements, combined local and long distance common battery switchboards.
mated traffic which is to be handled in the busiest hour. It also shows the number of local telephones which can be served if the average total long distance calls in the busiest hour (outward, inward, and through) per telephone served is 0.3 or 0.4 calls as indicated m the figure. More telephones can be served if the average calling rate is less and fewer can he served if the calling rate is higher. The traffic in the busiest hour depends upon the number of telephones in nearby local centrals whose long distance outlet is through this switchboard but the number does not include telephones whose outlet is through other switchboards.
d. Separate Local Common Battery Switchboard. Figure 11-12 shows the position requirements for this type of switchboard based on the estimated traffic which is to be handled in the busiest hour. It also shows the number of local telephones which can be served and which will generate this traffic if the average originating call rate is two or three calls per telephone in the busiest hour. More telephones can be served if the average calling rate is less and conversely, fewer can be served if the calling rate is higher. The traffic consists of local (loop-to-loop), outward trunk, and inward trunk calls.
475
PAR.
1114
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Total busiest-hour traffic (outward, inward, and through calls') Positions required Number of telephones which can be served by long distance switchboards
At 0.3 total long distance calls (inward, outward, andthrough) in the busiest hour per telephone served At 0.4 total long distance calls (outward, inward, andthrough)in the busiest hour per telephone served
1-60 1 1-200 1-150
60-160 2 200-534 150-400
160-260 3 534-867 400-650
260-360 4 867-1,200 650-900
360-460 5 1,200-1,533 900-1,150
460-550 6 1,533-1,833 1,150-1,375
550-640 7 1,833-2,133 1,375-1,600
640-740 8 2,133-2,467 1,600-1,850
740-830 9 2,467-2,767 1,850-2,075
830-920 10 2,767-3,067 2,075-2,300
Total busiest-hour traffic (outward, inward, and through calls) Positions required Number of telephones which can be served by long distance switchboards
At 0.3 total long distance calls (inward, outward, and through) in the busiest hour per telephone served At 0.4 total long distance calls (outward, inward, andthrough) in the busiest hour per telephone served
920-1,010 11 3,067-3,367 2,300-2,525
1,010-1,100 12 3,367-3,667 2,525-2,750
1,100-1,200 13 3,667-4,000 2,750-3,000
1,200-1,290 14 4,000-4,300 3,000-3,225
1,290-1,380 15 4,300-4,600 3,225-3,450
1,380-1,470 16 4,600-4,900 3,450-3,675
1,470-1,560 17 4,900-5,200 3,675-3,900
1,560-1,650 18 5,200-5,500 3,900-4,125
1,650-1,750 19 5,500-5,833 4,125-4,375
1,750-1,840 20 5,833-6,133 4,375-4,600
In addition to the basic assumptions in paragraph 1112 c, this table assumes:
1. The traffic is of both long and short haul type.
2. The number of calls per operator in the busiest hour depends on the number in the team on duty. The number of calls per operator per hour is:
1 operator 60 calls per operator hour
2 operators 80 calls per operator hour
3 operators 88 calls per operator hour
4 operators 90 calls per operator hour
5 or more operators 92 calls per operator hour
3. The switchboard face layout permits every operator to reach every line and trunk. Additional positions (end positions) may be required to assure this.
4. Tickets to be written on delayed calls only.
Figure 11-11.
Position requirements,
separate long distance switchboards.
e. Magneto Switchboard. Figure 11-13 shows the approximate number of local telephones and trunks that can be served by 1- and 2-posi-tion magneto switchboards, for two different originating busiest-hour call rates. It gives data for both local and combined local and long distance switchboards. It should be noted that even though a position can be equipped for 100 lines, satisfactory service can seldom be given to that number of lines by one operator. The traffic is assumed to consist of local (loop-to-loop), outward trunk, and inward trunk calls only.
f. Ratio of Telephones to Loops. The position requirements of figures 11-10, 11-11, and 11-12 show the number of positions required based on the number of telephones served and not on the number of telephone loops that are connected to the switchboards. More than one telephone on a loop is common and therefore in
most centrals there are more local telephones served than there are loops connected. The switchboards listed in TM 11-487 do not, in general, provide for selective-ringing partyline service, and the extra telephones on a loop are extension telephones in which the ringers (bells) may or may not be connected, as desired. On magneto loops it is common to have more than one telephone because the loops are long and it becomes more desirable to add to the number of telephones on a loop rather than build additional loops. The ringing is done by code, using one short ring to signal the central; and two, three, and four short rings, and combinations of long and short rings if more are necessary, to call individual stations. The probable resulting ratio in fixed plant may be 1.5 telephones per common battery loop and two telephones per magneto loop.
476
PAR.
1114
CHAPTER 11. TECHNICAL ADMINISTRATION
Total busiest-hour traffic (originating and inward calls) Positions required Number of telephones which can be served by loca I common battery switchboards
At two orig. calls per telephone in the busiest hour At three orig. calls per telephone in the busiest hour
1-150 1 1-53 1-35
150-400 2 53-140 35-93
400-650 3 140-228 93-152
650-900 4 228-315 152-210
900-1,150 5 315-402 210-268
1,150-1,380 6 402-483 268-322
1,380-1,610 7 483-563 322-375
1,610-1,840 8 563-644 375-429
1,840-2,070 9 644-724 429-483
2,070-2,300 10 724-804 483-536
Total busiest-hour traffic (originating and inward calls) Positions required Number of telephones which can be served by local common battery switchboards
At two orig. calls per telephone in the busiest hour At three orig. calls per telephone in the busiest hour
2,300-2,530 11 804-885 536-590
2,530-2,760 12 885-965 590-643
2,760-2,990 13 965-1,046 643-697
2,990-3,220 14 1,046-1,126 697-751 •
3,220-3,450 15 1,126-1,206 751-804
3,450-3,680 16 1,206-1,287 804-858
3,680-3,910 17 1,287-1,366 858-911
3,910-4,140 18 1,366-1,448 911-965
4,140-4,370 19 1,448-1,528 965-1,019
4,370-4,600 20 1,528-1,608 1,019-1,072
This table is based on the following assumptions:
1. The number of telephones served is 1.5 times the number of loops connected'to the central.
2. The switchboard handles local and incoming calls. Outward long distance calls are passed to a long distance board for handling.
3. The number of calls per operator in the busiest hour depends on the number in the team on duty. The number of calls per operator per hour is:
1 operator 150 calls per operator hour
2 operators 200 calls per operator hour
3 operators 220 calls per operator hour
4 operators 225 calls per operator hour
5 or more operators 230 calls per operator hour
4. Distribution of traffic (par. 1112 d)
Local calls..................... 40%
Outward trunk calls............. 30%
Inward calls.................... 30%
Total.......................... 100%
5. The switchboard face layout permits every operator to reach every local line and trunk. Additional positions (end positions) may be required to assure this.
6. No tickets are to be written.
Figure 11-12. Position requirements, separate local common battery switchboards.
Calling rate, combined local and long distance switchboard Telephones per position Trunks proposition
1 pos. • 2 pos. I pos. 2 pos.
Two originating calls. . . . 20-25 30 6-8 6-8
Three originating calls.. . 15 20 6-8 6-8
Calling rate, local switchboard Telephones per position Trunks per position
1 pos. 2 pos. 1 pos. 2 pos.
Two originating calls. .. . 40-45 55 8-10 8-10
Three originating calls. . . 25-30 35 8-10 8-10
This table is based on the following assumptions:
1. The number of telephones served is double the number of loops connected to the central.
2. An operator at a magneto switchboard can handle 80 percent as many calls as one at a common battery switchboard.
3. Fora 1-position board all trunks are assumed to be in one group, and for a 2-position board in two groups.
4. Distribution of traffic (par. 1114 e): Local calls.............................. 40%
Outward trunk calls................. 30%
Inward calls........................ 30%
Through (switched) calls.............. 0
Total.......................... 100%
5. Five minute holding time for trunked calls.
Figure 11-13. Telephone and trunk capacity, 1- and 2-position magneto switchboards.
656935 0—45------32
477
PAR.
1H5 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
1115. TELEPHONE TRUNK CIRCUIT REQUIREMENTS.
a General. The number of trunks required in a group between two switchboards to handle a certain number of calls is termed the trunk requirements. In order to determine the size of a trunk group, it is necessary to estimate the total number of calls in the busiest hour and the average holding time per call to be carried by the group. In telephone practice it is recognized to be wasteful of facilities to provide trunks so liberally that no calls will ever be delayed. As the number of calls increases beyond the number for which the group was engineered, the percentage of delayed calls increases. To maintain a desired grade of service the number of trunks in a group must be increased as the number of calls increases. With respect to the percentage of delayed calls, the grade of service it is feasible to render will in some cases depend on the availability of facilities such as conductors, carrier equipment, etc.
b. Total Trunk Equipments. The holding time and the number of calls in the busiest hour to be handled by each trunk group should be estimated. The number of trunks per group can then be selected from figures 11-14 and 11-15. The sum of the numbers of trunks in all the groups gives the minimum number of trunk equipments required. Some allowance should be made, of course, for growth. If the total number of trunk equipments can not be estimated by the above method at the time the total trunk equipments are specified, the following method may be used. Assume the traffic distribution given in paragraph 1112 and determine the number of trunked calls in the busiest hour originated per telephone. The product of this figure and the total number of telephones is the total number of trunked calls. Divide this figure by 7.5 calls to determine the total number of trunk equipments. Theater experience has shown that each trunk will carry on the average about 7.5 calls in the busiest hour for the central as a whole. Trunks usually will be either of two types. One type is 2-way ringdown, for use as long distance trunks and local trunks to magneto switchboards, and the other is the common battery type to other nearby common battery centrals and to manual or dial common battery centrals operated by civil organizations. In the average common battery central, about an equal number of each kind of trunk will be required.
c. Local Trunks. Figure 11-14 may be used in estimating each local trunk group between centrals such as those within a city and its environs. Local trunks usually do not exceed 10 miles in length; however, where lines are available they may extend to distances as great as 25 miles. The grade of service resulting from the use of these tables should under normal conditions be comparable with that from private branch exchanges in the United States. In interpolating, to find the trunk requirements, for example for 13 calls, judgment based on knowledge of the availability of conductors, the accuracy of the estimate, etc., should be the deciding factor in determining whether to use the figure for 12 or for 14 calls.
d. Long Distance Trunks. Figure 11-15 may be used in estimating each long distance trunk group between centrals separated by greater distances than mentioned in the preceding paragraph. The grade of service resulting from the use of this table should under normal conditions be comparable with that on long toll lines in the United States. In interpolating between the values shown, judgment is necessary, as in the case of local trunks.
e. Trunk Efficiency. Trunk groups are used most efficiently if all trunks between two centrals are used as one group to serve all users, rather than with a separate circuit or group reserved for a particular branch of the service. For example, figure 11-15 shows that eight trunks will carry 80 5-minute calls per group in the busiest hour, whereas two groups of four will carry only 35 each, or a total of 70 calls in the busiest hour. There may be situations where a trunk reserved for a particular user should be considered; this is seldom justified, however, unless each trunk will be required to handle at least 40 calls per day, even where it is not particularly difficult to provide the trunk.
f. Divided Route for Protection. A method sometimes used to protect the continuity of service on a trunk group between two centrals is to have two separate pole lines or cables between them using different routes for the two lines. However, the trunks would be used as a common group from the traffic standpoint for efficiency. The divided route idea is illustrated in figure 11-16-A.
g. Alternate Routes. An alternate route for reaching another central is desirable for use in case of trouble on the direct route or for use when the direct route is overloaded and the
478
PAR.
1115
CHAPTER 11. TECHNICAL ADMINISTRATION
Busiest-hour calls per group Trunks per local group
3-min holding time 5-min holding time 7-min holding time
1-3 1 1 1
4 1 1 2
6 2 2 3
8 2 3 4
10 3 4 5
12 3 4 5
14 4 5 5
16 4 5 6
18 4 5 6
20 4 6 7
22 4 6 7
24 5 6 7
26 5 6 8
28 5 7 8
30 5 7 9
35 6 8 9
40 6 8 10
45 7 9 11
50 7 10 12
55 7 10 13
Busiest-hour calls per group Trunks per local group
3-min holding tima 5-min holding time 7-min holding time
60 8 11 14
65 8 11 14
70 9 12 15
75 9 13 16
80 9 13 17
85 10 14 18
90 10 14 18
95 11 15 19
100 11 15 20
105 11 16 21
110 12 17 21
115 12 17 22
120 12 18 23
125 13 18 24
130 13 19 24
135 13 19 25
140 14 20 26
145 14 20 27
150 14 21 27
Figure 11-14. Local trunk requirements.
alternate route is not. These are usually available to reach most of the network centrals, but if a central has but one outlet, it may become necessary to build a line to provide it with an alternate route. Switching of calls at an intermediate point is required in the use of alternate routes. The alternate route arrangement is illustrated in figure 11-16-B.
h. Switchboard Face Equipment Layout. The trunk multiple should be located above the piling rail and below the local line multiple. The
number of panels per trunk multiple and per local line multiple is determined by the type of board to be provided. When end positions are required, some of the trunk and local line multiples are extended through part of these positions in order to place all jacks within the reach of the first or last operator position. The common battery trunks to civil centrals or other nearby military centrals should be located in the top part of the trunk multiple space and the long distance ringdown trunks below these. In
479
PAR.
1115
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Busiest-hour calls per group Trunks per long distance group
3-min holding time o-min holding time 7-min holding time
2 1 1 1
4 1 1 1
6 1 1 2
8 1 1 2
10 1 2 2
12 1 2 2
14 2 2 3
16 2 2 3
18 2 2 3
20 2 3 3
22 2 3 4
24 2 3 4
26 2 3 4
28 2 3 5
30 3 4 5
35 3 4 6
40 3 5 6
45 3 » 5 7
50 4 6 7
55 4 b 8
Busiest-hour calls per group Trunks per long distance group
3-min holding time o-min holding time » 7-min holding time
60 4 7 9
65 5 7 9
70 5 7 10
75 5 8 11
80 5 8 11
85 6 9 12
90 6 9 12
95 6 10 13
100 7 10 14
105 7 11 14
110 7 11 15
115 7 11 16
120 8 12 16
125 8 12 17
130 8 13 17
135 8 13 18
140 9 14 19
145 9 14 19
150 9 15 20
Figure 11-15. Long distance trunk requirements.
X Y
DIRECT ROUTE —
1ST ROUTE Q----------------------------
X --------- -----------^Y \ X
\ ALTERNATE ROUTE /
2ND. ROUTE Z
DIVIDED ROUTE £ ALTERNATE ROUTE
B
TL 54863
Figure 11-16. Divided and alternate trunk routes.
480
PARS.
1115-1117
CHAPTER 11. TECHNICAL ADMINISTRATION
1-, 2-, or 3-position switchboards, the trunks should be centrally located so that all operators may have ready access to them.
1116. RADIO TELEPHONE TRUNK CIRCUIT TRAFFIC CAPACITY.
a. Point-to-point radio telephone circuits are usually on a push-to-talk basis, which results in the average conversation time being longer than on a point-to-point wire telephone circuit because the push-to-talk technique is inherently slower and, besides, the listener cannot break in on the speaker. Furthermore, the percentage of circuit time lost on high-frequency circuits due to repetitions caused by noise may be greater. Therefore, a radio telephone channel may have as little as 50 percent of the message capacity of a point-to-point wire circuit.
b. Radio telephone circuits which use a separate frequency for each direction, as in radio links in a wire channel, do not use the push-to-talk method of operation. On v-h-f circuits noise is frequently negligible. Hence such circuits may have a traffic capacity per channel equal to that of wire circuits.
1117. TELEPHONE SWITCHBOARD REQUIREMENT CHECK LIST.
a. General. A requirement check list should be used in preparing a request for a central that is to be ordered through the Army Communications Systems, for the guidance of the personnel that will order equipment. The check list given in the following subparagraph is applicable for commercial-type multiple switchboards. It can also be used as a guide in ordering nonmultiple switchboards as well as tactical switchboards, by omitting the items that do not apply. Notes should be added to a request for a switchboard covering any special features that are desired.
b. Check List. The following check list is typical for use in setting up requirements for a commercial-type common battery multiple switchboard and associated equipment.
Number of operational positions.
Number of common battery line relay equipments.
Number of common battery lines carried through the multiple.
Number of magneto line equipments for long distance trunks and magneto lines, arranged to operate line lamps and busy lamps.
Number of magneto lines carried through the multiple.
Number of common battery trunk equipments, manual.
Number of common battery trunk equipments, dial.
Number of common battery trunk jacks in each appearance of the trunk multiple.
Number of interposition trunk equipments.
Number and distribution of interposition trunk answering jacks and lamps.
Number and distribution of miscellaneous trunk jacks for intraoffice and miscellaneous use.
Number of lamps.
Number of lamp caps and colors. (Total required equals the total number of lamp sockets provided in the switchboard.)
Number of vacant line signal plugs (to plug up unassigned jacks).
Number of cord circuits per position.
Type of cord circuits.
Number of supervisors’ circuits.
Number of operators’ head and chest sets.
Number of operators’ chairs.
c. Other Information. The notes to accompany a requirement check list can include such items as: maximum loop resistance of local common battery lines to be served; resistance of trunk loops (dial and common battery manual) ; working limits of trunk equipment in connecting centrals; whether the repeating coil type of trunk circuit is requested; phase, voltage, frequency, and reliability of available power supply, if known; operating room floor dimensions and ceiling height, if available; desired direction of growth, left to right or right to left; face layout of trunk and local line multiple; location of supervisors’ jacks; location and number of ticket boxes in blank multiple space; quantity and type of designation strips; whether spring-driven switchboard clocks or a walltype spring-driven clock, is desired.
481
PARS.
1118-1120
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Section V. TELEGRAPH TRAFFIC MANAGEMENT
1118. GENERAL.
a. Many considerations in connection with telegraph traffic are different from those for telephone traffic because telegraph traffic involves the handling of messages in written form. An over-all telegraph communication plan should include a tape-relay system, a switching service (exchange) system, and point-to-point private lines in combination with the tape-relay and exchange service systems. These facilities use wire and radio circuits which provide world coverage in the Army Command and Administrative Network for communication between headquarters within individual theaters of operation and for communication with the zone of the interior. In telegraph operation, switched (exchange) service is relatively less important than it is in telephony.
b. A tape-relay system is well suited to the accurate and efficient handling of large traffic loads at high speed. Communications to and from tributary stations are handled through relay centers equipped with reperforators and transmitter-distributors.
c. A switching (exchange) system permits direct to-and-fro communication between two or more stations through centrals and common trunk groups; relatively light traffic loads are handled economically in this manner.
d. Direct point-to-point private line service involves two or more stations on a fixed circuit and the facilities used are exclusive for interchange of messages between these stations.
e. This section pertains mainly to traffic management of signal centers where messages are received from, or placed on the network, and with teletypewriter centrals where switched calls are handled. For information relative to operating practices and traffic procedures, reference may be made to FM 24-8, FM 24-10, FM 24-14, FM 24-20, and Traffic Circular Letters 1, 2, 3, 4, 5, and 6 (available through Army Communications Service, O C Sig O).
1119. TYPES OF SERVICE.
a. Telegraph messages for transmission may be received by any means such as messenger, radio or wire telegraph, private-line teletypewriter, or a station on the teletypewriter
switching network. Most messages are filed in written form in much the same manner as in commercial telegraph systems; in this case the originator of a message is not connected with the recipient for to-and-fro communication; the semiautomatic tape-relay teletypewriter network is used for the major part of the traffic. In the switched service, the calling station is connected to the called station through a switching system consisting of one or more teletypewriter centrals; the two stations are then in direct contact and can work to-and-fro as in commercial TWX (switched teletypewriter service). Teletypewriter equipment is used for practically all of the transmission throughout Army networks. Morsecode transmission is used only to a minor extent, largely on radio circuits and on field-wire lines in the forward areas.
b. In a signal center, the equipment and associated facilities for the tape-relay message service are sometimes at separate locations from that of the switched service, and the problems of management of the two are different. In the tape-relay network, many messages are received on typing reperforators and transmitted automatically from transmitter-distributors; practically all messages are cryptographed and many of them are in multiple-address form (par. 1122g).
1120. SIGNAL CENTER TRAFFIC MANAGEMENT.
a. Duties of Officer in Charge. At a signal center, it is of advantage to assign officer responsibility for handling traffic along the following general lines. The officer in charge should exercise general supervision and be responsible for operation as a whole; interpret and apply directives; select and train personnel and provide them with necessary instructions, materials, and equipment; establish schedules and coordinate shifts of watch officers and personnel ; see that security features are properly observed; make analyses of traffic conditions with a view to effecting improvement; and adjust complaints and procedure difficulties.
b. Duties of Watch Officer. The communication watch officer should supervise the activities of personnel on duty in his shift; carry out instructions with particular reference to moving traffic rapidly and accurately, pre
482
PARS.
1120-1122
CHAPTER 11. TECHNICAL ADMINISTRATION
serving security, and dealing with delays, difficulties, and emergencies; and keep the officer in charge informed of any unusual developments. Section supervisors have duties similar to those of the watch officer and report to him.
c. Operating Personnel. The number of people required to operate a signal center depends primarily upon the volume of traffic and its distribution throughout the day.
d. Traffic Distribution by Hours. The distribution of traffic by hours of the day for a large signal center in the zone of the interior is shown in figure 11-17 for general informa-
loo, ||||i|||iri------1 I I I I I fJJ TT~
zt- cn \zl\ T7-RECEIVED ' T/" /
-ui io ->u \ x r~ .
oy ________V—_________-----------x-----------—
UD 25i-------A — n--J-----A------■-------:-----
o.m _______~—__________________—____—__________
24 01 04 09 14 19 24
Z TIME
TL 54751
Figure 11-17. Distribution of teletypewriter traffic by hours of a day for a large signal center in the zone of the interior.
tion. The peak in received traffic was at 1900 hours Z time (Greenwich civil time), which in this case corresponded to 1400 hours local standard time (Eastern time belt), and the peak in sent traffic was at 2000 to 2400 hours Z time. For a theater signal center, the time at which the peak occurs would be different, and the distribution of traffic over the 24 hours is apt to be less uniform than that shown in the figure. Hence a distribution chart of the traffic at a particular signal center should be made as soon as practicable after the center begins operations.
1121. LOCATOR SYSTEM.
For efficient delivery of messages to the various units, it is essential that the headquarters signal center arrange to be kept informed as to the location of every unit in its area, preferably by daily reports. Subsidiary centers need to have similar information for their respective areas. When a new unit arrives in an area it should be advised promptly where to pick up and where to file messages.
1122. TELETYPEWRITER NETWORK MESSAGE HANDLING METHODS AND OPERATION.
a. Manual-relay Station Methods. At manualrelay stations, messages are received on page-
type teletypewriters. Each message is provided with transmission instructions and routing information. An operator may retransmit the message to the next station by direct keyboard operation, or perforated tape may be prepared locally, in which case the transmission to the next station will be automatic.
b. Tape-relay Station Methods. Reception at tape-relay stations is on typing reperforators, which record the message in the form of perforated tape; the message is typed at the same time on the perforated tape. This received perforated tape is then placed in a transmitter-distributor for automatic transmission to the next station in accordance with routing instructions. An elementary traffic flow diagram of messages to, from, and within a semiautomatic tape-relay signal center is shown in figure 11-18.
c. Traffic Diagrams. Traffic routing information as illustrated by figure 11-19 will be required at each signal center to indicate how to reach distant signal centers. If a network is extensive, and the traffic diagram such as illustrated in figure 11-19 is too complicated for the operators to use, a route bulletin along the same general lines as illustrated in figure 11-3 can be provided for the operators. Traffic diagrams may be satisfactory for use in small networks.
d. Message Heading. Each message as written by the originator is directed to one or several addressees. These addressees are not signal centers except in the case of service messages pertaining to the handling of traffic. The message may be transmitted to some addressees for action and to others for information only. Most transmitted messages have a heading which is divided into two primary parts, namely: the signal center’s part and the originator’s part. The signal center’s part, which may be changed to suit conditions, consists of two portions, namely: the call and the preamble. The call consists of the called and calling station designations; the preamble consists of the message identifying number, the precedence and the transmission instructions. The originator’s part, which is fixed, is also made up of two parts, namely: the message address and the message instructions. The message address contains the originator’s name or equivalent, the date and time of filing, together with action
483
PAR.
1122
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
SENDING CIRCUITS I
MESSAGES COLLECTED & DELIVERED---------\
BY MESSENGER OR OTHER MEANS
--------------------------------------------------------1-------|-------------- coded SIGNAL CENTER 4 4
------* ।------| MESSAGE----------------------------------------------J ।
, |
C O D E D ----1-- ---------------- ----------1---
r MFSSAC.F X TRANS TRANS TRANS
CODE MtaaAut D|ST __ D(ST D|ST
ROOM ____ ... I L______
1 PLAIN
1 t TE7XT PLAIN TEXT OR
PLAIN TEXT ------|_^-. , TAPE li CODED TAPE
b tape I \Z RELAYED DIRECT
--------- ------------------- |Q TT 1 TYPING _ TYPING
1 REPERF “ “I REPERF
L-------- |--------| 1—J
PLAIN TEXT FOR I . |
----» ----- PERFORATING I ' MESSAGE TAPE । ROOM I
MESSAGE I CIRCUIT I I
CENTER _______
L- 15 TT । ।
-I——J 1 ’
p. AIN TEXT I FOR MAKING I I
^PLAIN TEXT___________________ PAGE COPIES | |
MESSAGE 4 4
I I
LEGEND: i .
' —-- MESSAGES CARRIED BY HAND V 1 /
_______ELECTRICAL CIRCUITS RECEIVING
CIRCUITS TL 5492ft
Figure 11-18. Elementary traffic flow diagram in a tape-relay signal center.
and information addresses as required. The message instructions contain signals to facilitate handling of multiple-address messages and the group count2 for text of message only.
e. Message Numbering.
(1) In the operation of a network wherein messages are relayed (manually or automatically), it is important that established procedures be followed for identifying messages and for checking the continuity of traffic to prevent losing any messages.
(2) In general, messages handled on a station-to-station direct communication basis carry a serial number and both stations involved check the number of messages sent and received. When a message is relayed manually it receives a new serial number.
(,?) In tape relaying, originating traffic is numbered consecutively with a message-identifying number including a channel letter when there is more than one circuit between
2 Each combination of characters (letters, figures, or symbols) separated from other combinations of characters by spaces, is called a group.
the two signal centers. When a message is relayed, the message-identifying number is retained but preceded by a channel message number with a channel letter if. necessary. These numbers serve to check the continuity of traffic between the first and last and all intermediate signal centers. In some cases, channel message numbers are inserted in the message tapes automatically. A new sequence of message-identifying numbers is commenced each 24 hours.
f. Message Number Checking. At a specified time, generally once every 24 hours, each station in the network makes a message number check with all stations to which messages have been transmitted during the past 24 hours, in order to find out if all sent messages have been received.
g. Multiple-address and Book Messages. A multiple-address message is one directed to a number of addressees and the contents of such messages often require coordinated action on the part of two or more of the addressees.
484
PAR.
1122
CHAPTER 11. TECHNICAL ADMINISTRATION
ENGLAND
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--- WIRE CIRCUITS
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Figure 11-19. Diagram of teletypewriter traffic routes.
485
PARS.
1122-1123
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Book messages are multiple-address messages which do not require coordinated action on the part of two or more addressees. Traffic operation practices are available and these describe a procedure in which a single tape is prepared for the original multiple-address message which is handled basically like a singleaddress message. The message is relayed throughout the network, and the network signal centers or stations prepare the message for delivery to the addressees within their respective delivery areas.
h. Service Messages. Test and check messages are transmitted throughout a network at specified times or when traffic conditions permit, to check circuit continuity and quality of transmission. Verification and correction of messages are handled informally or by service messages.
1123. TELETYPEWRITER CENTRALS AND ASSOCIATED STATIONS; OPERATION AND MANAGEMENT.
a. General.
(1) At a teletypewriter central, it is advantageous to assign officer responsibility along the general lines stated for signal centers in paragraph 1120.
(2) Teletypewriter central management also is concerned with operation of teletypewriter switchboards and related work, such as trouble-report handling, information and directory services, and monitoring. The activities include: personnel work; operator training; assignment of operating forces; message numbering; study of operating practices and traffic flow to see that efficient use is made of existing facilities; record work of various kinds; etc. Practices used in operating teletypewriter centrals should be uniform within a communication system. Switchboard instructions will be needed on: placing and completing calls, teletypewriter privacy calls, precedence of calls, conference connections, disconnection of circuits, prosigns (conventional abbreviations or procedure signals), and handling delayed calls.
(3) Combined U. S. Army and British Army switching procedure has not been prepared because of differences between switchboards and teletypewriters. However, British 15-line and 40-line teleprinter switchboards are used in some cases by the U. S. Army. Interoperation of these switchboards and U. S.
Army teletypewriter switchboards is not provided for.
(4) Instructions to the teletypewriter stations in regard to switched calls will be required which will fit in with the practices used at the switchboards. FM 24—14 prescribes the procedures for the establishment and control of teletypewriter connections involving one or more manual switchboards such as Switchboard BD-100. This manual also covers procedures for relaying messages manually and through centrals equipped with reperforators and transmitter-distributors but not with semiautomatic tape-relay equipment.
b. Operation of Switchboard BD-100. A teletypewriter station calls the switchboard by depressing the break key of the station teletypewriter for 2 or 3 seconds. This lights a line lamp on the switchboard. The switchboard operator calls a station by sending a short break and, if necessary, bell signals. The operator completes calls by means of patching cords, except when switchboards are arranged for group operation as described in chapter 3. In the latter case, cord circuits are used. (Refer to chapter 3 for traffic information on the handling of calls if the switchoards are arranged for group operation.) The operator signals a
Figure 11-20. Theater signal center operating room with' teletypewriter switchboards.
distant switchboard operator by plugging in on an outward trunk, waits 2 or 3 seconds, and then completes the patching connection to the calling station line. The necessary information is passed from the originating operator to the distant operator by typing. The operator may then disconnect the switchboard teletypewriter
486
PAR.
1123
CHAPTER 11. TECHNICAL ADMINISTRATION
for use on other calls. A disconnect signal, like a call signal, shows on a lamp; therefore the operator should monitor a circuit showing a lamp signal before taking down the connection. Figure 11-20 shows a teletypewriter operating room with means for switching, using Switchboards BD-100 arranged for group operation.
c. British Teleprinter Switchboards. The Brit-isn 15-line board has 7 cord circuits and the 40-line board has 15 cord circuits. The line circuits operate on a reversible one-way polar basis (switched simplex), the connections being cut through directly by means of the cords; the operator may then monitor by means of a high-impedance bridge circuit to ground. Station equipment may be British Mark IV Terminal Unit using Teleprinter 7B(WD). Broadcasting from the boards to as many as six lines is provided for. Further descriptive information on these boards will be found in chapter 3.
d. Traffic Diagrams. Either traffic diagrams or route bulletins, or both, should be provided for every teletypewriter central, located where they will be readily accessible to operators to indicate how to reach other centrals and stations. The information is particularly necessary when the distant central is reached through another central or has an alternate route. Route information is by diagram as illustrated in figure 11-19. For such networks ring-binder type route bulletins may be required with the names of centrals and routings arranged in alphabetical order similar to that shown in figure 11-3. In this case, the traffic diagrams located at the operators’ positions would cover only nearby points, direct points, and most frequently called points.
e. Written Practices Required. The various situations that may develop in handling the different types of calls indicate need for written instructions. The latest material available with any necessary modifications and additions should be provided before communication system service begins and should be modified periodically to suit any changes in conditions.
f. Operators Required. The number of operators required for a teletypewriter central primarily depends upon the calling rate during the busiest hour and the traffic distribution throughout the day, and is limited by the number of operator positions. Since the traffic in most of the other hours is considerably less than that in the busy hour, the operating force
can be reduced during those hours in proportion to the calls handled. In general, data will not be available to show the traffic distribution by hours of the day for a new installation, and it will be necessary to make arbitrary force assignments until data from actual operation of the switchboard can be obtained. An estimate of operator requirements for Switchboard BD-100 installations may be obtained from paragraph 1129.
g. Special Services.
(1) Information Calls. Information calls should be directed to the chief operator in busy hours but probably can be answered by operators in periods of light traffic.
(2) Trouble Reports. Trouble reports should be referred to the chief operator who should make a trouble ticket, similar to figure 11-6, which should be referred to the wire chief for attention.
(3) Service Complaints. Service complaints on such things as slow operator answer, delays, etc., should be referred to the chief operator.
h. Directories. Teletypewriter directory information is necessary for the use of operating personnel in the teletypewriter network at centrals and stations. Directory information can be transmitted by automatic tape transmission. The network control station can be responsible for the issuance of the directory. The frequency of reissue will depend on the activity in adding or removing stations in the network. Reports from each central as to changes since the last issue will be necessary in order to prepare copy for reissue of a directory. A directory should list the following: all teletypewriter switchboards alphabetically by name, with a list of circuits from this central to all others to which it has direct trunks; all major relay stations, with a list of circuits from each to all other centers; and all stations in operation, listed alphabetically by call signals, followed by the unit designation and the central to which they are connected. Example of items making up the above are:
(1) Teletypewriter Switchboards, ALMA SWBD-ALMA AREA-CCTS TO: LUCY SWBD.
(2) Major relay stations, LCDE-GHQ-CCTS TO: ALMA SWBD, LJAM SWBD.
(5) Stations in current operation, LBCD-5TH INF REGT-CCTS TO: ALMA SWBD.
i. Traffic Counts and Observations. Traffic
487
PARS.
1123-1124 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
counts may be made in a manner somewhat 1124. TYPICAL SIGNAL CENTER LAYOUT similar to that discussed in paragraph 1110. WITH ASSOCIATED FACILITIES.
Service-observing equipment equivalent to a. Figure 11-21 shows the different types of that used in large commercial installations facilities and equipment likely to be involved will ordinarily not be provided but checks of at a large theater signal center using wire operation by monitoring will assist in main- circuits and radio channels. The quantities of taining high standards. equipment and circuits are not specified and
SIGNAL CENTER
TELEGRAPH EQUIPMENT OFFICE
M D F I "1.1
TEST AND CONTROL V-F CARRIER
BOARD TELEGRAPH TERMINALS
□FOR OPERATION ON WIRE CIRCUITS ।----------------------,-OPEN WIRE LINES
[PACKAGED EQPT.) I ' °R CABLE
V-F CARRIER TELEGRAPH LINES
AF TERMINALS FOR D-C TELEGRAPH SPIRAL-FOUR CABLE
MULTICHANNEL EQUIPMENT-------------------------x
k \ _ RADIOTELETYPE I-.-,
5 X 7 CIRCUITS
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_______________________ MESSAGE
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V V \ ---------------
ItiT IriT MULTICHANNEL SINGLE SIDEBAND H.F., Cj—1 m RTR i RuTOP
| T ' | |HI | 2- TONE MODULATION RADIO CHANNELS |TD| TRANSMITTER DISTRIBUTOR
V W |tr| typing reperforator
0(0 SINGLE-CHANNEL SPACE - Dl V E R SIT Y I tt I KEYBOARD SENDING, PAGE RECEIVING
r4| FREQUENCY-SHIFT RADIOTELETYPE CHANNELS I 15 T 1 | TELETYPEWRITER
vb vb I .. __ I TRANSMITTER distributor AND I5TT
V Y I 19 1 ' | WITH KEYBOARD TAPE PERFORATOR
E3E3 SINLGLECtSnEEMODULFATION RAD.O CHANNELS LIJ CARRIER telephone EQUIPMENT
a'FOR SHIFTING CARRIER FREQUENCY OF RADIO TRANSMITTERS
ON SINGLE-CHANNEL CIRCUITS TL 54930
b'SPACE - DI V E RSI T Y FREQUENCY-SHIFT RECEIVING TERMINALS
Figure 11-21. Signal center with associated transmitter and receiver parks.
488
PARS.
CHAPTER 11. TECHNICAL ADMINISTRATION 1124-1125
Figure 11-22. Signal center m a tneater.
this sketch is not intended for use as a floor plan. From the signal center there will be, in addition to the wire and radio facilities, mes
senger routes for collection and delivery of messages.
b. Figure 11-22 shows a typical signal center in a theater, with sending and receiving teletypewriter equipment together with facilities for filing and delivering messages.
1125. TYPICAL WIRE AND RADIO NETWORKS.
a. Wire and Radio Teletypewriter Network. An example of a communication zone network using wire and radio for point-to-point circuits, and wire circuits for interconnecting teletypewriter switchboards, signal centers, and local stations is shown in figure 11-23. A teletypewriter installation at an operational base where messages may be received on page-type teletypewriters and transmitted automatically from transmitter-distributors, or manually from keyboards is shown in figure 11-24.
HQ SOLOC MTOUSA ADV. HQ UK BASE HQ NBS HQ QBS ADSEC I2TH ARMY GP HQ 6TH AG
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PSYCHOLOGICAL HEADQUARTERS 2 VILLAGOUBLAY ^^VERSAILLES
WAR I---IDEPT TELETYPEWRITER lOgAgf~ SHAEF MAIN
------- -----------SWITCHBOARD H32A2I----------—---------™---
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PARIS PARIS X-----------------------------
------ X VERSAILLES
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LILLE LEMANS ORLY ,---------------LTAMPES Z
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----— ----------------------- KEY ---- SIGNAL) ---------------------------------- / X-- WIRE
LOCAL ---1 t--- RADIO
SWBD .iTATinij SWBD 1-1
___ siAiiuN i y--------------NUMBERS ON LINES INDICATE NUMBER OF CHANNELS CENTER --------------------------- X-/ |T5~I TERMINAL EQUIPMENT
TL 54981
Figure 11-23. Typical communication zone teletypewriter network (wire and radio).
489
PAR.
1125
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Figure 11-24. Installation of teletypewriter equipment at an operational base.
b. Radio Morse Network. An installation of radio equipment (Morse operation) where messages are sent manually by telegraph keys and received by ear in headphones and recorded with typewriters, is shown in figure 11-25. A radio traffic diagram of a group of Morse networks in a theater is shown in figure 11-26.
Figure 11-25. Manual Morse code radio telegraph installation.
CHERBOURG LONDON 25TH REG. STA. 24TH REG. STA.
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-----------------------.MORSE --1--- ADSEC\ MOBILE \ N/ xffxr----------1 PRE KCi--------------------------------------------------------------------------------' ^-~oi,“anov b.s AO sec/ /jppLY NET
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ru-------------—-------------i \X/ —i
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X \ jX X \ ADCZ REG
CHANNEL SEC CONTINENTAL BASE \ U. S. ARMY \ STAT. PROV.
□-----------4 k xX x x NET \
CHANNEL 1-------X' X X \
BASE ADV. CQM z BLUE NET Xh.q1C0MZ._XX X
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______ X /A X. first us.army__________ seventh us.army \
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FIRST FRENCH ARMY ___________SIXTH AO X< X . । <
------- 7~~Zj -< y । 4 X first french armyX
SHAFE ----- XLTWELFTH ^X
I ________MORSE_______j h X MORSE
--* MORSE L ' X^
LEGEND NCS-NET CONTROL STATION
TL 54935
Figure 11-26. Radio Morse network traffic diagram.
490
PAR.
1126
CHAPTER 11. TECHNICAL ADMINISTRATION
Section VI. TELEGRAPH TRAFFIC ENGINEERING
1126. GENERAL.
a. Purpose.
(7) Telegraph traffic engineering information is given in this section for planning the number of trunks per trunk group, teletypewriter or manual, and the size of teletypewriter centrals based on estimated traffic. Some data, based on limited experience, are included as to average length of call, word groups 3 per message, and circuit capacity in word groups per day for both teletypewriter and Morse-code transmission. The tendency is to use teletypewriter operation for all of the heavier-traffic circuits and to confine usage of Morse code to certain mobile and front-line services.
(2) As a general rule, it will be advisable to use teletypewriter operation on any trunk which is required to handle traffic of over 10,000 groups per 24-hour day. Accordingly, very little traffic engineering will be required in the case of Morse-code operation and this section deals almost exclusively with teletypewriter traffic.
(3) The provision of private line facilities is seldom warranted between two stations that exchange an average of less than 40 calls a day.
b. Critical Considerations in Planning Teletypewriter Communications.
(1) The three most critical considerations in connection with furnishing military teletypewriter communication service are personnel, teletypewriter equipment, and line facilities. The relative importance of these items varies from time to time and in different areas. Army traffic is not stable; its peaks rise and fall and move from point to point, reflecting sudden changes in the course of the war and in the requirements of movement of troops and supplies. Therefore, the engineering methods should be sufficiently flexible to provide the relief required at any time, at any place, and for any of these considerations.
(2) The concentration of traffic into tape-relay network operation tends to reduce the over-all personnel requirements, but it
3 Each combination of characters (letters, figures, or symbols) separated from other combinations of characters by spaces, is called a group.
may concentrate .loads at relay centers which may materially overload personnel. Pending an increase in force, this may be relieved by handling as much of the traffic as possible by other facilities and by rerouting some of the traffic around the signal center affected.
(3) In case of shortage of teletypewriter equipment or of line facilities, the desirable procedure is to concentrate as much of the traffic as possible on the tape-relay network and minimize the switched and private line services.
