[Title 47 CFR ]
[Code of Federal Regulations (annual edition) - October 1, 1996 Edition]
[From the U.S. Government Printing Office]
47
Telecommunication
[[Page i]]
PARTS 70 TO 79
Revised as of October 1, 1996
CONTAINING
A CODIFICATION OF DOCUMENTS
OF GENERAL APPLICABILITY
AND FUTURE EFFECT
AS OF OCTOBER 1, 1996
With Ancillaries
Published by
the Office of the Federal Register
National Archives and Records
Administration
as a Special Edition of
the Federal Register
[[Page ii]]
U.S. GOVERNMENT PRINTING OFFICE
WASHINGTON : 1996
For sale by U.S. Government Printing Office
Superintendent of Documents, Mail Stop: SSOP, Washington, DC 20402-9328
[[Page iii]]
Table of Contents
Page
Explanation................................................. v
Title 47:
Chapter I--Federal Communications Commission (Continued).. 3
Finding Aids:
Material Approved for Incorporation by Reference.......... 663
Table of CFR Titles and Chapters.......................... 665
Alphabetical List of Agencies Appearing in the CFR........ 681
Table of OMB Control Numbers.............................. 691
List of CFR Sections Affected............................. 699
[[Page iv]]
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Cite this Code: CFR
To cite the regulations in this volume use title, part
and section number. Thus, 47 CFR 73.1 refers to title
47, part 73, section 1.
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[[Page v]]
EXPLANATION
The Code of Federal Regulations is a codification of the general and
permanent rules published in the Federal Register by the Executive
departments and agencies of the Federal Government. The Code is divided
into 50 titles which represent broad areas subject to Federal
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parts covering specific regulatory areas.
Each volume of the Code is revised at least once each calendar year
and issued on a quarterly basis approximately as follows:
Title 1 through Title 16.................................as of January 1
Title 17 through Title 27..................................as of April 1
Title 28 through Title 41...................................as of July 1
Title 42 through Title 50................................as of October 1
The appropriate revision date is printed on the cover of each
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LEGAL STATUS
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HOW TO USE THE CODE OF FEDERAL REGULATIONS
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EFFECTIVE AND EXPIRATION DATES
Each volume of the Code contains amendments published in the Federal
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OMB CONTROL NUMBERS
The Paperwork Reduction Act of 1980 (Pub. L. 96-511) requires
Federal agencies to display an OMB control number with their information
collection request.
[[Page vi]]
Many agencies have begun publishing numerous OMB control numbers as
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OBSOLETE PROVISIONS
Provisions that become obsolete before the revision date stated on
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of provisions in effect on a given date in the past by using the
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1963, 1964-1972, or 1973-1985, published in seven separate volumes. For
the period beginning January 1, 1986, a ``List of CFR Sections
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INCORPORATION BY REFERENCE
What is incorporation by reference? Incorporation by reference was
established by statute and allows Federal agencies to meet the
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This material, like any other properly issued regulation, has the force
of law.
What is a proper incorporation by reference? The Director of the
Federal Register will approve an incorporation by reference only when
the requirements of 1 CFR part 51 are met. Some of the elements on which
approval is based are:
(a) The incorporation will substantially reduce the volume of
material published in the Federal Register.
(b) The matter incorporated is in fact available to the extent
necessary to afford fairness and uniformity in the administrative
process.
(c) The incorporating document is drafted and submitted for
publication in accordance with 1 CFR part 51.
Properly approved incorporations by reference in this volume are
listed in the Finding Aids at the end of this volume.
What if the material incorporated by reference cannot be found? If
you have any problem locating or obtaining a copy of material listed in
the Finding Aids of this volume as an approved incorporation by
reference, please contact the agency that issued the regulation
containing that incorporation. If, after contacting the agency, you find
the material is not available, please notify the Director of the Federal
Register, National Archives and Records Administration, Washington DC
20408, or call (202) 523-4534.
CFR INDEXES AND TABULAR GUIDES
A subject index to the Code of Federal Regulations is contained in a
separate volume, revised annually as of January 1, entitled CFR Index
and Finding Aids. This volume contains the Parallel Table of Statutory
Authorities and Agency Rules (Table I), and Acts Requiring Publication
in the Federal Register (Table II). A list of CFR titles, chapters, and
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An index to the text of ``Title 3--The President'' is carried within
that volume.
The Federal Register Index is issued monthly in cumulative form.
This index is based on a consolidation of the ``Contents'' entries in
the daily Federal Register.