(4) It is essential that the users of teletypewriter service understand the current problem and the treatment which is used so that they will cooperate promptly in making the routing changes and shifts from one type of operation to another to meet the changing conditions. Accordingly, steps should be taken to keep them informed.
c. Estimates Required.
(1) The number of point-to-point circuits in any group will ordinarily be determined by estimating the total volume of traffic and dividing this by the traffic-carrying capacity per circuit. Traffic data for normal days should be used, avoiding unusual peaks, such as semimonthly traffic peaks which arise from the handling of routine reports, since it is not necessary to engineer the layout for such large volumes of traffic. In exceptional cases the number of circuits may have to be increased on account of quick delivery requirements. It is sometimes necessary to provide additional equipment in a signal center in order to equip direct lines between particular stations.
(2) The size of a teletypewriter switchboard and the sizes of its associated trunk groups are determined by the traffic to be handled in the busiest hour. This in turn is a function of the number of stations served, the number of calls per station in the busiest hour, and the average length of call.
(3) In engineering teletypewriter switchboard installations, it will be necessary to estimate the busiest-hour traffic, either from known data or from arbitrary assumptions. Paragraph 1129 below discusses the determination of teletypewriter switchboard requirements from estimates of busiest-hour traffic.
491
PARS.
1127-1128
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
1127. TRAFFIC EXPERIENCE DATA, POINT-TO-POINT CIRCUITS.
a. Experience in various theaters of operations has provided some useful telegraph traffic engineering data on point-to-point circuits.
b. Hand sending by International Morse code on the single basis, described in chapter 3, permits an average of about 6,000 net text groups (fig. 11-30, note 1) per channel per 24-hour day. This includes allowance for procedure signals, correction of errors, circuit interruptions, etc. It is believed that the performance varies rather widely, however, from one case to another. With comparatively skilled operators and favorable circuit conditions, 10,000 to 20,000 groups per day are possible. With duplex operation, the volume of traffic can be approximately doubled, as compared to single; that is, each direction of transmission has a capacity of at least 6,000 groups per day.
c. A stable point-to-point tape-sending teletypewriter circuit operated single at a nominal 60-word-per-minute speed may handle as many as 50,000 net groups of text per day in addition to the headings (par. 1122d). In duplex operation, this amount of traffic may be handled in each direction simultaneously. Such loads are achieved by keeping the circuit working to full capacity about 75 percent of the time in each 24 hours, the net text group speed being about 50 words per minute for tape transmission and 25 for keyboard operation. With keyboard sending, the capacity will be about one half that with tape sending. Unstable circuits generally carry less than half the above amounts.
d. If the ordinary command and administrative circuit is engineered to carry about one half the 50,000 groups per day (25,000 groups per day) by tape-sending, there will be adequate facilities available for handling the service in the busiest hour.
e. The average number of net groups of text per message is generally between 70 and 120 groups for telegraph traffic within a theater. Between a theater headquarters and the zone of the interior, the average may be as high as 220 groups.
1128. TRUNK CIRCUIT REQUIREMENTS; POINT-TO-POINT SERVICE.
a. Teletypewriter Point-to-point Service.
(7) .Telegraph trunk circuit require
ments for signal centers are drawn up for a theater of operations so that they are coordinated properly with the general communication plan. General information on the traffic-carrying of trunk circuits is given in this paragraph.
(2) To determine roughly the number of half-duplex trunks required between two points, the total volume of traffic per day (sent and received) should first be estimated by multiplying the expected number of messages per day by the assumed groups per message; dividing this volume by the 25,000 (par. 1127d above) gives a figure for the minimum number of trunks required for tape-sending. If engineered on this basis, there is adequate provision for service during the busiest hour. If the result does not give an integral number, it is then necessary to decide whether or not to provide the next higher integral number. Where physical limitations preclude making adequate provision for service during the busiest hour, or where for other reasons substantial delays can be tolerated during the busiest part of the day, the capacity of the trunk group can be determined on the basis of the higher figure of 50,000 groups per trunk per day.
(3) In the case of full-duplex trunks, the required number of one-way channels must be figured separately for the two directions of transmission. The larger of the two numbers then determines the number of full-duplex trunks which must be provided.
(4) In multichannel long-haul radio telegraph systems, certain channels are in some cases operated on a one-way basis. In this case, it will be necessary to make computations of the type outlined above for such channels on a one-way basis.
(5) In engineering additional facilities, it is customary to determine the requirements on the basis that the volume for a representative day is the average of the two busiest days of a normal week. This average peak-day volume is generally about 1/26 that for the total month. Messages sent and received in the busiest hour (excluding deferred messages) are the basis for determining the busy hour circuit load in words.
(6) The determination of requirements for radio stations for part-time communication on a scheduled or nonscheduled basis with a number of distant stations will have to be handled on a special basis for each particu
492
PARS.
1128-1130
CHAPTER 11. TECHNICAL ADMINISTRATION
lar case. When the volume of traffic to be handled with each of the distant stations, has been estimated, a plan or schedule of operation may be drawn up from which a decision may be reached as to the number and types of transmitters and receivers, including spares, which should be provided.
b. Morse-code Point-to-point Service. The number of Morse-code trunks required, either manual or automatic, can be readily estimated from the volume of traffic expected and an estimate of the operating speeds. Operating speeds will depend upon the skill of the operators; the extent to which the circuits will be affected by interference, both natural and man made, including jamming; transmission instability resulting from fading; equipment instability; improper adjustment; distraction caused by battle noise, etc. Net text manual speed will usually be 5 to 10 words per minute. Net text automatic speed varies greatly, from about 20 to about 300 words per minute, depending on the grade of transmission over the circuit; hence estimates of the speed obtainable may have to depend on specific experience over the same or similar routes.
1129. TELETYPEWRITER SWITCHBOARD POSITION REQUIREMENTS.
a. Switchboard BD-100. Figure 11-27 shows the number of Switchboards BD-100 and the number of operators required for two different busiest-hour calling rates. The length of message is of secondary importance in determining the number of operators required, operator time being used chiefly in setting up and taking down connections and incidentally in monitoring. The traffic handled by a teletypewriter central consists of local calls and calls over trunks to and from other centrals. The distribution between various types of calls with Switchboard BD-100 is unimportant, figure 11-27 being generally applicable. Switchboard BD-100 is equipped for 10 line circuits which can be used for either station lines or trunks. Three positions are therefore limited to a total of 30 trunks and station lines. Thus, if there are 25 teletypewriter station lines, only five trunks can be installed. These switchboards are nonmultiple, and connections are made by means of patching cords. Eighteen-inch and 72-inch patching cords are supplied with each board. If more than three positions of switchboard are required, impro
vised group arrangements of the equipment should be considered (ch. 3).
Calling rates, in calls (outward and inward) in the busiest hour per line served* Number of Switchboards BD-100 Operators required b Working lines*
1.5 1 1 1-10
2 1 11-13
2 2 14-20
3 2 21-30
4 3 31-40
5 3C 41-50
2.0 1 1 1-10
2 2 11-20
3 2 21-24
3 3 25-30
4 3C 31-40
5 3d 41-50
a Station lines and trunks use identical switchboard terminations and equivalent supervisory features. Lines include station lines and trunks to other switchboards.
D One teletypewriter is required for each operator.
c Service may be slowed up during peak loads.
d Service may be unsatisfactory during peak loads.
Figure 11-27. Switchboard and operator requirements, Switchboard BD-100.
b. Commercial-type Multiple Teletypewriter Switchboards. Figure 11-28 shows the position requirements of commercial-type multiple teletypewriter switchboards. These switchboards allow teamwork between operators on adjacent positions which gives them a greater traffic-carrying capacity than that of Switch- -boards BD-100, which do not permit teamwork; that is, operators assist adjacent operators in handling peaks of traffic. These data have been included for general information, although it is expected that the Signal Corps will seldom use boards of this type.
1130. TRUNK CIRCUIT REQUIREMENTS; SWITCHED SERVICE.
a. General.
(1) The number of trunks bears no fixed relation to the number of station lines. In
(556933 O—45-------33
493
PAR.
1130
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Total busiest-hour traffic (outward, inward, and through calls') Positions required Number of teletypewriter loops plus trunks
At 1.5 calls (outward, inward, and through) in the busiest hour per teletypewriter loop served At 2 calls (outward, inward, and through) in the busiest hour per teletypewriter loop served
1-20 1 1-13 1-10
21-48 2 13-32 10-24
49-78 3 32-52 24-39
79-104 4 52-70 39-52
105-138 5 70-92 52-69
139-169 6 92-113 69-85
170-202 7 113-135 85-101
203-238 8 135-159 101-119
This table is based on the following assumptions:
1. Each operator handles all types of calls and the total busiest-hour traffic is the sum of all types.
2. Distribution of traffic:
Local calls.............. 20% to 10%
Outward trunk calls...... 40% to 45%
Inward calls............. 40% to 45%
Total................. 100 100
3. The switchboard face layout permits every operator to reach every loop and trunk.
4. If busiest-hour calls per teletypewriter are assumed to be different from the above, the number of teletypewriter loops shown should be reduced in inverse ratio to the calling rates.
Figure 11-28. Position requirements, commercial-type multiple teletypewriter switchboards.
order to determine the number of trunks required in an individual group, it will be necessary to estimate the number of calls to be carried by the group in both directions. An effort should be made to provide facilities and operating personnel adequate to handle the maximum volume of traffic which is likely to be offered in connection with preparing for and carrying out expected military operations.
(2) As in the case of telephone traffic (par. 1115e), more teletypewriter traffic can be handled if all service between two switchboards is handled over one trunk group, rather than by having certain circuits reserved for a particular branch of the service.
One group can handle more traffic than two groups of half the size.
(3) Trunk circuit requirements may be estimated either from the holding time or from the group count as described in subparagraphs b and c below.
b. Trunk Requirements Based on Holding Time. Figure 11-29 shows the number of trunks required in a group for various numbers of busiest-hour calls of three different average holding times, namely: 15, 20, and 25 minutes. Trunks may be held in some cases for periods up to several hours and, if this condition is to apply to a large percentage of connections, the trunk groups may require liberalizing beyond what is shown in figure
Total busiest-hour calls per trunk group (outward plus inward) Trunks per trunk group
15-minute holding time 20-minute holding time 25-minute holding time
1 1 1 1
2 2 2 2
3 2 2 3
4 2 3 3
5 3 3 4
6 3 4 4
7 3 4 5
8 4 4 5
9-10 4 5 6
11-12 5 6 7
13 5 6 8
14 6 7 8
15 6 7 9
16-17 6 8 9
18 7 8 10
19 7 9 10
20 7 9 11
Figure 11-29. Teletypewriter trunk circuit requirements based on holding time.
494
PARS.
1130-1131
CHAPTER 11. TECHNICAL ADMINISTRATION
11-29. Available information indicates that the average length of call (holding time) is about 20 minutes in a teletypewriter exchange network.
c. Trunk Requirements Based on Group Count. Figure 11-30 shows the number of trunks required in a trunk group for various numbers of word groups transmitted in the busiest hour.
The information in the table covers keyboard transmission at an average net speed of 23 groups per minute, and one based on tape transmission at an average net speed of 50 groups per minute (ch. 3). The requirement for trunks that are to be utilized for both keyboard and tape transmission may be obtained from these two columns by interpolation.
Total busiest-hour group count per trunk group (outward plus inward) Trunks per trunk group
Keyboard transmission Tape transmission
1-650 1-1,400 1
650-1,550 1,400-3,400 2
1,550-2,600 3,400-5,700 3
2,600-3,700 5,700-8,000 4
3,700-4,700 8,000-10,300 5
This table is based on the following assumptions:
1. One group of text is assumed to consist of five typed characters and a space.
2. Twenty-three net groups per minute is taken as the average message speed with keyboard transmission.
Total busiest-hour group count per trunk group (outward plus inward) Trunks per trunk group
Keyboard transmission Tape transmission
4,700-5,900 10,300-13,000 6
5,900-7,200 13,000-15,700 7
7,200-8,400 15,700-18,400 8
8,400-9,700 18,400-21,100 9
9,700-10,900 21,100-23,800 10
3. Fifty net groups per minute is taken as the average message speed with tape transmission.
4. Group counts are for the message text only; they do not include headings. For definition of group see paragraph. 1122d, note 2.
Figure 11-30. Teletypewriter trunk circuit requirements based on group count.
Section VII. LOCAL CABLE PLANT ENGINEERING
1131. INTRODUCTION.
a. General. Army fixed plant building projects or installations may justify cable distribution plant to serve a local area. The cable will be lead-covered, nonquadded, and paper-insulated, and is known as exchange cable. In general, the circuits will leave the central in feeder cables which will connect to distributing cables. Distributing cables are provided with terminals giving ready access to the cable pairs for connection to the drop wire or house wiring installed along with the telephone.
b. References. The methods of constructing aerial cable for this type of outside plant are given in TM 11-363. Some of this lead-covered, paper-insulated cable may be required along building walls or in buildings. Construction methods for this type of cable are given in American Telephone & Telegraph Company, Specification 3931, Block Cable Construction,
^nd American Telephone & Telegraph Company, Specification 3933, House Cable Placing. Underground lead-covered, paper-insulated cable probably will be restricted to buried cable placed by hand or plow as described in chapter 9.
c. Information Required. A plan or map, drawn to scale, of the project, showing the estimated number of telephone, telegraph, and signal circuits required in each building will be necessary to plan the cable plant. All uses of cable conductors should be included, such as for fire alarms, crash alarms, emergency reporting systems, and radio control circuits. The conductor requirements for long distance trunk circuits must be determined so that necessary quadded cable and loading can be provided, as described in chapter 5. The location of the telephone and teletypewriter centrals and the signal and message centers should be shown.
495
PARS.
1132-1134 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
1132. NECESSARY RECORDS.
a. General. The information mentioned in the preceding paragraph will permit the development of the cable plan and the records. The records are described in the following subparagraphs. In small installations, certain of the records can be combined. The function of these records is to supply all information relating to the cable, required by the planning engineer and cable test man. They furnish the means for maintaining a continuous record of cable fills which are the guides to future growth. The records should be tracings so that multiple prints can be made. A typical cable map record is shown in figure 11-31. The data recorded should include:
(1) The number of pairs, gauge of conductors, and count (pair numbers) of each cable.
(2) For quadded cable: the type of cable; the number of quads; their gauge and count; the number of nonquadded pairs, their gauge and count.
(3) The type of terminal, count (pair numbers terminated), and designation of each terminal by geographical location (pole number or serial number).
(4) Cumulative cable lengths from the telephone central main distributing frame end of the cable to the center of each cable terminal splice, each splice where a branch cable is spliced to the main cable, and other splices of importance to the planning engineer and cable test man.
(5) When the telephone lines are loaded, the location of each loading pot, type of case, its distance from the central, number and type of phantom and side circuit loading coils, and the count of the cable pairs to which they are spliced.
b. Cable Records. Cable records described above should be provided for the following:
(I) Aerial Cable. This map may suffice for the entire lead-covered, paper-insulated cable used in a small area, whether the cable is underground, aerial, block, or house cable. If the installation is large, this map can be limited to the aerial cable only.
(2) Underground Cable. A separate map for this type of cable will only be required in unusually large installations. In a medium or small installation, this map can be combined with the aerial cable map mentioned in subparagraph (1) above.
(5) Block Cable. This map is used where the distributing cable around a group of buildings is so extensive that the information about it cannot be included on the aerial cable record. These cables may terminate in a cross-connection box (cross-box) where they cross-connect to the cable that feeds them, which may be aerial or underground.
(4) House Cable. This map is used only where an extensive distributing cable system is used in a large building. In small installations, this cable information can also be carried on the aerial cable record.
c. Cable Pair Records. Cable pair records, discussed in paragraph 1149e, show the location of terminals on each cable and the count (pair numbers) that appears in each terminal. They show what service is on each working pair and at which terminal the service is connected. They are used and maintained by the circuit assignment personnel in preparing installation orders for telephones, teletypewriters, etc.
1133. CABLE SIZES AND GAUGE.
a. Cable Sizes. Ordinarily the cable sizes in numbers of pairs diminish progressively from the central out toward the cable ends, at suitable points, rather than being uniform from end to end. This is indicated in figure 11-31. The cable should ordinarily be reduced in size about 50 percent at each diminishing point. The diminishing points, which will be determined in accordance with the line requirements along the cable run, should be at junctions of branch cables, and the multipling explained in paragraph 1135 should be so arranged as to make greatest use of the pairs that are dropped at each point.
b. Gauge of Conductors. Satisfactory telephone service requires that the gauge of cable conductors be such that the transmission loss in the station loops served by a central will not exceed specified limits (ch. 2). Information as to limits of various switchboards is given in TM 11-487. The conductors provided usually will be 22 gauge.
1134. SIZE AND LOCATION OF TERMINALS.
The location of distribution terminals along aerial and block cables is determined directly by the location of equipment and the number of circuits that are to be established through the terminals to serve this equipment. As a general rule, a terminal should be placed where
496
PAR.
CHAPTER 11. TECHNICAL ADMINISTRATION 1134
= T-I4-^_________________________________________________,
S__,_,|_260 FOURTH AVENUE
2233 IA --------------- -------------------------
symbols ” n n r~i r'42 1
O> O — —I
_________ * V p I
0 = POLE JOINTLY USED BY 0 _____!=!_L~ L~1 1-----1
POWER AND COMMUNICA- 15 ----1 I-- ----------------------
T'ONS SYSTEM = _ 16 AA □ QT]
O = TELEPHONE POLE NOT 2 T ~ 6-15 0 | H L
JOINTLY USED. 1935 14 ।---1 1--1 L------------------------
26-22 = 26 PAIR CABLE 28~22 /fL □ □ M I 35 |
WITH 22 GAUGE 0 <•><•>'•> .
CONDUCTORS 13 --------------- ------ L~l 1 L. ■ I
THIRD AVENUE
51-22 = 5l PAIR CABLE WITH , IF R 28(”) SoD-----3oH------aTP)-32?^i---
22 GAUGE CONDUCTORS I6251 0 <4 j W-----22k------2LL 32l, _
12 U / o « * ?
1-22 = 101 PAIR CABLE WITH L—26-22 S', 2 1 -
_ , 0 3 T-15 2 T-16 4 T-17
T-13 = TERMINAL NUMBER || 2080' 2235' 2387'
16 -----= 16 PAIR TERMINAL - _ 10
6-15 WITH PAIRS 6 TO 15 2 T-12 7-|0
TERMINATED THERE ,32o' = T-0 26 - 22 T-ll •*
6 = NUMBER OF PAIRS 51-22 * \ ll64‘____\ 76 ~ 101 / I4661 8 101
WORKING OUT OF 1-51-----\ SECOND AVENUE
THE TERMINAL p-Vi--------A-|_____#_____atzcuNU AVLNUt
> 4 = POINT WHERE CABLE r- ryy-, \ X/n n n ® N °
SIZE CHANGES. 260
. _ I - 22 (X 4 27
721' = DISTANCE FROM MIDDLE _ £7 g ----------------------
OF TERMINAL SPLICE TO X 1-----------1 I--1 □ □ □ Io] fZl □ □
MDF IN CENTRAL- _ 10 I L ~ ~ ~ « t <0
4 r°7i 3 0 53-62 ,\n »"
[—~8' | ULI L-1 4 I 420 N 1
_______________________ rf)
T.'g B B B/7
w _ 19 18 L) l7O V _ *16 —----- BURIED
E 07 ON 26-22 \2 24-39 51-22
“1 ~x 1-26—A 150' 1-51
s 5 T-4 j T-3 K-7 k
607' 455' X“^
0 100 200 300 CENTRAL
SCALE |-----1---1--1
FEET NOTE: IT IS CUSTOMARY TO NUMBER ALL POLES
Figure 11-31. Cable record map. TL54902
497
PARS.
1134-1136
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
excessive use of drop wire paralleling the cable would otherwise be required to reach the equipment served. The usual terminal sizes are 10-, 16-, and 26-pair. The size chosen for a specific location should not be smaller than three times the number of circuits that are to be served through the terminal, with liberal interpretation of this rule. Therefore, a terminal should be placed on any pole that is located where three or more lines will terminate to serve the immediate vicinity, or where long runs consisting of one or two drop wires would be required to reach another terminal.
1135. CABLE MULTIPLING.
a. Distribution Cable Terminal Multipling.
(I) Repeated termination, or overlap of the same cable pairs at more than one terminal is known as multipling. The multipling of cable pairs offers almost unlimited permutations and combinations but practical considerations and operating features usually narrow the field to a comparatively few feasible plans. The choice of multipling arrange
ment must consider future requirements and the following objectives:
(a) To provide for probable variations in location and amount of growth with a mininum number of cable transfers.
(5) To make the same cable pairs (counts) available by overlap at a sufficient number of terminals to permit the best possible use of circuit pairs.
(c) To avoid early congestion in any one terminal or cable pair count.
(2) A method of multipling which provides good flexibility is illustrated in figure 11-32. The pair counts in a series of eight terminals are given, which illustrate the overlap of pairs so that each pair appears in more than one terminal. Figure 11-31 is an example of the application of the principles involved.
b. Feeder Cable Multipling. The multipling of feeder cables consists in assigning the pairs of distributing cables, subsidiary cables, terminals, and stubs. This presents a problem similar to that explained in the preceding paragraph for distributing cables. The main objectives are flexibility, even distribution of ultimate lines, and avoiding early congestion of cable counts which would necessitate cable transfers to provide relief.
1136. CABLE CONGESTION AND RELIEF.
a. Congestion. Periodic examination of the cable pair records (par. 1149e) will show whether cables or portions of cables are approaching maximum fill, that is, maximum number of pairs in use which it is practicable to permit before relief is decided upon. Excessive fill will restrict the freedom that is necessary in making new arrangements for the use of pairs. Congestion also will cause resort to temporary expedients, such as long drop wire runs, in order to connect additional telephones. Certain terminals or branch cables may approach congestion before the cable as a whole is in need of relief. When the line assignment personnel notice approaching congestion, it should be their responsibility to notify the proper authorities.
b. Relief.
(I) General. The object of relief is to provide adequate numbers of cable pairs and terminals in the congested location, without creating congestion in other localities. Allowance should be made for spare pairs for existing lines and for reasonable growth. Methods of relief for cables approaching congestion include cable transfers, the use of cross-connecting terminals, reinforcement, replacement, or division. The first two named are for short term or temporary relief. A complete relief plan may include various combinations of two or more of the methods as one project.
(2) Cable Transfers.
(a) A cable transfer is the shifting of one or more terminals, distribution circuits,
498
TO CENTRAL
------SIZE TERMINAL
IN NUMBER OF
NO. I PAIRS
Ir ill ['ri || |-| O 1-^-6 /—COUNT OF
----------- 1-16 / TERMINAL -----------1 /NO 2 (PAIR NUMBERS -----------16 TERMINATED) „zzzzzzzzz---s
_ i____i___ -J /------TERMINAL SYMBOL
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£ 2| ZZZZZZZZZ w 16 = NO-4-4 TERMINAL
uj ------------ 'O 36 S| 6 NUMBER
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z ,, T2 5-4----NUMBER OF
ZZZ'ZZZ'Z PAIRS WORKING
____■____Z_ uj 1£ c OUT OF THE
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ZZZZ’ZZZ" L 25-40
..till IIFIHfl J 16 g NO. 8
51 4 8 36-51 6
TERMINAL \ NUMBERS----*
LAYOUT APPLICATION
TL 54903
Figure 11-32. Cable multipling.
PARS.
1136-1138
CHAPTER 11. TECHNICAL ADMINISTRATION
or branch feeder circuits from certain conductors in one cable to other conductors either in the same or a different cable. The result of this plan i$ a redistribution of both existing lines and expected growth in existing cables, thus making idle pairs available where they can be used to the best advantage.
(b) Cable transfers will provide relief in specific terminals or sections of cable by changing the count of the pairs in congested terminals so as to effect a redistribution of existing lines. This method is applicable when the congestion results from the multipling of certain pairs at two or more points, and when it is feasible to transfer to other cables or to other counts in the same cable which contain spare facilities.
(3) Cross-connecting Terminals. A crossconnecting terminal (cross-box) may occasionally be used to provide relief to a congested cable or cable complements. These cross-connecting terminals permit a redistribution of working lines on the telephone-central side of the cross-connecting terminals. The cross-connecting terminals are inserted at some suitable point along the cable thus permitting any spare pair toward the central to be connected to any pair in the distant end of
the cable. This method of relief is resorted to only when the possibilities of relief by cable transfers have been exhausted. Cross-connecting terminals also permit feeding one or more distribution cables in which the total pairs exceed the pairs in the feeder cable. They have the disadvantages that they increase the work of assignment, installation, and maintenance.
(4) Reinforcement. Reinforcement is the placing of cable parallel to the existing cable with the transfer of some of the branch distribution cables from the original to the new cable.
(5) Replacement. Replacement of a section of the cable is used when the relief must be confined to the original route and the capacity of the pole line or underground plant in that route has been reached.
(6) Division. Dividing the congested cable consists in cutting the existing cable at one or more points and providing a different feeder to the central for the severed section or sections. This arrangement is mainly applicable to the distribution cables but may, under certain conditions, be used to provide relief of a feeder cable. It results in two or more cables each of which provides facilities for some existing lines and a certain amount of growth.
Section VIII. TRUNK PLANT ENGINEERING
1137. GENERAL.
After determining the long distance trunk circuit requirements, based on traffic engineering procedures discussed in preceding sections, certain information must be available in order to make the best possible use of materials and equipment, so that an intelligent choice can be made between several different methods that might be used to provide the circuits. This information should be secured before making any definite plans as to how the circuits are to be obtained. Reference can be made to FM 24-20, TM 11-363, TM 11-368, TM 11-369, TM 11-462, TM 11-487, TM 11-2001, TM 11-2022, TM 11-2253, and to other chapters of this manual.
1138. INFORMATION REQUIRED.
a. General. When engineering long telephone and telegraph trunk circuits which are to be relatively permanent, a considerable
amount of information should be assembled regarding the conditions involved and circuits required. The information needed is listed in the following subparagraphs. When engineering short telephone and telegraph trunk circuits which are to be less permanent, a number of the items listed will not be required; the amount of information needed in any specific case will depend on the circumstances. In general, more complete information will be required for the installation of fixed plant equipment than for tactical equipment. The procedure to be followed after this information has been made available is indicated in paragraph 1139.
b. Circuit Information Check List. The following list includes the items of circuit information required:
(1) Number of telephone circuits required between any two centrals or points and the desired net loss of each.
499
PAR.
1138
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
(£) Date each circuit is needed.
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Figure 11-33. Line route map.
504
CHAPTER 11. TECHNICAL ADMINISTRATION
PAR.
1141
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505
PAR.
1141
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
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TELEPHONE CIRCUITS
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2 A-C tVFR 3-4______VFR_____3-4 VFR^'^VFR 3-4 VFRfD~FJ.TC 3 -4_VFR_____3-4 LTCLT9 3~4 LTC,-|lTC| 3-4 LTC rtrsl 5-6 LTS B.s
!A-K UTS_7L8_LTS j m -XII^ZLTS.1^ r hw
45MI L1L.IS—L3LIC. |D_O --^5_6 22L, IH-Q
I04CS tl8 _. L_ HIfiJ33 MI LtiZF3^|
LTS I04CS LTS |04 CS
5-6 !^Je 5-6 22Ml 5 - 6 30MI
,04CS LTS I04CS I04CS
PjK Q | ________ o|~ 1LTS|
notes:
I PIN POSITIONS ABOVE LINE,H2,INDICATE V.F.TELEPHONE 5. ABBRE VI AT IONS FOR USE ON CIRCUIT RECORDS 5 (CONTINUED)
AND D-C TELEGRAPH WIRE CIRCUITS. ___________TYPE OF EQUIPMENT____ _________________TYPE OF EQUIPMENT__
2. PIN POSITIONS IN LINE,)l-2 (.INDICATE CARRIER CHANNELS, CUE C CARRIER,EAST TERMINAL, CU ALLOCATION VFT VOICE-FREQUENCY CARRIER TELEGRAPH
TYPE C OR H ,ON ASSOCIATED PAIRS . CSE C CARRIER . EAST TERMINAL , C S ALLOC AT ION TERMINAL
3 T iNinir ATF1 PHAMTOM t INF CUW C C A R RIE R , WEST TERMI N AL , C U ALLOC AT 10 N VFC VOICE - FREQUE NCY CARRIER TELEGRAPH
o. A INUILA MHAN I L> M Lint . C SW C C A R R IE R , WEST TE RMINAL . C 5 ALLO C AT I ON CHANNEL TERMINAL
4. EACH CARRIER SYSTEM SHOULD BE NAMED AND NUMBERED. CSR C CARRIER . REPEATER CS ALLOCATION B VOICE-FREQUENCY RINGER
THIS CHART SHOWS THE FOLLOWING SYSTEMS : CUR C CARRIER . REPEATER CU ALLOCATION CTR C CARRIER TRANSFER SET
TYPE C SYSTEMS TYPE H SYSTEMS V-F CARRIER WE H CARRIER , EAST TERMINAL HTR H CARRIER TRANSFER SET
A-D NO. I A-B NO-I " TELEG. SYSTEMS HW H CARRIER , WEST TERMINAL BRG BRIDGING CIRCUIT ON A VOICE REPEATER
A-D NO-2 D-O NO. I A-H NO. I HR H CAR RIE R, REPEATER T D-C TELEGRAPH REPEATER
A-H NO. I G-H NO.I A-D NO.I VFR VOICE - FREQUE NCY REPEATER REG D-C REGENERATIVE TELEGRAPH REPEATER
D-H NO.I F-P NO.I D-H NO.I LTS LINE TERMINATI NG AND SIMPLEX PANEL TT TELETYPEWRITER STATION
D-H NO.2 H-R NO.I D-F NO.I LTC LINE TERMINATI NG AND COMPOSITE PANEL TL 53205 -S
D-F NO.I F-P NO.I
Figure 11-35. Circuit layout chart (continued on opposite page).
507
PAR.
CHAPTER 11. TECHNICAL ADMINISTRATION 1141
telegraph circuits
___________________________]’ IF <’ jF ‘if-IF I o I A- H •— -£__________------------------ -----------------------------------------------------3 --—. |Q| A- H
vft \-\ \&A -
I I2A-H»--J| t----J-------------------------------------------------------------------------------------------------2 ---.H2A-H
IOI A-D*— r-I-------------------------------r--It-------*IOID-H*-f--------------------------------------------------Ir-------*101 D-H
VFT \ 9-10 \ \ 9-10 \ VFT VFT \ 9-|0 \ \ 9-10 \ VFT
\ CH2 \ \ CHS \ \ CHS \ \ CH2 \
II2A-D*—--fe ----------------------------------2 t I-*II2D-H*-—J ——--------------------------------------------4 L 2—.II2D-H
113A-0 4-----1-----7 REG T ---------7-REG T !-----L||3D-H 4---!____4------4______T REG 7 _________T "ES . .T____!__X, 113D-H
, I4A-d4-----2-----T_R_EG_T_--------l7--REG 7 I---2----XII4D-h4 2 T 7------T REG T_________2_REG_y_______2____X.n40 H
iisa-d*!-----2-----T-RES T----------I7 REG T---2----4115D.H4j---2----7------L______7 REG T_________T REG T_______2___—*iisd-h
,01 A- i------X.l01fr0J_-------T. REG... 7 -4-----I.H6D. h4--*----7------7 ------T__REG__T_--------T REG T ------4-----X, ll6 D. H
im. rX 7 T REG T 7 7 ~ 7 7 7 „ T 7 T T T REG T 7 T T 7 T
•01 A- C •—|-------—-----------------*1010-0 -----------’IOID-G ----------------------------------------*101 G-H ---------- 101G- H
102 A- B •—-2------X.|OI B-c4--§----2-OSC-O 4----«-----X1010- F 4-8-----I-----X------4 101F - H 4--2----17 REG 7!-----2-----Z. 101F - H
103 A- B •—--------—*|02B-c4--2-----X.I03C-D 4---?------X|02D-f4---2---J------7-------4 ------1----?----XiO2G-h4J-----?------. ,02G.H
io4a-b4-----12----lZ,103B<4-—r—12---I0 2 TS _
Z3____VF/? 33 5.0 __+jo_ z yy 30 0 *______->7.5 2
C VFR 33.5 175 + >0 Z'X 2>2.5 -2 2 TS
ron.. Tn SYSTEM CHAN. OR GAUGE LENGTH ASSOCIATED
iv QR LINE flIRES A TYPE NILES COhlOCTED EQUIPMENT a ~_ ZZZZZZZ___________________________ZZZZZZZ °____________________________
________<3 4- 6________1-2 /OUCj 125 cjf?_____________________
G_________________________________________________Cj/?
c &-C 1-2 IQUC-i too cJC <5
fa^Ll -^_SA 1 c t_£_C______________________________________
TL 54963
Figure 11-36. Telephone circuit record card.
b. Distribution and Maintenance of Records.
(7) The distribution and maintenance of records should be limited to actual need, with due regard to security requirements.
(2) The essential records for area offices are the line route maps and circuit diagrams for their particular area, the equipment record for each central and repeater station, and the circuit record cards for each trunk circuit in the area.
(3) The wire chief at each central and repeater station will require an equipment record of his office showing the chief items of equipment that are used in trunk circuits, a circuit record card for each through or terminating trunk circuit, and a circuit diagram for that part of the system for which he is responsible. The last, for use in trouble clearing, should show junctions, etc. He will also require and keep up to date the circuit assignment index.
(4) The best rule that can be given for issuance of new circuit diagrams is to do it as
often as necessary, that is, when major changes occur or minor changes accumulate.
(5) An economical procedure is to require the urea offices to post ordinary changes on their circuit diagrams, leaving it up to them to request new copies when needed, either because too many changes have accumulated or because their records are wearing out.
(6) Circuit record cards should be distributed to every location that will have work to do in connection with establishing or maintaining the circuit, including terminal centrals, intermediate centrals, and repeater stations. The cards should accompany the circuit order that establishes the circuit or they can be sent later in case of telegraphic circuit orders.
CIRCUIT RECORD * TELEGRAPH
CIRCUIT to/-(if-C-P)_____________________ DATE !0 lOlaj m?
SPEED 36 7 PPM_____ HALF DUPLEX PH FULL DUPLEX II
CONTROL OFFICE C-_____________________________________________
_______FROM____________TO_______ LINE OR PIN OR COEFFI-
STATION OR TYPE OF STATION OR TYPE OF CARRIER CARRIER LENGTH CTENT
OFFICE EQUIP OFFICE EQUIP SYSTEM CHANNEL
K rnnM /Z______________J_____no, 5i. 3 2
_____f ________P o 3 75 ', ,o
<3 -j c 3 6 c y so >______
J rrniJA 6 J-G /-2 nAu. I____________o
« 0.~7T
______________- - — -______________________________________
C. VtJ_____P_______YrC. C-5*l CU 5_________Zoo 3
■P_____v/j_____£_______Pi P-E____5-1. otocu ro_____7
______________C- 6 --------------------------_________________
C J_______P________cP 1-r 50 7
P A________7? P-P !-2 5 2^
. I I I 7
<• I b । ; c _______ \ o .£
I~r~l—F-pq--, f£lF* 2 3 4’—ttn—l**°l—1*^1—@"T__@—CZO
. L__.| ;._.J ; ;
L------ ------------J
LEGEND
I TT |= TELETYPEWRITER | T |=D-C TELEGRAPH REPEATER
|reg| = d-c regenerative |vfc|=voice - frequency TELEGRAPH REPEATER CARRIER TELEGRAPH
TL 54962
Figure 11-37. Telegraph circuit record card.
1142. COMPUTATIONS FOR RECORD CARD, VOICE-FREQUENCY REPEATERED CIRCUIT.
a. This paragraph describes a method which can be used to obtain the data required to fill out a record card (fig. 11-36) for a circuit using packaged voice-frequency repeaters. The required information consists of the amplifier gain, the attenuator loss, and the repeater output level for each repeater on the circuit. The column BAL is provided on the record card for recording the value of the balance between the
508
PAR.
1142
CHAPTER 11. TECHNICAL ADMINISTRATION
line and the network, as measured in accordance with the procedures given in manuals on the repeater.
b. Transmission level diagrams based on information given in chapter 5 and illustrated in figure 11-38 will indicate the transmission levels into and out of the repeater and the required gain of the repeater, for each direction of transmission. This information, together with the input and output equipment losses, can be used to determine the required amplifier gain and attenuator loss. An example of the factors involved in making the amplifier and attenuator adjustments is shown in figure 11-39. The input and output equipment losses, the magnitude of which depends upon the types of connecting lines, are shown in figures 11-40 and 11-41. Equipment losses for 4-wire •circuits are given in figure 11-42.
c. An example of the computations involved in repeater adjustments is shown in figure 11-43. It is assumed that the repeaters are used on an 080 copper-steel open wire line. The computations are made in the following manner:
(1) Prepare a level diagram (chs. 5 and 12) such as that shown in figure 11-38.
ABC
© © @
-M—*—{XH1—M-
© ® @
NUMBERS IN CIRCLES ARE REPEATER GAINS; PLAIN NUMBERS ARE LINE LOSSES
CIRCUIT LAYOUT
LEVEL DIAGRAM, A TOC DIRECTION
TL 53204-3
Figure 11-38. Level diagram for a voice-frequency circuit and repeater.
(2) Compute an attenuator loss such that the transmission level at the amplifier input (fig. 11-39) will be as close as possible to -23 db after taking into account the input equipment loss and the transmission level at the repeater input, as read from the level diagram. The attenuator is adjustable in 2.5 db
AMPLIFIER ofpr.Tro
OUTPUT
LEVEL (+IOdb pVTPUT
■0R LESS> t , (iSoR
lev'll repeater ! °db
INPUT AMPLIFIER i
LEVELINPUT LEVEL "ADJUSTABLE) I
]TO ATTENUATOR (ADJUSTABLE) ;
_______t AMPLIFIER-----| ■ATTENTUATOR/ INPUT LEVEL • LOSS —I ((ADJUSTABLE)'--------* 1 «.Z I
■ LEVEL DIAGRAM j
INPUT ATTENUATOR , AMPLIFIER I OUTPUT .
(L ^“lossT^
1 i 1 rH I r< ' : I
-------1- ATT. 1------------1---
, I INPUT INPUT I
b^T-J— ouAtNp°ut -£>et. netQ— o a“° t —“——west
EQUIP. EQUIP
REPEATER CIRCUIT
TL 54857
Figure 11-39. Two-wire voice-frequency repeater circuit and level diagram.
steps from 0 to 17.5 db, so in general it will not be possible to adjust exactly to -23 db. The transmission level at the amplifier input should be computed for the attenuator setting used.
(3) Compute the level at the amplifier output (fig. 11-39). This is equal to the transmission level at the repeater output, as read from the level diagram, plus the output equipment loss.
(4) Compute the amplifier gain by subtracting the transmission level at the amplifier input from that at the amplifier output.
d. The computations given in subparagraph c above cover only one direction of transmission, A to C. Similar computations are required for the opposite direction of transmission, C to A.
e. The procedure for 4-wire circuits is essentially the same as that described for 2-wire circuits.
656935 0—41
34
509
Type of circuit Side or phantom Equipment losses (db) *
Input Output
165 Copper Side 6.0 4.5
165 Copper Phantom 6.3 4.5
128 Copper Side 6.0 4.5
128 Copper Phantom 6.3 4.5
104 Copper Side 6.0 4.5
104 Copper Phantom 6.3 4.5
080 Copper Side 6.2 4.4
080 Copper Phantom 6.4 4.5
165 C-S 40% Side 6.5 4.4
165 C-S 40% Phantom 6.4 4.6
128 C-S 40% Side 6.9 4.2
128 C-S 40% Phantom 6.7 4.4
104 C-S 40% Side 6.9 4.1
104 C-S 40% Phantom 6.8 4.3
080 C-S 40% Side 7.5 3.«9
080 C-S 40% Phantom 7.4 4.1
128 C-S 30% Side 6.9 4.1
128 C-S 30% Phantom 6.8 4.3
104 C-S 30% Side 7.5 3.9
104 C-S 30% Phantom 7.3 4.2
109 GS Side 8.9 3.8
109 GS Phantom 8.8 3.9
083 GS Side 7.7 3.7
083 GS Phantom 7.8 3.9
Switchboard side of terminal repeater 5.5 5.0
“ The losses are for 1,000 cycles and 600-ohm measuring sets. Figures apply to any spacing of wires which may be found, since impedance variations from this cause are small (ch.5).
Figure 11-40. Equipment loss data for packaged voicefrequency repeaters on open wire circuits.
Type of circuit Loading system * Equipment loss (db)b
Input Output
Paper-insulated cable
16 ga. side 6000-88-50 5.0 4.2
16 ga. phantom 6000-88-50 6.0 4.4
19 ga. side 6000-88-50 5.0 4.2
19 ga. phantom 6000-88-50 6.0 4.4
16 ga. side 6000-172-63 6.2 4.1
16 ga. phantom 6000-172-63 6.0 4.3
19 ga. side 6000-172-63 6.2 4.1
19 ga. phantom 6000-172-63 6.0 4.3
16 ga. side 6000-44-25 6.0 4.4
16 ga. phantom 6000-44-25 4.9 4.6
19 ga. side 6000-44-25 6.1 4.3
19 ga. phantom 6000-44-25 5.9 4.6
16 ga. side 3000-88-50 6.2 4.1
16 ga. phantom 3000-88-50 6.1 4.2
19 ga. side 3000-88-50 6.2 4.1
19 ga. phantom 3000-88-50 6.1 4.2
16 ga. side Nonloaded 10.8 3.5
19 ga. side Nonloaded 10.7 3.5
Rubber-insulated wire and cable
Wire W-143 Nonloaded 10.9 3.3
Wire W-143 3300-44 7.5 4.3
Wire W-143 3300-88 6.1 4.2
Cable Assembly CC-358-( ) 1320-6 6.1 4.6
Switchboai d side of terminal repeater 5.5 5.0
"■ The first number is the coil spacing in feet, the second is the inductance of the side circuit loading coil in millihenries, and the third, when present, is the inductance of the phantom loading coil in millihenries.
bThe losses are for 1,000 cycles and 600-ohm measuring sets.
Figure 11-41. Equipment loss data for packaged voicefrequency repeaters on 2-wire cable circuits.
510
PARS.
1142-1143
CHAPTER 11. TECHNICAL ADMINISTRATION
Type of circuit Loading system a Equipment loss (db) b
Input Output
19 ga. side 6000-88-50 2.4 1.0
19 ga. phantom 6000-88-50 2.4 1.0
19 ga. side 6000-172-63 2.4 10
19 ga. phantom 6000-172-63 2.4 1.0
Type of circuit Loading system a Equipment loss (db) b
Input Output
19 ga. side 6000-172-63 2.4 1.0
19 ga. phantom 6000-172-63 2.4 1.0
19 ga. side Nonloaded 5.9 1.0
Switchboard side of terminal repeater 5.5 5.0
a The first number is the coil spacing in feet, the second is the inductance of the side circuit loading coil in millihenries, and the third, when present, is the inductance of the phantom
loading coil in millihenries.
b The losses are for 1,000 cycles and 600-ohm measuring sets.
Figure 11-42. Equipment loss data for packaged voice-frequency repeaters on 4-wire cable circuits.
Item Transmission levels, losses, and gains Values obtained from Repeater location (fig. 11-38)
.4 B C
1 Level at repeater input Figure 11-38 0 -9 -8
2 Input equipment loss Figure 11-40 5.5 7.5 7.5
3 Attenuator loss Computed 17.5 7.5 7.5
4 Level at amplifier input Computed (item 1 — item 2 — item 3) -23 -24 -23
5 Level at repeater output Figure 11-38 +6 +6 -6
6 Output equipment loss Figure 11-40 3.9 3.9 5
7 Level at amplifier output Computed (item 5 + item 6) 9.9 9.9 -1
8 Amplifier gain Computed (item 7 — item 4) 32 9 33.9 22
Figure 11-43. Illustration of computations of attenuator loss, amplifier gain, and amplifier output.
Section IX. CIRCUIT ASSIGNMENT WORK
1143. GENERAL
a. The problems of making circuit assignments for both radio and wire circuits in a theater of operations are somewhat similar. Circuits in the fixed plant, such as long distance telephone trunks and radio circuits, may be assigned by the theater of operations signal staff as indicated in figure 11-1. Circuits extending beyond the fixed plant into the tactical zone may be controlled from theater headquarters. The circuit assignment work described in the following paragraphs applies particularly to the long distance telephone and radio circuit assignments made by the staff
for the fixed plant. However some of the suggestions may have application in the assignment of tactical circuits.
b. The work of preparing and issuing trunk circuit orders is called trunk circuit assignment work. The organization responsible for the initial system circuit layout should continue to operate as a centralized assignment organization for the day to day circuit changes, unless otherwise specified.
c. Each long distance wire or radio trunk circuit added, changed, or discontinued will require a circuit order authorizing the work. It should be issued to each location which will
511
PARS.
1143-1145 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
have work to do in connection with the order or which will be involved in maintaining the circuit. Written orders are desirable for record purposes, but it may be necessary at times to transmit them by telephone or teletypewriter with subsequent confirmation by a written order. A circuit order assigns the facilities that are to be used to make up a trunk circuit. A pair, a phantom, a carrier channel, a simplex, or a composite channel are called facilities.
d. Because of the various types of long distance wire circuit facilities and terminal equipment, circuit assignment work is frequently complicated and must be planned and carried out with extreme care. There may be 25 or more circuit orders per week in a given active theater of operations, depending upon its size. Many of the orders will require rapid and accurate planning and execution.
e. Radio circuit changes may not be as numerous as in the wire service but will require similar distribution of circuit orders to the locations involved in changes.
1144. CENTRALIZED CIRCUIT ASSIGNMENT OFFICES.
a. General. In the proper handling of circuit assignment work, centralized circuit assignment offices are necessary. The one for wire service probably will be in the wire engineering group and the one for the radio service probably will be in the radio group. However, control for a base section area may be delegated to base sections, if desirable. The' assignment office, in the wire service, functions to plan the work required to accomplish the desired circuit changes, and to coordinate it within the various organizations involved. The office in the radio service coordinates call sign and frequency assignments. Responsibility for prompt execution of the plans normally is delegated to a particular office known as the control office, and designated by the centralized assignment office (par. 1105).
b. Wire Service; Requirements. In order to ac-accomplish the work required of a centralized circuit assignment office in the wire service, the basic requirements are:
(1) Skilled and careful personnel, aware of the importance of this work.
(2) Records of facilities and equipment available or in prospect, and of the current use of existing facilities and equipment.
(5) Requirements for circuit changes.
(4) Knowledge of the field personnel who will be engaged in the actual work, particularly with regard to their qualifications for doing such work.
(5) Authority to issue, and means of issuing circuit orders for necessary changes.
(6) Means for receiving reports of completion on circuit orders issued.
(7) Systematic designation of facilities and circuits.
c. Wire Service; Personnel. The personnel requirements for an assignment office in the wire service are:
(1) Engineers with ability to plan and direct the work and whose duties include:
(a) Proper design of circuits and circuit changes to meet allowable transmission losses in the most economical manner with minimum lost circuit time in making circuit changes.
(b) Prompt investigation of all difficulties encountered in new or existing circuit layouts and issuance of adequate instructions for applying suitable remedial measures.
(2} Clerical personnel to:
(a) Prepare and maintain records.
(&) Prepare and issue authorized circuit orders and circuit record cards.
d. Radio Service. The personnel assigned to this work should be engineers or others with a thorough understanding of radio communication. They must have authority and means for issuing circuit orders for necessary changes.
e. Records. In assuming control of an existing record layout, a review as to its adequacy and accuracy should be made. Where record layouts are to be newly established, careful work is required to provide a satisfactory record. Improving the records is a continuous process, requiring constant alertness to detect errors, conscientious reporting of errors found, and a routine for such reporting. The records listed in paragraph 1141 are essential for wire circuit assignment offices.
1145. LONG DISTANCE WIRE CIRCUIT ORDERS; GENERAL.
a. Circuit orders for long distance wire trunks may be issued in different forms and convey various information.
b. Planning of these trunk circuit orders requires skill and ingenuity in order to devise a
512
PARS.
1145-1146
CHAPTER 11. TECHNICAL ADMINISTRATION
smoothly working arrangement for making a required set of circuit changes in proper sequence. The objective is to give adequate, concise, and precise instructions.
c. In the ordinary case, particularly at the start, the assignment office is likely to be continually pressed to set up more or different circuits. This will require careful scheduling and coordination so that, as far as possible, the more urgently needed circuits are established first, and future changes can be scheduled with a fair degree of assurance that the schedule can be met. In addition to ordinary circuit changes, temporary changes may have to be made quickly to minimize the effects of line trouble or to meet a temporary increase in traffic to a particular office. Wire chiefs on their own initiative may make temporary patches to replace a section of a trunk that is in trouble.
1146. CIRCUIT ORDER DETAILS.
a. Introduction to Order. The introduction to a trunk circuit order should show pertinent information as follows:
(7) Date and place of issuance, serial number, and the person who has authorized it to be issued.
(£) Purposes for which the order is issued. This normally consists of statements summarizing the changes covered, including such items as circuits added, discontinued, or changed; facilities or equipment released from service (as when they are to be removed) ; and the establishing of a new central or signal center or the moving of an existing one.
(3) Conditions under which the changes are to be made, including such items as:
(a) New facilities or equipment required for completion of the order, showing the time at which they are expected to be available (and preferably under what order they are being installed). The places involved can correct their records from circuit orders.
(b) Coordination with other circuit orders, such as, assumes circuit order CO 259 in effect.
(c) Time when order is to be completed, as on a specific date, as soon as possible, etc.
(d) Assignment of responsibility for supervising the execution of the changes, usually one of the following arrangements:
1. Circuit control offices.4 (If there are several separate and distinct changes on one order, the control office on each individual circuit involved controls the work on that circuit.)
2. Circuit control office of the principal circuits involved (if there are several changes most of which involve the one control office.)
3. The office that will have to execute all of the changes. (If a new entrance cable is being installed and many circuits have to be transferred from their existing entrance facilities to the new cable, thus involving various control offices.)
(e) Completion tests required, if different from the standard tests.
(f) Completion reports required, if different from the regular reports. (In case of special urgency, telegraph or telephone report may be required.)
(g) Special conditions, such as, circuits involved may be taken out of service only between 2400 and 0500 hours.
(h) An index or list of items, especially in the case of large orders. Such a list may be used conveniently for assigning supervision and indicating completion reports as required.
b. Body of Order. The body of the circuit order can be prepared in memorandum form, written in a systematic manner. It should indicate the end of groups of related changes, commonly called steps, that is, the points at which work can be stopped without leaving any circuits out of service, and should show an item number for each change. The style preferably should permit transmission by teletypewriter, facsimile, or even by telephone. It can list a moderate number of related changes or a large number of independent changes. Where a large number of similar changes are required, time can often be saved
4 The importance of establishing a control point in European international telephony was recognized at the Budapest plenary meeting of the CCIF (International Consultative Committee on Telephony) in September 1934 at which the following rule was recommended: “One of the stations through which a circuit passes is responsible for satisfactory transmission on that circuit. This station is called the control station; it is chosen by agreement between the technical departments of the Administrations and operating companies involved. Unless otherwise arranged between the technical departments interested, the control station will be one of the terminal stations of the circuit.”
513
PAR.
1146 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
by tabulating the changes, that is, describe the change once and list the circuits and facilities involved. The order should be a natural arrangement to consist of the information the engineer would normally write out in planning an order, working either directly from records or, in a complicated case, from a work diagram, to describe the changes. This narrative form of order places reliance on the assumption that the centrals, repeater stations, and signal centers have circuit record cards for each existing circuit entering or passing through their office, and receive cards with the circuit order for each new or rearranged circuit. There is considerable opportunity for use of abbreviations. A sample circuit order and a sample completion report shown in figures 11-44 and 11-45, respectively, illustrate the application of many of the above items.
FROM LAYY WIRE DIV, FHQ271500A
TO CENTRE CITY WIRE CHIEF FAC
WIRE OFFICER, 3243RD SIC RECT
PLANT BRANCH WESTERN EASE SECTION CSO L/C ATLANTIS ATTN LINES OFFICER 3 COY, 91ST L/C SIGNALS HUDSON WIRE CHIEF
L.D. CIRCUIT ORDER NO. $27
27 APRIL 1944
PURPOSE DISCONTINUE SERVICE SNAPPY /KINGSTON/ TO LOOKOUT START SERVICE SNAPPY /KINGSTON/ TO TOPPER
REQUIREMENTS NEW PAIR HUDSON - TOPPER, HUDSON WIRE CHIEF PROVIDES. REMOVE PAIR CENTRAL CITY-LOOKOUT, SIGNAL OFFICER WBS RECOVERS.
SUPERVISION CENTRAL CITY WIRE CHIEF SUPERVISES THESE CHANGES WHICH ARE TO BE COMPLETED FORTHWITH.
DETAILS
1. DISCONTINUE SNAPPY /KINGSTON/ - LOOKOUT SPEECH CIRCUIT L OF C$2 FROM PR 2* CENTRAL CITY - KINGSTON U C CABLE
LOCAL FACILITIES 'KINGSTON - SNAPPY ARE REUSED BY ITEM 4. LOCAL FACILITIES CENTRAL CITY - LOOKOUT TO BE REMOVED.
2,3 REROUTE SNAPPY / KINGSTON/ - FLINT SPEECH CIRCUIT
L OF C $7 AND S PLUS D, L OF C 73 THEREON FROM PR 13 CENTRAL CITY - HUDSON U G CABLE PH 29/30 HUDSON-
KINGSTON U G CABLE TO PR 24 CENTRAL CITY - KINGSTON U G CABLE CLEARED BY ITEM 1. ASSUMES LD C024S IN EFFECT
4. ADD L OF C 51, SNAPPY /KINGSTON/ - TOPPER SPEECH CIRCUIT ON PH 29/30 HUDSON - KINGSTON U G CABLE
AT KINGSTON REUSE LOCAL FACILITIES RELEASED BY ITEM 1 AT HUDSON PROVIDE NEW LOCAL FACILITIES.
5. LEAVE IDLE PR 13 CENTRAL CITY - HUDSON U G CABLE BT 271500A
AP K TL 53207-3
Figure 11-44. Sample circuit order.
TO WIRE DIV. FHQ
WIRE OFF 32S3 SIC REGT
CSO L/C ATLANTIS.'.ATTENTION LINES OFFICER PLANT BRANCH WESTERN BS HUDON WIRE CHIEF
FROM CENTRAL CITY WIRE CHIEF
COMPLETION REPORT TOLL CIRCUIT ORDER NO. $27 27 APRIL 1944
1. LD CIRCUIT ORDER $2? COMPLETED WITHOUT EXCEPTIONS 28/4/44 2100
2. ALL OFFICES CONCERNED HAVE BEEN NOTIFIED
CH 290810A
AR TL 53208-3
Figure 11-45. Sample completion report.
c. Special Circuit Orders. Special circuit orders may be desirable, such as a preliminary order to prepare for later changes, subdivision of a large order into parts, or a supplement to the original order covering changes in plan. The supplement should cancel the items in the original order which are incorrect or no longer required, and then list the changes. Extensive corrections are very difficult to handle. In each of these special cases the various parts of the order carry the one serial number as CO 1^0A, or CO llfOA supplement No. 1, to show its relation to the original order CO HO.
d. Distribution of Orders. Distribution of circuit orders and cards should be direct to all concerned and not via lines of organization. Wherever possible, circuit orders should be originally delivered in written form. When greater speed is required, transmission of orders by teletypewriter is the first choice. The teletypewriter test wire network which generally exists along the main routes can be used for the distribution of circuit orders. Oral orders are the last choice and should be confirmed promptly by written orders and circuit record cards to avoid errors and omissions in records. The circuit assignment office should keep a record of the distribution made on all orders and cards issued.
e. Filing of Circuit Orders and Cards.
(1) The circuit assignment office should maintain a complete file of all circuit orders (with useful work sheets) and circuit record cards issued, transferring cards to a dead file when they are superseded. It is frequently convenient to refer to these dead cards in planning later changes or reviewing former layouts.
(2) Area offices, centrals, repeater stations, and signal centers need to maintain only an active card file, destroying superseded cards when the superseding change is com
514
PARS.
1146-1149
CHAPTER 11. TECHNICAL ADMINISTRATION
pleted. Circuit orders need be retained only until they are completed or for a short period, such as one month, after completion.
1147. CIRCUIT ORDERS FOR PACKAGED CARRIER EQUIPMENT.
a. The general plan can be applied to trunk circuits using packaged carrier equipment. However, some differences in detail will be re-
quired. TM 11-2022 and TM 11-2037 give complete details of the circuit order information required for use with packaged carrier equipment. , ,
b. It is desirable to send a complete set of the various forms to each place involved in a change of circuit layout. When this is not practicable the equivalent information should be sent by teletypewriter or telephoned.
Section X. INSTALLATION
1148. GENERAL.
This section gives a general outline of the practices applicable to the installation of telephones, teletypewriters, centrals, signal centers, and carrier equipment. The information relates chiefly to fixed plant installations and mobile equipments. References are given to the appropriate technical manuals that apply to the different types of installations.
1149. TELEPHONE STATION INSTALLATION.
a. General. The methods, wire, miscellaneous material, and tools used in placing telephone and teletypewriter wires outside and inside of buildings, and for placing the telephones, are described in detail in TM 11-474 and FM 24-20. Placing cable outside and inside of buildings is discussed in section VII.
b. Installation of Drop Wires.
(1) Wiring Practices. Commercial practice is followed in the methods of terminating drop wires on poles and buildings. Drop wires are used in spans between poles, from pole to building, from open wire to telephone protector, and from cable terminal to telephone protector. A variety of fixtures such as drive hooks, clamps, drive anchors, toggle bolts, knobs, and insulator supports are available. Clearance from objects that may damage the "Wire covering by abrasion is important. Suitable clearance is necessary above objects such as tracks, roadways, and traveled pathways. Separation from power wires in crossings, parallels, and joint use must be observed. Requirements on clearances are given in TM 11-474.
(2) Types of Drop Wire.
(a) Wire W-50, twisted pair, solid No. 14 B&S gauge hard drawn copper separately insulated with rubber compound and asphalt-
impregnated weatherproof braid with a tracer thread in the braid of one wire.
(b) Wire W-108, two conductors, solid No. 17 B&S gauge bronze or copper-clad steel, separately insulated with rubber compound on each wire but both wires encased in the same outer covering which is asphalt-impregnated braid with a tracer ridge on the compound of one conductor.
(c) Wire W-108-A, is a modification of Wire W-108 in having solid No. 18 B&S gauge conductors; otherwise the same as Wire W-108.
(d) Commercial parallel drop wires, designated BP, TP, BR, or TR (Western Electric Company designations). The BP (same as W-108) and TP (same as W-108-A) are for normal runs, and BR and TR, which have heavier braid and heavier rubber insulation on the individual conductors, are for drops subject to slight abrasion against foliage or branches.
c. Telephone Station Wiring.
(I) General. The practices for wiring inside of buildings to connect the outside wire to the protectors and from there to the telephones, are similar to those of the commercial telephone companies and are shown in detail in TM 11-474.
(2) Wiring Practices. If the point of entrance is subject to choice, it should be located to obtain minimum length of inside wire and in such a manner that the inside wiring can be protected from ordinary mechanical and moisture damage. Sections of the wire likely to be subject to damage should be wrapped with friction tape. Wiring should usually be run clear of the floor and fastened about every 3 feet with wiring nails or cleats, or be supported in drive rings. Drive rings permit
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PAR.
1149 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
greater flexibility, as four to six pairs can be strung through the same rings. On semipermanent installations, splices should be soldered or made with sleeves. The installation time per telephone will average approximately 0.75 man hour under ordinary conditions.
(3) Telephone Location. In locating a telephone, the installer should be guided by the wishes of the using personnel, but should have a few fundamental requirements in mind and endeavor to fit these in with the wishes of the user. These requirements are: a location where the bell will be clearly heard by the user; a dry location; separation from metallic substances such as radiator or sink; sufficient light at all times, particularly for dial telephones; accessibility for inspection and repair; and avoidance of excessive vibration. Backboards should be used where bell boxes or wall telephones are to be mounted on masonry, solid metal, metal lath, or metal sheath walls, and on rough, uneven, or damp surfaces.
(4) Protector Location. Electrical protection of telephones is discussed in chapter 10. If a suitable location for the protectors cannot be found inside the building, they may be placed outside if located where it is well sheltered from rain and snow. Inside protectors may be mounted on any substantial surfaces or on a backboard if the surface is rough or damp. They may be mounted on ceilings. On walls they should be mounted with the fuses vertical. Outside use requires a special mounting for certain types of protectors.
(5) Protector Grounding. This subject is covered in chapter 10.
(6) Types of Station Wire.
(a) Wire W-117, twisted pair, solid No. 22 B&S gauge tinned soft copper, separately insulated with a rubber compound dnd green cotton braid. Supersedes Wire W-33.
(b) Wire W-118, 3-conductor, solid No. 22 B&S gauge tinned soft copper, separately insulated with rubber compound and green cotton braid, with red thread in one braid and a yellow thread in a second and no tracer in the third.
(c) WPB (War Production Board) special wire, a commercial product, twisted pair solid No. 22 B&S gauge, tinned soft copper, separately insulated with rubber compound and with a single brown cotton braid covering both conductors, giving the appear
ance of a single wire, with a raised ridge as tracer on the rubber compound of one wire. It is a permissible substitute for Wire W-117.
(d.) Wire W-143 or Wire W-110-B, described in chapters 5 and 9, may be used in damp locations.
(e) Duct wire, twisted pair, solid No. 22 B&S gauge tinned soft copper, separately insulated with rubber compound and a tight-wrapped paper jacket impregnated with a sealing, waterproof compound. It should not be used where subject to abrasion. It has no Signal Corps code number or equivalent.
(/) Bridle wire, Wire W-69-A, a description of this wire is described in paragraph 1151e.
(g) GN station wire, a Bell System commercial-type wire, twisted pair, solid No. 22 B&S gauge tinned copper, separately insulated with rubber compound, covered with cotton braid, with a red tracer thread in the braid of one. It is obtainable in either brown or ivory and offers an inconspicuous installation against colored backgrounds. It can be used in damp but not wet locations. Under most conditions GN wire may be substituted for either inside or bridle wire.
d. Installation Order Routine.
(1) Necessity. A routine to systematize the installation of telephones and teletypewriters may be needed at locations where more than four or five installers will be working at one time. In any case, an order routine can assist in orderly handling of the installation work, plant records, switchboard marking, and directory work. It also can be used in processing requests for the installation, change, or termination of wire service such as local telephone or teletypewriter stations. The functions involved in the origin and completion of an installation order for a telephone, are: origination of service request; approval; assignment of facilities; central office cross-connection work; installation and test; property record work; switchboard marking; ancl directory work.
(2) Adaptability. The routine can be varied to meet different conditions, such as for those cases where civilian facilities are required. In using civil plant, the civilian telephone authority, civilian installers and civilian wire chiefs will be involved, in addition to the Army personnel, in completing service orders. Some of the functions listed in the sub
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1149
CHAPTER 11. TECHNICAL ADMINISTRATION
paragraph above may be combined in the smaller areas.
(3) Forms. A form, with at least (hree copies, will be desirable, which will indicate the facilities to be used, and the address of the telephone location.
(4) Distribution. One copy should be held by the approval authority and two should be forwarded to the assignment clerk. The latter should enter the cable pair and switchboard assignments on both copies. One should go to the wire chief who performs the work of connecting the loop at the switchboard and who forwards his copy to the chief operator after he has tested the loop with the installer. The chief operator should post the directory record and return the copy to the approval authority. The second, or work copy, should be forwarded by the assignment clerk to the telephone installer. The installer should call the wire chief for test upon completion of his work and indicate the amount and type of equipment used and forward his copy to the wire chief. The wire chief should record pertinent information, such as the type of equipment used, on a new line record card for the installation, and then forward this copy to the property clerk who makes his records therefrom and files the order. Variations and
modifications may be found desirable to fit conditions not covered in the above routine.
e. Installation Records.
(1) Switchboard Assignment Records. It may be desirable to maintain local records at each central which will show the quantities of line and trunk equipments that are available, particularly at the larger switchboards, so that assignments can be made correctly in connection with service growth.
(2) Line Record Cards. Line record cards are individual for each local loop, as shown in figure 11-46 and in TM 11-473. Information they carry is necessary in connection with maintenance work. Suitable columns for trouble records permit one set of cards to be used for both assignment and trouble clearing purposes. The line record cards should be filed numerically in a suitable way, convenient to the trouble clerk.
(3) Trunk Circuit Record Cards. Trunk circuit record cards are individual for each telephone and telegraph trunk or point-to-point circuit that enters the central. These are shown in figures 11-36 and 11-37.
(4) Cable Records. Where lead-covered, paper-insulated cable, or other multipair cables are installed for the entrance cables to the centrals, for local loop distribution plant, or
NV. D.. A. G. O. Form No. 11-145
(Old W. D., S. C. Form No. 1156 which may continue iu use) 12 June 1944
LINE RECORD CARD
(File take-outs in dead file; do not destroy) (USE PENCIL ONLY)
TEL. No. 1ST PARTY RING No. CLASS OF SERVICE DATE INSTALLED ACCESS TO TRUNKS?
NAME OR OFFICIAL POS. STREET ADDRESS BLDG. No.
AUTHORITY FOR INSTALLATION LOOP RES. OF LINE 0HM8
TEL. No. 2d PARTY RING No. CLASS OF SERVICE DATE INSTALLED ACCESS TO TRUNKS?
■NAME OR OFFICIAL POS. STREET ADDRESS BLDG. No.
AUTHORITY FOR INSTALLATION LOOP RES. OF LINE OHMS
TELEPHONE BOX COPE STAND CODE EXTEN. CODE ARRESTER CABLE PAIR CABLE PAIR TERM. PINS MULT.
MFR. W. OR D. MFR. CODE
1ST PARTY GRP. OK PANEL
2d PARTY TERM. OK JACK
TROUBLE RECORD (Use Ink or Typewriter)
REPORTED TEST SHOWED TROUBLE FOUND CLEARED
DATE HOUR BY— TROUBLE DATE HOUR BY—
A P A P
A P A P
A P A P
A P p
P p
P A P
(OVER) ,0—26329-2
TL 54923
Figure 11-46. Line record card, Signal Corps Form 1156.
517
PARS.
1149-1150
CHAPTER 11. TECHNICAL ADMINISTRATION
for long distance trunks, cable records are required to show the individual pair assignments. A cable record is shown in figure 11-47 and in TM 11-473.
SIGNAL CORPS, UNITED ST/
POST TELEPHONE SYSTEM CABLE Rl
CABLE No. —2.—.......— name of post EOF
AERIAL OR UNDERGROUND UG-. NO. OF PAIRS >02 GAUGE £?_ S. C. TYP1'
HUNDRED ----- (FOR CABLES OF OVER 102 PAIRS USE FOLLOWING PAGES. INDIO TIlZ
BLOCK OR TERMINAL NUMBER AND LOCATION A
O o «j J
S I
5 £» J « \
* 4 * * <
h n S ? O /
J f " >
% § >___________________________________________
I >_________________________________________________80 ’
p°L_______T_______________________________ZZZZZZ3
I II 25 82 '
I !2|_____________________________________________ 83
I l3| 84 "I
I Ki________________________________________________85
I l5l_______________________________________________as 1
I |8I_______________________________________________22
I |T|____________________________________________ .1®
I l8|_______________________________________________89
I **[ 70
12O| ____________________________________________ ZZZ I
la jto ___________________________________________
|22] 73
I*3! 74
IM_________________________________________________ 75 _
[M__________________________________________________76 \
IM________I______________________________________ 77 2'
IM 76 “\
IM 79 J
S3z™ Z^F__________________________________ZZZZ ®°3
30__________________________________________________8£ .'
13*1 82 i
TL-7470
Figure 11-47. Cable record, Signal Corps Form 1160.
1150. TELEPHONE CENTRAL INSTALLATION.
a. References. Several technical manuals include useful information on installing centrals, telephones, teletypewriters, and the associated equipment. These are: TM 11-353, TM 11-457, TM 11-458, TM 11-471, TM 11-473,
TM 11-474, TM 11-487, TM 11-2001, TM 11-2022, TM 11-2037, and FM 24-20.
b. Installation of Tactical Centrals. Instructions for installaton of tactical switchboards and telephone central office sets are given in the technical manuals that are furnished with them. The work is relatively simple because the switchboards and associated equipment are designed for rapid installation with a minimum of effort and skill. Figure 11-48 shows an installation of two Telephone Central Office Sets TC-4 and figure 11-49 shows an installation of two Telephone Central Office Sets TC-1.
Figure 11-48. Installation of two Telephone Central Office Sets TC-4.
Figure 11-49. Installation of two Telephone Central Office Sets TC-1.
c. Installation of Fixed Plant Telephone Centrals.
(1) General. The major features of fixed plant telephone central installation work are described in TM 11-471. These features are:
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CHAPTER 11. TECHNICAL ADMINISTRATION
placing the equipment; constructing the cable rack; running, lacing, stripping, butting, splicing, and forming switchboard cable; skinning and soldering cable conductors; installing and testing the power plant; installing the wire chief’s cabinet; and adequate marking of the equipment by stenciling. The work is summarized in the following subparagraphs.
(2) Common Battery Multiple Switchboards. Commercial multiple switchboards require extensive cabling between the switchboard sections, and between the switchboard and the relay racks and distributing frame. Power plant wiring is also required. The cabling, on all but one commercial-type multiple switchboard, requires forming, attaching, and soldering of the multiple cable conductors to the multiple jacks and distributing frame by the installers on the job. The exception is the Western Electric Company No. 12 switchboard, in which the multiple cable is attached to the multiple jacks and terminal blocks at the factory. The power wiring always is done completely on the job. Commercial switchboard cables are of several types, numbers of conductors, and wire gauges. ASF catalog Sig 5 lists a considerable number of switchboard cables of various make-ups and sizes. Power wires are made in sizes from small rubber-covered solid conductor wire to the large stranded wires. Wire and switchboard cable is furnished by the Army Communications Service in proper quantities and sizes to fit the requirements of each installation.
(3) Location of Central. Factors to consider in selecting a suitable location for a central include: nearness to the center of the area served; availability of necessary space; fire hazards; floor strength; roof strength; door or window size to permit entry of equipment units; water supply; sanitary conveniences ; heat; light; electric power availability; dampness; building vibration; disturbing noise; exposure to bomb damage requiring shielding of windows; and protection from bursting water pipes. It may be necessary to provide supplementary strengthening of the floor, walls, or roof.
(4) Location of Switchboard. Factors to consider in placing a telephone switchboard include: clearance of not less than 6 feet between keyshelf and wall; 3 feet from rear of board to wall; not less than 2 feet from wall
at fixed end of board; door clearance to avoid striking board; space for added positions in case of growth; and light. Low type switchboards should not have their backs towards windows as the light will shine directly in the face of the operators and make it difficult to see lighted switchboard lamps. Backs of high switchboards should be toward the windows. Direct light from a window or skylight should not fall on the face or keyshelf of a lamp signal switchboard. Strong light makes it difficult for the switchboard operators to see whether the lamp signals are on or off. If such a location cannot be avoided, suitable blinds should be used to control the light.
(5) Location Of Associated Equipment. Chapter 2 gives a typical layout of a telephone central. Distributing frame clearance should be not less than 40 inches from the face of protectors to the wall; not less than 40 inches from the face of the terminal strips to the wall or nearest obstruction; and not less than 1 foot from the permanent end to the wall. Sufficient space on the other end for growth to the ultimate size should be allowed. Where wall-type distributing frames are used, the protectors should be mounted as near the cable entrance as possible. Relay racks, where required, preferably should be installed approximately 40 inches from, and parallel to, the terminal strip side of the distributing frame. Cabling between the distributing frame, the switchboard, and the relay racks and power plant preferably should be run overhead.
(d) Typical Installation. Figure 11-50 il-
Figure 11-50. Installation of commercial-type multiple switchboard.
519
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1150 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
lustrates a fixed plant commercial-type multiple switchboard in the process of installation. Figure 11-51 illustrates the installation of a main distributing frame.
Figure 11-51. Installation of main distribution frame for a commercial-type multiple switchboard.
d. Fixed Plant Centrals; Installation Intervals and Man-hours.
(1) General. The interval for the installation of commercial switchboards and associated equipment in buildings will depend on the number of positions, the number of installers, the experience of the installers, and whether the work is done by one, two, or three
shifts per day. Inexperienced installers will increase the intervals considerably.
(2) Installation Intervals. Installing intervals are given in figure 11-52 for commercial switchboard installations, based on working a seven day week. Intervals can be reduced about one half if two shifts are used and about two thirds if three shifts are used. The intervals are based on an installing force of normal size. The use of more men will lessen the intervals but crowding limits the practicable size of the force. The interval required to put a switchboard into service can be shortened by deferring such work as cable lacing, stenciling, etc., until after the service begins. The intervals given are based on the assumption that no delays occur because of material shortages, and are for the completion of the entire job, except in the figures on the rush basis, in which case it is assumed that as much work as possible would be deferred until service begins.
(3) Installation Man-hours. The manhours of work required to complete the installation of a multiple telephone central can be estimated by using time factors for a few major items of work, as shown in figure 11-53.
(4) Example of Use of Man-hour Data. An example of the use of the man hour data for 4 switchboard of eight operating positions, one end position, one test position, (total 10 positions), 1,000 lines, power plant, chief operator’s cabinet, wire chief’s cabinet, and repair clerk’s desk, is given in figure 11-54.
No. of positions (incl. end and trouble pos.) Normal installing force (men; including supervisor) Interval with normal force working 56 hours per week per man (weeks) Interval on rush basis (days)a
1 shift 2 shifts 3 shifts
3 4 4 to 5 2 to 2)4 1^4 to 1)4 5
4 4Yi 42/2 to 5/^ 2)4 to 2% 1^4 to 1)4 6
5 5V2 5 to 6 2)4 to 3 1)4 to 2 7
10 8 7M to 8% 3% to 4l/2 2V2 to 3 9
15 10 8^ to W 4)4 to 5)4 3 to 3)4 11
20 11^ 9/4 to 11J4 4% to 5)4 3)4 to 354 13
25 13H 10)4 to 12)4 5|4 to 6)4 3)4 to 4J4 15
a The interval on a rush basis assumes a 3-shift work schedule, with as many installers on each shift as is practicable, and deferring as much work as possible such as stenciling, etc., until after service begins.
Figure 11-52. Installation intervals for commercial type multiple telephone centrals.
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CHAPTER 11. TECHNICAL ADMINISTRATION
Work items Man-hour factor • M ultiplier
New office
Basic allowance6 (jobs with 1 to 5 positions) 30 Job
Basic allowance5 (jobs with more than 5 positions) 130 Job
To line-up switchboard (jobs with more than 8 total positions only) 50 Job
Operating positions 40 Positions
End position (blank position) 10 Positions
Trouble or test position 20 Positions
Switchboard face equipment 0.019 Lines
Lines 1.7 Lines
Chief operator’s cabinet 25 Cabinet
Repair service desk 25 Desk
Wire chief’s cabinet 25 Cabinet
Power plant (jobs with 1 to 8 positions) 100 Job
Power plant (jobs with more than 8 positions) 200 Job
Adding equipment to existing switchboard.
Basic allowance6 30 Job
Positions 40 Positions
Line circuits added 1.2 Lines
Added multiple 0.019 Lines times appear- ances
Extending the multiple in an existing switchboard.
Basic allowance6 20 Positions
Lines extended 0.13 Lines
Line appearances added 0.019 Lines times appearances added
» Add 20 percent to the computed hours for abnormal job material handling, record work, janitor work, etc. conditions. This gives the productive hours. Add another b This time is allowed for organizing the job. 20 percent to the productive hours, to cover supervision,
Figure 11-53. Telephone switchboard installation man-hour data.
521
PAR.
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Item Man-hours
Basic allowance................................... 130
To line-up switchboard............................. 50
Operating positions 8x40.......................... 320
End position....................................... 10
Test position...................................... 20
Switchboard face equipment 1,000 x 10 x 0.019.. 190
Lines 1,000 x 1.70.............................. 1,700
Chief operator's cabinet........................... 25
Repair service desk................................ 25
Wire chief’s cabinet............................... 25
Power plant..................................... 200
2,695
20% for abnormal job conditions......... 539
TOTAL productive labor.......... 3,234
20% for supervision, clerical, etc...... 649
TOTAL........ 3,883
Figure 11-54. Example of use of man-hour data.
1151. CARRIER EQUIPMENT INSTALLATION.
a. Spiral-four Equipment. TM 11-2001 contains detailed instructions for the installation of the carrier equipment used with spiral-four cable. Any one station on a single system has only a small amount of equipment, which is easily arranged. However, when more than one system is being used, or when a single system is to be placed alongside other equipment, a logical floor plan should be established. The main considerations are adequate passage ways, working space, and convenient wiring and interconnecting layouts. It is usually desirable to locate the telephone equipments together and the telegraph equipments together, to avoid cpngestion when it is necessary to have work in progress about each group of equipment. Cabling between the units and to the power equipment, outside plant, etc. should be overhead when possible. Wire W-69-A (subpar. e below) is provided with the equipment for use in making interconnections.
b. Packaged Carrier Equipment. TM 11-2022 and TM 11-2037 contain detailed instructions for the installation of packaged carrier equipment. Figures 11-55 and 11-56 show a typical packaged carrier equipment installation. The following information must be furnished the installer: line layout chart; circuit diagram; circuit record cards for both telephone and telegraph trunks; floor plan layout; list of
Figure 11-55. Packaged carrier equipment installation.
trunk assignments; equipment list of packages furnished; office wiring diagram; and equipment wiring record. Immediate steps should be taken by the installer to obtain any of the data that may be lacking. If the information cannot be obtained, the installer should refer to TM 11-2022 and to the technical manuals furnished with the individual units of equipment and endeavor to work out the needed information. The equipment cabinets are open at the bottom and are placed on timbers. Cableruns along the floor connect the lines of cabinets. A method of constructing the cable runway and cabinet supporting timbers is shown in figure 11-57. Panels of the same type preferably should be grouped together; for example, all line terminating and simplex panels should be mounted adjacent to each other. Each unit is wired for several optional wiring arrangements, each option being for a particular set of conditions. The manuals furnished with the equipment describe in detail the connections required for each option. A list of connec-nection tables, figures, etc. (corresponding to the options) should be made up by the installer
522
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CHAPTER 11. TECHNICAL ADMINISTRATION
Figure 11-56. Packaged carrier equipment installation.
in advance. After setting up the equipment the wiring is run, including power wiring, but fuses should not be placed until testing is to begin. Cross connections to other cabinets should be made through the open bottom. Wiring from entrance cable or protectors is direct to the equipment. Initial local tests of each equipment unit are necesary, after which circuit and system line-up tests and telegraph circuit transmission measurements can be made.
c. Packaged Carrier Cross-connections.
(1) To establish a long distance telephone trunk circuit or a telegraph circuit certain cross-connections must be made between various equipments. In small offices where all of the equipment can be placed in one line of bays, the separation between all the terminals in the office is small and the labor of running wires from terminal to terminal is small. Saving on this labor does not justify a distributing frame. In a large office the amount of labor required to run wires from terminal to terminal could be large. To reduce this labor, it may be desirable to have a distributing frame with permanent wire from there to the equipment for certain of the circuits. This will not, how-
XXxXX^
N°LUMBER FROM PACKING CASES OR OTHER XXXXXZ' 'if X'
SCRAP LUMBER MAY BE USED FOR CON- s' XX/XX..X °>X
STRUCTION OF CABLE RUN COVER- XZX^XiXX^ X^ ' .
2:LAYOUT SHOWN WILL CARE FOR THREE , XXX/ZX .X
LINES OF CABINETS WITH SEVEN CAB- XXX'XX X X/\
INETS PER LINE XXXX/ZX X' XXk<
xx/^xx^^ x^^ xXX/^^xx^ <0”X r4"x4-
/^xxy xxX%x .
x'^ /xxy
x' XxXXXX^ -X3 XX^^^x/
X XXfxXHX cP-v xxfxXZx'
XXX
XX>- &XXXX XXXXXX '°Z v ^X
X’
x/xxx2 x 4
^^e^X X^XXX.XXxX^ XZX> XX« >X>XX / XXx
3X4)
COVER FOR CABLE RUN ' ^XXX^4
A— |"x 2" SPACED TO FIT BETWEEN 2"X 4" FORMING SIDES OF CABLE RUN. ’L 54951
Figure 11-57. Method of constructing cable runway and cabinet supporting timbers for packaged carrier equipment.
523
PARS.
1151-1152
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
ever, reduce the number of wiring changes required for a circuit change.
(2) For example, on a type C carrier terminal there are three distinct possibilities for consideration as to what circuits to bring out to a frame, to facilitate the making of circuit changes or assignments. One is to bring out a small group (8 wires) which permits reassigning channels and telegraph composite legs only, if the channels are 2-wire. Bringing out 42 more wires to the frame permits changing any of the three channels from a 2-wire to a 4-wire termination or vice versa, at the frame. Bringing out 18 others permits the voice frequency circuit on which the carrier is superposed to be connected to any voice-frequency repeater or other equipment, at the frame. The cross-connection blocks can be either of the following: vacant terminals on an existing frame in the office; protection and distributing frame X-61823G (packaged unit) ; or a separate distributing frame of the type usually furnished with telephone switchboards. Although it is convenient to have all the wires that are involved in circuit changes brought out to a distributing frame, there are certain disadvantages. These are that fewer men can work on changes at one time and that exact records must be maintained as to what is connected to each punching of the terminal blocks on the distributing frame.
d. Wire for Packaged Carrier Cross-connections.
(1) Type AM, No. 20 AWG paired wire, solid tinned copper conductors, each of which is covered with enamel, double cellulose acetate yarn, cotton braid, and colored lacquer, one conductor black and the other black-red. This is Western Electric Company P368247 wire, of which considerable quantities are furnished with each packaged equipment.
(2) Type AM, No. 20 AWG single wire, same as item (1) as to insulation but single wire, colored green. This is Western Electric Company P368403 wire, of which about 2,500 feet is included with each packaged test board.