[[Page vii]]
A List of CFR Sections Affected (LSA) is published monthly, keyed to
the revision dates of the 50 CFR titles.
REPUBLICATION OF MATERIAL
There are no restrictions on the republication of material appearing
in the Code of Federal Regulations.
INQUIRIES
For a legal interpretation or explanation of any regulation in this
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For inquiries concerning CFR reference assistance, call 202-523-5227
or write to the Director, Office of the Federal Register, National
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Richard L. Claypoole,
Director,
Office of the Federal Register.
October 1, 1996.
[[Page ix]]
THIS TITLE
Title 47--Telecommunication is composed of five volumes. The parts
in these volumes are arranged in the following order: Parts 0-19, parts
20-39, parts 40-69, parts 70-79, and part 80 to end, chapter I--Federal
Communications Commission. The last volume, part 80 to end, also
includes chapter II--Office of Science and Technology Policy and
National Security Council, and chapter III--National Telecommunications
and Information Administration, Department of Commerce. The contents of
these volumes represent all current regulations codified under this
title of the CFR as of October 1, 1996.
Part 73 contains a numerical designation of FM broadcast channels
(Sec. 73.201) and a table of FM allotments designated for use in
communities in the United States, its territories, and possessions
(Sec. 73.202). Part 73 also contains a numerical designation of
television channels (Sec. 73.603) and a table of allotments which
contain channels designated for the listed communities in the United
States, its territories, and possessions (Sec. 73.606).
The OMB control numbers for the Federal Communications Commission,
appear in Sec. 0.408 of chapter I. For the convenience of the user
Sec. 0.408 is reprinted in the Finding Aids section of the second
through fifth volumes.
A redesignation table appears in the Finding Aids section of the
volume containing part 80 to end.
For this volume, Elizabeth N. Thomas was Chief Editor. The Code of
Federal Regulations publication program is under the direction of
Frances D. McDonald, assisted by Alomha S. Morris.
[[Page x]]
[[Page 1]]
TITLE 47--TELECOMMUNICATION
(This book contains parts 70 to 79)
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Part
Chapter I--Federal Communications Commission (Continued).... 73
[[Page 3]]
CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION (Continued)
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SUBCHAPTER C--BROADCAST RADIO SERVICES
Part Page
70-72 [Reserved]
73 Radio broadcast services.................... 5
74 Experimental radio, auxiliary, special
broadcast and other program
distributional services................. 351
76 Cable television service.................... 466
78 Cable television relay service.............. 631
79 [Reserved]
Supplemental Publications:
Annual Reports of the Federal
Communications Commission to Congress.
Federal Communications Commission
Reports of Orders and Decision.
Communications Act of 1934 (with
amendments and index thereto), Recap.
Version May 1989.
Miscellaneous Publications:
Broadcast Operator Handbook, 1976
edition.
[[Page 5]]
SUBCHAPTER C--BROADCAST RADIO SERVICES
PARTS 70-72--[RESERVED]
PART 73--RADIO BROADCAST SERVICES--Table of Contents
Subpart A--AM Broadcast Stations
Sec.
73.1 Scope.
73.14 AM broadcast definitions.
73.21 Classes of AM broadcast channels and stations.
73.23 AM broadcast station applications affected by international
agreements.
73.24 Broadcast facilities; showing required.
73.25 Clear channels; Class B and Class D stations.
73.26 Regional channels; Class B and Class D stations.
73.27 Local channels; Class C stations.
73.28 Assignment of stations to channels.
73.29 Class C stations on regional channels.
73.30 Petition for authorization of an allotment in the 1605-1705 kHz
band.
73.31 Rounding of nominal power specified on applications.
73.33 Antenna systems; showing required.
73.35 Calculation of improvement factors.
73.37 Applications for broadcast facilities, showing required.
73.44 AM transmission system emission limitations.
73.45 AM antenna systems.
73.49 AM transmission system fencing requirements.
73.51 Determining operating power.
73.53 Requirements for authorization of antenna monitors.
73.54 Antenna resistance and reactance measurements.
73.57 Remote reading antenna and common point ammeters.
73.58 Indicating instruments.
73.61 AM directional antenna field strength measurements.
73.62 Directional antenna system tolerances.
73.68 Sampling systems for antenna monitors.
73.69 Antenna monitors.
73.72 Operating during the experimental period.
73.88 Blanketing interference.
73.99 Presunrise service authorization (PSRA) and Postsunset service
authorization (PSSA).