(
TRANSMITTER 2T0 IO
PARK A MILES
\ UP TO --------------
--------I V2 Ml. LOCAL -------- SIGNAL "T- VHF EQUIR C E NTER
H r \ \ LOCAL
STANDBY \ \
RECEIVERS 1 10 l0\ VHF EQUIP
----—------ MILES N |----
TO TELEGRAPH A \\ ^F
TELEPHONE SYSTEMS REGULAR
(WIRE & VHF RADIO) --------------- RECEIVERS
TL 54938
Figure 11-59. Relative locations of signal center and associated radio transmitters and receivers.
(3) It is desirable to have independent wire routes to each transmitter park, each capable of handling the traffic through all transmitters, with a supplementary wire route of about half that capacity between the two .parks. By providing suitable terminal blocks at the ends of the wire circuits, they can be rerouted in case one of the main routes is lost. In determining the number of wires in each route, provision should be made for one or more wire telephone circuits for intercommunication between the signal center and the radio attendants. Information covering the layout of radio parks is given in chapter 6.
(4) The receivers for regular use should likewise be located at a distance from the signal center, principally to avoid the man-made noise usually encountered at places where there is considerable activity. These receivers
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
are preferably placed in the opposite direction from the transmitter to obtain maximum freedom from interference. The distance from the signal center will vary from 1 to 10 miles, as governed by available sites which are satisfactory from a technical standpoint, as discussed in chapter 6.
Figure 11-60. Fixed plant radio transmitting station, (showing three Radio Transmitters BC-339 in the right center).
(5) Duplicate radio receiving equipment for standby service can usually be located within or adjacent to the signal center, since the antenna systems for this service are usually much less extensive and conspicuous than transmitting antennas.
Figure 11-61. Fixed plant radio transmitting station.
(6) For interconnecting the signal center with both transmitter and receivers, buried cable is ideal. Where this is not practicable, aerial lead-covered or rubber-covered
Figure 11-62. Fixed plant radio receiving station, (showing Hammarlund super-pro receivers in the foreground and National HRO receivers, with their associated spare coil sets on the wall, at the right).
cable, open wire, or long range tactical wire can be used.
(7) Under circumstances where the wire circuits are unreliable or alternate routes are not feasible, inultichannel v-h-f radio links between the signal center and the remote radio transmitters and receivers can be used effectively. Either wire or v-h-f radio may be used for regular operation, with the other serving as a standby, depending on local circumstances.
e. Radio Station Layout. The physical layout of different radio stations will vary considerably, depending on local conditions and other factors. Figures 11-60, 11-61, 11-62, and 11-63 show photographs of portions of a few fixed
Figure 11-63. Fixed plant radio receiving station, (showing single side band receiver Western Electric Company D-99945 in left foreground).
528
PARS.
1154-1155
CHAPTER 11. TECHNICAL ADMINISTRATION
planr military radio station installations. They show orderly layout with sufficient room for maintenance. A floor plan for a 10-kw radio transmitter station is shown in figure 11-64.
lighting
TRANSFORMER-|
FUSE BOX-i FROM
POWER rSds source
T?enterL 44 4’1 LIGHTING A^l DUCT ■ - - SWITCH firPOWER SWITCH
c:>TELEPHONE CABLE I fifi
-1 Is^RGEh l^l/
/ '-WALL WALL-7 | | | TANKi—4 4s J- 48” • /
8’MIN.
TELEPHONE
M EE-8-( )
IV aSURGE TANK MOUNTED WITH 2’
fiX CLEARANCE TO WATER COOLER.
/ / / / / f TL 55000
Figure 11-64. Floor plan requirements and equipment arrangement for 10-kw radio transmitter.
1155. MOBILE INSTALLATIONS.
a. General.
(1) Mobile arrangements of telephone centrals, teletypewriter centrals, carrier terminal sets, and multichannel radio terminal or relay sets can be provided for tactical conditions where the equipment may have to be moved frequently and where the vehicles or mobile shelters are available. There are no Signal Corps standards of this type available except for the Telephone Central Office Set TC-2. The information and drawings contained in this paragraph are intended to serve as a guide for making such arrangements. For this purpose, the sets can be mounted in standard Army semitrailers or shelters.
(2) The first consideration in making
such an arrangement is to determine the inside
dimensions of the available truck, semitrailer,
or shelter. Consideration should be given to the head room and a check should be made to see that there are no inside projections or offsets in the floor which will interfere with the layout of the equipment. In arranging the
equipment, care should be taken to see that there is ample space for items such as the operators’ chairs in the front of a switchboard, and aisle space in the rear of switchboards and around the frames, power, and testing equipment for maintenance. In case there is more space available than is needed for operation and maintenance, the equipment should be located so that the unused space can be used to store the power equipment and packing cases when the outfit is being moved. Where it is necessary to add windows in semitrailers or shelters or if blackout restrictions preclude windows for light and air, consideration should be given to adding forced convection unit heating equipment and the necessary lighting outlets at the same time. TM 11-2525 describes the Miller utility heater model 0G-31-A which is a portable unit suitable for heating trailers and shelters.
(3) Minimum lighting requirements have been shown on some of the floor plans. Care should be taken in locating the lighting outlets and windows to see that the amount of light provided on the face and keyshelf of a switchboard is not of high intensity, which would make it difficult for the operator to see the lamp signals.
(4) The equipment which is to remain in place should be securely fastened to the floor. In most cases it may be necessary to supply supplementary bracing from the top of the switchboards or frames to the ceiling or side walls to prevent tipping when the outfit is being moved. It may also prove desirable to secure the operators’ chairs to the floor. The procedure for fastening the components of Telephone Central Office Set TC-2 by either lag screws, bolts and nuts, or toggle bolts to the shelter, as described in Changes 2 to TM 11-340 (15 April 1944), may be used in other arrangements. Other methods of fastening equipment, which may be employed in the mobile installations, are described in HQ, AAF, Technical Order No. 03-1-39, Instructions for Operation and Maintenance of Cargo Tie-Down Equipment. These methods, which are used in securing cargo in Army cargo planes, make use of two tiedown rods, a beam, and a jack.
(5) When motor vehicles are used for transportation of mobile installations, consideration should be given to the possibility of deep-water fording. The waterproofing of such
529
PAR.
1155
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
CASE CS-72 — |— CASE CS-63 |-CASE CS-63
(REMOVED DURING = BATTERY BB-46 BATTERY BB-46
OPERATION) ।
---------------= -i ■! j Mjr T~ MAINTENANCE -----------------------------------------------2O"_•— 20"—t ► PANEL BD-98 J
I EQUIPMENT ------f ... ---!_i <7
I TE-44-A J] ®T ] -----
I (CH-58) I i MAINTENANCE I I I 0 f'-
। II EQUIPMENT । "co BE-RA- N
\____[__|_________________[] | ME-6 (CH-59) । 75 36 |
/ ; ,------------------ ] •—*—31J-"-------—265------------------••-------267”——•
/ 11 i i ! ...... ....... 7 r r2—h
/ I 1 | CASE CS-70 ] !•--- CASE CS-71 *- CASECS-73 CASE j, •-----FRONT
/ -l HO-I7-(&)OR
I________________0 I 4 HO-27-(8)
01 CABINET . ["paulin ] J
BE-79 -IN 1 DUCK , SWITCH- -Hsr _ ' II
POWER UNIT PE-75-(&) 1 [(SEE NOTE 1 BOARD cy 0-------1---fl--1
REMOVED DURING I I 1 BD-89 CHAIR / T
OPERATION । I--------J I M-205/W J
j h~2o^' It l54~~4—344" .11 T 25-j
L. ■ I 134" ...................|---- ■
- 'V -lx»
N CM
0 INDICATES RECOMMENDED APPROXIMATE LOCATION OF LIGHTING EQUIPMENT
NOTES
I THIS FLOOR PLAN SHOWN IN TM 11-340 CHANGES 2 DATED 15 APRIL 1944
2 INSIDE HEIGHT OF SHELTER HO-I7-(8.)OR HO-27-(&) AT CENTER IS 60 3/4"
3 ONLY INSIDE DIMENSIONS OF SHELTER HO -17-(&) OR H0-27-(8.) ARE SHOWN
4 RECOMMENDED LOCATION OF PAULIN DUCK
TL 54971
Figure 11-65. Floor plan of one-position Telephone Central Office Set TC-2 in Shelter HO-17-( ) or HO-27-( ).
vehicles for this purpose is described in TM 9-2853. These arrangements, in general, provide breather pipes and exhaust extensions to a point above the expected water level.
b. Mobile Telephone Centrals.
(1) General. Mobile telephone central arrangements are included for a 1-or 2-po-sition switchboard mounted in a Shelter H0-17-( ) or HO-27-( ) or a semitrailer, and for a 4-position switchboard in a semitrailer. Arrangements similar to these have already been used in the theaters of operations.
(2) One- or 2-position Telephone Switchboard.
(a) The arrangements for mounting a 1- or 2-position switchboard using Telephone Central Office Set TC-2 in Shelter H0-17-( ) or HO-27-( ) are described in Changes 2 to TM 11-340 (15 April 1944). Shelters HO-17-( ) and HO-27-( ) are identical, except that shielding is provided in Shelter HO-17-( ). When available, Shelter HO-27-( ) should be used for the Telephone Central Office Set TC-2.
(b) The bare floor plan showing the complete installation of all items in Shelter HO-17-( ) or HO-27-( ) for a 1-posi-
tion Telephone Central Office Set TC-2 is shown in figure 11-65. For a 2-position switchboard, another floor plan arrangement in Shelter HO-17-( ) or HO-27-( ) is shown in fiure 11-66. This figure also shows the arrangement of equipment in a Trailer, Cargo, 1-ton, which is required in addition to the shelter for transporting some of the equipment. In both of these cases the Shelter is transported in Truck, Cargo, 21//2-ton, 6x6.
(c) An arrangement for mounting a 2-position Telephone Central Office Set TC-2 in a semitrailer, is shown in figure 11-67. This arrangement is not described in TM 11-340. This plan requires the use of a Semitrailer, Van, 3-ton (6-ton gross) and has sufficient room for storing the unfastened equipment when the outfit is being moved.
(---•<--- 24"--• -- 23"---• <--26"----•*--- 26" --*
FULL DOOR AT-A ^'32 H 4 3 2 1 j —
TOP, TAILGATE \ L~ «____________•___________«------------<- SWBDS 8" 0 — SEMITRAILER, VAN
AT BOTTOM CASE ~l 1 BD-HO J_______________ 3-TON (6-TON GROSS)
(PROVIDE \ CS-69 ----------~7 Fl RACK FM-31
BLACKOUT CUR- \ l(REMOVED , /----( 0/--------( /-------\0 /--------\ I BatTERIES BB-46
TAIN ENTRANCE \ I DURING 1 I I ll I nl! BATTERIES BB 46
WHEN DOOR IS \ |OPERATION)| \ CHAIR I \ CHAIR / \ CHAIR / \ CHAIR / " z
OPEN AND TAIL- \ |,_||JL"_j \M-205 Ze" \M-205 / \ M-205 / \ M-205 / I »_____ _______
GATE IS DOWN) , \l-8_ _J 1 c/l*---_____________________________________________________ | | _____
L—-------------------------------------------------- 2 । 8 j"---------------------------—----------------
—------------------------- 96" -•*-----------------------•
--------------,-- CASE CS-70
--------------- (WITH CASE CS-63 ------------L—-_________1--------------U------------ INSIDE) li '!----------------------------------'
I!
46„ 1 il_____ ____II—------------«— TRAILER ’
Il (I- ~ CARGO, l-TON
11 'l ll
---------------- 28^ ------Hl---- 19" --H|- — 23g —hL------- 23 g ---CASE CS-60----i'-------[j------------85-----------II
(WITH CASE CS-73 ----------------->___________ll_____________ ____________
INSIDE) I -JI ,,-------------» CASE CS-70
(WITH CASE CS-63
-I_______________________________■ -Jl ' ---INSIDE)
-POWER UNIT PE-75-0 ® INDICATES RECOMMENDED APPROXIMATE LOCATION OF LIGHTING OUTLETS NOTES: I. ONLY INSIDE DIMENSIONS OF SEMI- 2 HEADROOM OF SEMITRAILER IS
TRAILER AND TRAILER ARE SHOWN 76'/2". T(_ 54967
Figure 11-68. Floor pl ::i oj 4-position Telephone Central Office
Set TC-10 in Semitrailer, Van, 3-ton (6-ton gross) and Trailer, Cargo, 1-ton.
533
PAR.
1155
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
-- 2-CASES CS-7O ------ CASE CS-69
(ONE ON TOP OF OTHER) MOUNTED ON TOP
(EACH WITH CASE CS- OF CASE CS-6O „ - . - „„ . ,
63 INSI DE) (REMOVED (REMOVED DURING /— REMOVED DURING --- PANEL INSIDE TRAILER TO
DURING OPERATION) OPERATION) / OPERATION CONNECT TO OUTSIDE LINES
\ T £222 2^-222^^ Z222J,---------3,1" "-85^ ------* f
\ -h>-----------I CASE CS-61 !/ 2-CASES CS-59 (ONE ON TOP OF OTHER) | I
\ ' [(REMOVED DURING/ (REMOVED DURING OPERATION) „„„
\ ! I OPERATION) //\__________________________________________ J 24" A?)
\ । i-----------a «~|----------------------------------------,
\ • 1 CASE [l-CART-7 ~i 1
\ I ICS-66 jl (-5 72 I 2-CASES CS-59 (ONE ON TOP OF OTHER)
\ ____T__________________.L-H^L-isr-d (REMOVED DURING OPERATION) I ~ "IpOWER PLANT~
\ । j | I 0 ||___£___J__________________________________________। FRAME BD-90(MOUNT-
\ f> • | ----1-----L—I---------------------------------------- ~ ” FM-19 ED ON FLOOR)
\ 09p (._19L___J t (X) (4 VERTICALS) ...RECTIFIER RA-
\ ! 1 8 I I 352 36 AND CABINET
\ I ------------ ,,3' ------------- BE-75(MOUNT-
\ I_,-|«l_____J 364 CABINET ED ON TOP)
\ r~298 1----7*1 BE'72
CASE CS-6O \-------—* (4— 13”-*-----------------------------------------------------
WITH CASE CS- \ ---I_- - ________' __________________ 106"----------------------------.4___24" __>-• 4__°3"---•> 4-2 3"--♦ 4---26 "----*
73 INSIDE (BOTH) ‘ 3a / ,uo *• ~ rociMT
REMOVED DUR-l 1-----1-----L-----12 3 4 ----------j-l I KUN I
ING OPERATION)) |POWER UNIT PE-75 .4------------4------------4-------------4—SWITCH- “ -1-1-----------
\ I (REMOVED DURING BOARD |6-
\ | OPERATION) BD-IIO 2
\ I I _________ ____________ _____________ ____________ I
I [POWER UNIT PE-75 | ( \ (V) ( -TrD _ ,.,RACK rM-3' ®
\ '(REMOVED DURING \ CHAIR / I CHAIR / I CHAIR / ^ \ CHAIR / STEP-UP ----------------• |51 BATTERIES CT.-D,^?V1
\j OPERATION) I \“-20\46r \M-205 / \m-20s/ APPROX. 2 BB_46 CABINET
FULLDOORAT----4 l,------36"-------•>[ I 2 J------3I>.---► 6" <—12" ♦ 6" «
TOP, TAILGATE _____________________I 1 1
AT BOTTOM J '----------------------------------1-------------------------------------------------------------------------------------- jf—
(PROVIDE BLACK- p4-----------72" APPROX.------------>
OUT CURTAIN _____________________________________________________________ 240"__________________________________________________________»
WHEN DOOR IS
OPEN AND TAIL- LCASECS-57 SEMITRAILER,
GATE IS DOWN) MOUNTED ON TOP VAN, 6-TON
OF CASE CS-60 (IO-TON GROSS)
(REMOVED DURING OPERATION)
0 INDICATES RECOMMENDED APPROXIMATE LOCATION OF LIGHTING OUTLETS
NOTES
I ONLY INSIDE DIMENSIONS OF SEMI- 2. HEADROOM IS 67 1/2" IN REAR AND
TRAILER ARE SHOWN. APPROXIMATELY 78“ IN FRONT
TL 54 9 68
Figure 11-69. Floor plan of 4-position Telephone Central Office Set TC-10 in Semitrailer Van, 6-ton (10-ton gross).
534
PAR.
1155
CHAPTER 11. TECHNICAL ADMINISTRATION
rTERMINAL STRIP TO
/ TERMINATE OUTSIDE r~'S4
/ LINES 9j 'DROP IN FLOOR-< I*-I7"-*i3J~-I7*-»|»- H-14*"*
J SEE NOTE 2 I
\ " I 1 Pl-- I! Mt.t
\ o I l5lN (B) ,A. ... (E) (E) *| |--mi?
\ Z I I N (A) (A) T . / | {G) |
\“‘S I =!—fl— r-X^l
V I I pr ’ r-----------1 (■---I L’ ! F~i =A./
\ | |.Mq LJ L.J J iraxn 1 :if H-----n rr—IL____________________________I
7\ I |r (B) DroATiriKi\ I zx •’E.Llt.rx SI Al IO N \ ? x/ xt
OPERATION) I ZX X OPERATOR) /> /K OPERATOR) 2 /X *
rj 1 / \ \ \ x / / X
/;_______________________j / \ \ /y \ 'fix?, / / X
/ ' / \ \ // X. / / X.
/ /TELETYPEWRITER'S /xZ ZX /TELETYPE WRITERS_______JL
f X.TG-7-B ON CHEST TG-7-B ON CHESTZ
I r---------------------------ch-50-b r—---------i NX CH’50’B /
/ • । \ /v l J ' i ! \i’'- z
/ | POWER UNIT PE-75-D I \ // ----V =, । I X. X /
/ I (REMOVED DURING I \/z A l_________I X/X
/ “I* ! OPERATION) । 'Z SWBD \ T SWBD
/ 2 । । | BD-IOO \ | , |/ BD-IOO I l—I---------
/ I-------------------------------1 !*-■ 16"—-S*- -8"-4i--16"---X-IO4’-» -----164"—• 4" <-
/ 6 GROUND RODS GP-27 OR MX-I48/G \ _ / 2 2
LINE UNIT BE-77-A -1 ® LRECTIFIER RA-87
(REMOVED DURING OPERATION)____________ (MOUNTED -| GRO 2______0_____8.4 8 INSERT REAR Plug IN JACK
__________;____________________RT (L) GRO________R______2 8 3 .. . .... -----------
l* as o________2ZZ ZZZZZZZZZZZZ zrt (D gro 2 2ZZZZZ ° ZZZZ 84 6 - ■ ■ ~;--------------------——-
______________________________2RT (L) ~ GRO______R______2 6 2 6-... TEST NOTES'._ --------- - ------------------------—---
l-t INDICATES THAT THERE IS MORE Than ONE RELAY WITH THE SAME DESIGNATION 2 PRIOR TO ISSUE 5-0, TEST VALUE WAS 9 MA.
TO STATION LINE ~" * I 1 Q ;--------
DIRECT OR THRU EMERGENCY r 1 '
TRANSFER KEY CKT ___Q ----1[I
_■ (LIT
Jr 2 R—t----1—
J [ 2RT 1 ^§2-1—r>. ।—
I I • thru aux i SiG. CKT i
■i"z
TL-7590
PARS.
1164-1165
CHAPTER 11. TECHNICAL ADMINISTRATION
ment. Spare relays, properly adjusted, should be available at all times for replacement purposes.
1165. POWER PLANT MAINTENANCE.
a. General. This paragraph discusses the maintenance of engine-generator sets, storage batteries, rectifiers, and ringing generators. Other matters pertaining to power supplies are covered in chapter 7. Some power equipments require daily or more frequent inspection. Further information on maintenance is contained in TM 11-430, TM 11-473, and in information furnished with the equipment.
b. Engine-driven Generator Sets. Information on the maintenance of gasoline engines used with generators is given in chapter 7. The information for the maintenance of diesel engines similarly used is given in the manuals provided with the engines. Each diesel engine model is intended to be lubricated by, and operated on, certain grades of oil. Because it is not always possible to obtain the suitable grades of oil, the engines are frequently run on and lubricated with improper grades with resultant maintenance difficulties, and comparatively short life.
c. Storage Batteries.
(1) These may be either the enclosed or open type. The open type probably will be encountered only in civil plants. All storage batteries generate explosive gas, and care must be exercised to prevent igniting this gas by sparks, including those from static, or nearby flame. Distilled water should be used in replacing that which evaporates. The use of impure water may be unavoidable but it should be recognized that the life of the battery may be shortened thereby. Improper charging rates will adversely affect the plates in a manner readily apparent in open type batteries but difficult to observe in enclosed types. Charging rates should be adjusted so that the specific gravity of individual cells, when properly filled, is maintained according to instructions provided with the particular battery. New batteries, when shipped dry, require the addition of electrolyte and always require preliminary charging before placing them in service. This may take 24 hours or more. The acid is corrosive to most metals, wood, and clothing and, if spilled, can be neutralized by a strong soda and water solution, ((A pound of soda per gallon of water).
(2) Individual cell voltage readings should be taken after a full charge. Different cells may show different voltage readings. The allowable limit of variation from the average for the string of cells, is 0.05 volts for large and 0.10 volts for smaller cells. These voltage readings preferably should be taken while the cells are on charge at the maximum charging rate used on the battery. A voltmeter with a 3-volt scale is desirable.
(3) Several methods of charging batteries for particular centrals are available and will be determined when the job is engineered. The charging method has considerable bearing on the life of the battery. The recent designs of power plant which use regulated tube rectifiers require little attention and result in long battery life.
d. Rectifiers.
(7) In general, the maintenance required for rectifiers may be confined to a few items, such as the replacement of tubes, rectifying discs, fuses, and electrolytic capacitors.
(2) In the case of Tungar or other tube type rectifiers, the replacement of tubes, which have burned out or otherwise become inactive, will be required. With the disc type rectifiers, whether selenium or copper oxide, their disc assemblies will usually have to be replaced when the particular rectifier output indicates its voltage has fallen off about 20 percent of its rated value, unless specific application dictates earlier replacement.
(1
0 1
10 10
20 100
30 1000
-10 0.1
-20 0.01
-30 0.001
-120 1 trillionth
lOn 10n
db Power ratio (P-i/Pf) (approximate)
5 3.2
15 32
25 320
35 3200
-5 0.32
-15 0.032
-25 0.0032
-35 0.00032
db Power ratio (P-i/P'i) (approximate)
1 1.25
2 1.6
3 2
4 2.5
5 3.2
6 4
7 5
8 6.3
9 8
10 10
db Power ratio (P1/P2) (approximate)
-1 0.8
-2 0.63
-3 0.5
—4 0.4
-5 0.32
-6 0.25
-7 0.2
-8 0.16
-9 0.125
-10 0.1
Figure 12-1. Relation betwen db and power ratio.
c. Figure 12-1 is a table of db and the corresponding power ratios. Figure 12-2 expresses the relation graphically. Adding db corresponds to multiplying power ratios. Thus from figure 12-1, the power ratio corresponding to 36 db, or 30 + 6 db, is 1000 x 4 = 4000.
553
PARS.
1203-1204
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
d. As one example, in a well designed telephone circuit the electrical power at the receiving end of the circuit is not less than about one thousandth of that of the electrical power at the start of the circuit. From figure 12-1 we see that the db corresponding to this power ratio of one thousandth is —30 db. The ratio of input to output powers in this case is 1,000, and from the figure the db corresponding to this ratio is 4-30 db.
I 1 7" ! I t IO.OOO;
——— — - -0.5/- ------------------. >,000/
--------------------0.3/----------------------3,000z—
= = —01' .... ■==. -1,000-; 1===^
- — ZZZZ----------— c :5oof- —
------------4^03/--------------------300/------------
-----------fir 1--------------------/_______________ o / O /
— ----- -01 ' - - ~IOO, • -------
-------IqosZ- ■ ■■ —■ = - —so7 = —
-------.003/----------------------30/—---------------
----.001- —— — ■ ----10- f —
0005/- — — = —5 7- = ZZZZZ ZZZZZ
—7o003----------------------3t/ ---------------------
•OOOlZ-------------------------1Z---------—I______________
-40 -30 -20 -10 0 10 20 30 40
db TL 54828
Figure 12-2. Relation between power ratio and db.
e. As shown in figure 12-1, changing the sign of a given number of db from plus to minus, or vice versa, is equivalent to taking the reciprocal of the corresponding power ratio. This also may be stated as
P P
db = 10 log — = —10 log — P2 Pi
This is a convenient relationship to remember when using ordinary logarithm tables since it is somewhat simpler to employ the logarithms of numbers larger than unity. This is also useful in relation to the determination of gains or losses when P1 and P2 apply to the input and output powers of a network which may contain either gain or loss.
f. The db is a useful unit for another reason. One db corresponds' to about the smallest change in sound power that a careful observer can detect when the sound is at a medium loudness level. A person’s senses detect changes in terms of ratios, much more nearly than they detect the absolute amount of the change. For example, when a person is riding on a train and the speed increases from 1 mile per hour to 11 miles per hour, he readily notices the difference; however, if the speed increases from 60 to 70 miles per hour, the change is much less noticeable. The absolute increase in speed is the same in both cases but the percentage change is much larger in the first instance and therefore the change is more noticeable. This principle also applies to a person’s hearing and some of his other senses. Thus, it is appropriate to measure changes in telephone power in terms of the db, which is a unit corresponding to a fixed percentage change in power.
g. Relations between db and current or voltage ratios are given in paragraph 1207. The neper, another unit value for power ratios, is described in paragraph 1208.
1204. USE OF THE db IN EXPRESSING TRANSMISSION LOSSES AND GAINS.
a. The transmission loss of a circuit, or of a part of a circuit, is the db corresponding to the ratio of input to output powers. Thus, if the input power is greater than the output power the circuit has a positive transmission loss. If, on the other hand, a part of & circuit has an amplifier in it, such that the output power is greater than the input power, then this circuit element has a negative transmission loss, or a positive transmission gain. This gain is measured by the db corresponding to the ratio of output to input power.
b. Very often when designing a circuit it is necessary to find the transmission loss resulting from connecting together a number of component parts. The use of the db is convenient in making this calculation, because the total transmission loss in db is merely the sum of the losses in the individual parts3. For example, a circuit may run from a supply depot to corps headquarters, then to division headquarters, and then to a local command post. If the loss
3 When the impedances of the individual parts are matched to each other.
554
PARS.
1204—1206
CHAPTER 12. TRANSMISSION YARDSTICKS
from the supply depot to corps headquarters is 6 db, that from corps headquarters to division headquarters is 6 db, and that from division headquarters to the local command post is 12 db, then the total loss from supply depot to command post is obtained by merely adding these numbers and is therefore 24 db.
c. As another example, the power received from one mile of very wet Wire W-110-B is only about 50 percent of the power put in at the sending end. This 50 percent is reduced another 50 percent in the second mile and the resulting 25 percent is reduced another 50 percent in the third mile and so on. By the end of about 10 miles only 0.1 percent is left. Obviously multiplying 50 percent by 50 percent 10 times in order to determine the loss of 10 miles of wire is an awkward method. The use of the db gets rid of this awkwardness. As seen from the above table, when the output power is half of the input power, the corresponding transmission loss is 3 db. In the case in question this is for 1 mile. The transmission loss for 10 miles can be obtained by adding up the 10 individual losses or, in other words, by multiplying the loss per mile by 10. The resultant loss is 10 x 3 = 30 db.
d. In adding together the transmission losses and gains of parts of a circuit which contains amplification, it is important to keep correct account of plus and minus signs. To do this, the transmission through each element of the circuit can be expressed in terms of loss, a gain being counted as a negative loss. For example, if a circuit has a transmitting repeater with 6-db gain; a line section with 20-db loss; an intermediate repeater with 19-db gain; another line section with 20-db loss; and a receiving repeater with 9-db gain: then the over-all loss (net loss) of the circuit is — 6 -|- 20 —19 J-20 — 9 = 6 db. An alternative method is to express the transmission through each element of the circuit in terms of gain, and to count each loss as a negative gain. The important thing is to adopt one system for use throughout the problem, and not to mix losses and gains indiscriminately.
e. The db is commonly used to express losses in transmission lines used in radio circuits, such as a line connecting the radio transmitter with its antenna. It can also be used to express losses in the radio path proper, when sufficient data are available. Other examples of the use of the db in radio are in chapter 6.
1205. STANDARD TESTING POWER.
It will be noticed that the above discussion has been about power ratios, not absolute powers. A decibel is a measure of power ratio. When telephone circuits are set up and tested, it is common to use a standard testing power of 1 milliwatt (one thousandth of a watt). Testing powers received at various parts of the circuit are then measured in terms of db referred to this standard testing power. The db referred to a milliwatt is abbreviated dbm. Thus 1 milliwatt is 0 dbm; 100 milliwatts are 4-20 dbm; 0.01 milliwatt is —20 dbm, etc4. When a circuit is lined up, a standard source of 1 milliwatt testing power is connected to the sending end of the circuit (commonly the sending switchboard), and the received powers at various points are compared with the received powers which would be expected from the design of the circuit. Thus in a circuit consisting of 10 miles of very wet Wire W-110-B, the received testing power would be about —30 dbm. If an amplifier with 20-db gain were connected at the receiving end of this wire, the received power at the output of this amplifier would be —30 4-20 = —10 dbm.
1206. TRANSMISSION LEVEL AND NET LOSS.
a. In laying out circuits, it is often convenient to consider the relative power level at a given point, referred to the start of the circuit (transmitting switchboard). The start of the circuit is conveniently designated as zero transmission level. If the loss from the start of the circuit to a point X is 15 db, then the transmission level at X is —15 db. If there is a gain of 10 db from the start of the circuit to a point Y, then the transmission level at Y is 4-10 db. Transmission level diagrams are often convenient in engineering telephone circuits, because there are lower and upper transmission levels beyond which it is not safe to go. An example of such a diagram is given in figure 12-3.
b. If the transmission level at the receiving end of circuit is —L, then the net loss of the circuit (sum of losses minus sum of gains) is evidently L.
4 In the past, power levels in radio transmitters and receivers have sometimes been rated in terms of db referred to a power of 6 milliwatts instead of 1 milliwatt; and this reference point has sometimes been called zero level in radio instruction books. This usage is not recommended.
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c. The net losses in the two directions of transmission over a given circuit are usually but not necessarily the same. The net loss may vary with frequency and with the amount of transmitted power. If no statement about these items is included, the frequency is usually taken as 1,000 cycles, and the power as 1 milliwatt, at the transmitting switchboard.
d. For a length of circuit such as a repeater section the loss will, in general, be different at different frequencies in the transmitted frequency band. When these differences are large they are usually reduced by equalization. A network placed in the circuit in order to equalize the transmission losses at various frequencies is known as an equalizer.
1207. RELATION BETWEEN db AND VOLTAGE OR CURRENT RATIOS.
In practice it is often convenient to measure the voltage or current at a given point, rather than to measure the power at this point directly. If the impedances at two points in a circuit are equal, the ratio of the powers at these two points equals the square of the ratio of the corresponding currents, or the square of the ratio of the corresponding voltages. Thus if the power, current, and voltage at one point are respectively Pj, It, and Vt and the corresponding quantities at the other point are P2, I2, and V2,
P1_(I1)^_(V1)^
P2 (12)2 (V2)2*
Referring to the definition of a decibel given above,
db = 10 log—1,
n2 it is seen that db = 10 log -—— (I2)2
T V
or db = 20 log — = 20 log —-.
12 V2
Thus it is seen that where the impedances at the two points are equal, the db are equal to 20 times the logarithm of the ratio of currents at the two points, or 20 times the logarithm of the ratio of voltages at these two points. The db is, however, fundamentally a measure of power ratio. Figure 12-4 is a table of db and the corresponding voltage or current ratios in
the case where the impedances are equal. Where the impedances at the two points are unequal, the db can be obtained by using power ratios. Adding db corresponds to multiplying current ratios or voltage ratios. Thus from figure 12-4, the current ratio corresponding to 36 db, or 30 + 6 db, is 32 >< 2 = 64.
LEVELS, IN db, ARE CIRCLED
TL 54829
Figure 12-3. Sample transmission level diagram.
1208. THE NEPER.
An alternative unit of power ratio, which is sometimes used in Europe, and also in mathematical investigations, is the neper. To convert nepers to db, multiply nepers by 8.7. This conversion factor may be of use in converting European figures of transmission loss, etc., to values in db. Mathematically, the neper is defined by
1, Pt nepers = -loge — 1 2
where PT and P2 are two powers and e=2.718 is the base of the Naperian system of logarithms.
1209. MEASUREMENT OF POWER IN TRANSMITTED SPEECH; THE VOLUME UNIT (VU).
It is sometimes necessary to measure the power in the speech currents on a telephone circuit. Speech power is not steady like that from a testing oscillator, but varies from moment to moment. Hence a special technique and a special measuring instrument are needed for measuring speech power. The instrument designed for this purpose is known as a volume indicator. It consists essentially of a meter used as an indicating device and certain controls for changing its sensitivity. Its impedance is high enough to permit bridging across ordinary telephone circuits with negligible loss, and its frequency characteristic is approxi-
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CHAPTER 12. TRANSMISSION YARDSTICKS
mately flat from about 50 to 10,000 cycles. The meter, known as the vu meter, is arranged to have a particular dynamic characteristic (speed of response to a suddenly applied voltage), which approximates the performance of the human ear. When electrical speech currents are fed into a vu meter, the meter needle will move about in response to the speech currents; the characteristics of speech are such that the motion of the needle will approximately follow a certain pattern with peaks and valleys in the deflection. The average of the three highest peaks per 10 seconds, disregarding occasional extreme peaks, is taken as the indication of the meter needle. The scale of vu is a db scale, such that a 1,000-cycle sine wave testing power of 1 milliwatt (0 dbm) reads 0 vu on the volume indicator5. Details are given in Bell System Practice Section E47.153. Zero vu corresponds approximately to the power fed into a telephone line when a loud talker talks into an Army local battery telephone set connected to the line, or to the power obtained from a telephone when Army personnel talk over radio circuits to planes in flight.
1210. CROSSTALK.
On account of the relatively high frequencies used in telephone communication and in telegraph communication other than d-c telegraph, there is a marked tendency for the transmission currents to stray from their appointed path and for part of the transmission to appear in other circuits. This phenomenon is known as crosstalk. Crosstalk is measured in the same terms as those used for transmission'1. Thus, if there is a power PA at a point A on a circuit and a resulting power PB at a point B in another circuit, due to crosstalk from the first circuit, then the crosstalk loss from A to B, in p
db, equals 10 log —-. It will be observed that P B
crosstalk loss, like transmission loss, relates
B In former volume indicators the reference point of the db scale was known as reference volume; this corresponded to a 1,000-cycle sine wave calibrating power of + 8 dbm (about 6 milliwatts).
8 Crosstalk loss is also sometimes expressed in terms of crosstalk units. The scale of crosstalk units is such that 1 million crosstalk units equals 0-db crosstalk loss; 1.000 crosstalk units equals 60-db crosstalk loss; 1 crosstalk unit equals 120-db crosstalk loss, etc. In circuits of equal impedance, the crosstalk unit expresses the current in the disturbed circuit as millionths of the disturbing current.
db . Approximate current ratio or voltage ratio
0 1
5 1.78
10 3.2
15 5.6
20 10
25 17.8
30 32
-10 0.32
-20 0.1
-30 0.032
-120 0.000001
20n 10n
6 2
12 4
18 8
24 16
-6 0.5
-12 0.25
-18 0.125
-24 0.063
db Approximate Current ratio or voltage ratio
1 1.12
2 1.25
3 1.41
4 1.58
5 1.78
6 2.0
7 2.25
8 2.5
9 2.8
10 3.2
-1 0.9
-2 0.8
-3 0.7
—4 0.63
-5 0.56
-6 0.5
-7 0.45
-8 0.4
-9 0.36
-10 0.32
Figure 12-4. Relation between db and current ratio or voltage ratio, where impedances are equal.
to power ratio and not to absolute powers. Crosstalk is discussed further in chapter 5.
1211. NOISE.
a. Measurement of Noise. Noise is also measured on a db scale. This applies both to noises in electrical circuits and to acoustical noises. Electrical circuit noises are referred to a zero or reference power of 1 micromicrowatt (90 db below 1 milliwatt). If a 1,000-cycle power of this small amount is fed into an ordinary telephone set, a listener in a quiet room can barely hear the resulting sound. Telephone instruments do not have the same efficiency at all frequencies, and this is also true for the human ear. Since telephone receivers are usually most efficient in the speech-frequency band in the neighborhood of 1,000 cycles, a micromicrowatt at frequencies other than 1,000 cycles will not be as audible in a telephone set as a micromicrowatt at 1,000 cycles; and equal electrical noise powers at different frequencies
656935 0—45------37
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will not have the same interfering effect. Noises in electrical circuits (circuit noises) are commonly measured by means of noise meters, of which the Western Electric Company 2B noise measuring set (fig. 12-5) (stock No.
TL 54830
Figure 12-5. Western Electric Company 2B Noise Measuring Set.
3F4265) is most common. In these noise meters the different interfering effects of different frequencies are taken care of by a frequencyweighting network which is incorporated in the noise meter. The noise meter is calibrated at 1,000 cycles, in terms of the above mentioned reference power of 1 micromicrowatt (90 db below 1 milliwatt). Noise meters have a db scale. One micromicrowatt at 1,000 cycles reads 0 db on the noise meter, and is called reference noise (RN). A noise 35 db greater than this is written 35 dbRN. The meter needle of the noise meter has a dynamic characteristic which is approximately the same as that of the vu meter and which therefore corresponds approximately to the performance of the human ear.
b. Addition of Noises.
(1) If two circuit noises combine or add, for example, the noises at a circuit terminal which originate in two repeater sections; it is approximately correct to add the noise powers. It is not correct to add the db values. For example, two noises, of 30 and 36 dbRN, do not give a resultant noise of 66 dbRN; the resultant noise is 37 dbRN, as can be seen by using the information in paragraph 1203 to convert each noise into the corresponding power ratio referred to reference noise. Since 30 db corresponds to a power ratio of 1,006, the first noise
power is 1,000 times the reference; similarly the second noise power is 4,000 times the reference; the sum of these powers is 5,000 times the reference, and the corresponding db value is (par. 1203) 37 db above reference noise.
(2) The following is a short-cut method of adding two noise powers, or other powers, expressed in db above a common reference point. Take the difference between the two db values; in the following table find the number corresponding to that difference, and add it to the larger db value.
Difference: 0 0.5 1 1.5 2 3 4 5 6
Add: 3 2.8 2.5 2.3 2.1 1.8 1.5 1.2 1.0
Difference: 7 8 9 10 11 13 16 20
Add: 0.8 0.6 0.5 0.4 0.3 0.2 0.1 0.0
For example, to add noises of 30 and 36 dbRN: the db difference is 6, hence from the table 1.0 should be added to the larger one (36 dbRN), giving the result: 37 dbRN.
(3) Several noises may be added by repeated applications of this process. If the noises are all equal, the following table may be used; the db value specified is added to the db value of one noise.
No. of equal noises: 2 3 4 5 6 7 8 9 10 100
db to be
added: 3 4.8 6 7 7.8 8.4 9 9.5 10 20
For example, if a circuit has five repeater
sections and if the noise at the terminal from each repeater section is 28 dbRN, the total noise at the terminal is 28 4- 7 = 35 dbRN.
c. Signal-to-noise Ratio.
(1) Many circuits have receiving amplifiers with gain which is adjustable over a fairly wide range of values. This is particularly true of radio circuits, especially those with automatic volume control. In such circuits the ratio of the received signal to the received noise often is more significant than the absolute value of either the signal or the noise, as a criterion of the understandability of the received telephone message. This signal-to-noise ratio is often expressed in db. The signal-to-noise ratio in db is thus the db corresponding to the ratio of signal power to noise power.
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(2) In the literature various ways of expressing the signal-to-noise ratio have been used, particularly in radio circuits. In such circuits it is wise to use the term speech-to-noise ratio to indicate the ratio of speech power to noise power, when both are measured by the same kind of meter. In radio circuits it is generally inconvenient to measure the speech power at radio frequencies since this is contained in sidebands which are generally weaker than the carrier which is present at the same time. In this case the radio carrier and the radio noise may be measured, and the ratio of the two preferably called the carrier-to-noise ratio', or, alternatively, the speech-to-noise ratio, for a known talker volume, can be measured at the radio receiver output. The relation between the speech-to-noise ratio and the carrier-to-noise ratio depends on the degree to which the talker modulates the transmitter, and thus depends on the type of radio transmitter and how it is used. For example, it is difficult to talk loudly enough to fully modulate some handy-talkie sets. As another example, in a multichannel radio system such as radio sets AN/TRC-3 and AN/TRC-4 combined with 4-channel carrier terminal equipment, the degree to which a given single talker can safely modulate the transmitter is necessarily less than that which a comparable single-channel system can use. Again, there is no universal method of measuring radio noise and different methods may yield different numerical values for the same noise. The net result is that quoted values of radio signal-to-noise ratio need interpretation before using them in systems engineering. A standard method of measuring signal-to-noise ratio of a radio receiver (equipment noise only) is to connect to its input a standard signal generator, and to measure the output of the radio receiver (for example, by using a vacuum-tube voltmeter), first with both the signal carrier and the modulation on (30 percent modulation at 400 cycles) and then with only the carrier on. The ratio of the two measurements is taken as the signal-to-noise ratio of the receiver for the particular test conditions.
d. Noise Requirements. It has been found that when telephone speech and noise are both measured by means of a noise meter, and when the noise is typical power induction or is uniformly distributed over an ordinary tele
phone channel, a signal-to-noise ratio (more accurately, speech-to-noise ratio) of. 6 db is about as poor as can be used for marginal understandability, and a ratio of about 13 db is as small as should be permitted as an engineering basis for laying out telephone circuits. On many Army landline circuits the average talker volume at the terminals of Telephone EE-8-( ) is thought to be about —5 vu. If speech volume is measured on a Western Electric Company 2B noise measuring set (unmodified) it will not read as high as it will when measured on a vu meter because the noise meter contains a frequency weighting network while the vu meter is flat over the voice-frequency range. This reduction in reading has been determined to be about 8 db. Therefore, by comparing the reference points of the noise meter scale and the volume indicator scale, it follows that this average volume of —5 vu will be a noise meter reading of —5 + 90 (subpar, a above) —8 = 77 dbRN. If this speech is transmitted over a 30 db point-to-point circuit, the speech at the receiving end will read 77 —30 = 47 dbRN. In order to provide a speech-to-noise ratio of 13 db, the noise at the receiving end must be 47 — 13 = 34 dbRN. Assume, instead of a point-to-point circuit, the 30 db is made up of a 6 db sending loop, three 6 db via trunks (long distance circuits suitable for switched connections as shown in chapter 2), and a 6 db receiving loop. Then, as in the case of the 30 db point-to-point circuit the noise at the end of the receiving loop must be 34 dbRN to obtain a 13 db speech-to-noise ratio. Assume that the noise on the receiving loop is negligible, and that the noise on the last via trunk is attenuated 6 db before it reaches the telephone at the end of the receiving loop. Also assume that the noise which reaches the receiving loop from other parts of the circuit may be neglected, because it is attenuated more and will therefore be small in comparison with the noise on the last via trunk. Then the noise on the last via trunk, as measured at its junction with the receiving loop, should not exceed 34 + 6 = 40 dbRN. In practice, in order to allow some margin for below-average talkers, long distance tactical wire circuits are designed for 35 dbRN, instead of 40 dbRN, whenever practicable. In commercial cable or carrier circuits the noise requirement is 29 dbRN at the receiving toll switchboard (com
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
monly the — 9-db transmission level) ; this does not compare directly with the values for Signal Corps Circuits, since Signal Corps and commercial arrangements for building up via circuits are different.
1212. NOISE IN THE AIR.
Acoustical noises are also measured on a db scale. Such noises and other sounds are measured by means of an instrument called a sound-level meter. This consists of a microphone, a calibrated amplifier with frequency networks corresponding to the way in which the ear appreciates loudness of single frequencies at different loudness levels, and an indicating meter like that used in circuit-noise meters. Sounds are measured in terms of the power per square centimeter in the sound wave. They are measured in terms of db above a power of density of 10“16 watts per square centimeter at 1,000 cycles. This extremely small power density is just audible in the ear of a person with somewhat better than average hearing acuity, who is situated in a place which has no other sound than the 1,000-cycIe tone in question. It is called reference sound level. The range of acoustic noises and other sounds which is encountered in practice is extremely wide; and therefore, the db scale is particularly useful in measuring them. Figure 12-6, which is abstracted from one of many such tables which have appeared in the literature, gives an approximate idea of the sound levels in db for certain common noises and other sounds.
Approximate sound level
Source or description of noise (db)
Threshold of painful sound.................. 135
Airplane (observer outdoors, 20 feet from propeller) ................................ 120
Riveter, 35 feet away....................... 105
Elevated electric railway, 20 feet away.... 95
Very noisy street, New York or Chicago. ... 85
Very busy traffic, London.................... 80
Ordinary conversation, 4 feet away......... 70
Rather quiet New York City residential street, afternoon........................... 65
Quiet automobile, 25-50 feet away............ 55
Quiet suburban street, London, evening no traffic..................................... 35
Average whisper, 5 feet away................. 25
Rustle of leaves in gentle breeze............ 15
Threshold of hearing for acute ear............ 0
Figure 12-6. Sound levels.
1213. RADIO R AND S SCALES.
a. In ear reception of radio signals, the following scales are in general use to express the
S2—Weak
S3—Fairly good
S 4—Good
S5—Very good
listeners’ judgment of the signal strength, S', and readability, R, of the message.
SI—Barely perceptible R1—Unreadable
R2—Readable now and then
R3—Readable with difficulty
R4—Readable
R5—Perfectly readable
In earlier versions of these scales the numbers ran up to 10.
b. Some radio receivers have S meters, to give an indication of signal strength, from 1 to 5. The higher the number, the greater the signal strength; otherwise the numerical values have no precise meaning. The S meter scales on different types of set, even from the same manufacturer, generally will not agree.
1214. RADIO FIELD INTENSITY.
a. The field intensity, or field strength, of a radio wave is measured in microvolts per meter, or in db referred to one microvolt per meter. It is the voltage gradient, or space rate of change of voltage, of the wave. It has both a magnitude and a direction. This direction is that of the lines of electrostatic force at the point in question. A short, straight antenna placed in this direction will pick up more voltage from the wave than if placed in any other direction. The wave is said to be polarized in the direction of the electrostatic force lines. Thus if the electrostatic force lines are horizontal, the wave is horizontally polarized; if they are vertical, the wave is vertically polarized7.
b. Assume a dipole antenna (a straight antenna broken at its center to permit connection to apparatus) of length L meters in a radio field of E microvolts per meter, is placed in the direction to collect maximum voltage from the field. Also assume it is remote from other objects, and is connected to a radio receiver whose input impedance matches that of the dipole through a transmission line with negligible loss. Then if the length of the antenna is short compared to a half wave-length of the radio wave in question, the voltage across the receiver input is 0.25 LE microvolts; if the antenna length is a half wave-length, the voltage across the receiver input is 0.32 LE. Since the free-space wave-length in meters
7 Sometimes the term vertical polarization is used to mean any polarization which is not horizontal.
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CHAPTER 12. TRANSMISSION YARDSTICKS
times the frequency in megacycles equals 300, it will be found that at a frequency of about 48 megacycles the voltage (in microvolts) across the receiver input with the above halfwave dipole setup is numerically equal to the field intensity (in microvolts per meter). The impedance of a half-wave dipole remote from other objects is about 73 ohms resistance.
1215. ANTENNA EFFECTIVE HEIGHT AND ANTENNA GAIN.
a. The effective height of an antenna is the ratio of the open-circuit voltage at its terminals, when it is used as a receiving antenna, to the field intensity near the antenna producing this voltage. The effective height of a short grounded vertical antenna, on ground waves, is about half its physical length.
b. The gain of an antenna, with respect to a reference antenna and in a given direction, is the ratio of the power which must be supplied to the reference antenna to the power which must be supplied to the given antenna, when each radiates the same field in the given direction. The gain may be expressed in terms of power ratio or in db. The reference antenna must be specified. It need not be a physically realizable antenna; an easily computable ideal antenna, such as a half-wave dipole in free space, is a good reference antenna. The transmitting gain of an antenna is the same as its receiving gain, for the same direction and polarization of the radio field relative to the antenna.
1216. IMPEDANCE MATCHING.
a. Characteristic Impedance. The impedance of a uniform line (more accurately, its characteristic impedance) is the impedance obtained when the line is very long (mathematically, when it is of infinite length). A general idea of the meaning of characteristic impedance may be obtained from figure 12-7 in which
IMPEDANcF^^: Tj^-v\^1ERMINAT 0N
TL 5483
Figure 12-7. Schematic of wire line.
the line is represented as being made up of a large number of series and shunt impedance elements. For a line with a large number of these elements, that is, a very long line, it is apparent that the current sent into the line will be affected very little by the value of the termi
nating impedance at the distant end. For example, if the line has an attenuation of 20 db, even if it is open-circuited or short-circuited at the far end, the impedance at the sending end will not differ from characteristic impedance by more than two percent.
b. Impedance Mismatch.
(I) In communication systems a circuit is seldom, if ever, entirely uniform. The telephone or telegraph stations at the terminals differ in impedance characteristics from the lines to which they are connected. On switched connections the loops and trunks are generally of different construction and differ in impedance. Likewise, the trunk may be made up of different types of lines which also differ in impedance. There are, however, connections in which the same type of line is used throughout the entire circuit between telephone terminals, such as some point-to-point circuits, connections through small tactical switchboards where the entire wire plant may be of one type such as Wire W-110-B, or loop-to-loop connections through the larger switchboards.
(2) When lines or apparatus of unlike impedances are connected together in a communication system the transmission between telephones can be affected in the following ways unless corrective measures are applied.
(a) Transmission losses may be introduced because of reflections (par. 1217).
(b) Telephone repeater balance may be impaired (par. 1218).
(c) Sidetone at the telephones may be increased (par. 1219).
(d) Crosstalk may be increased. The effect, on crosstalk, of connecting together lines of different impedances is explained in chapter 5.
(e) Standing waves may be produced on radio transmission lines (par. 1217i and j) ; and the operation of radio transmitters may be affected (par. 1217h).
1217. REFLECTION LOSS.
a. It is a characteristic of wave motion that in passing from one medium to another a certain part of the energy propagated by the wave is reflected. For example, light-waves striking a pane of glass or some other denser medium are in part transmitted and in part reflected. The amount of energy reflected depends upon the physical properties of the
561
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ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
media through which the wave passes; the greater the dissimilarity, the greater the reflection. Similarly, in communication circuits, wherever there are dissimilarities in the transmission media, that is, differences in impedances of the various parts of a circuit, part of the electrical wave will be reflected toward the source and the remainder will be transmitted toward its destination. In the case where sending and receiving impedances have the same phase angle, the reflection loss is equal to the ratio (expressed in db) of the delivered power with an ideal matching transformer inserted between these impedances to the delivered power without inserting the transformer. A more general definition of reflection loss is given below in subparagraph f.
b. In a simple circuit, consisting of a line connecting two telephones such as shown in figure 12-8, the major part of the total trans-
TELEPHONE = TELEPHONE
TL 54832
Figure 12-8. Simple telephone circuit.
mission loss between the telephones is generally the attenuation of the line. In addition, since the impedance of the telephone is different from the impedance of the line there are reflecting effects, generally small, where each set is connected to the line. Furthermore, if the line is composed of long sections of different types of wire, such as open wire and field wire, there is a reflection loss at each junction, and the total reflection loss in the line equals the sum of the reflection losses at each junction. The reflection loss is not large unless there are considerable differences in magnitude or phase angle of the impedances, as illustrated in figure 12-9. Figure 12-10 gives values of reflection loss versus the ratios of the magnitudes of the two impedances and their difference in phase angle.
. c. When a very short section of line is inserted into a line of another type, the total loss due to reflections at the ends of the short length is materially smaller than would be obtained if the inserted section were long. In a voice-frequency cable circuit, this would be true if the attenuation of the short length were 1 db or less; further illustrations are given in chapter 5. In an open wire radio transmission line, this
would be true if the line were substantially shorter than a quarter wave.
Lines Impedance (ohms') at 1,000 cycles Reflection loss (db)
Z R-jX
Wire W-110-B (wet) and 080 C-S 405 /42° 930/31° 300-j270 791-j481 0.7
Wire W-110-B (wet) and 109 GS 405/42° 1390/27° 300-j270 1230-j630 1.5
Spiral-four (CC-358-( ) ) and 080 C-S 485/12° 930/31° 475-jl05 791-j481 0.4
Figure 12-9. Reflection losses between dissimilar lines.
d. Where reflection losses are large it is the usual practice in commercial wire telephone circuits to connect circuits of unequal impedances by means of a suitable inequality ratio repeating coil. By this means the magnitudes, but not the phase angles, of the two impedances may be made equal. Other methods of impedance matching, sometimes used in radio work, are quarter-wave line sections, transmission lines of tapered cross-section, and vacuum-tube impedance-transforming devices.
e. If a source of power has an internal impedance Zx = Ri 4- jXi and is connected to a load Z2 = R2 + jX2, maximum power is delivered to the load when the resistances Rt and R2 are equal and the reactances Xi and X2 are of equal magnitude and of opposite phase. However, from the standpoint of controlling effects on telephone repeater balance, crosstalk, or sidetone, it is better to make the two reactances equal in both phase and magnitude, and to make the two resistances equal. In wire lines, particularly repeatered circuits, effects on repeater balance, crosstalk, and sidetone are generally more important than adjusting impedances to obtain maximum delivered power.
f. The reflection loss, in db, at the junction of two impedances Zi and Z2, has been customarily defined by the formula
2VzX
Here Zi and Z2 have both magnitude and phase, and must be added with due regard to phase8.
8 One way of doing this is to use the equivalent formula
(I^+RsF-HXi+X^ °g 4v/(R12+X12)(R22+X22)
562
PAR.
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CHAPTER 12. TRANSMISSION YARDSTICKS
180 °j i*?/ ?i “?i si m । *?/ *ii ©I
„ «o7 fl fl fl y/ y/ fi nJ y/ / / / /
o80 7/Yy Yy / /YYYYcYYYyY^YYY^ 1 70*^y s^YYsYY^YYYYY/ Yy^Y > . - ■ ^YY/yYYYYYYyYyYYY
60 =~"s'^— s' 's'y'^s' /"y'-yy" y / y" * t„o -0.8^^ y >7y YYYYy Y/xy y Y Y / s' s' y y s' y y y y / / y n y y y
4 o° - - 0.4-y^-y -// y y yy _y .y/ /__. 'iy\ y — Y ^7
^yyY^yyYYZYZy-^^
y / // // / 7/s / / / w / y>.
20° —/ —-Z-—(-—-7— /-—-7— /—-7—-7—-7 —-7— /—-7—-7— 7.—2Z
1 °° ~/ Y Y Y Y °/ V—7 m Y t—t Y—Y~
0[z_0/ py l°7 0/ j "I । / "I p/ I 1 /_2d_"d
1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
VALUES OF r
NOTES: VALUES OF THE REFLECTION LOSS FOR ANY TWO IMPEDANCES Zx AND Zy ARE HERE GIVEN AS A FUNCTION OF THE RATIO AL = p/ 0 WHERE F IS THE RATIO OF THE MAGNITUDES ZY
AND 0 IS THE DIFFERENCE BETWEEN THE ANGLES OF THE TWO IMPEDANCES. THE RATIO IS ALWAYS TO BE TAKEN BY DIVIDING THE LARGER IMPEDANCE BY THE SMALLER, THAT IS, SO THAT F WILL NOT BE LESS THAN UNITY. IT IS IMMATERIAL WHETHER 0 IS POSITIVE OR NEGATIVE.
NEGATIVE VALUES OF REFLECTION LOSSES ARE REFLECTION GAINS.
TL 54881
Figure 12-10. Reflection losses; decibels.
(The | | sign indicates the numerical or absolute value of the quantity within it.) The reflection loss depends on both the magnitudes and phases of the two impedances. When one impedance has a positive reactance (inductive) and the other has a negative reactance (capacitive), a reflection gain is sometimes obtained. In general, a reflection gain is obtained when maximum power is delivered.
g. Reflections are a matter of concern in the design of radio circuits, since it is often desired to transfer the maximum proportion of power from transmitter to antenna, or from antenna to receiver.
h. Large reflection gains are obtainable when connecting radio transmitters or receivers to certain types of antennas, such as short whips, whose impedance is mostly reactive. Adjusting the reactance of the radio set to cancel that of the antenna circuit is sometimes called tuning or resonating the antenna. Some radio
transmitters, such as those designed to operate only with whips which are short compared to a quarter wave, have built-in tuning circuits suitable for obtaining the needed reflection gain only when used with the particular type of antenna for which they were designed9.
i. Assume that there is a transmission line between the radio transmitter and antenna, and the impedances of the line and the transmitter are equal, but the antenna impedance is different from this. Then, as the electrical wave from the radio transmitter (called the incident wave) is transmitted over the line it meets a reflected wave returning from the antenna end of the line. The resultant wave, formed as the incident and reflected waves combine in and out of phase, is called a standing wave. If a volt
0 When a radio transmitter is operated with an anten-
na materially different from that for which it is de-
signed, there may be danger of improperly loading it,
thereby drawing excessive plate current from the out-
put tube.
563
PARS.
1217-1218
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
meter is bridged across the line and is moved along the line, the ratio of maximum to minimum voltmeter readings is called the standing wave ratio. When the standing wave ratio is unity, there are no reflections. Let Zx and Z2 be the impedances of the line and antenna respectively. When the phase angles of Zx and Z2 are equal, the standing wave ratio equals Zx/Z2 (customarily the larger impedance is used as the numerator). Another measure of the magnitude of the standing wave is the reflection coefficient r.
_ Zi — Z2 Zi+Z2
The reflection coefficient is the ratio of the reflected current to the current which would have been transmitted into the antenna if its impedance had been equal to the line impedance. From this formula it is evident that when the line impedance is equal to the antenna impedance the reflection coefficient is zero and there is no reflected wave. The reflection coefficient is used in wire transmission as well (par. 1218d). The relation between reflection coefficient, r, and standing wave ratio, S, is as follows for the case of a line of negligible attenuation :
S=l±lfi 1-1 r I
For example, if a line of about 350-ohms impedance is connected to a dipole antenna of about 70-ohms impedance, the reflection coefficient, r, is 2/3, and the standing wave ratio, S, is 5. Reference may be made to TM 11-314.
j. Large standing wave ratios are accompanied by voltage and current peaks on a radio transmission line. They may cause breakdown of insulation on a line from transmitter to antenna; introduce higher losses if nonlinear effects such as corona are involved; or produce unwanted radiation. On the antenna proper, however, standing waves are a benefit in many cases, when the antenna is designed to make use of them to increase the radiation in desired directions.
1218. REPEATER BALANCE.
a. Since a vacuum-tube amplifier permits transmission in one direction only, it is common practice in 2-wire telephone circuits to use two amplifiers to make up a repeater, one to provide amplification in one direction and
the other to provide amplification in the opposite direction. If these amplifiers were merely connected together, each amplifier input to the other output, the circuit would sing or howl. A circuit which will permit such amplifiers to be used on a 2-wire line without establishing a singing path between the two amplifiers is shown in figure 12-11.
AMPLIFIER
JLQjJ HYBRID
COIL I
■ dW dUULr- —vWL/—*-----—1.QQO /'
LINE A NET NET LINE 8
------------ , rffiTp—] ----- i hybrid
coil pRRT
Lb- > ■ -• J I
amplifier
Tl 54783
Figure 12-11. 22-type repeater.
b. The action of the hybrid coil is similar to that of the Wheatstone bridge; that is, when a vdltage is applied across a particular pair of terminals, no current will flow through an impedance connected across the two other terminals of the bridge if certain well-known conditions regarding the ratios of the impedances of the four arms of the bridge are satisfied. Referring to figure 12-11, if a voltage is impressed on terminal number 2 no current will flow in terminal number 1 if the impedances of the line and network are identical. The greater the difference between the impedances of line and network, the greater will be the amount of current which flows in terminal number 1 and the greater will be the tendency of the repeater to sing. Further discussion of the use of hybrid coils in repeatered circuits is given in TM 11-457 and TM 11-475.
c. Since perfection cannot be attained even in the most carefully designed telephone circuits, there is always some transmission across the hybrid coil; consequently the amount of amplification which can be provided by a repeater without singing is limited. The sum of the gains of the two amplifiers must always be less than the sum of the losses across the two hybrid coils in order to prevent singing. In practice, to allow for variations in the circuit, a margin is provided between total loss and total gain.
564
PAKS.
1218-1219
CHAPTER 12. TRANSMISSION YARDSTICKS
d. The return loss between two impedances is a measure of the similarity between the impedances ; these might be the line and network impedances, or the impedances of two types of line. It is expressed in db and equals 20 times the logarithm of the reciprocal of the numerical value of the reflection coefficient (par. 1217i), namely, return loss
R=20 log I Z1+Zz J Zi—z2
The loss across an ordinary hybrid coil is about 6 db greater than the return loss.
e. Since speech transmission through a repeater must be practically uniform over the band of frequencies used for speech transmission, about 200 to 2,800 cycles, it can be seen that transmission loss across the hybrid coil must be sufficiently great at all frequencies in this band to prevent singing at any one of them. Filters usually are employed to prevent singing at frequencies outside the speechtransmission band.
f. It is obvious that good balance usually cannot be obtained by matching the line impedance at a single frequency by means of a simple network consisting of a resistor and a capacitor or inductor. Excellent balance between line and network could, of course, be obtained by duplicating in the network each element of the line, but this is an impractical solution. In practice, fixed networks are used or variable networks are provided which can be adjusted in the field to match approximately the characteristic impedance of the types of lines in common use. The networks are furnished as part of the repeater.
g. To obtain good balance between a line and a network, the line must be reasonably uniform. Where apparatus is placed between the hybrid coil and the line, duplicate apparatus is usually placed between the hybrid coil and the network. A line irregularity which is distant from the repeater is less important than one which is close to the repeater. If a repeater section is composed of two dissimilar lengths of line in tandem, Lx and L2 of characteristic impedance Zx and Z2, and if the repeater connected to Li matches Zx and the repeater connected to L2 matches Z2 then the return loss at the junction of Li and L2 is R, as given by the formula in subparagraph d above, but the return loss at the repeater connected to Li, is R + 2A, where A is the attenuation of
Li. This can be seen by noting that a current starting at the repeater would traverse L„ be partially reflected at the junction of Li and L2, and traverse Li again before the reflection reached the repeater.
h. Where a given repeater is connected to a circuit whose impedance is quite irregular or unstable, or to circuits of different impedances (terminal repeater), a compromise network (resistance plus capacitance) is ordinarily used, and the repeater gain must be restricted.
i. Sometimes a 21-type repeater is used. As shown in figure 12-12 this type of repeater
AMPLIFIER
LINE A LINE 0
-----------------------------------------------------------
HYBRID COIL TL 54782
Figure 12-12. 21-type repeater.
contains one amplifier, one hybrid coil, and no balancing networks; freedom from singing is obtained by the impedance balance between the lines on the two sides of the repeater. In figure 12-12, a current coming from line A will divide equally between the amplifier input and output circuits if the amplifier output and input impedances are such as to balance the hybrid coil; none will go directly to line B. The amplifier input current will, how’ever, be amplified; and if the impedances of lines A and B are equal, the amplified current will flow equally in them, none of it returning to the amplifier input. The current in line B is the useful current. The current returned to line A propagates toward the original source as an echo. If lines A and B have unequal impedances, some of the amplifier output current will return to its input; if the inequality is great enough at some frequency, the repeater will sing. Transmission from line B to line A takes place in the same manner as described above for line A to line B.
1219. SIDETONE.
a. In the antisidetone circuits of the most commonly-used telephones, the transmission loss in the sidetone path between the micro-
565
PARS.
1219-1220
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
« F—~ Illi H~ I I 111 1 111 1-111111-1 I I’ [ I 11:
| ZZZZ^\^^Z--------ZZZZZZZZZZZ LOSS C'N db) = 20 LOG|0 ZZZ2
5----------------------------- ---------------------------------------------------------
4 WHERE As/S- -^ + v5 OR -1--* Z?
3--------CvtU''^ ------------- Z| Zz Zc ------------------------------------------------
2 ———---------------------------——.— --------
0-8-------— -F-\ \ -------- Z| Zz -----------------------------------------—
<« 07-------------\------------------------ -----------------------------------------------
o o.6-------------l_A_X_AAs\^X s s -------- -----------------------------------------------
-i os-------—-i- y \ va\ \--------------------n ~ va ~ —
04--------------1 \ \ \ \W \ V \ \ X------- , r—► --------
o.3-------------Zt : lSSxX'XSZ--------------X.—JX
\ \\\sW \\W\ Z| Zz
o.2-------------L. -— \ l-i —\ \\ . \—Nc- \ X r\ N >. I--... ....-----------—————--------
® *? ® l bR R/b ^^^a o4 CR* |o rT R >R/c dR R/2C
BALANCED NETWORK 3.R/2 3-r/2
|o R/^Xf/2 R/2X«/2 ^CR^^ DIAGRAM - D d«/2 R/2C O- ■ ! Q DIAGRAM - H
INSERTION loss db a. b 1 b 1 a £ C 1 C d 1 c C d 2C 1 2C
0 1 0 00576 869 0.0115 174 0.00576 174 0.0116 864 0 0114 86.4 0.0116 874 0 0232 43.2
02 0.0115 43.4 00230 869 00115 86.9 0 0233 42.9 0 0228 42.9 0.0233 439 0.0466 21.5
0.3 0 0173 28.9 0 0345 57.9 00173 579 00351 285 00340 28.5 00351 29 5 00703 14.2
0-4 0.5 00230 0 0286 21-7 ' 17.4 0 0461 00576 434 34.8 0-0230 00288 43.4 34.8 00471 0.0593 21-2 169 00450 0.0559 21.2 16.9 00471 00593 222 179 0.0943 0-119 10.6 8.44
0 6 00345 14.5 0 0691 290 00345 290 0.0715 .14 0 0.0667 14.0 0-0715 150 0143 6.99
07 0.0403 12.4 00807 248 0.0403 24.8 0.0839 11-9 00774 119 0-0839 12.9 0-168 596
06 0 0460 10-8 0 0922 217 0-0460 217 0-0965 10 4 0.0880 10-4 0.0965 114 0.193 5.18
09 00516 9.63 0 104 193 00518 19.3 0-109 9.16 00984 9.16 0 109 102 0.218 4.58
1. 00575 867 0-115 174 00575 17.4 0122 820 0.109 8.20 0122 920 0-244 4.10
2 0.H5 4 30 0.232 872 0-115 872 0-259 3.86 0 206 3.86 0.259 4.86 0.518 1.93
3 0 171 2.84 0.352 585 0.171 5.85 0.413 2.42 0.292 2.42 0-413 3.42 0.825 1.21
4. 0-226 2.10 0.477 4.42 0 226 4.42 0.585 1.71 0.369 1.71 0 585 2.71 1.17 0.855
5. 0.280 164 0.608 3.57 0.280 3-57 0.778 1.28 0.438 128 0.778 2.28 1.56 0.642
6 0.332 1 34 0.747 3.01 0.332 3.01 0.995 1.00 0.499 1.00 0995 2.00 1.99 0.502
7. 6. 0.382 0.431 112 0.946 0 896 1.06 2.61 2.32 0 382 0.431 2.61 2.32 1-24 1.51 0.807 0-661 O 553 0.602 0.807 0 661 1-24 151 181 1 66 2.48 3.02 0.404 0.331
9. 0-476 0-812 1.23 2.10 0.476 2.10 |.82 0.550 0 645 0.550 1.62 1.55 3.64 0.275
10. 0.519 0.703 1.42 1-92 0.519 1.92 2. 16 0-462 0.684 0-462 2.16 1.46 4.32 0.231
20. 30. 0 818 0.939 0-202 0-0633 495 15.8 1-22 1.07 0.818 0.939 1.22 107 900 30-6 Olli 00327 0-900 0-968 0 111 0.0327 9.00 30.6 I. II 103 18.0 61.2 0.0556 0.0163
40. 0.980 0 0200 500 102 0.980 1.02 99.0 0-0101 0 990 0.0101 990 1.01 198. 0.00505
50. 60. 0994 0 998 0-00632 0.00200 158 500 1.01 1.00 0.994 0.998 101 1.00 315. 999 000317 000100 0.997 0.999 0.00317 OOOIOO 315 999 1.00 1.00 630 2000 0.00159 0.000301
* THE CHARACTERISTIC IMPEDANCE OF THE NETWORKS IN DIAGRAMS A TO D IS R OHMS
TL 54836
Figure 12-14. Resistance networks causing stated losses when inserted between two resistors of R ohms each.
point the value of a single one of the impedances can be divided by the number of impedances, before entering the chart.
c. Figure 12-14 gives insertion loss of several types of resistance networks which might be used to intentionally insert loss when it is needed. The choice between different types of networks depends on their suitability to the particular problem, and on the available resistors.
d. Figure 12-15 shows a 3-way pad which can be used to connect three circuits of impedance R + jO together with 6-db loss between any two circuits, and with no reflections produced in the circuits.
1221. IMPORTANT FACTORS IN TELEGRAPH TRANSMISSION.
a. Telegraphy uses codes in which characters are represented by combinations of two conditions of variable duration. One condition is called marking and the other spacing, these corresponding respectively at the transmitter
to the closed and open positions of a key. Marks and spaces are represented, for example, by positive and negative currents, by current-on and current-off, tone-on and tone-off
TL 54925
Figure 12-15. Three-way 6-db pad.
as in radio with ear reception, or by alternating currents of two different frequencies. The relative positions in time of the transitions from one condition to the other indicate the intelligence in the message, the values of the currents during steady-state marking and
567
PARS.
1221-1222
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
spacing conditions being of secondary importance. This applies particularly to relay or similar reception, either wire or radio. Any over-all uniform shift or delay in transit is unimportant.
b. With point-to-point radio transmission and ear reception, however, where interfering currents, that is noise, may tend to override the signals, the most important consideration is the maintenance of a satisfactory value of signaling current in comparison with the interference. If a satisfactory signal-to-noise ratio is maintained, the signals can be understood since there is usually nothing in the radio transmission system to cause any material change in the relative timing of the transitions.
1222. TELEGRAPH SIGNAL DISTORTION.
a. It is usual to express the over-all transmission impairment of telegraph signals in terms of the time displacement of the transitions from their proper positions. This is given in percent of the duration of a unit signal element of the code. Such displacement of a transition is referred to as distortion. Time distortion should be clearly distinguished from distortion of the signal wave-shape, which may or may not cause time distortion of the transitions. Where signals are repeated into a local circuit by a receiving relay, the time distortion is a complete over-all measure of the transmission impairment. Time distortion is occasioned by a combination of such factors as wave-shape distortion, attenuation, interference, and variations in voltages and adjustment of relays. For satisfactory operation the distortion should not reach an amount which would result in ambiguous or incorrect interpretation of the received signals.
b. In the case of manual telegraphy, this distortion has been expressed, for a particular marking or spacing impulse, as the algebraic sum of the displacements of the two transitions determining the beginning and ending of the impulse. In other words, this is the lengthening or shortening of the pulse expressed in percent of a perfect unit pulse, the lengthening of marks being considered positive and their shortening negative.
c. Teletypewriter operation requires a different manner of specifying distortion, as will be clear from an examination of a teletypewriter signal. Such a signal, as indicated by
figure 12-16, consists of a start pulse of unit length, a selecting period five time-units in length, and a stop pulse. In general any one of the five elements of the selecting period may be either marking or spacing. When such *a signal is transmitted to a teletypewriter, by a
•-----------------j----------------------•
SELECTION UNITS
•-STOP-* START^— 2 3 4-^-5-^- STOP — START -----
POINTS
TL 54833
Figure 12-16. Teletypewriter character “J”; undistorted.
receiving relay for instance, the beginning of the start pulse causes the selective mechanism of the receiving machine to commence rotation; it will then rotate in substantial synchronism with the sender for a revolution, until brought to rest by the stop latch. At the midpoint of each of the five selection units or pulses, an examination of the received signal is made and, accordingly as the armature of the receiving relay is resting on marking or spacing, mechanical parts will be positioned so that one particular character and no other will be typed.
d. In case any particular transition of the selecting group is displaced in either direction by 50 percent or more of a selection unit, a wrong selection will inevitably be made. Figure 12-17 depicts a character with such a distortion of pulse 2. Since each selection point
—---------------j-------------------•
SELECTION UNITS ______._____A___________
STOP -• STARTI 2 -j»- 3 4 5 STOP -• START •-
' I I POINTS
Figure 12-17. Teletypewriter character “J”; with over 50
percent distortion of pulse 2.
is timed with respect to the beginning of the start pulse, the displacement of the various transitions from their proper position relative to the beginning of the start pulse is of significance, rather than the total lengthening or shortening of any particular unit pulse, as in
568
PARS.
1222-1223
CHAPTER 12. TRANSMISSION YARDSTICKS
manual telegraphy. In the foregoing explanation an ideal receiving device was assumed; actual teletypewriters do not perform the selecting functions instantaneously exactly at the midpoints of the five intervals, consequently the distortion tolerance is generally between plus or minus 35 and plus or minus 40 percent.
e. Telegraph distortion may be conveniently divided into three different components. The first of these is bias, which means that some asymmetrical condition, such as voltage unbalance, improper relay adjustment, or change in received signal strength, has caused all marks to be either too long or too short. The bias of a circuit may be checked by transmitting reversals, that is, a steady stream of unit marks and spaces, or repeated space-bar teletypewriter signals. The latter requires special treatment since the marking and spacing intervals are unequal.
f. The second kind of distortion is called characteristic, for the reason that it depends upon the electrical and mechanical characteristics of the circuit and the particular signal combination which is being transmitted. This form of distortion is caused mainly by typical imperfections in the signal wave-shape impressed upon the receiving relay, occasioned, for example, by the effect of a low-pass filter with comparatively low cut-off in a d-c telegraph circuit.
g. The remaining type of distortion is called fortuitous, this being a random effect due to interference from other communication facilities and from power systems, chatter of relay contacts, etc.
1223. TELEGRAPH TRANSMISSION COEFFICIENTS.
a. Introduction. Various types and lengths of telegraph line sections and extension circuits differ in the amount of signal distortion which they cause. Furthermore, the performance of a given section or other part of a network varies from time to time because of changes in weather conditions, adjustments, etc. To predict the transmission capabilities accurately is difficult, but a system of transmission ratings, called coefficients, has been established which will be useful in planning. In this rating system, each part of a network is assignee} a numerical coefficient in accordance with the impairment of transmission which it produces,
the higher the number the greater the impairment. The coefficients for the parts of a proposed layout are added to obtain the over-all coefficient, which will indicate whether or not the circuit can be expected to operate satisfactorily.
b. Over-all Performance of Circuits.
(1) In a complete telegraph circuit, even one of comparatively simple make-up, the total distortion is made up of contributions from a considerable number of sources. It rarely happens that practically all contributing factors will combine in the most unfavorable manner, that is, so as to cause the maximum distortion which is possible due to direct addition of all increments. To evaluate the transmission quality, measurements can be made from which the rate of occurrence of errors or false characters may be predicted for various types of circuits.
(2) It has been found that, with either teletypewriter or Morse-code reception, signals with total distortion of less than about 35 percent are not likely to cause an error.
(3) Although a high degree of stability is desirable in operation of telegraph circuits, it is not practicable to design them so that they will operate perfectly at all times, particularly with long and complicated layouts. If any over-all connection, as a matter of long-time average does not produce more than one error in 1,500 characters, the service will be considered high-grade for Signal Corps purposes in the theater of operations. A circuit at the border line of this limit might operate with very few errors for a number of days and then have fairly frequent errors over a period of several minutes to an hour. In some cases layouts with a higher percentage of errors will be considered satisfactory. To meet the requirements, the rear-area fixed communications should be designed to provide as good operating performance as practicable to allow for the probable poorer performance of the forward-area facilities. If the occurrence of errors interferes seriously with handling traffic, steps should then be taken to improve transmission if practicable, as, for instance, by readjustment, by direct substitution of other facilities, or by a change in the circuit layout.
c. Prediction of Performance of Networks.
(1) The basic idea in the establishment of coefficients for use in network planning is that increments of distortion from different
569
PARS.
1223-1225 ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
sources generally combine at random, the most probable resultant total value being equal to the square root of the sum of the squares. A convenient approximation in determining whether the distortion limit will be exceeded is to add the squares rather than the first power of the distortions. Accordingly, coefficients are made proportional to the square of a representative value of distortion for the particular section in question. From observations of distortion or from the corresponding coefficient, it is possible to predict with reasonable accuracy the probable rate of occurrence of errors for a single link or for several links in tandem.
(2) As stated above, an average rate of occurrence of one error in 1,500 characters in Signal Corps teletypewriter operation is believed to be satisfactory for usual service requirements. In the system of coefficients (ch. 3), this corresponds to an over-all coefficient of 15. If the requirements are more lenient, a limit of 18 or 20 corresponding to one error in about 300 characters could be used. It will be appreciated that the higher the over-all coefficient, the more frequent will be the occurrence of periods of material duration during which the circuit will not be usable, so that the service will be inferior and more maintenance effort may be required.
(3) In using the coefficients, a layout diagram is first drawn and a coefficient is selected for each part of the transmission circuit. Then a computation is made of the over-all coefficient from each terminal station to every other terminal station, including those at the end of each branch. If any such over-all figure exceeds the established limit, it will then be necessary either to substitute better transmission facilities or divide the path into parts by the insertion of one or more regenerative repeaters. Since such a repeater reforms and retimes the signals, it is then necessary only to compute the over-all coefficient from each terminal to a regenerative repeater and from one regenerative repeater to another to see whether or not the limit is exceeded.
d. Bell System Coefficients. The coefficients which have been established for circuits used in Bell System service are generally lower in value than those given in chapter 3 because these circuits are generally set up to give higher quality transmission. For instance, a carrier telegraph section is assigned a value of 1.5 in a representative case. D-c polar and
polarential line circuits have values ranging from about 2 for the most favorable case up to about 6 for extreme conditions, the average being about 3.5. Local loop circuits are generally in cable and are treated individually to improve the signal wave-shape, and these have coefficients ranging from 0.2 for short loops to about 2 for 35-mile loops. The limiting overall coefficient is set at 10 because the service requirements for commercial use are generally high.
7224. TELEGRAPH TRANSMISSION MEASUREMENT.
a. It is generally practicable to measure the total distortion of teletypewriter signals in the field, and this is valuable as it furnishes a direct indication of the grade of transmission. Determination of the characteristic and fortuitous components of distortion separately is not generally practicable, but in many cases a check is made of the important factor of bias during certain lining-up procedures, and it is advantageous to make such checks in case of transmission difficulties.
b. Bias is a variable factor and generally may be minimized by proper adjustment of relays and operating currents. One method of checking bias is to apply repeated teletypewriter space-bar signals at one end of the circuit and observe the received signals in a local circuit at the other end. These received signals are measured with a bias-measuring circuit arranged so that its meter needle vibrates about zero when receiving unbiased space-bar signals. Another method involves the same kind of test but uses, for the test signals, a series of equal marks and spaces known as telegraph reversals. Reversals will not be retransmitted properly by a regenerative repeater. Space-bar signals will be regenerated, thereby removing the bias. Accordingly when such tests are made through regenerative repeaters the bias will be checked only in that part of the circuit beyond the last regenerative repeater.
7225. MEASUREMENT BY TELETYPEWRITER.
a. The orientation range finder provided on teletypewriters may be used conveniently to give an indication of total distortion. For best results machines should be in good adjustment and care taken in making the observations. The finder and its scale are shown by figure 12-18. The scale is graduated in percent of a
570
PAR.
CHAPTER 12. TRANSMISSION YARDSTICKS 1225
unit dot length and the range finder arm may be moved from 0 to 120 on the scale. Adjustment of this finder causes the selection points (fig. 12-16) to be shifted with respect to the beginning of the start pulse and when the shift is sufficiently great, errors will be made by the teletypewriter. The range over which the finder may be moved without errors being typed is reduced by any distortion of the incoming signals.
>--LOCAL RANGE LIMITS-y
\ LINE . /
REDUCTION IN \ H RANGE y / REDUCTION IN
MARGIN AT \ | | LIMITS ///--MARGIN AT
UPPER END \ *| J'/ LOWER END
OF RANGE ~-X7 / °F RANGE
BO 60 40
X^XXX+X
\
TL 54835
Figure 12-18. Teletypewriter orientation range finder.
b. In determining the range, the range finder is first moved towards one end of the scale until errors appear in the copy and then moved back slowly until no error occurs in one or two lines of page printing. Similarly, the range finder is moved towards the other end of the scale until errors occur and then moved back slowly until there are no errors. The difference between the two scale readings at the points where errors disappear is the orientation range.
c. Representative orientation ranges for different degrees of signal distortion for well-adjusted teletypewriters are as follows:
distortion Orientation range
Very little..................................... 80
Moderate ....................................... 60-70
A ve rage ................................... 50
Large ................................Less than 40
d. Representative orientation ranges with practically perfect signals and a teletypewriter in good condition are 10-90 and 15-95 on the scale. In general, best operating results will b'e obtained when the finder arm of the receiving teletypewriter is set at the middle of the local range. It is often not practicable to
make a determination in the field of this setting and in such cases an arbitrary setting of about 55 is used.
e. Practically perfect signals for orientation tests are supplied by a properly adjusted transmitter-distributor or a signal-distortion test set. Keyboard signals may also be used where better methods are not available. Since keyboards usually have noticeable distortion, a satisfactory local test with these signals is a range of 70 or more.
f. The differences between limits determined by local test and the corresponding limits obtained when receiving signals over a line, give directly the reduction in margins due to signal distortion. These reductions, as illustrated in figure 12-18 are a direct measure of the total signal distortion.
g. Signal bias affects one limit more than the other; marking bias reduces the upper limit, spacing bias raises the lower limit. Characteristic and fortuitous distortions cause reductions in the margin at both limits with miscellaneous signals.
h. Correct teletypewriter motor speed is important in maintaining the operating margins and a check of speed should always be made before measuring ranges. The speed should be checked with a tuning fork of the proper type. A two percent variation from the correct value will result in 12 percent distortion at the end of the fifth pulse. Therefore, the speed should be kept within one percent of the correct value.
i. Tests may be made of the distortion tolerance of teletypewriters (or teletypewriters in combination with line circuits) by applying predistorted signals. Signal distortion test sets are arranged to supply miscellaneous teletypewriter signals having both marking and spacing bias adjustable from zero to about 40 percent or more. Well adjusted teletypewriters should type correctly when the signals from the test are biased by as much as plus or minus 35 percent in a local test circuit10. With line sections between the test set and the teletypewriter, the tolerance should not be less than plus or minus 15 percent for highgrade army service.
10 A circuit including the sending and receiving elements of the teletypewriter and a suitable resistor which, with a normal voltage of 115 volts, will provide a normal operating current of 60 milliamperes. The local test circuit is sometimes included in the teletypewriter.
571
APPENDIX
LIST OF PUBLICATIONS
Field manuals
FM 11-5
FM 11-21
FM 11-22
FM 24-5 FM 24-8
FM 24-10
FM 24-14
FM 24-18 FM 24-20 FM 24-75
FM 55-50
FM 55-55
Title
Technical manuals
Title
T echnical manuals
TM 9-2853
TM 11-200
TM 11-230C
TM 11-232
TM 11-233
TM 11-235
TM 11-239
TM 11-241
TM 11-242
TM 11-244
TM 11-245
TM 11-250
TM 11-272
TM 11-273
TM 11-275
TM 11-277
TM 11-280
Mission, Functions and Signal Communication in General
Signal Operations in the Theater of Operations (when published)
Signal Operations in the Corps and Army
Signal Communication
Combined Teletypewriter (Teleprinter Procedure)
Combined Radiotelegraph (W/T) Procedure)
Teletypewriter Switching and Relay Procedure
Radio Communication
Field Wire Systems
Telephone Switchboard Operating Procedure
Military Railroads and the Military Railway Service
Railway-Operating Battalion
TM 11-281
TM 11-308
TM 11-310
TM 11-311
TM 11-312
TM 11-314
TM 11-333
TM 11-340
TM 11-341
TM 11-351
TM 11-352
TM 11-353
TM 11-354
Title
Preparation of Ordnance Materiel for Deep Water Fording
Radio Sets SCR-AF-283, SCR-AG-183, SCR-AH-183, SCR-AJ-183, SCR-AK-183, SCR-AL-183, SCR-AN-183, SCR-AL-283, and SCR-AN-283
Radio Set SCR-694-C
Radio Set SCR-177-B
Radio Set SCR-188-A
Radio Sets SCR-536-A, SCR-536-B, and SCR-536-C
Radio Set SCR-203
Radio Sets SCR-197-B, SCR-197-C, SCR-197-D, SCR-197-E, and SCR-197-F
Radio Set SCR-300-A
Radio Set SCR-281-D
Radio Set SCR-511-A
Radio Set SCR-288
Radio Sets SCR-210-A, -B, -C, -D, -E, -F, -G, -H, and -J; and SCR-245-A, -B, -C, -D, -E, -F, -G, -H, -J, -K, -L, -M, -N, and -P
Radio Sets SCR-193-A, SCR-193-B, SCR-193-C, SCR-193-D, and
SCR-193-E, -G, -H, -J, -K, -KB, -L,
-M, -P, and -Q
Radio Set SCR-284-A
Radio Set AN/VRC-1
Radio Set SCR-299-A, SCR-299-B, SCR-299-C, and SCR-299-D
TM 11-355 TM 11-355B TM 11-356
TM 11-358
TM 11-359 TM 11-363
TM 11-366
TM 11-368
TM 11-369
TM 11-371
TM 11-374
TM 11-375B
TM 11-377
TM 11-430
TM 11-438
TM 11-441
TM 11-455
TM 11-456
TM 11-457
TM 11-458
TM 11-462
TM 11-471
TM 11-473
TM 11-474
TM 11-475
Radio Sets SCR-399-A and SCR-499-A
Remote Control Unit RM-29-(*)
Schematic Diagrams for Maintenance of Ground Radio Communication Sets
Test Equipment IE-17-E
Remote Control Equipment
RC-47-A, -B, -C, -D, and -G (Control
Unit RM-12-(*) and Control Unit
RM-13-(*) and Associated Equipment)
Antennas and Antenna Systems Telephones EE-8-A and EE-8 Telephone Central Office Set TC-2 Telephone Terminal CF-l-A (Carrier) and
Repeater CF-3-A (Carrier) X-61687
Telegraph Sets TG-5 and TG-5-A
Printers TG-7-A, B, TG-37-B, Chests
CH-50-A and CH-50-B,-Chests
CH-62-A and CH-62-B
Installation and Maintenance of Telegraph
Printer Equipment
Telegraph Printer Sets (Teletypewriter)
EE-97 and EE-98, Teletypewriter Sets
EE-97-A, EE-98-A, and EE-102
Telegraph Terminal CF-2-A (Carrier)
Telegraph Terminal CF-2-B (Carrier) Radio Teletype Terminal Equipment
AN/FGC-1 or AN/FGC-1X
Telegraph Central Office Set TC-3
Line Unit BE-77-A and Line Unit BE-77
Pole Line Construction
Vulcanizing Equipments TE-54-A and TE-55-A
Tactical Open Wire Pole Line Construction
Spiral-Four Cable
Cable Assemblies CC-345 (5 Pair), CC-355-A (10 Pair) and Associated
Equipment
Tape Facsimile Equipment RC-58-B
Facsimile Equipment RC-120, RC-120-A, and RC-120-B and Facsimile Set
AN/TXC-1
Boehme Automatic Keying and Recording
Equipment
Batteries for Signal Communication except those pertaining to Aircraft
Operations Center AN/TTQ-1
Recorder BC-1016
Radio Fundamentals
Wire Telegraphy
Local-Battery Telephone Equipment
Common Battery Telephone Equipment Reference Data
Telephone Central Office Installation
Central Office Maintenance
Substation Installation
Principles of Long Distance Telephone and Telegraph Transmission
656935 O—45- —38
573
LIST OF PUBLICATIONS
Technical manuals
TM 11-487
TM 11-498
TM 11-509
TM 11-600
TM 11-601 TM 11-602 TM 11-605 TM 11-607 TM 11-615 TM 11-617 TM 11-618
TM 11-619
TM 11-620
TM 11-630
TM 11-637
TM 11-755
TM 11-801
TM 11-802
TM 11-803
TM 11-813
TM 11-816
TM 11-820
TM 11-821
TM 11-828
TM 11-829
TM 11-832
TM 11-834
TM 11-835
TM 11-836
TM 11-853
TM 11-895
TM 11-866
TM 11-868
TM 11-872A
TM 11-874
TM 11-884
Title
Electrical Communication Systems Equipment
Fundamentals of Telephone and Manual Telegraphy
Radio Sets SCR-522-A, SCR-522-T2, SCR-542-A, and SCR-542-T2 (when published)
Radio Sets SCR-508-(*), and SCR-528-(*), and SCR-538-(*)
Radio Sets SCR-808-A and SCR-828-A
Radio Set AN/MRC-1
Radio Set SCR-509-A and SCR-510-A
Radio Set AN/VRC-2 (when published)
Radio Set SCR-609-A and SCR-610-A
Radio Set AN/TRC-7
Radio Set AN/TRC-8; Radio Terminal
Set AN/TRC-11; Radio Relay Set
AN/TRC-12 (when published)
Radio Set SCR-619 (when published)
Radio Set SCR-608-A and SCR-628-A
Preliminary Instructions for Radio Set SCR-506-A
Radio Set AN/VRC-3
Grounds, Grounding Procedure, and Protective Devices for Wire Communication Equipment
Power Amplifier BC-340-G and Water
Cooling Unit RU-2-A
Radio Transmitters Wilcox Types 96-200A and 96-200B
Radio Transmitters Wilcox Types 96C and 96C3; Rectifier Unit, Wilcox Type 36A;
Modulator Unit, Wilcox Type 50A
Radio Transmitter BC-610-E and
Associated Equipment
Radio Transmitting Equipment RC-263
Radio Transmitter T-4/FRC, Radio
Transmitter T-5/FRC, Power Rectifier PP-l/FRC, Modulator MD-l/FRC, Switch Panel SA-2/FRC, Oscillator O-2/FRC, Amplifier AM-2/FRC
Radio Transmitter (Press Wireless Type PW-15) (when published)
Radio Transmitter BC-365-F and Remote Control Unit RM-10-F
Radio Set AN/VRC-4 and Transmitter Type TS-25-3 and Receiver Types RS-25-3 and RS-25-4
Radio Transmitting Equipment, Single Sideband (Western Electric Co. Type D-156000) (when published)
Radio Transmitter PW-981-A, 2.5 kw
Radiotelegraph Transmitter (Press Wireless
Types PW-40-B and PW-40-BA) (when published)
Radio Transmitter
BC-339-A, -B, -C, -D, -E, -F, -G, -H,
-J, -K, and -L (when published)
Radio Receiver (Wilcox Types CW and F3) and Receiver Bay (Wilcox Type 113A) (when published)
Radio Set SCR-593-A and SCR-593-C
Radio Receivers BC-779-B, BC-794-B, and BC-1004-C and Power Supply Units RA-74-C, RA-84-B, and RA-94-A
Radio Receiver 128-AY
Diversity Receiving Equipment
AN/FRR-3A
Radio Receiver AN/GRR-2
Radio Receiving Equipment, Single Sideband (Western Electric Co. Type D-99945) (when published)
TM 11-903
TM 11-914
TM 11-914C
TM 11-954
TM 11-955
TM 11-957
TM 11-967
TM 11-1055
TM 11-2002
TM 11-2003
TM 11-2004
TM 11-2005
TM 11-2007
TM 11-2008
Technical manuals
TM 11-900
TM 11-2001
TM 11-2009
TM 11-2020
TM 11-2024
TM 11-2022
TM 11-2023
TM 11-2026
TM 11-2027
TM 11-2028
TM 11-2029
TM 11-2031
TM 11-2032
TM 11-2034
TM 11-2035
TM 11-2037
TM 11-2038
TM 11-2043
TM 11-2053
TM 11-2054
TM 11-2059
TM 11-2200
TM 11-2201
TM 11-2203
TM 11-2204
TM 11-2205
TM 11-2206
Title
Power Units PE-75-C through PE-75-T
Power Unit PE-77-(*)
Power Unit PE-201-A
Power Unit PE-201-C
Rectifier RA-43-B
Rectifier RA-37
Rectifier RA-87
Power Transfer Panel CN-22/F
6 kw R. F. Amplifier PA-1A, Rectifier
RA-1A, and Antenna Tuning Unit Al-1 A
Complete 100-mile Spiral-Four Carrier System
Substitute Telephone Central Office Equipment
Carrier Hybrid CF-7
Repeater Set TC-18 (Terminal)
Repeater Set TC-19 (Intermediate)
Telephone Repeater TP-14
Converter Set TC-33 (Carrier, 2-Wire— 4-Wire) and Repeater Set TC-37 (Carrier, 2-Wire)
Telegraph Terminal CF-6 (Carrier)
Line T erminating and Simplex Panel (Packaged Equipment)
Voice-Frequency Ringer (Packaged Equipment) (when published)
Application of Packaged Equipment to Open-Wire Lines
Installation Instructions for Type C CarrierTelephone (Packaged Equipment) (Moisture-Resistant)
Type C Carrier Telephone (Packaged
Equipment) (Moisture-Resistant) (when published)
Installation Instructions for Voice-Frequency Telephone Repeaters (Packaged Equipment) (Moisture Resistant)
Voice-Frequency Telephone Repeaters (Packaged Equipment) (Moisture-Resistant) (when published)
Voice-Frequency Carrier Telegraph (Packaged Equipment) (when published)
Line Terminating and Composite Panel and Type C Transfer Panel
D-C Regenerative Telegraph Repeater (Packaged Equipment)
D-C Telegraph Repeater (Packaged Equipment)
Telegraph Switchboard SB-6/GG
Installation, Operation, and Maintenance of Open-Wire Offices (Packaged Equipment)
Installation Instructions for Type H Carrier Telephone (Packaged Equipment)
Telephone TP-3
Automatic Telegraph Service Monitoring Sets
Multichannel Voice-Frequency Carrier Telegraph Terminal Equipment for Single Sideband Radio Telephone System (when published)
Telephone TP-9
Bias Meter I-97-A
Reperforator Teletypewriter Sets TC-16 and TC-17
Teletypewriter Set AN/TGC-1
Dual Diversity Receiving Equipment
(Wilcox Type CW3-D)
Exciter Unit O-5/FR
Telegraph Terminal Set AN/TCC-1, Telegraph Terminal TH-l/TCC-1, and Filter F-2/GG
574
LIST OF PUBLICATIONS
Technical manuals
Title
Technical
manuals
Title
TM 11-2207
TM 11-2208 TM 11-2210
TM 11-2211
TM 11-2214
TM 11-2215
TM 11-2216
TM 11-2217 I
TM 11-2220
TM 11-2250
TM 11-2252
TM 11-2253
TM 11-2256
TM 11-2257
TM 11-2510
TM 11-2513
TM 11-2515
TM 11-2601
TM 11-2603
TM 11-2611
TM 11-2614
TM 11-2615
TM 11-2617
Radio Teletype Code Room and Signal Center, Installation Procedure and Maintenance Guide (when published)
Test Set TS-2/TG
132A2 Teletypewriter Subscriber Set and Associated Equipment
133Al Teletypewriter Table and Associated Printer Apparatus
133A2 Teletypewriter Subscriber Set and Associated Equipment
Teletypewriters TT-5/FG and TT-6/FG
Teletypewriters TT-7/FG and TT-8/FG
Distortion Test Set (4TDXD1/DTS)
(when published)
Reperforator Transmitters TG-26-A and TG-27-A
Reel Equipment CE-11
Converter CV-2/TX
Open-Wire Construction for Fixed Plant Application
Limiter Amplifier Type 3BLH and Speaker Type 6AL
Power Units, Fahnstecl Nos. 1161 and 1152
Master Power Meter Panel
Test Set I-193-A
Diversity Receiving Combining Equipment
Radio Set AN /TRC-1, Radio Terminal Set
AN/TRC-3, Radio Relay Set
AN /TRC-4, and Amplifier Equipment
AN/TRA-1
Radio Set AN/TRC-2
Antenna Kit for Rhombic Receiving Antenna
Assembling and Erecting 30-Foot Gin-Pole-Type Trylon Ladder Towers
Foundation Steel Pedestal Base for 73'7" Guyed Radio Tower
Antenna Kit for Rhombic Transmitting Antenna
TM 11-2621
TM 11-2629
TM 11-2632
TM 11-2656
TM 11-2667
TM 11-2671
Technical bulletins
TB SIG 13
TB SIG 28
TB SIG 37
TB SIG 52
TB SIG 61
TB SIG 66
TB SIG 67
TB SIG 72
TB SIG 73
TB SIG 78
TB SIG 101
TB SIG 121
Remote Control Equipment AN/TRA-2
Antenna Kit for Double-Doublet Receiving
Antenna
Remote Control Equipment RC-261
Antenna Kit for Doublet Transmitting
Antenna
Remote Control Equipment RC-289
Radio Transmitter (Wilcox Electric Types 96A, 96C, and 96C3) (when published)
T itle
Moistureproofing and Fungiproofing Signal Corps Equipment
Instructions for Treatment of Teletypewriter Paper Rolls
Grounding Requirements and Procedure Applicable to Wire Communication and Associated Electrical Apparatus
Connection and Line-Up Procedure for Switchboards BD-100 Interconnected with Other Teletypewriter Equipment By Wire Lines and By Carrier Telegraph Equipment
Uses of Adapter Plug U-4/GT
Winter Maintenance of Signal Equipment
Laying Field Cable Under Water
Tropical Maintenance of Ground Signal Equipment
Open-Wire Transpositions
Instructions for Initial Line-Up and Check of Levels in Standard Multichannel Radio Communication System
Long-Range Tactical Wire W-143
Instructions for Tying and Use of Weave Tie for Field Wires and Cables
575
INDEX
jAk Par.
or fig.
A-0, A-l, A-2, A-3 emission.............. 603b
A-27 Antenna (Phantom) (TM 11-630). . . 677b
A-28 Antenna (Phantom) (TM 11-242). . . 677b
A-29 Antenna (Phantom)................... 677b
A-62 Antenna (Phantom) (TM 11-600). . . 677b (photo) 6-148
A-82 Antenna (Artificial) (TM 11-311).... 677b
A-83 Antenna (Phantom) (TM 11-620). . . 677b (photo) 6-149
Absorption of radio signals.......... 643c
648
Absorption peak (crosstalk)...... 547a(2)
Adapter Plug U-4/GT.................. 218
Airborne radio sets...........(table) 6-170
Aircraft Accessories Corp, radio equipment.....................(table) 6-173
Aircraft, transmission to............ 601c
617
Aircraft Warning Systems Operations Center, AN/TTQ-1............... 243
(photo) 2-41 691g
Air gap protectors................... 1003a
1010b
Airways Section, ACS, radio sets. . . (table) 6-173 Allocations (See Frequency allocations of carrier systems).....................
Alternate trunk routes............... 1115g
AM type wire, cross-connecting..... 1151d
A-m and f-m.......................... 603c
605
Amplitude modulation, use of......... 603c
605
AN-56-A Antenna Mast................. 627a
(photo) 6-39
AN/ARC-1 Radio Set............(table) 6-174
AN/ARC-3 Radio Set............(table) 6-170
AN/ARC-4 and -4X Radio Transmitting
& Receiving Equipment.....(table) 6-174
AN/ARC-5 Radio Set............(table) 6-174
AN/ARC-9 Radio Set............(table) 6-170
AN/ARR-11 Radio Receiving Set.. (table) 6-170
AN/ART-13 Radio Set...........(table) 6-170
AN/CRC-2 Radio Set............(table) 6-171
AN/CRC-3 Radio Set............(table) 6-169
AN/FCM-1 Test Set (X-61819T)......... 508d
AN/FCM-2 Test Set (X-61821L)......... 508d
AN/FCM-3 Test Set (X-66031B)..... 349a(2)
AN /FCM-4 Test Set (mobile test unit X-63699A)...................... 242
AN/FCM-5 Test Set (test and control board X-66034A)................ 242
AN/FCM-6 Test Set (X-61822C)......... 348a(2)
AN/FGC-1 Radio Teletype Terminal
Equipment (TM 11-356)............ 326
341a (table) 6-172 (table) 6-173 (photo) 3-66
Page 220 332 332 332
332 332 332
332 333
410 281
296 179
21 360
367 219 241
37
38
351 451
455 366
478 524 220 222 220
222 260
260 372 361
372 372
361 361
361 364
358 134 134
109
36
36 108
77 95
366 369
96
Par. or fig.
AN/FRR-3A Diversity Receiving Equipment (TM-U-872A).............(table) 6-172
(table) 6-173
AN/GRR-2 Radio Set (TM 11-874. (table) 6-173 AN/GRR-3 Radio Set...........(table) 6-173
AN/MRC-1 Radio Set (TM 11-602)...... 330d
(table) 6-169
AN/MRC-2 Radio Set.................. 347c
(table) 6-169
AN/TCC-2 Carrier System (100 mile spiral-four) (TM 11-2001)............. 522
AN/TGC-1 Teletypewriter Set (TM 11-2203)................................ 325h
(photo) 3-36
AN/TRA-1 Amplifier Equipment (TM 11-2601)....................... (photo) 6-169
AN/TRA-2 Remote Control Equipment (TM 11-2621)......................... 691b
(photo) 6-163
AN/TRA-7 Radio Teletype Equipment. . 437c(6) AN/TRC-1 Radio Set (TM 11-2601).... 342a (table) 6-169
AN/TRC-2 Radio Set (TM 11-2603).................(table) 6-169
AN/TRC-3 Radio Terminal Set (TM 11-2601)............................... 621
622b (drawing) 6-34 (photo) 6-35 (photo) 6-36 (table) 6-169
AN/TRC-3 and -4, mobile installation.. . 1155e (drawing) 11-72
AN/TRC-4 Radio Relay Set (TM 11-2601)............................... 621
622b (drawing) 6-34 (photo) 6-35 (photo) 6-36 (table) 6-169
AN/TRC-7 Radio Set (TM 11-617)..................(table) 6-169
AN/TRC-8 Radio Set (TM 11-618) (table) 6-169
AN/TRC-11 Radio Terminal Set (TM 11-618).............................. 622c
(table) 6-169
AN/TRC-12 Radio Relay Set (TM 11-618)................................. 622c
(table) 6-169
AN/TRC-13 Radio Set..........(table) 6-173
AN/TTC-1 Telephone Central Office Set. 221b AN/TTQ-1 Operations Center, AWS (TM 11-438)........................... 243
(photo) 2-41 691g
AN/TXC-1 Facsimile Set (TM 11-375B) 401c AN/VRC-1 Radio Set (TM 11-277) (table) 6-169
AN/VRC-2 Radio Set (TM 11-607, when published)...................(table) 6-173
Page
366 369
569
369
82 358
106 359
143
76
76
359
349
350
107
98 359
359
251
254
254
255
255
359 536
537
251
254
254
255
255 359
359
359
359
359
360
360
369
23
37
38
351
121
360
369
577
INDEX
AN-Ant
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig. Page
AN/VRC-3 Radio Set (TM 11-637) (table) 6-169 360
AN/VRC-4 Radio Set (TM 11-829) (table) 6-173 369
AN/VRC-5 Radio Set...............(table) 6-169 360
ANB-M-C1 Microphone............ 217b (5) 15
Antennas: Dimensions.......................... 637 274
(drawing) 6-65 274
661d 310
(table) 6-133 319
Effective height of.......... 616b(2) 237
1215a 561
Efficiency.................... 604b(3) 222
(*See also under individual antenna 664 316
types)
Gain............................. 624b 259
(See also under individual antenna 1215b 561
types)
Resonating...................... 1217h 563
Siting............................ 618 246
(drawing) 6-27 to 247
6-29
Tuning................................ 1217h 563
Antennas, high frequency................ 657 308
Balloon-supported half-rhombic (inverted vee)....................... 668 317
Beverage antenna (See Wave antenna)
Broadband antennas: Beverage....................... 665 316
673d 324
Double doublet................. 671 321
(drawing) 6-135 320
Doublet receiving antenna, .(drawing) 675c 327
(drawing) 6-144 328
Horizontal rhombic............. 670 318
(drawing) 6-132 318
Wave antenna................... 665 316
673d 324
Center-fed half-wave antenna..... 662 311
661 310
Coaxial dipole................... 628 262
(drawing) 6-41 261
Crowfoot antenna................. 673c 323r
(drawing) 6-138 323
Delta-matched doublet transmitting antenna................................ 672 321
(drawing) 6-136 321
Dimensions............................ 661d 310
(table) 6-133 319
Directional antennas............. 623a 258
657f 308
Frequencies below 800 kc....... 673d 324
Full-wave horizontal wire...... 667 317
Half-rhombic, balloon-supported (inverted vee).................... 668 318
Horizontal rhombic............. 670 318
(drawing) 6-132 318
On-ground antenna.............. 666 318
Sloping—wire antenna........... 660 310
(drawing) 6-120 310
Wave antenna (Beverage)........ 665 316
673d 324
Double doublet receiving antenna. 671 321
(drawing) 6-135 320
Doublet antenna, folded.......... 662d 312
Efficiency, various h-f antennas. 664 316
(table) 6-130 316
End-fed half-wave antenna, improvised. 663 313
Fixed plant antennas............. 669 317
675 325
Par. or fig.
Antennas, high frequency (contd)
Fixed plant antennas (contd)
Delta-matched doublet transmitting antenna......................... 672
(drawing) 6-136
Double doublet................. 671
Frequency below 800 kc......... 673
Horizontal rhombic..............670
Parks, antenna................. 675
Space-diversity antenna systems.... 674
Transmitting doublet (delta-matched) 672
(drawing) 6-136
Flat-top (Marconi) (inverted L) (T antenna)...................... 673b
(drawing) 6-137
Frequencies below 800 kc: Crowfoot.......................... 673c
(drawing) 6-138
Flat-top (Marconi) (T antenna)...... 673b
(drawing) 6-137
Inverted L.......................... 673b
Wave antenna (Beverage)............ 673d
Full-wave horizontal wire............. 667
Grounding of.......................... 657d, e
1010
Half-rhombic balloon-supported (inverted vee)................... 668
Half-wave horizontal antennas......... 651
652 661 to 663 (drawings) 6-87 to 6-89
Page
321
321
321
323
318
325
325
321
321
323
322
323
323
323
322
323
324
317
308
455
317
299
300
310
289
BC-191-( ) circuit revision for halfwave doublet (drawing) 6-123
BC-610-B circuit revision for halfwave doublet................(drawing) 6-124
Center-fed, improvised.............. 661
662
(drawing) 6-123
(drawing) 6-124
End-fed, improvised................. 663
(drawing) 6-127
Folded doublet...................... 662d
(drawing) 6-125
(drawing) 6-126
Height of........................... 661b, c
663a(3)
Length of..................... 661d
Length versus frequency....(table) 6-121
SCR-299, SCR-399, SCR-499 use of. 661e
662a 663c
(drawing) 6-122
Standard tactical half-wave h-f
antenna........................ 661e
Transmitter loading................. 663b
(table) 6-129
Horizontal rhombic.................... 670
(drawing) 6-132
Dimensions..................(table) 6-133
Dissipation line.................... 670b(2)
Receivers multipled on one antenna . . 670c (2) 675c
Receiving........................... 670c
(drawing) 6-134
Site, choice of..................... 670d
Tilt, angle of...............(table) 6-133
Transmitting........................ 670b
Horizontal wire, full wave............ 667
Inverted L............................ 659
673b
(drawing) 6-119
Inverted vee.......................... 668
311
312
310
311
311
312
313
313
312
313
313
310
315
310
311
311
311
315
311
311
315
314
318
318
319
319
320
327
319
319
320
319
318
317
309
323
310
317
578
INDEX
Ant
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par.
or fig. Page
Antennas, high frequency (contd) Marconi................................. 673b 323
(drawing) 6-137 322
On-ground antenna..................... 666 317
Parks, antenna........................ 675 325
BC-610s.....................(drawing) 6-143 327
Receiving........................... 675c 327
Multicoupler model S-8853-1...... 675c(5) 325
Multiplying receivers on one antenna.................;......... 670c (2) 320
675c 327
Separation between r-f transmission lines............................... 675b(3) 326
Separation between transmitting and receiving antennas.................. 675a 325
679 336
Separation between transmitting antennas....................... 675b 326
Transmitting.................... 675b 326
(drawing) 6-142 327
Phantom antennas (dummy) (artificial). 677 332
Polarization diversity............ 674b 325
(drawing) 6-140 325
Signal centers, antennas at......... .. 675 325
Sloping wire antenna............... 660 310
663 313
(drawing) 6-120 310
(drawing) 6-128 314
(table) 6-129 314
(table) 6-130 316
Space-diversity antenna systems....... 674 325
T antenna............................. 673b 323
Tactical antennas..................... 657 to 308
668
Balloon-supported half-wave rhombic. 668 317
Center-fed half-wave antenna........661 310
662 311
(drawing) 6-123 311
(drawing) 6-124 312
Efficiency of....................... 664 316
End-fed half-wave antenna........... 661 310
663 313
Full-wave horizontal wire........... 667 317
Half-wave horizontal antenna........ 651 299
652 300
661 to 310
663
Inverted L.......................... 659 309
Inverted vee........................ 668 317
On-ground antenna. ................. 666 317
Sloping wire........................ 660 310
663 313
Wave antenna........................ 665 316
Whip antenna........................ 658 309
Wave antenna (Beverage)............... 655 306
673d 324
Wave tilt........................... 665c 316
673d 324
Whip antenna.......................... 640c 309
650 277
652 298
658 300
(drawing) 6-117 309
Antennas, very high frequency:
Anti-interference antenna, improvised.. 636 273
(drawing) 6-64 274
Arrays......................... 623a 258
632 266
Broadband antennas: Full-rhombic................... 634 269
Ground-plane, AS-110( )/TRC-7. . . 630c 264
Vertical half-rhombic........ 633 267
Dimensional data,.............. 637 274
(drawing) 6-65 274
Par.
or fig. Page
Antennas, very high frequency: (contd) Directional............................. 623a ‘ 258
632 to 266 636
Advantages.......................... 620a (4) 250
624 258
Anti-interference antenna, improvised 636 273
Arrays.............................. 623a 258
632 266
Front-to-back ratio.....•........... 632a, c 266
635a 273
Full-rhombic........................ 634 269
Gains............................... 624b, c(l) 259
632 to 266
635
Half-wave dipole with corner reflector. 635 273
Signal-to-interference ratio, effect on. 624c (1) 259
Three-element directional array..... 632 266
Unbalance, r-f transmission line.... 624c (2) 259
Vertical half-rhombic (inverted vee). . 633 267
Director (part of antenna array)..... 632a 266
Flexible dipole (limp antenna)....... 631 264
(drawing) 6-48 264
6-51 Full-rhombic........................ 634 269
(drawing) 6-58 270
(drawing) 6-59 270
Construction details................ 634b 269
(drawing) 6-58 270
(drawing) 6-59 270
Dimensions.......................... 634c 271
637 274
Directional patterns......(drawing) 6-62 272
Vertical and horizontal compared.... 634d 272
Ground-plane antennas.............. 630 263
AS-110/TRC-7...................... 630c 264
(drawing) 6-47 264
RC-291 Antenna Equipment.......... 630a 263
(photo) 6-44 263
RC-292 Antenna Equipment.......... 630b 264
(photo) 6-46 263
RC-296 Antenna Equipment.......... 630b 264
TM-217 (coupling unit)............ 630b 264
(photo) 6-45 263
Half-wave dipole...................... 627 260
(drawing) 6-38 260
AN-56-A Antenna Mast.............. 627a 260
(photo) 6-39 260
Coaxial........................... 628 262
(drawing) 6-41 261
Dimensions........................ 637 274
Impedance......................... 1214b 560
Improvised........................ 627b 261
(drawing) 6-40 261
(drawing) 6-68 276
RC-81 Antenna Equipment........... 627a 260
(drawing) 6-38 260
(photo) 6-39 260
Half-wave dipole with corner reflector. . 635 273
(photo) 6-63 273
Inverted vee (See Vertical half-rhombic antenna)
Limp antenna (See Flexible dipole)
Mutual interference reduction......619c(l) 249
620a(3)(4) 250
623c 258
624c (2) 259
632c 266
633h 269
636a 273
678 to 335
686
579
INDEX
Ant-BD
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig.
Antennas, very high frequency: (contd) Nondirectional antennas............. 623
626 to 631
Polarization........................ 619
1214a
Radiator (part of antenna array).... 632a
Reflector (part of antenna array)... 632a
R-f transmission lines (See R-f transmission lines under R)
Rhombic............................. 633
634
Siting.............................. 618
633e 634b (4) 634c(4)
Tactical. .......................... 623 to
636
Three-element directional array..... 632
AS-19A/TRC-1 Antenna System. ... 632a (drawing) 6-52 (photo) 6-53
AS-20/TRC-1 Antenna............... 632a
AS-99/TRC-1....................... 632d
Interference between radio circuits... 632c
Vertical coaxial antenna............ 628
Antenna kit P-8212 (Galvin Mfg. Co.) 628a (drawing) 6-42
Antenna type 1509 (Fred M. Link Co.) 628a Skirt............................. 628a
Vertical half-rhombic............... 633
Coupling unit.............(drawing) 6-57
Dimensions........................ 633d
Page
258
260
249
560
266
266
637
(table) 6-55
Directional pattern......... 633f
(drawing) 6-56
Mutual interference......... 633h
RC-63 Antenna Equipment..... 633a
(drawing) 6-54
Transmission gains.........(table) 6-55
Vertical “J”....................... 629
(drawing) 6-43
Whip............................. 626
(drawing) 6-37
Anti-interference antenna, improvised.... 636
Antisidetone coil.................... 205d
Antisidetone telephone............... 1219a
AR-10A (Harvey Wells), U. S. Navy radio equipment................(table) 6-174
Array, antenna....................... 623a
632
Artificial antennas (Phantom).........677
AS-19A/TRC-1 Antenna System........... 632a
(drawing) 6-52 (photo) 6-53
AS-20/TRC-1 Antenna................... 632a
AS-51/MRQ-2 Antenna Assembly (TM 11-2610)....................... 668
AS-99/TRC-1.......................... 632d
AS-HO/TRC-7 Antenna Assembly.......... 630c
(drawing) 6-47
Assault wire, W-130, WD-3/TT
(See W-130 Wire)
Assignment records, telephone switchboard 1149e
ATB/ARB radio set, U. S. Navy.. (table) 6-174
ATC (AN/ART-13) radio transmitting
267
269
246
268
271
272
258
266
266
266
266
266
267
266
262
262
262
272
262
267
269
268
274
268
268
268
269
267
267
268
263
262
260
259
273
10
565
371
258
266
332
266
266
266
266
317
267
264
264
equipment, U. S. Navy..........(table) 6-174
Attenuation equalizer.................. 1206d
Attenuation of r-f lines...............638
676d
Attenuation of wire lines.............. 536
Cable, lead-covered...........(table) 5-39
(table) 5-40
517
373
373
556
275
329
160
165
167
Par. or fig. Page
Attenuation of wire lines (contd) Open wire lines..................(table) 5-38 164
Phantom circuits....................... 536c 160
Rubber-covered wires and cables. (table) 5-39 166
Auroral disturbances..................... 640b 277
641d(3) 278
Automatic International Morse code....... 303a, c 46
Automatic keying & recording (Boehme).. 330 81
Automatic switching (See Dial).
Automatic trunks......................... 214d 18
234 32
235 33
AVR-7H (RCA) radio receiver, U. S. Navy.............................(table) 6-174 373
AVT-12B (RCA) radio transmitter, U. S. Navy.............................(table) 6-174 373
AVT-23 (RCA) radio transmitter, U. S. Navy.............................(table) 6-174 373
AWS, information and operations centers. 243 37
(photo) 2-41 38
B
Balanced 2-wire carrier system..... 520e 141
523 145
Balancing capacitors................ 568 209
Balancing network Antisidetone telephone................ 1219a 565
Repeaters........................... 1218f 565
Balloon-supported half-rhombic antenna. . 668 317
Band width of filter, telegraph........ 309c 58
Bare wire physical data..........(table) 9-19 439
Basic radio propagation conditions.....64Id 278
643 281
(TM 11-400 andTBll-400-( ) series). 643d 281
Batteries:
Dry, aging, temperature, humidity, regulation............................ . 703 383
Lead storage, life, regulation......... 704 384
Battery supply circuits, telephone....... 227 29
Baud, telegraph.......................... 303a 46
“B” Board, telephone switchboard.........821b 410
BC-315 Radio Transmitter.........(table) 6-173 366
BC-325-1 ) Radio Transmitter.... (table) 6-173 366
BC-339-( ) Radio Transmitter
(TM 11-836)....................(table) 6-172 365
(table) 6-173 366
BC-340 Radio Amplifier (TM 11-801) (table) 6-173 366
BC-365-( ) Radio Transmitter (TM 11-828)......................(table) 6-172 365
(table) 6-173 366
BC-401-( ) Radio Transmitter.... (table) 6-173 366
BC-447-( ) Radio Transmitter
(TM 11-827)....................(table) 6-172 365
BC-460-( ) Radio Transmitter (TM 11-812)......................(table) 6-173 367
BC-610 Radio Transmitter (TM 11-813) (table) 6-173 367
Antenna park for several sets. (drawing) 6-143 327
Circuit for half-wave doublet antenna......................(drawing) 6-124 312
BC-642 Radio Transmitter.........(table) 6-173 367
BC-779-( ) Radio Receiver
(TM 11-866)....................(table) 6-172 366
BC-794-( ) Radio Receiver (TM 11-866)......................(table) 6-172 366
BC-939-A Antenna Tuning Unit........ 658 309
(photo) 6-118 309
BC-1100 Radio Transmitter (TM 11-816) (table) 6-173 367
BD-72 Switchboard (TM 11-330)....... 219 22
BD-89 Switchboard (TM 11-340)...... 221b 23
580
INDEX
BD-Cap
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par.
or fig. Page
BD-91 Switchboard (TM 11-336)....... 221b 23
BD-95 Switchboard (TM 11-2052)...... 220 22
BD-96 Switchboard (TM 11-332). (photo) 2-26 23
BD-100 Switchboard (teletypewriter) (TM 11-358)............................ 337 91
338 92
1123b 486
(photo) 3-59 91
Position requirements.......... 1129a 493
(table) 11-27 493
BD-110 Switchboard (TM 11-338).... 223b 25
BE-54-A Switchbox................. 211b 13
BE-77, -A and -B, Line Units, telegraph (TM 11-359)....................... 327b 78
(photo) 3-39 78
Beverage antenna (wave antenna)... 665 316
673d 324
Bias, telegraph.................. 1222e 569
1224 570
Blackouts, radio................ 604b(2) 221
640b 277
641d(3) 278
Boehme, automatic telegraph....... 330 81
Boehme, mobile (AN/MRC-1)........(table) 6-169 358
330d 82
Book messages.................... 1122g 484
BP or BR drop wire............. 1149b (2) 515
Bridged multiple switchboard...... 223c 27
Bridging losses................... 537 160
(table) 5-41 168
British Army open wire line: Multi-airline (MAL)............... 505d 133
559b 195
913 440
(drawing) 9-20 440
Tandem operation with American.. 560 197
Transpositions.................. 559 195
British radio sets...............(table) 6-175 375
British telegraph apparatus......(table) 3-83 114
Carrier telephone terminal (1 + 4)... 352 112
Marklll......................... 346c 103
347d 107
Teleprinter 7B (WD)............. 350e 111
Broadband h-f antennas (See Antennas, h-f, broadband).
Broadband v-h-f antennas (See Antennas, v-h-f, broadband).
Bulletins, route........................ 1107f 464
(drawing) 11-3 464
1123d 487
Bunnell 6-kw radio amplifying equipment (TM 11-1055).............‘........(table) 6-172 365
Busiest hour traffic.................... 1112 470
1114 474
1115 478
C carrier (See Carrier telephone systems) C-4.1 Coil, loading............... 545e(2)
C-114 Coil, loading.................. 512c
(table) 9-14
C-161 Coil, repeating.................513a
Cable locator........................ 919d
Cable, r-f............................ 676
(drawing) 5-146
(table) 6-147
Cable, rubber-covered (See Rubber-covered wires and cables).
178
136
435
137
446
329
330
331
Par. or fig.
Cables, lead-covered:
Aerial and underground construction. .. 915
Attenuation......................(table) 5-39
(table) 5-40
Capacitance............................. 506
(table) 5-39
(table) 5-40
Capacitance unbalance................... 568
570a
Circuit lengths...................... 542a(3)
Congestion and relief................... 1136
Electrical characteristics.......(table) 5-39
Engineering, local plant (See Local plant engineering)
Entrance and intermediate (See Entrance and intermediate cables under E)
Page
441
165
167
133
165
167
209
213
498
165
Failures............................. 1162f
Fills............................... 1132a
1136a
4-wire operation...................... 566
Grounding............................. 1011
Identification of pairs............... 565e
567f
Impedance.....................(table) 5-39
Incidental cables (See Entrance and in-
termediate cables under E) Large cables......................... 542b
Loading (See also Loaded cable under L) 512 (table) 5-40
Loading coils........................ 915d
Loading pots, American, British, and
German........................... 918a
Loading system data, American civil system........................(table) 5-40
Locating buried cable.................919d
Multipling..................(drawing) 11-32
Nonquadded (paired).................. 506b
(table) 5-40 Open wire line inserts (See Entrance
and intermediate cables under E) Placement data (aerial).......(table) 9-22
Protection........................... 1008
1009
Quadded.............................. 506b
(table) 5-40
Records.............................. 1132
(drawing) 11-31 (table) 11-47 Rehabilitation (See Rehabilitation
543
496
498
208
455
207
209
165
163
136
167
442
445
167 446
498
133
167
443
454
454
133
167
496
497
518
under R) Reinforcement.......................... 1136b
Repair of.............................. 919
Repeater spacings.................. 542a(l)
543b
Replacement............................ 1136b
Resistance......................(table) 5-39
Segregation for 4-wire operation....... 567
(drawing) 5-85
Spiral-four.................... 506b
Splicing........................ 542
565b
Submarine....................... 507
Talking ranges..................(table) 5-44
Terminals...................... 565c
Size and location........... 1134
Tip cable...................... 506c
Transfers...................... 1136b
Transmission data...............(table) 5-39
2-wire operation................ 570
Underground and aerial construction. .. 915
Cage, antenna...................(drawing) 6-144
Cage, radio transmission line............ 676b (3)
Call order ticket...................... 1108g
Capture effect in f-m transmission....... 605b
498 445 162 163 498
166 208 209 133
162 206 134
171 207 496 134 498
166 213 441 328 329
466 223
581
INDEX
Cap-Cen
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig.
Captured plant (See Rehabilitation)
Carrier hybrid system (CF-7) (See Carrier telephone systems)
Carrier shift (frequency shift)....... 308a(5)
Carrier systems, general.................520
Carrier telegraph Filter F-2/GG.......... 333g
Carrier telegraph systems (voicefrequency) :
British Army telegraph equipment (table) 3-83 C carrier telephone system, carrier telegraph on............................... 306c
Carrier telegraph equipment............ 332
333g 341
Channel frequency spacing.............. 306a(l)
Coefficients, carrier telegraph line sections................................. 317 to
319 (table) 3-20 1223c,d
Crosstalk coupling................. 306a(2''
Extension circuits..................... 315
(table) 3-19 305f
Frequency band width, carrier......’.... 304b
306a(l,
H carrier telephone system, carrier telegraph on.......................... 306c
Line section lengths................... 314
Multichannel radio teletypewriter arrangements for tactical use........ 342
Multichannel v-f carrier telegraph system on single-sideband radio telephone system...................... 341c
Multichannel v-f carrier wire telegraph. 306
Packaged carrier telephone, carrier telegraph on.......................... 306c
526d
Packaged equipment (See Packaged equipment under P)
Repeater spacings, carrier telegraph... . 314
Specific telegraph level............... 306a(3)
Speech-plus-duplex system (S+DX). . . 307
Speech-plus-simplex system (S+SX) (British).......................... 307
Spiral-four cable, carrier telegraph on... 306b
Voice-frequency band used.............. 304c
Carrier telephone systems................ 520
Balanced 2-wire system (CF-7).......... 520e
523
C carrier system...................... 528
Circuit lengths and repeater spacings (table) 5-48
Carrier hybrid system (CF-7).......... 520e
Page
56
141
86
114
53
83
86
95
52
64
65
487
52
63
63
52
49
52
53
62
98
98
52
53
148
523
Circuit lengths and repeater spacings. 543c (table) 5-46
Entrance and intermediate cable length limits........................ 545c
Frequency range...............(table) 5-14
Circuit lengths..............■....... 543
Dropped circuits on carrier pairs.... 532
Equipment installation............... 1151
Equivalent 4-wire system (CF-4)........ 520f
521 525
Circuit lengths and repeater spacings. ........................(table) 5-48
Fixed plant carrier systems................. 526
Limits for length of incidental cables. 545e
II carrier system...................(photo) 5-27
62
53
54
111
54
53
49
141
141
145
150
174
141
145
163
172
174
142
163
154
522
142
142
147
174
148
177
149
Par. or fig.
Carrier telephone systems (contd)
H carrier system (contd)
Circuit lengths and repeater spacings (table) 5-48
Open wire converter system (CF-4).... 520f 525 Circuit lengths and repeater spacings ...........................(table) 5-48
Limits for length of incidental cables. 545d
(table) 5-48
Packaged equipment (See Packaged equipment under P)
Pair-per-system operation of CF-l-A... 524
543d
(table) 5-47
Page
174
142
147
174
176
174
Physical 4-wire systems.................. 520d
Repeater spacings....................... 543
Section lengths......................... 543
Signaling............................... 529
Spiral-four carrier system (See also CF-1)................................... 521
522
Circuit lengths and repeater spacings. 543b
(table) 5-45
Frequency range................(table) 5-14
Spiral-four 100-mile carrier system (AN/TCC-2).............................. 522
SpiraLfour terminals, mobile installation 1155c
(drawing) 11-70
Station maintenance. . ................. 1160e
System coordination on open wire lines. 530
Tactical carrier systems................ 521
2-wire balanced system.................. 520
Carrier-to-noise ratio..................... 1211c (2)
CC-344 Cable Stub (TM 11-371).. (table) 9-14
CC-345 Cable Assembly (5-pair)
(TM 11-371):
Description.............................. 911c
(table) 9-15
Talking range....................(table) 5-44
Transmission data................(table) 5-39
Weight...........................(table) 5-1
CC-355-A Cable Assembly (10-pair)
(TM 11-371):
Description.............................. 911c
(table) 9-15
Talking range....................(table) 5-44
Transmission data................(table) 5-39
Weight...........................(table) 5-1
CC-358 Cable Assembly (spiral-four
(TM 11-369):
Bridging-Access Plug U-23/G.............. 503c
Circuit lengths.......................... 543b
(table) 5-45
Construction methods.....................911b
Description of........................... 503c
(table) 9-15
Repeater spacings....................... 543b
(table) 5-45
Talking range...................(table) 5-44
Transmission data...............(table) 5-39
Weight..........................(table) 5-1
CE-11 Reel Equipment (TM 11-2250)
(photo) 2-9
Center-fed half-wave antenna, improvised. 661
662
(drawing) 6-123
(drawing) 6-124
146
163
173
141
163
163
152
142
143
163
172
142
143
532
535
541
152
142
141
559
435
438
436
171
166
132
438
436
171
166
132
Centrals, telephone...................... 213
AN/TTC-1 Telephone Central Office Set 22 lb
Civil, interconnection with Army......801 to
807
131 163 172 434 131
436 163 172 171 166
132
13 264 311 311 312
17
23 399
582
INDEX
Cen—Cir
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par.
or fig.
Centrals, telephone (contd) Combined local and long distance..... 214b
Combined versus separate local and long distance........................... 1113h
Commercial versus tactical........... 1113d
Commercial versus tactical.......... 1113d
Common battery versus magneto service. 1113g
Communications Zone, typical layout for 214f
(drawing) 2-22
Distributing frames.................. 238
Engineering.......................... 1138f,g
Foreign, civil (.Sec Foreign civil central
offices) Installation of...................... 1150
Large versus small................... 1113e
(drawing) 11-17
Local................................ 214b
Longdistance......................... 214b
Maintenance.......................... 1160d
1162d
Maintenance and testing equipment... . 242
Mobile............................... 1155b
MobiletestunitX-63699A (AN/FCM-4) 242
Monitoring, observing and recording
equipment................... 241
PBX (Private branch exchange)...232
Power equipment................. 240
Protectors...................... 239
Recording equipment.............241
Ringers......................... 236
Signaling equipment............. 236
(photo) 2-38
(photo) 2-39
Switchboards (See also Switchboards, under S)............'.................. 215 to
226
TC-2 Telephone Central Office Set
(photo) 2-28
TC-10 Telephone Central Office Set
(photo) 2-30
Test and control board X-66034A
Page
17
473
471
471
472
20
19
36
501
518
471
483
17
17
541
543
36
530
36
36
31
36
36
36
34
34
33
34
20
(AN/FCM-5)......................242
Testing and maintenance equipment.... 242
Typical centrals................... 214
(drawing) 2-21
Centrals, teletypewriter: BD-100 Switchboard.................. 337
Group operation.................. 338
Operation........................ 1123b
Position requirements............ 1129a
(table) 11-27
Commercial type.................... 1127b
Position requirements......(table) 11-28
Mobile............................. 1155d
SB-6/GG Switchboard................ 339
CF-l-( ) Telephone Terminal (TM 11-341)...................... 522
AN/TRC-3 and -4 Radio Sets, use with. 622
AN/TRC-11 and -12 Radio Sets, use with............................622
Carrier hybrid circuit lengths and repeater spacing..................(table) 5-46
Circuit lengths.................(table) 5-45
Equalizer for Wire W-143............. 522c
(drawing) 5-18
Frequency range.................(table) 5-14
Lead-covered cables, use with.......... 522e
Mobile installation................... 1155c
(drawing) 11-70
Open wire, use with.................... 522d
530b
Open wire converter circuit lengths and repeater spacing................(table) 5-48
24
25
36
36
17
18
91
92 486 493 493
492
494 536
94
143 254
254 143
172 172 144
144 142 144 532
535 144 152
174
Par. or fig.
CF-l-( ) Telephone Terminal (TM 11-341) (contd)
Pair-per-system operation............. 524
543d
(table) 5-47
Repeater spacings..............(table) 5-45
Wire, W-143, use with................. 522c
CF-2-( ) Telegraph Terminal (TM 11-355 and355B)........................... 332
AN/TRC-1, AN/CRC-3 Radio Sets, use with........................ 342
CF-l-( ) Telephone Terminal, use with 306 CF-6 Telegraph Terminal, use with.... 332c Connection with British equipment. . . . 352 4-wire connection to CF-l-( )......... 306b
Mobile installation................... 1155c
(drawing) 11-70 Radio teletypewriter arrangements,
improvised....................... 342 to
346
Regenerative repeater connection (drawing) 3-56
Schematic....................(drawing) 3-15
Sending and receiving circuits, (drawing) 3-71 2-wire connection to CF-l-( )......... 306b
CF-3 Repeater (Carrier) (TM 11-341)... 521
522
CF-4 Converter (Carrier, 2 or 4-wire) (TM 11-2008).......................... 525
543d (table) 5-14 (table) 5-48
CF-5 Repeater (Carrier, 2-wire) (TM 11-2008)....................... 525
CF-6 Telegraph Terminal (Carrier) (TM 11-2009)......................... 306b
332c
CF-7 Carrier Hybrid (TM 11-2003)........ 523
(table) 5-14
Chadless tape, teletypewriter........... 303b
Changed telephone numbers, switchboard. 1108k(3)
Characteristic impedance................ 1216a
Chief operator, telephone central, duties. . 1107c
Circuit engineering and administration:
Assignment index................<..... 1141a(6)
Assignment of circuit orders.......... 1145 to
1147
(drawing) 11-44 (drawing) 11-45
Assignment office, functions.......... 1144
Control, long distance circuits...... 1105c
Designations, trunk plant............. 1140
Diagram............................ 1141a(4)
(drawing) 11-34
Holding time.......................... 1110d,e
1115
Information check list, trunk plant... 1138b
Layout, trunk engineering............. 1139
Layout chart................(drawing) 11-35
Orders................................ 1145
Content............................. 1146
Distribution of..................... 1146d
Packaged carrier equipment.......... 1147
Sample....................(drawing) 11-44
(drawing) 11-45
Record Cards.......................... 1141
1142 1149e(2)
Content............................. 1141a(5)
(drawing) 11-36 (drawing) 11-37
Packaged voice-frequency equipment. 1142
Page
146
163
173
172
143
83
98
52
83
112
53 532 535
99
90
53
100
53 142 143
147 163
142 174
147
53
83 145 142
47 467 561 462
503 512
514
514 512 461
502
503
505 469 478 499
502
506 512
513
514 515 514
514 503 508 517
503 508 508 508
583
INDEX
Cir-Cro
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par.
or fig.
Circuit engineering and administration (contd) Record cards (contd)
Sample......................(drawing) 11-38
(drawing) 11-39 (tables) 11-40 to 11-43
Records, trunk plant................... 1141
Switchboard (See Switchboards, telephone, features and equipment).
Traffic capacity (See Point-to-point . circuit).
Circuit lengths, telephone, wire and cable (table) 2-3
C carrier.......................(table) 5-48
Carrier hybrid system (CF-7)... (table) 5-46
H carrier.......................(table) 5-48
Lead-covered cable...................... 542a (3)
Open wire converter (CF-4)......(table) 5-48
Open wire pairs.................(table) 5-13
Pair-per-system operation of CF-1 (table) 5-47
Spiral-four............................ 543b
(table) 5-45
Circuit types, voice-frequency telephone, wire and cable:
Balanced (metallic).................... 510
4-wire................................. 515
Ground return.......................... 510
Loaded................................. 512a
Metallic............................... 510
Nonloaded.............................. 512
Nonrepeatered.......................... 513
Phantom................................ 511
Repeatered voice-frequency............. 514
2 wire................................. 515
Page
509
509
510
503
9
174
172
174
162
174
141
173
163
172
Civil central offices (See Foreign civil central offices).
135
138
135
136
135
136
137
135
137
138
Clearing trouble, telephone central..... 1164
Climatic effects........................ 1168
Humidity........................... 1170
Moistureproofing and fungiproofing. . . . 1171
Remedial measures.................. 1172
Temperature........................ 1169
CN-22/F Power Transfer Panel (TM 11-967)..................... 707d
Coaxial cable........................ 638a
676b(2)
Coaxial dipole........................... 628
(drawing) 6-41
Code ringing on party lines.............. 1114f
CODEZ, automatic Morse code.............. 303a
Coefficients, telegraph transmission..... 317 to
319
(table) 3-20
Army................................ 1223c
Bell System.......................... 1223d
Collins radio equipment.........(table) 6-173
Combined local and long distance telephone centrals........................... 214b
1113h
Command radio sets, ACS........(table) 6-172
Commercial power..................... 702
Common battery: Cord circuits........................ 230 to
232 (drawing) 2-36 1113i
Loop............................... 214e
(drawing) 2-6
Switchboards....................... 225
1113g
Telephones......................... 208
543 550 551 551
552 550
387 275 329
262 261 476
46
64
65 569 570 368
17 473 365 383
30
31
473
18
12
28
472
11
Par. or fig.
Common battery (contd)
Trunk circuit, outgoing automatic, incoming ringdown...................234
Trunks................................ 214d
Communication keyboard, teletypewriter . 322a
Communication range (See Distance range)
Communication systems:
Comparisons: Radio versus wire..................... 103 to
104
Telegraphy versus telephony......... 105 to
109
Planning for.......................... 1103
Power ranges.......................... 1202
Staff and field organization.......... 1105
Technical functions................ 1104
(drawing) 11-1
Communications, radio................... 601
Facilities............................ 603
Reliability........................... 606
Complaints, service..................... 1108k(3)
1123g
Composited circuits..................... 305e
526c
Construction, cable and wire lines: Fixed plant........................... 912e
Planning.............................. 902 to
905
Surveying............................. 903
Tactical.............................. 911
912
Work organization..................... 905
Continuous-wave radio telegraph (c-w)... 308a (2) 603b 645b(3)
Control station, long distance circuits. . . . 1105c
Converter, facsimile, AN/TXC-1..........401c
402e
Coordination in planning a communication system............................... 1103b
Coordination of systems on open-wire lines. 530
Cord circuits, telephone switchboard:
Common battery..................... 1113i
Cut-through......................... 232c
(drawing) 2-37
Local............................... 230
PBX................................. 232c
(drawing) 2-37
Universal........................... 231
(drawing) 2-36
Magneto............................... 230
1113i
Cord repair, switchboard................ 1157g
Cord switchboards....................... 221
Cordless switchboards................... 220
Corner reflector........................ 635
Corrections for v-h-f field strength estimates.............................. 616
Corrective maintenance.................. 1158
Counterpoise............................ 650b
659a 663a
(drawing) 6-119
(drawing) 6-137 (drawing) 6-138
Coupling several receivers to one antenna.. 679c (2) 675c(2)
CP-12, -13 Counterpoise................. 649b
Crossarms: 8-way (British)........................ 559
Field wire...................(drawing) 9-12
4-way (British)....................... 559
Open wire........................... 912b
10-pin................................ 558
Page
32
18
68
2
3
4 459 553 460 460 461 219 220 223 467 487
52 148
440 423
423 434 438 424
55 220 291 461 121 124
459 152
473
32 32 30 32 32 30
31
30 473 539
23 22 273
237 543 290 308 319 310 322 323 336 327 297
195 433 195 438 194
584
INDEX
Cro—Div
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig.
Crossarms: (contd) »
Type A................................ 558
Cross-connecting terminals.............. 1136b
Cross-connecting wire.................. 1151d,e
Cross modulation........................ 686
Crosstalk:..............................547
548a 1210
Amplification......................... 550
Capacitance unbalance................. 568
Combining crosstalk losses............563
(table) 5-82
Conditions close to front............. 547a
Coupling.............................. 548
Distant-end........................... 548
Disturbed circuit..................... 548
Disturbing circuit.................... 548
Entrance and intermediate cables......562
Equal level crosstalk loss............ 550b
Estimates of U.S. versus French versus
Italian lines..............(table) 5-80
Far-end............................... 548a
(drawing) 5-54
Far-end crosstalk loss................ 550c
French lines................(drawings) 5-77 to
5-79
Input-to-output crosstalk loss........•.. 549
Interaction crosstalk................. 55Id
5-76
Level difference...................... 550e
Loss.................................. 548
1210
Measuring crosstalk, methods and apparatus........................... 564
(table) 5-84
Near-end.............................. 548
Output-to-output crosstalk loss....... 548c
Reflection crosstalk...........(drawing) 5-60
. Repeater spacing effects.............. 550d
Signal-to-crosstalk ratio.............:. 549
Standards of.......................... 549
Terminology........................... 548
Transpositions (See Transpositions, under T)
Units................................. 1210
Volume................................ 5-55
Crowfoot antenna........................ 673c
(drawing) 6-13r
CS frequency allocation................. 528c
CU frequency allocation................. 528c
Current ratio, db relation.............. 1207
(table) 12-4
Cut-off frequency.......................512a
Cut-off jacks........................... 222b
Cut-off of conversation, timed..........816
Cut-over program........................ 1157c
Cut-through and non-cut-through cords .. 807b
CV-2/TX Converter, facsimile (TM 11-2252)....................... 402e
CW-49507A (Navy) Headset Assembly... 212b(3)
C-w telegraph (keyed carrier)........... 308a (2)
603b 645b (3)
(tables) 6-169 to 6-175
Page
194 498 524 343
179
180 557
181 209
201
202
179
180
180
180 180
201
182
200 180
180 183
198
181
184
197
183 180
557
202 205
180 181
185
183 181
181
180
557 181' 323 323 150 150 556
557 136
24 407 539 402
124
14 55
220 291
355
Db (See Decibel) Dbm..................................... 1205
DbRN................................... 1211a
555
557
Par.
or fig. Page
D-c resistance (See Resistance, d-c)
Decibel (db).............................. 1203 553
Current ratio relation............. 1207 556
(table) 12-4 557
Power ration relation............(table) 6-110 302
(table) 12-1 553
(drawing) 12-2 554
Transmission losses and gains...... 1204 554
Voltage ratio relation............. 1207 556
(table) 12-4 557
Zero level......................... 1206 555
Delayed calls, telephone............ 1108c 466
Recording desk.................... 1108f 466
Tickets......................... 1108e,g 466
(drawing) 11-5 467
Delta-matched doublet antenna......... 672 321
Designation cards for packaged carrier telegraph equipment................ 1152e 525
(drawing) 11-58 525
Designation strip marking, trunk... 1107e 464
DF radio equipment.................. 601c 219
(table) 6-171 362
Diagrams: Circuit............................ 1141a 503
(drawing) 11-35 506
Traffic.......................... 1107f 464
' 1122c 483
1123d 487
Dial: Central offices, foreign................. 822 to 410
833
Cords.................................. 1113i(4) 473
Jacks.................................. 1113i(4) 473
234 32
Number plates.......................... 814 406
Pulse speeds........................... 813d 406
Switchboards........................... 217 20
Differential sending (telegraph)......... 305c 51
Diplex operation, telegraph.............. 325g 75
Dipole antenna mountings, improvised ... 662 311
(drawing) 6-68 276
Dipole antennas (See Doublet antennas)
Directional h-f antennas (See Antennas, h-f, directional)
Directional v-h-f antennas (See Antennas, v-h-f, directional)
Director (part of antenna array).... 632a 266
Directory: Telephone........................... 1109 468
Teletypewriter................... 1123h 487
Disconnect signals, telephone...... 1108b 465
Dispatchers telephone equipment, railway. 248 39
Dissipation line, rhombic antenna. 670b(2) 319
Distance range, radio: H-f................................. 644c 283
647 294
(table) 6-74 284
V-h-f............................. 610 225
612 228
613 229
(drawing) 6-23 242
Distortion, telegraph (See Signal distortion telegraph)
Distortion test sets, DXD1 and DXD4’ (TS-383/GG) telegraph.................... 349b 109
Distributing cable................."..... 1131a 495
Distributing frames...................... 238 36
Diversity antenna system................. 657h 308
674 325
Diversity reception, radio............... 304d 49
308a(6) 56
674 325
(photo) 6-141 326
585
INDEX
Div-Fad
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig. Divided trunk routes. ................. 1115f
(drawing) 11-16
Dot cycle, telegraph................... 303a
Dotting speeds, telegraph.............. 304a
Double-doublet receiving antenna....... 671
(drawing) 6-135
Doublet antenna for SCR-299, SCR-399,
Doublet antennas..................... 661e(l)
627
628
631
662
671
672 (drawings) 6-123 to
6-126
(photo) 6-140
(drawing) 6-144
Drainage, protector.................... 1008
Drop wire, types and installation........ 1149b
Dropped circuits on carrier pairs........ 532
Dummy antennas (See Phantom antennas)
Dummy loads (lamps) for radio transmitters............................(table) 6-150
Duplex operation......................... 304f
621c 622
Dust static.............................. 654f
DXD1 and DXD4 (TS-383/GG) telegraph test sets........................... 349b
E
Page 478 480
46 49
321 320
311 311 260 262 264 311 321
321 311
325 328 454 515 154
334
50
251
254
305
109
E layer................................. 641a
650c
Earth resistivity...................... 1013
EE-8 Telephone, local battery (TM 11-333).......................... 206
Bridging loss......................... 206d
Speech power output................... 206b
EE-89-A Telephone Repeater.............. 516a
541b
(photo) 5-8
EE-97-A Teletypewriter Set (TM 11-354) 324c
(photo) 3-28
EE-99-A Telephone Repeater............... 516b
(photo) 5-9
EE-101 Ringing Equipment (TM 11-342). 529 EE-105 Telephone Unit (TM 11-2014)... ,532e Electrical protection (See Protection)
Elevation, effective, of antenna....... 616b (2)
6176
11 Switchboard (Western Electric Co.) (drawing) 2-31
Emergency Switchboard SB-18/GT.... 218 (photo) 2-23
Emission types......................... 603b
(tables) 6-169 to 6-175
End-fed half-wave antenna...... 661e(2)
663 (drawing) 6-127
(drawing) 6-128
Height of.................... 663a(3)
SCR-299 and SCR-399, use with... 663c
Transmitter loading............. 663b
(table) 6-129
Engine-driven generators (See Generators, engine driven)
277 299 457
10
11
10
138 161
139
71
71
139 139 152 154
237 245
26
21
21 220 355
311 313
313
314
315
315 315 315
Par.
or fig.
Engineering:
Local cable plant (See Local plant engineering)
Telegraph traffic (See Traffic, telegraph, engineering)
Telephone system...................... 201
501
Telephone traffic (See Traffic, telephone, engineering)
Trunk plant (See Trunk plant engineering)
Entrance and intermediate cables........ 506a
531
545
Autotransformers for........... 545e (3)
C-4.1 loading................... 545e(2)
Crosstalk......................... 562
Insertion loss.................... 538
(table) 5-42
Length limits..................... 545
(table) 5-49
Loading, improvised............... 545
(drawings) 5-50 to
5-52
Equalization....................... 1206d
Equalizer for Wire W-143................ 522c
(drawing) 5-18
Equipment losses, telephone............. 539
(table) 5-43
(tables) 11-40 to
11-42
Equivalent 4-wire system................ 520f
543e
Exchange cable.......................... 1131a
Experience data:
Telegraph traffic..................... 1127
Telephone traffic..................... 1112
Exploring loop, radio................ 654e(2)
Extension circuits, telegraph........... 305f
315
(table) 3-19
Extensions, telephone................... 1114f
Page
5
131
133
153
174
178
178
201
160
169
174
175
174
175
556'
144
144
161
169
510
142
163
495
492
470
305
52
63
63
476
F
F, Fl, and F2 layers................... 641a
F-2/GG, Filter, carrier telegraph (TM 11-2206)....................... 333g
F-36/FC Carrier Filter (X-66217C)...... 508d
F-37/FC Carrier Filter (X-61823B)...... 508d
Facsimile:
Distortion........................... 405b
Equipment............................ 401c
Frequency band widths................ 408c
Limits............................... 405d
Multiple echo........................ 406c
Noise and fading..................... 408d
Operating............................ 408e
Page (See Page facsimile)
Printer.............................. 411
Privacy..............................407
Radio and wire circuits.............. 405
406
409
Tape...........................:.......403
409d
Telegraph and telephone comparisons.. . 408
409
Word speeds.......................... 408b
Fading, radio.......................... 641 d
642a
309g
277
86 134 134
126 121
128
126
127 128 128
130
127
126
127
129
125
129
127
129
127 278 279
58
586
INDEX
Fed-Fre
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Pa-, or fig. Federal radio equipment........(table) 6-173
Feeder cables......................... 1131a
Field cable and wire, r-f attenuation
of.......................(drawing) 6-146
Field cable, rubber (See Rubber-
covered cable)
Field functions in a communication system. 1105b
Page 369 495
330
(drawing) 11-1
Field intensity, free space radio..........617a(2)
(drawing) 6-23
Field intensity, radio.................... 1214
H-f..................................... 645b
646 648 (drawing) 6-92
(See also under H-f radio transmission) V-h-f.........................(drawing) 6-6
(drawing) 6-7 614 to 617 621e 622e, f
(See also under V-h-f radio transmission)
Field manuals (See Appendix).............
461
461
241
242
560
291
292
296
293
227
227
229
253
253
Field strength radio................... 1214
Field wire (See Rubber-covered wire)
Fighter control radio sets, v-h-f. . . (table) 6-171
Filter, band widths, telegraph......... 309c
551 switchboard (Western Electric Co.)... 221b
Fixed plant h-f radio equipment........656
Flat-top antenna....................... 673b
(drawing) 6-137
Flexible dipole antenna, improvised....631
(drawing) 6-48
Dimensions....................(tables) 6-49 to
6-51
F-m and a-m............................ 603c
605
Folded doublet antenna................. 662d
(drawing) 6-125 (drawing) 6-126
Forecasts of radio conditions..........641d(3)
64 le 643d
Foreign civil central offices.......... 801 to
807
All relay dial....................... 829b
830
Asia................................. 823b
Automanual........................... 829
Battery and generator feeders, PBX.... 815
British.............................. 820d
824a
Capacity, terminal................... 804a
Central battery signaling (CBS)...... 807b
808g 811 820
China................................ 822c
Common battery manual................807
812 821
Common battery remote control dial. .. 832 Cuba................................. 824a
D system............................ 828
Demiautomatic.......................828
Denmark............................. 822b
828d
Dial................................. 807d
813
Dial number plates.............(table) 8-7
(photo) 8-8 (photo) 8-9
573 560
362
58
23
306
323
322 264
264
265
220
222 312
313
313 278
279
281 399
419
419
411
418 406
409
411
400
402
404
405 409
411
401
405
410
420 411
418
418 410 418 402
405
406
407
407
Par.
or fig. Page
Drop selector......................... 827 417
Ericcson power driven dial............ 823 111
Europe................................ 822c 411
823b 411
829d 419
832e 420
83le 420
830c 419
France................................ 820d 409
825c 415
French Colonies....................... 820d 409
825c 415
Hasler dial system.................... 826 415
Italian Colonies...................... 827c 418
Magneto (local battery) manual........ 807a 401
810 404
819 409
Magneto remote control dial........... 831 419
Merck Fallwaehler..................... 827 417
Mexico................................ 822c 411
North Africa.......................... 825c 415
827c 418
R-6 dial system....................... 825 415
Reliability........................... 804b 400
Rotary power driven dial.............. 822 410
Semiautomatic......................... 829 418
Signaling problems.................... 810 404
813 405
Signaling ranges (supervision and ringing)................................ 809 404
South America......................... 822c 411
823b 411
Step-by-step.......................... 824 411
Strowger automatic.................... 824 411
Sweden................................ 833c 421
Swedish crossbar...................... 833 421
Switzerland........................... 826 415
Thomson-Houston....................... 825 415
Timed cut-off conversations........... 816 407
Transmission problems................. 808 403
Transmitter battery supply............ 808 403
812 405
Foreign loading systems.................571a 214
(table) 5-89 215
Foreign wire plant rehabilitation....... 915 to 441
919
42B1 Carrier Telegraph Equipment........341b 97
4-wire circuits: Carrier................................. 520 141
Voice-frequency....................... 514 137
515 138
566 208
569
(See also CF-l-( ) French open wire line transposition.......561
Frequency allocations of carrier telegraph
systems.......................(table) 5-35
Frequency allocations of carrier telephone systems.................................. 534
British........................(drawing) 5-33
CF-1 (spiral-four)...............(table) 5-14
CF-4 (open wire converter).....(table) 5-14
CF-7 (carrier hvbrid)............(table) 5-14
CS.................................... 528c
CU...................................... 528c
French.........................(drawing) 5-34
German.........................(drawing) 5-37
Japanese.......................(drawing) 5-36
Type C system........................... 528
Type H system........................... 527
U. S. Army.....................(drawing) 5-33
211
197
158
155 156
142 142
142
150
150
157
159
158
150
149
156
587
INDEX
Fre-H-f
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig.
Frequency assignment, radio..............604
608b 640d 642 643 678
Frequency band selection, radio........604
678
Allocation, U. S. Army............... 604c
Designations...................... 604a(2)
Radio set stability.................. 604d
Transmission characteristics......... 604b
Frequency band widths, telegraph....... 304b
306a(l)
Frequency bands of radio sets....(tables) 6-169 to
6-176
Frequency control...................... 604d
640d 642i
Frequency control, type of, in specific radio sets...........................(tables) 6-169 to
6-174
Frequency coordination of open wire lines. 530b Frequency coverage chart, tactical ground radio sets....................(drawing) 6-176
Frequency diversity.................... 304d
308a(6)
Frequency Meter Set SCR-211............ 642i
(photo) 6-71
Frequency modulation, use of........... 603c
605
Frequency-shift, space-diversity....... 304d
308a(5),(6) 347
AN/FGC-1............................. 341a
(photo) 3-66
AN/FRR-3A.....................(table) 6-172
(table) 6-173
AN/MRC-2............................. 347c
(table) 6-169
Wilcox 4CW3-D.................(table) 6-173
Frequency range, tactical carrier telephone systems.........................(table) 5-14
Frequency to wavelength, conversion....637
Frequency weighting network............ 1211a
Full-duplex operation, telegraph....... 304f
Full-rhombic antenna...................634
670
Full-wave horizontal antenna........... 667
Fungiproofing equipment................ 1171
Fuses, line............................ 1003b
G
Par. or fig. Page
Ground-to-air radio sets (table) 6-171 362
(table) 6-173 366
Ground-wave distance ranges:
H-f 644b, c 283
647 294
(table) 6-74 284
(drawing) 6-86 288
(drawings) 6-96 to 295
6-101
V-h-f 610 22*5
612 228
(drawing) 6-23 242
Ground-wave field intensity:
H-f 645b 291
646 292
(drawings) 6-93 to 294
6-95
V-h-f 614 to 229
617
621e 252
622c 255
(drawing) 6-6 227
(drawing) 6-7 227
Ground-wave transmission, radio 604b(l) 221
607 223
642 279
646 292
644 282
645 290
Grounding 1011 455
Grounds, resistance of 1013 457
Group count, message 1122d 483
1130c 495
(table) 11-30 495
Guided propagation, radio........... 607b 223
Guying, pole fine... .................... 912f 440
(drawing) 9-24 448
H
Gain, transmission........................ 1204
Gasoline, leaded, use in small motors.....714
Generators, engine-driven................. 710
Cold climate operation..................711c
Installation............................ 712
Leaded gasoline, effects of............. 714
Noise reduction, acoustic,..............713
Voltage regulation......................715b (2)
GF/RU Radio set, U. S. Navy. ... (table) 6-174
GN station wire, description.............. 1149c(6)
GO-9 radio transmitting equipment, U. S.
Navy..........................(table) 6rl74
Graded multiple in dial switching......... 807d(3)
Ground mobile radio sets...........(table) 6-169
(table) 6-171
(table) 6-173
Ground-plane antennas..................... 630
Ground-return telephone circuits.......... 510
Page 221 224 277 279 281
335 221 335 222
221 222 221
49
52 355
222 222
280
355
152
380
49
56 280 280 220 222
49
56
105
95
96 366 369 106 359 370
142 274 557
50 269 318 317 551 452
554
395
393
394
394
395
395
396
373
516
373
403
355
362
366
263
135
H carrier (See Carrier telephone systems).
H carrier telephone system, telegraph on.. 306c 53
Half-duplex operation, telegraph 304f 50
Half-wave dipole antenna 627 260
628 262
631 264
661e(l) 311
662 311
1214b 560
Half-wave dipole antenna with corner
reflector 635 273
Half-wave horizontal antenna, h-f 661 to 310
663
651 299
652 300
(drawings) 6-87 to 289
6-89
Hallicrafters radio equipment (table) 6-173 369
Hammarlund radio equipment (table) 6-173 370
Head and chest sets 212c(l) 15
Headset Assembly CW-49507A (Navy)... 212b(3) 14
Headsets 212c(l) 15
Heat coils 1003c 452
Hellschreiber 411 130
Heterodyning of two radio frequencies,
spurious response due to 685 343
H-f and v-h-f radio transmission
comparisons 608 224
609 224
640 277
588
INDEX
___Hig
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par.
or fig. Page
High frequency (h-f) antennas (See Antennas, h-f).
High frequency (h-f) radio band, definition of.........................................604a 221
High frequency (h-f) radio transmission. . 639 to 277
656
Absorption of signals................... 643c 281
648 296
Antenna pattern corrections:
Receiving 652 300
(drawing) 6-108 301
(drawing) 6-109 301
Transmitting 649b 298
(drawing) 6-105 298
(drawing) 6-107 300
Auroral disturbances 640b 277
641d(3) 278
Comparison of h-f and v-h-f. 608 224
609 224
640 277
Elayer 641a 277
F, Fl, and F2 layers 641a 277
Field intensity 645b 291
646 292
648 296
Fixed plant installations.... 656 306
669 to 676 317
(photos) 6-112 to 306 6-116
Frequency assignment............. 640d 277
642 279
643 281
678 335
Frequency choice, sky-wave transmission 643 281
Basic radio propagation conditions.. . 643 281
64le 279
TB ll-499-( ) series........ 643d 281
• (drawing) 6-72 281
Distance range versus muf. ... (table) 6-73 282
Periodic predictions........... 643d 281
641e 279
Frequency coverage chart. . . . (drawing) 6-176 380
Frequency Meter Set SCR-211............ 642i 280
(photo) 6-71 280
Ground-wave and sky-wave transmission............................... 642 279
644 282
(drawing) 6-70 280
Calculations of performance.......... 645 290
653 301
Field intensities required........ 645b 291
(drawing) 6-92 293
Field intensities: Ground-waves........................ 646 292
(drawings) 6-93 to 294
6-95
Sky-waves..................... 648 296
(drawing) 6-102 296
(drawing) 6-103 297
Ground-wave distance range.. 644b, c 283
647 294
(table) 6-74 284
(drawing) 6-86 288
(drawings) 6-96 to 295
6-101
Ground-wave field intensities.. 645b 291
646 292
(drawings) 6-93 to 294
6-95
(drawing) 6-91 292
Performance estimates, procedures for calculating......................... 653 301
Par.
or fig. Page
High frequency (h-f) radio transmission
Ground-wave and sky-wave transmission (contd) Periodic estimates of transmission
range 644e 290
Radiated power versus ground-wave
distance 647 294
(drawings) 6-96 to 295
. Shadow chart (drawing) 6-101 6-86 288
Sky-wave performance 644d 287
(drawings) 6-87 to 289
Ground-wave distance range 6-89 644b,c 283
(table) 647 6-74 294 284
(drawing) 6-86 288
(drawings) 6-96 to 295
6-101
Half-wave horizontal antenna, power
corrections 661 to 310
Power corrections 663 651 299
(drawing) 6-107 300
Receiving corrections 652 300
(drawing) 6-109 301
Ionosphere conditions 641d 278
Ionosphere layers 641a 277
Maximum usable frequency (muf) 641b 278
Muf 643 641b 281 278
Noise grade areas (drawing) 6-90 291
(drawing) 6-91 292
Noise identification 654e 305
Noise reduction at receiving locations. . 620b 250
Optimum working frequency (owf) 654 641b 643 304 278 281
Owf 641b 278
Pattern efficiency 643 649 281 297
(drawing) 650c 6-105 299 298
(drawing) 6-107 300
Power corrections:
Half-wave horizontal 651 299
Whip 650 298
Precipitation static 654f 305
Radiated power 649 297
Radiation efficiency 649 297
(drawing) 650b 651b 6-104 298 299 298
(drawing) 6-107 300
Receiving antenna pattern correction... 652 300
(drawing) 6-108 301
(drawing) 6-109 301
Reliability of circuit 655 306
(drawing) 6-111 306
Single-tone modulation 603b 220
Skip distance 308a (3) 308b(2) 345 641c 55 56 102 278
Skip zone 641c 278
Sky-waves 604b(l) 221
« 641 642 277 279
(See also Ground-wave and sky-wave transmission, above)
Sporadic E 641d(2) 278
640b 277
645b 654f 291 305
589
656935 0—45-------39
INDEX
Hig-Jun
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig. Page
High frequency (h-f) radio transmission
(contd) Transfer efficiency.................... 649 297
650a 298
Transmission range, ground wave (See
Ground-wave distance range, above)
Whip antenna corrections............... 650 298
652 300
Pattern efficiency.................. 650c 299
(drawing) 6-105 298
Radiation efficiency................ 650b 298
(drawing) 6-104 298
Receiving pattern correction........ 652 300
(drawing) 6-108 301
Transfer efficiency................, 650a 298
High speed automatic telegraph (Boehme) 330 81
High voltage, protection from...... 1003a
Hills, radio transmission over........ 615 231
616 237
642 279
644c(3) 283
673a 323
Holding time, circuit............... lllOd 469
1115 478
1130b 494
(table) 11-29 494
Horizontal polarization............... 619 249
623c 258
HS-17 Head and Chest Set.................. 221c(l) 15
HS-19 Head and Chest Set.................. 212c(l) 15
HS-30 Headset............................. 212c(l) 15
(drawing) 2-19 16
Humidity and related effects on equipment 1170 551
1172 552
Hybrid coil, action of............... 1218b 564
I-193-A Test Set (TM 11-2513)............ 348a
(photo) 3-75
Identification of cable pairs............ 565e
567f
Image response........................... 683e
Impedance:
Cable, lead-covered............(table) 5-39
Characteristic........................ 1216a
Matching.............................. 1216
1217d
Nominal impedance..................... 512
Open wire lines................(table) 5-38
R-f lines............................. 638
676
Rubber-covered wires and cables. (table) 5-39
Wire lines............................ 536
IN-28 Insulator.......................... 533c
Incidental cables (See Entrance and intermediate cables).
Information calls........................ 1108c
1108k(l)
1123g
Information center for aircraft warning service.................................. 243
Insertion loss........................... 538
1220
(drawing) 12-13 (table) 5-42
Inspections, periodic: Equipment................................ 1157e
Line................................... 1157d
107
108 207 207 341
165 561 561
562
136
164 275 329
166 160
187
466
467
487
37
160
566
566
169
539
539
Par.
or fig. Page
Installation intervals, commercial type telephone switchboards...................... 1150d 520
(table) 11-52 520
Installations, mobile (See Mobile installations).
Installations, telegraph:
Line transmission equipment............ 1154b 526
Signal center equipment................ 1154c 526
1154d 527
(drawing) 11-59 527
Teletypewriter central................. 1153 525
Installations, telephone.................. 1148 515
Cable record..................(drawing) 11-47 518
Cable runway..................(drawing) 11-57 523
Carrier equipment...................... 1151 522
Centrals, fixed plant.................. 1150c 518
(photo) 11-50 519
(photo) 11-51 520
Centrals, tactical..................... 1150b 518
(photo) 11-48 518
(photo) 11-49 518
Drop wires............................. 1149b 515
Line record cards.............(drawing) 11-46 517
Order routine.......................... 1149d 518
Records................................ 1149e 517
Station wiring......................... 1149c 515
Telephone station...................... 1149 575
Work time installing centrals.......... 1150d 520
(t ables) 11-52 to 520
11-54
Insulators IN-15, IN-128 (same as TW).. 553 186
912c 438
Interception, radio messages.............. 608b 224
620a 249
Intercommunication system................. 211 13
Interconnection of Army and commercial switchboards (See Switchboards, telephone, interconnection of Army and commercial).
Interference, radio....................... 620b 250
640a 277
675a(2) 325
678 335
Intermediate cables (See Entrance and intermediate cables).
Intermedi ate-frequency response.......... 683d 341
International Morse code.................. 303 46
Interoperation, British and American telegraph................................... 350 to 110
352
Interrupter (vibratory ringer)............. 708c 391
Inverted L antenna........................ 659 309
673b 323
(drawing) 6-119 310
Inverted vee antenna...................... 633 267
668 317
Ionosphere conditions..................... 641d 278
Ionosphere layers......................... 641a 277
Island-to-island radio transmission (See
Sea-water, radio transmission over, and Mountains, radio transmission over.)
Italian open wire line transpositions..... 561 197
Jefferson Travis radio equipment... (table) 6-173
Jungle, radio transmission in......... 616c
618b
642d
644c
646b
368
226
246
279
283
292
590
INDEX
Jun-Loo
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Jungle wire lines.......................
Par. or fig. 923 tc 927
Page
447
Par. or fig.
K
K 100 (Kellogg Switchboard and Supply
Co.) Switchboard.............(photo) 2-27
Keyboard types, teletypewriter.......... 322a
Keyed carrier (c w).................... 308a(2)
Krarup cable............................ 569j
918
24
68
55
213
445
Layouts: Mobile
(drawings)
1157
11-63 to
11-70
Radio station............................ 1154e
Signal center, typical................... 1124
1154c
(drawing) 11-21
Telegraph systems....................312 to
320
Telephone systems................... 202 to
204
539
528
528
488
526
488
60
5
Lead-covered cables (See Cables, lead-
covered)
(drawing) 5-53
(drawing) 11-38
(drawing) 11-39
Level, sound........................ 1212
(table) 12-6
Level, transmission................. 1206
Level, zero......................... 1206
Level diagram....................(drawing) 5-53
(drawing) 11-38
(drawing) 11-39
Lightning, protection from............... 1003a
1008
1012a
Line, telephone........................... 204c
Line failures............................. 1162f
Line inspections, periodic................ 1157d
Line lamp distribution.................... 1107i
Line maintenance, long distance........... 1160c
Line-of-sight distance, radio............. 617a(2)
(drawing) 6-23
Line priority marking, telephone switchboards................................... H07j
Line record cards......................... 1149e
(drawing) 11-46
Line route map........................... 1141a
(drawing) 11-33
Line units, telegraph.................... 327
Link, Fred M., radio equipment.. .(table) 6-173
Link, telephone.......................... 204c
Load distribution, switchboard........... 1107i
Loaded cable circuits:................... 512
Continuously loaded (Krarup)........... 569j
Cut-off frequency...................... 512a
End section............................ 569i
178 509 509 560 560 555 555
178 509 509 451 454 456
6 543 539 465 540 241 242
465 517 517 503 504
77 368
6 465 136 213 136 212
4-wire:
Irregularities in loading coil inductance
and spacing................... 569
Loss from loading irregularities
(drawing) 5-86
Parallel and series connections of
phantom loading units........... 569b
Identification of. :....................572
211
211
211
215
Loading cable circuits (contd) Losses...........................(table) 5-40
Mid-coil termination.................. 569i
Rehabilitation........................ 569
570b
Transmission loss............(drawing) 5-91
2-wire:
Capacitance unbalance......... 570a
Irregularities................. 570
Junction return loss..........(table) 5-88
Return loss of loading irregularities (drawing) 5-87
Loading (definition)............... 512a
Loading, storm...................... 906
Loading coils: American.......................... 571b
(table) 5-90
Cases (pots).................... 918a
C-114-A......................... 512c
Lead-covered cable.............. 915d
Nonphantom...................... 571c
Phantom......................... 512f
Rubber-covered wires...........(table) 9-14
Loading systems: American civil....................(table) 5-40
Foreign............................... 571a
International circuits (CCIF).... (table) 5-89 Method of designating................... 512b
Local battery telephones................ 206
Local circuit, telephone................ 204c
Local extensions, telegraph............. 305f
Local plant engineering and administration: Cable congestion and relief............. 1136
Cable multipling...................... 1135
(drawing) 11-32
Cable terminals....................... 1134
Distributing cable.................... 1131a
Exchange cable........................ 1131a
Feeder cable.......................... 1131a
Map..........................(drawing) 11-31
Records............................... 1132
Size and gauge of cable............... 1133
Local trunk............................. 214d
Requirements.......................... 1115c
(table) 11-14
Locator systems, signal center.......... 1121
Lock-in supervisory signals............. 231b
231c 1113i(2)
Long distance telephone engineering and administration:
Line maintenance...................... 1160c
Switchboard operating................. 1108c
’ Trunk requirements................... 1115d
(table) 11-15
! Trunk trouble........................... 1162b
| Wire circuit orders (See Circuit engineering) Long distance trunk...................... 214d
Long range tactical Wire W-143.......... 910d
(table) 9-9
Loop, telephone......................... 204c
214e (drawing) 2-6
Common battery........................214e
Magneto............................... 214e
Loop circuits, telegraph................ 305f
Loop limits, transmission and signaling... 237 1113e (table) 2-40
Loop plant engineering (See Local plant engineering and administration)
, Loops, ratio to telephones.............. 1114f
Page
167
212
211
213
216
213
213
214
213
136
214
215 445 136
442 215
137 435
167 213
215
136
10
6
52
498 498
498 496
495 495 495
497
496
496
18 478 479 483
30
31
473
540 466 478
480 542
18 431 432
6
18
12
18
18
52
34
471
35
476
591
INDEX
Los-Muf ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig. Page
Loss: Battery supply..................... 208 11
(table) 2-7 12
Insertion........................ 1220 566
(drawing) 12-13 566
Net.............................. 1206 555
Reflection....................... 1217 561
(drawing) 12-10 563
Return.......................... 1218d 565
Transmission..................... 1204 557
Low-frequency (1-f) radio band..... 604a 221
M
M-6-( )/UR Microphone (lip)............ 212b(3) 14
MAB radio set, U. S. Navy........(table) 6-174 371
Machine switching (See Dial, switchboards
under D)
Magneto loop........................... 214e 18
Al agneto switchboards................. 224 28
1113g 472
Telephone and trunk capacity. . . (table) 11-13 477
Maintenance............................ 1156 538
Carrier and repeater station......... 1160e 541
Centrals............................. 1160d 541
1162d 543
1162e 543
Corrective........................... 1158 540
Dispatching installers and repairmen.. . 1160f 541
Line cable failures.................. 1162f 543
Long distance line................... 1160c 540
Long distance trunk trouble.......... 1162b 542
Mobile radio repair shop.......(photo) 11-77 550
Personnel requirements............... 1160 540
Power failures....................... 1162g 543
Power plant.......................... 1165 547
Preventive........................... 1157 539
1162c 542
Radio................................ 1166 548
Rectifier............................ 1165d 547
Repeater station..................... 1160e 541
Ringer............................... 1165e 547
Routine tests........................ 1157e 539
Service order work................... 1159 540
Storage battery...................... 1165c 547
Telegraph equipment.................. 1164g 546
Telephone station.................... 1160b 540
Teletypewriter....................... 1160b 540
1164e 545
1164f 545
Testing and clearing trouble......... 1164 543
Tools and test sets.................. 1167 549
Tropical............................. 1168 550
Trouble expectancies................. 1160b 540
1160c 540
Trouble recording.................... 1162 542
Trouble reporting.................... 1161 541
Trouble reports...................... 1163 543
(drawings) 11-73 to 542
11-75
Winter............................... 1168 550
Maintenance and test equipment, telephone switchboard...................... 242 36
MAL (Multi-airline).................... 505d 133
559b 195
913 440
(drawing) 9-20 440
Manual cordless switchboards.............. 220 22
Manual telegraphy (definition)............ 106a 3
Map, line route........................... 1141a 503
(drawing) 11-33 504
Par.
or fig. Page
Marconi antenna........................... 673b 323
(drawing) 6-137 322
Mark, teletypewriter...................... 304b 49
1221
Master power meter panel (TM 11-2510).. 7O7e
Maximum usable frequency (muf) radio... 641b 278
643 281
MC-543 Conversion Kit (See SCR-399 in table)..........................(table) 6-169 355
Mew..................................... 603b 220
Medium frequency (m-f) radio band....... 604a 221
673 323
Message center.......................... 1120 482
(drawing) 11-18 484
(drawing) 11-21 488
Message handling methods, teletypewriter network.......................... 1122 483
302 45
Messages: Book messages........................... 1122g 484
Delivery.............................. 1121 483
Heading............................... 1122d 483
Multiple address...................... 1122g 484
Numbering............................. 1122e 484
Service messages...................... 1122h 486
Messenger wire, physical characteristics (table) 9-19 439
Meteorological conditions, effect on v-h-f radio transmission...................... 617e 246
Microphones............................. 212b 14
Response-frequency characteristi cs (drawing) 2-15 15
Microvolts per meter.................... 1214 560
MK-2/GSM Moisture and Fungus-Proofing Equipment........................... 1171c 552
MM radio set, U. S. Navy.........(table) 6-174 371
Mobile centrals......................... 1155b 530
Mobile installations.................... 1155 529
AN/MRC-1 Radio Set.................... 330d 82
(table) 6-169 358
AN/MRC-2 Radio Set.................... 347c 106
(table) 6-169 359
AN/TRC-3 and-4 (radio relay).......... 1155e 536
(drawing) 11-72 537
CF-l-( ) and CF-2-( ), (spiral-four). 1155c 532
(drawing) 11-70 535
Radio repair shop..............(photo) 11-77 550
Telephone centrals.................... 1155b 530
(drawings) 11-65 to 530
11-69
Teletypewriter centrals............... 1155d 536
(drawing) 11-71 536
Modulation, f-m and a-m, for telephone use 605 222
Modulation, types of in radio transmitters................................. 603 220
(tables) 6-169 to 355
6-174
Moistureproofing equipment.............. 1171 551
Monitoring, observing and recording equipment............................... 241 36
Monitoring set X-66421A, teletypewriter. 349c 110
Monitoring of telephone service......... 1110c 469
Monocord magneto switchboards........... 219 22
Mountains, radio transmission over...... 610d 226
617 241
618d 247
642 279
673a 323
(drawing) 6-86 288
MU radio set, U. S. Navy..........(table) 6-174 371
Muf (Maximum usable frequency), radio. 641b 278
643 281
592
INDEX
Mul-Obs
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig. Page
Multi-airline (MAL)..................... 505d 133
559b 195
913 440
(drawing) 9-20 440
Multichannel radio systems.............. 603d 220
622 254
Multichannel, telegraph................. 306a 52
308b 56
310 59
311 60
341 95
342
Multicoupler model S-8853-1, RCA........ 675c (5)
Multipair rubber-covered cable (See also CC-345 and CC-355).................. 911
Multiple address messages............... 1122g
Multiple switchboards................... 223
Multipling, cable....................... 1135
(drawing) 11-32
Multipling radio receivers.............. 670c (2)
675c
Mutual interference between radio sets. . . 678 to 686 Heterodyning of two r-f frequencies, spurious response due to................ 685
Reduction of.......................... 678
H-f.................................. 657f
665b 670a 675a(2) 675b(2) 675b(4) 675c(5) 675c(6)
V-h-f................................ 619c(l)
620a
98 328
434
484
25 498 498 320
327 325
623c 624c(2) 632c 633h 636
Responses of radio receivers............ 682 to
685
(drawings) 6-158 to 6-161
Spurious receiver outputs............... 681
(drawings) 6-154 to
6-157
Spurious transmitter outputs............680
686 (drawings) 6-151 to
6-153
Transmitter to receiver................. 679
MV radio set, U. S. Navy...........(table) 6-174
MW radio set, U. S. Navy...........(table) 6-174
MX radio set, U. S. Navy...........(table) 6-174
N
343
335
308
316
318
325
326
326
328
328
249
249
258
259
266
269
273
338
340
338
339
337
343
337
336
371
371
371
National radio equipment..........(table) 6-173
Navy radio sets (U. S. Navy)......(table) 6-174
Neper................................... 1208
Net loss................................ 1206
Networks, wire and radio telegraph...... 1125a
(drawing) 11-23
(drawing) 11-26
Neutral circuit, telegraph.............. 305a
Noise Acoustical............................. 1212
Addition of noises................... 121 lb
Ambient noise (room noise)........... 1212
Carrier-to-noise ratio............... 1211c(2)
370
371
556
555
489
489
490
50
560
558
560
559
Par.
or fig. Page
Noise (contd) Identification, radio................... 654e 305
In operating rooms.................... 1107k 465
Measurement of acoustical........ 1212 560
Measurement of electrical....... 1211a 557
Measuring set, 2B (Western Electric Co.) (table) 5-84 205
(photo) 12-5 558
Motor-generator, acoustic noise from. . . 713 395
(drawing) 6-91 292
Radio........................... 620b 250
644a(2) 283
654 304
(drawings) 6-90 to 291
6-92
Reduction at radio receivers.... 620b 250
654 304
Reference noise (RN)........... 1211a 557
Requirements................... 121 Id 558
Room noise (ambient)................... 1212 560
Signal-to-noise ratio.................. 1211c 558
Sound levels....................(table) 12-6......560
Speech-to-noise ratio.................. 1211c(2) 559
Nondirectional antennas, v-h-f........... 623 258
626 to 260
631
Non-lock-in supervisory signals...... 1113i 473
Nonrepeatered voice-frequency circuits. . . 513 137
Talking ranges...................... 540 161
(table) 5-44 170
o
O-5/FR Exciter Unit (TM 11-2205)..... 341a(5) 97
(photo) 3-67 96
OA-3/FC Regenerative Repeater (X-66031A)........................... 334b 87
331b 83
335b 88
336 88
(photo) 3-53 88
OA-4/FC Carrier Terminal (X-61822A).. 332d 85
331b 83
(photo) 3-50 85
OA-5 /FC Carrier Terminal (X-61822B). . 331b 83
332d 85
(photo) 3-50 85
OA-6/FC Telegraph Repeater (X-61824A) 334c 87
331b 83
(photo) 3-52 87
OA-7/FC Telephone Repeater (X-61821 J) 508d 134
(photo) 5-11 140
OA-8/FC Telephone Repeater (X-61821K) 508d 134
(photo) 5-12 140
OA-9/FC Carrier Repeater (X-61819S). . 508d 134
(drawing) 5-30 151
OA-10/FC Carrier Repeater (X-66217B). 508d 134
(photo) 5-27 149
OA-11/FC Carrier Terminal (X-61819P). 508d 134
(photo) 5-29 151
OA-12/FC Carrier Terminal (X-61819R). 508d 134
(photo) 5-29 151
OA-13/FC Carrier Terminal (X-66217A). 508d 134
(photo) 5-26 149
OA-14/FC Line-composite Terminal (X-61823C)............................. 508d 134
OA-15/FC Line-simplex Terminal (X-61823H)............................. 508d 134
Observations, traffic.................. 1110a 468
1110c 469
1123a 486
593
INDEX
Obs-Pat
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par.
or jig.
Observing, service...................... 11 10c
Observing, monitoring and recording equipment .............................. 241
Off-premise extensions.................. 232a
Officer-in-charge, telephone central.... 1107b
On-ground antenna.......................666
One-way polar circuit, telegraph........ 305b
One-way reversible, telegraph........... 304f
Open wire, r-f attenuation and impedance. 676
(drawing) 6-146
Open wire converter carrier system (CF-4) 525 Frequency range..................(table) 5-14
Open wire lines:........................ 505
Attenuation......................(table) 5-38
British Army lines..........v,......... 913
559
(drawing) 9-20
CF-1, CF-3, CF-4, CF-5 on open wire lines................................ 522d
Construction methods................... 912
Construction time...............(table) 9-1
Crossarms.............................. 912b
Entrance and intermediate cable inserts
(See Entrance cables) Fixed plant construction............... 912e
Four-crossarm transpositions...........557
French................................. 561
Frequency coordination................. 530b
Guying................................. 912f
Impedance.......................(table) 5-38
Insertion loss of cables............... 538
(table) 5-42
Insulators............................. 553
912c
Italian................................ 561
Jungle construction.................... 925
Level coordination on open wire lines... 530c Pair assignment for spiral-four and
carrier hybrid systems............ 530b (3)
530b (4)
(drawing) 5-31
Phantom circuit......................... 511
Physical Characteristics........(table) 9-19
Pole pair.............................. 530b (5)
Pole selection......................... 907
Protection............................. 1008
1012b
Rapid pole line construction........... 912g
Page 469
36
31 j
462 :
317 |
52
50
329
330
329 147
142
133
164 440
195 440
144 438 422
438
Replacing temporary construction (drawing) 9-20
Resistance......................(table) 5-38
Rubber-covered wire insert, length limits.......................... 545
(table) 5-49
Sagging................................ 908
Spacing................................ 908
Span length............................ 908b
912d(2)
Storm loading............................ 906
Survey notes, typical......(drawing) 9-2
Surveying and staking.................. 903
System coordination....................530
Tactical construction.................. 912d
Talking range...................(table) 5-13
(table) 5-44
Transmission data...............(table) 5-38
Transpositions (See Transpositions under T)
Twin pairs......................(table) 5-38
Weight, space, and construction time (table) 9-1
440 193 197 152 440 164 160 169
186 438 197 447 153
152 152 153 135 445
152 425 454 456 440 445
440 164
174 175 425
425 425 439 425 424 423 152 439
141 170
164
165
422
Par.
or Jig.
Open wire lines (contd)
Wind velocity contact nomogram (drawing) 9-8 Wire sizes, American, British, and
Page
French.....................(table) 9-21
Operating, telephone and telegraph traffic: Instructions, traffic.................. 1106b
Personnel requirements................ 1107h
1120c
1123f
Practices, telephone traffic..........1106b
Telegraph switchboard (BD-100)....... 1123b
Telephone switchboard................. 1108
Operating room noise.................... 1107k
Operating speeds, telegraph............. 106
303 304a 1128b
Operation, teletypewriter............... 303b(l)
Operations centers, AWS (AN/TTQ-1)... 243
(photo) 2-41
Operator attitude....................... 1107d
Optimum working frequency (owf), radio. 641b
643
Orientation range, teletypewriter....... 320
1225b
Range finder.................(drawing) 12-18
Osmoplastic B........................... 925b
Owf (optimum working frequency), radio. 641b
643
430
442
462 465 483 487 462 486
465 465
3 46
46 493
47 37
38 464 278 281
67 571 571 447 278 281
P-16 Headset............................ 212c(2)
P type wire, cross-connecting.......... 1151d(3)
Packaged equipment...................... 508c
Telegraph............................. 331b
Carrier............................ 333
348a(2)
D-c................................ 334c
335 349a (2)
. Telephone............................. 508d
Carrier............................ 526 to
529 1151
Voice-frequency.................... 518
Pads, resistance.................(table) 12-14
(drawing) 12-15
Page facsimile: Converter............................... 401c
402e
Elemental area...............(drawing) 4-6
Equipment............................. 401c
Fixed net equipment................... 402f
Map transmission...................... 401a
Receiver.............................. 402c
Scanning.............................. 402a
Synchronization....................... 402d
Transmitter........................... 402b
Page teletypewriter..................... 322b
Pair-per-system operation of CF-l-( )... 524 543d
(table) 5-47
Pan-American Airways radio equipment (table) 6-173
Parks, antenna.............................. 675
Party line service, selective ringing....... 1114f
Pattern corrections, receiving.............. 652
Pattern efficiency.......................... 649
650c
(drawing) 6-105
(drawing) 6-107
17 524 134
83
86
108
87
88
109 134
148
522 140 567 567
121 124
124 121
125 121
123 122 124 123
68 146 163 173
367 325
476 300 297 299
298 300
594
INDEX
PBX-Pro
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig.
PBX (Private Branch Exchange): Battery and generator feeders............ 815
Cord circuits.......................... 232c
Cut-through and non-cut-through cords. 807b 232c
Night and through-dial key............. 232e
Off-premise extensions................. 232a
Ringing bridge......................... 232b
Switchboard............................ 232
Tie-trunks............................. 232a
Trunk-hunting group.................... 802c
807c
Trunks................................. 232a
802a
PE-248 Interrupter....................... 708c
PE-250 Interrupter....................... 708c
Peg counts............................... 1110a
Perforated tape.......................... 322c
Personnel requirements: Maintenance............................. 1160
Switchboard installation............... 1152 to
1154
Switchboard operation.................. 1107h
1123f
Phantom antennas......................... 677
Carbon resistors....................... 677c(4)
Improvised............................. 677c
Lamps, incandescent.................... 677c
Phantom circuit.......................... 511
536c
Phraseology, telephone operators’........ 1108j
Planning a communication system.......... 1103
Planning a radio installation:
Electrical requirements................ 602c
Governing factors...................... 602b
Physical conditions.................... 602b
Reliability of a radio circuit......... 606
655
Service requirements................... 602b
Signal center......................... 1154d
1154e
Types of radio facilities............. 603a
Typical networks..............(drawing) 11-23
Plug counts. ...................... lllOe
Point-to-point circuit: Telephone.......................... 204a
(drawing) 2-1
(table) 2-3
Telety pe wri ter................ 1118d
Requirements................... 1128a
Traffic experience data........ 1127
Typical network............(drawing) 11-23
Polar circuit, telegraph........... 305b
Polar relay.......................(photo) 3-76
(photo) 3-77
Polar relay test set..................... 348
Polarential circuit, telegraph........... 305c
Polarization diversity, radio reception.... 304d 674b (drawing) 6-140
Polarized waves, radio................... 619
623c 1214a
Poles: Classification........................... 907
(table) 9-3
Decay and termites.....................912h
Preservative (Osmoplastic B).......... 925b
Protection............................ 1012a
Selection of........................... 907
Sizes for various wire lines....(table) 9-3
Supports, 2" x 4" and 4" x 4"........ 912g
Page
406
32
402
32
32
31
31
31
31
399
402
31
399
391
391
468
68
540
524
465
487
332
333
332
332
135
160
467
459
220
219
219
223
306
219
527
528
220 489
469
6
7
9
482
492
492
489
50
108
109
107
51
49
325
325
249
258
560
425
426
440
447
456
425
426
440
Par.
or fig. Page
Position requirements: Telephone switchboard.................... 1114 474
Teletypewriter switchboard............ 1129 493
(table) 11-28 494
Power, a-c and d-c:
Equipment: Engine-driven generators............... 710 393
Power packs......................... 706 386
Power panels........................ 707 387
Rectifiers.......................... 706 386
Ringing units....................... 708 391
Transformers........................ 705 386
Factor, effect on generator output.... 715 396
Line, protection from.................. 1002b 451
Line transformer connections.. (drawing) 7-2 388
Panels................................. 707 387
Plan of operation.............(drawing) 7-4 391
Plant maintenance...................... 1165 547
Rated, power of radio sets............ 615b(2) 231
649b 298
(tables) 6-169 to 355
6-174
Rating, engine-generators.............. 715c 396
Teletypewriters....................... 328 79
Ratio, db relation..............(table) 12-1 553
(drawing) 12-2 554
(table) 6-110 302
Power levels, carrier telegraph......... 306a (3) 53
Power ranges in communication systems. . 1202 553
Power Transfer Panel CN-22/F............ 707d 387
Precipitation static.................... 654f 305
Prediction of ranges, v-h-f............. 610 to 225
613 (drawings) 6-6 to 227 6-8
Predictions of maximum usable fre- 64 le 279
quency........................... 643d 281
(drawing) 6-70 280
Press Wireless Co. radio equipment. (table) 6-172 365
(table) 6-173 367
Preventive maintenance............... 1157 539
1162c 542
Priority line marking, telephone switchboards................................... 1107j 465
Priority lines, special operation of.... 1108k(4) 467
Private branch exchange (PBX)........... 232 31
Private lines, telegraph...t............ 1126a (3) 491
Probe, radio............................ 654e(3) 305
Project planning, communication systems. 1103d 460
Propagation (See Radio propagation
under R)
Protection: Cable (lead-covered)..................... 1008 454
1009 454
Extent required....................... 1002 451
Grounding............................. 1011 455
Lightning............................. 1003a 451
1008 454
1012a 456
Line transmission equipment............ 1012b 456
Open wire............................. 1008 454
1012b 456 •
Pole.................................. 1012a 456
Radio station.......................... 1010 455
1012a 456
Sneak current.......................... 1003c 451
Spiral-four cable..................... 1009c 455
Switchboard............................ 1004 452
239 36
1006 453
1007 453
Telephone.............................. 1005 to 452
1007
595
INDEX
Pro-Rai
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig.
Protection and distributing frame X-61823G................................. 1151c(2)
Protection location, telephone station.... 1149d(4)
Protector drainage........................ 1008
Protector grounding, telephone station.... 1149c(5)
Protectors, air gaps, blocks, fuses, heat coils 1003
1010b
Push-to-talk switch, telephone............ 205c
Page
524
517
454
516
451
455
10
Par.
or fig.
Q
Quadded cable..................... 506b
Quadded cable loading units....... 571b
Quarter-wave r-f matching section.. 638c (2)
676g
133
214
275
Radio station protection............... 1010
1012a
Radio system planning (See Planning a radio installation)
Radio telegraph systems, truck channel requirements............................ 1128a (4)
Radio telephone trunk traffic capacity.... 1116
Radio teletypewriter arrangements:.....340
AN/FGC-1 Radio Teletypewriter
Terminal Equipment (TM 11-356) 326 341a (table) 6-172 (table) 6-173 (photo) 3-66 (drawing) 3-38
AN/MRC-2 Radio Set, mobile.. (table) 6-169 347c
Page 455 456
492 481
95
77
95 36C 36f
R
R and S scales, radio........................... 1213
RA (Bendix) radio receivers,
RA-43-( ) Rectifier (TM 11-954)......... 706c
Radiated power, radio................... 649
Radiation efficiency.................... 649
650b 651b (drawing) 6-104 (drawing) 6-107
Radiator (part of antenna array)........ 632a
Radio and wire teletypewriter network. . . 1125
Radio communication, main characteristics 104
Radio communication, main fields of use.. 103
Radio equipment layout, signal center. . . . 1154d (drawing) 11-59
Radio frequency (See R-f)
Radio installations, high power, typical.. . 654 (photos) 6-112 to 6-116
Radio maintenance....................... 1166
Radio Morse network..................... 1125b
(drawing) 11-25
Radio propagation:
High-frequency:
Basic conditions, TB ll-499-( ).... 641d 643
Forecasts........................... 641d(3)
641e 643d
Ground-wave......................... 646
Sky-wave............................ 648
Velocity of......................... 676e
Very-high-frequency................... 611
Radio receivers multipled on one antenna. 670c(2) 675c
Radio relay systems..................... 309e
603d 621 622
560
374
387
297
297
298
299
298
300
266
489
2
2 527 527
304
306
548 490 490
AN/TRA-7 Radio Teletype Equipment 347c (6) British Apparatus-Telegraph, Mark III. 346e 347d
CF-2-( ) Telegraph Terminal, use of... 342 to 346
C-w teletypewriter operation, transmitter keying circuit................. 344c
(drawing) 3-72
Receiving circuit............ 344d
42B1 carrier telegraph........... 341b
(table) 6-174
Frequency shift operation, tactical radio sets............................. 347
Multichannel operation, tactical radio sets................................... 342
Multichannel, single-tone.............341b
Power input to tactical radio sets,
Single-channel, frequency-shift, space-diversity, fixed plant....... 341a
Single-channel operation, tactical radio sets......................... 343
Single-sideband........................ 341c
Single-tone modulation, tactical radio sets......................... 345
603b
Radio repair shop in Truck M-30. (photo) 11-77
Radio s?t characteristics:.................. 693
Airborne........................(table) 6-170
Airways Section, ACS............(table) 6-173
British.........................(table) 6-175
Command radio, ACS..............(table) 6-172
Frequency coverage chart. ... (drawing) 6-176
Navy, U. S....................(drawing) 6-174
Tactical, for ground use........(table) 6-169
V-h-f fighter control...........(table) 6-171
Radio set interference (See Mutual interference between radio sets)
Radio station layout, typical........... 1154e
278 281 278 279 281 292 296 331 227 320 327
58 220 251 254 550 354 360 366 375 365 380 371 355 362
528
359
106
107
105
107
98
101
102
101
97 372
105
98
97
99
95
99
98
102
220
Transmission considerations (See Telegraph transmission over radio) Radio transmission (See H-f transmission or V-h-f transmission)
Radio transmission characteristics at various frequencies (general discussion) 604b
Radio transmitter power comparisons, telegraph................................. 309
(table) 3-17
Radio versus wire......................... 103
104
Railway train dispatching telephone system:............................. 244
Dispatchers’ telephone equipment...... 248
Emergency service..................... 247
Method of operation...................246
Protection............................ 252
Selector equipment: Dispatchers’........................ 248
(photos) 2-43 to 2-45
Way station......................... 249b
Selector operation.................... 251
Signaling ranges....................... 251
Way station equipment:.................249
Selector.....................(photos) 2-47 to
2-48
Telephone.................(photo) 2-46
221
56
57
2
2
38
39
39
39
44
39
40
41
44
44
41
41
41
596
INDEX
Ran-Rep
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par.
or fig. Page
Ranges of v-h-f transmission, prediction... 610 to 225 613
(drawings) 6-6 to 227
6-8
Rated power of radio sets................ 615b (2) 231
649b 298
(tables) 6-169 to 355
6-174
RAX radio receiver, U. S. Navy... (table) 6-174 374
RBM radio receiver, U. S. Navy... (table) 6-174 371
RBQ radio receiver, U. S. Navy. . . (table) 6-174 371
RBZ radio receiver, U. S. Navy.... (table) 6-174 371
RC-47-( ) Remote Control Equipment
(TM 11-312).................... 691c 349
(table) 6-162 348
(photo) 6-164 350
RC-52 Radio Transmitting Equipment
(table) 6-173 367
RC-58-B Facsimile Equipment
(TM 11-374).................... 401c 121
RC-63 Antenna Equipment (TM 11-2616) 633a 267
(drawing) 6-54 267
RC-81 Antenna Equipment.................. 627a 260
(drawing) 6-38 260
(photo) 6-39 260
RC-120 Facsimile Equipment
(TM 11-375B, TM 11-2252)............ 401c 121
RC-256 Radio Receiver.............(table) 6-169 360
RC-257 Radio Transmitter..........(table) 6-169 360
RC-261 Remote Control Equipment
(TM 11-2632)........................ 691d 350
(table) 6-162 348
(photo) 6-165 350
RC-289 Remote Control Equipment...... 691e 350
(table) 6-162 348
(photo) 6-166 351
RC-290 Remote Control Equipment......69If 351
(table) 6-162 348
(photo) 6-166 351
RC-291 Antenna equipment (SCR-300). . 630a 263
(photo) 6-44 263
RC-292 Antenna equipment (SCR-300). . 630b 264
(photo) 6-46 263
RC-296 Antenna equipment (SCR-300). . 630b 264
RCK radio receiver, U. S. Navy. . . (table) 6-174 371
Readability, radio R scale............... 1213 560
Receivers, telephone.....................212c 15
Compensated magnetic type............. 206c 10
Resonant magnetic type................ 209c 12
212c(2) 17
Receiving wave antenna................... 665 316
673d(2) 324
(drawing) 6-139 324
Record cards (See Circuit engineering and administration)
Recording, monitoring and observing equipment................................ 241 36
Records:
Cards................................. 1141 503
1142 508
1149e, (2) 517
Circuit assignment work............... 1144e 512
Installation.......................... T149e 517
1152e 525
Local cable plant engineering......... 1132 496
Trunk plant engineering............... 1141 503
1142 508
Recovery of outside plant................ 920 to 446
922
Rectifier maintenance.................... 1165d 547
Rectifiers, power........................ 706 386
Par.
or fig. Page
Reference noise (RN)..................... 1211a 557
Reference sound level.................... 1212 560
Reference volume......................... 1209 556
Reflection coefficient................... 1217i 563
Reflection loss.......................... 1217 561
(drawing) 12-10 563
Reflector (part of antenna array)........ 632a 266
Regenerative repeater, telegraph, (X-66013A) (OA-3/FC)..................... 335 88
336 88
Regulation, generator: Automatic........................... 715f 397
Inherent.......................... 715e 397
Rehabilitation of captured wire and cable circuits...................... 565 206
917 to 445
919
American loading coils............ 571b 214
(table) 5-90 215
Foreign loading systems........... 571a 214
(table) 5-89 215
4-wire operation.................. 566 208
Capacitance unbalance........... 568 209
Loading considerations.......... 569 211
570b 213
Segregation of cable pairs...... 567 208
(drawing) 5-85 209
Identification of cable pairs..... 565e 207
567f 209
Identification of loaded circuits. 572 215
Loading coil inductance measurements.. 572b 215
Splicing cable.................... 565b 206
Telegraph operation............... 573 217
2-wire circuit operation............... 570 213
Capacitance unbalance.........)...... 570a 213
Loading considerations.......... 570b 213
Relay circuit requirement table.... (table) 11-76 546
Reliability of a radio circuit...... 606 223
655 306
Remote control of radio sets:...... 687 to 344
692
Control line, voice transmission.. 690 346
Improvised arrangements........... 692
(drawing) 6-168 352
Line losses....................... 690f 347
Push-to-talk operation............ 689 345
Typical equipments................ 691 347
(table) 6-162 348
(photos) 6-163 to 350
6-167
Voice transmission requirements... 690 346
692e 354
Repair shop, radio, mobile.....(drawing) 11-77 550
Repeater balance..............•.......... 1218 564
Balancing networks. .. ............... 1218f 565
Hybrid coil, action of................ 1218b 564
Line irregularities, effect of........ 1218g 565
Return loss........................... 1218d 565
Singing............................... 1218c, e 564
Repeater station maintenance............. 1160s 541
Repeater station:........................ 1138f,g 501
Engineering........................... 1138f, g 501
Maintenance........................... 1160e 541
Repeatered voice-frequency circuits......514 137
Comparison with nonrepeatered.........519 140
11-42 Gain adjustments....................... 533c 154
546a 179
Line-up of.......................... 1142 508
Repeater adjustments, sample computation..................... 1142c 509
(table) 11-43 511
597
INDEX
Rep-Rub
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig. Repeatered voice-frequency circuits (contd)
Talking range......................... 541
Tandem operation.......................533
Transmission level diagram... (drawing) 5-53
(drawing) 11-38
(drawing) 11-39
Types................................. 514
Repeaters, radio (See Radio relay systems)
Page
Repeaters, telegraph.................... 324c
304e 327 334
Repeaters, telephone, carrier:
CF-3 telephone repeater............... 521
522
CF-5 (2-wire)......................... 525
Locations in carrier systems.......... 530
Spacings, carrier..................... 543
C carrier....................(table) 5-48
Carrier hybrid system........(table) 5-46
CF-4 converter...............(table) 5-48
Effects of crosstalk................. 550d
H carrier....................(table) 5-48
Open wire converter..........(table) 5-48
Spiral-four carrier (CF-1)...(table) 5-45
Repeaters telephone voice-frequency: Balance............................... 1218f
EE—89—A......................... 516a
541b (photo) 5-8
EE-99-A......................... 516b
(photo) 5-9
4-wire.......................... 514e
Gains............................546
Packaged......................... 518
541d
Portable.............................. 516
Spacings............................. 542a(l)
TP-14................................. 516c
541c 21-type............................... 514b
1218i (drawing) 12-12
22-type............................... 514c-
1218b
(drawing) 12-11
161
154
178
509
509
137
71
50
77
87
163
142
143
147
152
163
174
173
174
183
174
174
172
565
138
161
139
139
139
138
179
140
161
138
162
139
161
137
565
560
138
564
2-wire versus 4-wire................... 515
Repeating coils on voice-frequency circuits, purpose of............... 513a
Reperforator............................. 303b
Reperforator-transmitter................. 324b
Reports, trouble......................... 1108k (2)
1123g 1163
(drawing) 11-73
(drawing) 11-74
Resistance, d-c:
Cable, lead-covered.............(table) 5-39
Open wire lines.................(table) 5-38
Rubber-covered wires and cables. (table) 5-39
Resistance pads...................(table) 12-14
(drawing) 12-15
Resistivity, earth....................... 1013
Return loss.............................. 1218d
Return losses, combining................. 570
Reversals, telegraph..................... 1222
R-f transmission lines:.................. 638
676
Attenuation of open wire............... 676d
638
(drawing) 6-146
557 138
137 47
71 467 487 543 542 542
165 165 165 567 567 457 564 213 568 275 329
329 275 336
Par. or fig. Page
R-f transmission lines (contd) Cables, r-f.................... 676b (2) 329
676d(3) 329
(drawing) 6-146
(table) 6-167 351
Cage......................... 676b (3) 329
Coaxial cable.................. 638a 235
676b(2) 329
Impedance relations............ 676g 331
Improvised..................... 638c 275
676f 331
Losses in field cable.......... 638b 275
(drawing) 6-146 330
Open wire line............... 676b (1) 329
676d 329
(drawing) 6-145 330
Quarter-wave matching section. 638c (2) 275
676g 331
Separation between........... 675b (3) 326
Spaced-wire line, improvised.... 638c 275
676f 331
(drawings) 6-66 to 275
6-68
Unbalanced and balanced lines. 654d(l) 305
675 325
676c 329
676d(3) 329
W-110-B or W-143 wire for r-f transmission lines.................... 638c(l) 275
676f 331
(table) 6-147 331
Ringdown trunks......................... 214d 18
234 32
Ringers................................. 236 34
529 152
708 391
1165e 547
Ringing (See Signaling)
Ringing, code........................... 1114f 476
Ringing bridge.......................... 232b 31
Ringing range, voice-frequency.......... 231 30
Rivers, radio transmission over......... 618d 247
RM-7 Control Unit................(table) 6-162 348
RM-14 Remote Control Unit........(table) 6-162 348
RM-21 Remote Control Unit........(table) 6-162 348
RM-29-( ) Remote Control Unit (TM 11-308)............................. 691f 351
(photo) 6-167 351
RM-39-( ) Remote Control Unit (TM 11-2667)............................ 691e 350
RM-52 Remote Control Unit........(table) 6-162 348
RM-53 Control Unit...............(table) 6-162 348
RN (reference noise).................... 1211a 557
Room noise.............................. 1212 560
Route bulletins......................... 1107f 464
1122c 483
1123d 487
RTA-1B (Bendix) radio set, U. S. Navy (table) 6-174 374
Rubber-covered wires and cables:
Attenuation....................(table) 5-39 165
Cable hangers................(drawing) 9-16 437
Capacitance....................(table) 5-39 165
Circuit lengths...................... 542a(l) 162
543b 163
(table) 5-45
Common types.....................(table) 5-1
Construction methods, wire............... 909 to
916
Electrical characteristics.......(table) 5-39
Impedance........................(table) 5-39
Jungle construction, wire................926
927
172
132
429
165
166
448
450
598
INDEX
Rub—Sea
ELECTRICAL COMMUNICATION SYSTEMS ENGINEERING
Par. or fig.
Rubber-covered wires and cables: (contd) Loading. . ......................... 512
Physical characteristic.........(table) 5-1
(table) 9-9
(table) 9-14
Repeater spacing....................... 542a (1)
543b
(table) 5-45
Resistance......................(table) 5-39
Spaced aerial pairs.................... 504
Stabilized and nonstabilized........... 503e
Submarine.......;..................... 507b
916
Talking ranges..................(table) 5-44
Transmission data...............(table) 5-39
Twin pairs............................. 504
(table) 5-38
s
Page
136 132
432 435
162 163
172
165 133
132
134 442
170
165 133
165
S meters................................ 1213b
S + DX.................................. 307
333 351
S + SX.................................. 307
Sag, open wire lines.................... 908
Measurement of........................ 908c
(drawing) 9-7
Sag difference........................ 556c
Sag and tension tables: Field wire lines.................(table) 9-15
Open wire lines...............(tables) 9-4 to
9-6
Spiral-four cable..............(table) 9-15
(table) 9-18
SB-6/GG Telegraph Switchboard (TM 11-2035)...................... 339
(photo) 3-64
SB-18/GT Emergency Switchboard..........218
(photo) 2-23
Scanning, facsimile..............•...... 402a
Schuttig radio equipment.........(table) 6-141
(photo) 6-172
SCR-177-A Radio Set..............(table) 6-169
SCR-177-B Radio Set (TM 11-232) (table) 6-169
SCR-183 Radio Set (TM 11-200).. (table) 6-170 SCR-187 Radio Set................(table) 6-170
SCR-188 and -A Radio Set (TM 11-233)
(table) 6-75
(table) 6-169
SCR-193-( ) Radio Set (TM 11-273) •
(table) 6-76
(table) 6-169 SCR-197 Radio Set (TM 11-241). .(table) 6-169 SCR-203 Radio Set (TM 11-239).. (table) 6-169 SCR-209 Radio Set................(table) 6-169
SCR-210 Radio Set (TM 11-272).. (table) 6-169 SCR-211 Frequency Meter................ 642i
(photo) 6-71
SCR-245 Radio Set (TM 11-272).. (table) 6-169 SCR-274N Radio Set...............(table) 6-170
SCR-281 Radio Set (TM 11-244).. (table) 6-172 SCR-283 Radio Set (TM 11-200).. (table) 6-170 SCR-284-A Radio Set (TM 11-275)
(table) 6-77
(table) 6-169
SCR-287 Radio Set................(table) 6-170
SCR-288-A Radio Set (TM 11-250)
(table) 6-169 SCR-293 Radio Set................(table) 6-169
SCR-294 Radio Set................(table) 6-169
560 54
86
111
54 425 428 429 193
436 427
436 437
94 94
21
21
122 326 366 355
355 360 360
286 355
286 355 355 355 355
350 280 285 356 361
365 361
286 356 361
356 356 356
. Par.
or fig. SCR-298-C Radio Set..........(table) 6-169
SCR-299 Radio Set (TM 11-280)....... 661e
662a 663c
(table) 6-169
SCR-300 Radio Set (TM 11-242)....... 661e
663c (photo) 6-1 (table) 6-169
SCR-399 Radio Set (TM 11-281)....... 661e
(photo) 6-78
(photo) 6-79
(table) 6-169 SCR-499 Radio Set (TM 11-281). .(table) 6-169 SCR-506 Radio Set (TM 11-630). (photo) 6-80
(table) 6-169
SCR-508 Radio Set (TM 11-600). (photo) 6-2
(table) 6-169
SCR-509 Radio Set