73.127 Use of multiplex transmission.
73.128 AM stereophonic broadcasting.
73.132 Territorial exclusivity.
73.150 Directional antenna systems.
73.151 Field strength measurements to establish performance of
directional antennas.
73.152 Modification of directional antenna data.
73.153 Field strength measurements in support of applications or
evidence at hearings.
73.154 AM directional antenna partial proof of performance
measurements.
73.157 Antenna testing during daytime.
73.158 Directional antenna monitoring points.
73.160 Vertical plane radiation characteristics, f(
Subpart A--AM Broadcast Stations
Sec. 73.1 Scope.
This subpart contains those rules which apply exclusively to the AM
broadcast service and are in addition to those rules in Subpart H which
are common to all AM, FM and TV broadcast services, commercial and
noncommercial.
[47 FR 8587, Mar. 1, 1982]
Sec. 73.14 AM broadcast definitions.
AM broadcast band. The band of frequencies extending from 535 to
1705 kHz.
AM broadcast channel. The band of frequencies occupied by the
carrier and the upper and lower sidebands of an AM broadcast signal with
the carrier frequency at the center. Channels are designated by their
assigned carrier frequencies. The 117 carrier frequencies assigned to AM
broadcast stations begin at 540 kHz and progress in 10 kHz steps to 1700
kHz. (See Sec. 73.21 for the classification of AM broadcast channels).
AM broadcast station. A broadcast station licensed for the
dissemination of radio communications intended to be received by the
public and operated on a channel in the AM broadcast band.
Amplitude modulated stage. The radio-frequency stage to which the
modulator is coupled and in which the carrier wave is modulated in
accordance with the system of amplitude modulation and the
characteristics of the modulating wave.
Amplitude modulator stage. The last amplifier stage of the
modulating wave amplitude modulates a radio-frequency stage.
Antenna current. The radio-frequency current in the antenna with no
modulation.
Antenna input power. The product of the square of the antenna
current and the antenna resistance at the point where the current is
measured.
Antenna resistance. The total resistance of the transmitting antenna
system at the operating frequency and at the point at which the antenna
current is measured.
Blanketing. The interference which is caused by the presence of an
AM broadcast signal of one volt per meter (V/m) or greater strengths in
the area adjacent to the antenna of the transmitting station. The 1 V/m
contour is referred to as the blanket contour and the area within this
contour is referred to as the blanket area.
Carrier-amplitude regulation (Carrier shift). The change in
amplitude of the carrier wave in an amplitude-modulated transmitter when
modulation is applied under conditions of symmetrical modulation.
Combined audio harmonics. The arithmetical sum of the amplitudes of
all the separate harmonic components. Root sum square harmonic readings
may be accepted under conditions prescribed by the FCC.
[[Page 10]]
Critical directional antenna. An AM broadcast directional antenna
that is required, by the terms of a station authorization, to be
operated with the relative currents and phases within the antenna
elements at closer tolerances of deviation than those permitted under
Sec. 73.62 and observed with a high precision monitor capable of
measuring these parameters.
Critical hours. The two hour period immediately following local
sunrise and the two hour period immediately preceding local sunset.
Daytime. The period of time between local sunrise and local sunset.
Effective field; Effective field strength. The root-mean-square
(RMS) value of the inverse distance fields at a distance of 1 kilometer
from the antenna in all directions in the horizontal plane. The term
``field strength'' is synonymous with the term ``field intensity'' as
contained elsewhere in this Part.
Equipment performance measurements. The measurements performed to
determine the overall performance characteristics of a broadcast
transmission system from point of program origination at main studio to
sampling of signal as radiated. (See Sec. 73.1590)
Experimental period. the time between 12 midnight local time and
local sunrise, used by AM stations for tests, maintenance and
experimentation.
Frequency departure. The amount of variation of a carrier frequency
or center frequency from its assigned value.
Incidental phase modulation. The peak phase deviation (in radians)
resulting from the process of amplitude modulation.
Input power. Means the product of the direct voltage applied to the
last radio stage and the total direct current flowing to the last radio
stage, measured without modulation.
Intermittent service area. Means the area receiving service from the
groundwave of a broadcast station but beyond the primary service area
and subject to some interference and fading.
Last radio stage. The radio-frequency power amplifier stage which
supplies power to the antenna.
Left (or right) signal. The electrical output of a microphone or
combination of microphones placed so as to convey the intensity, time,
and location of sounds originated predominately to the listener's left
(or right) of the center of the performing area.
Left (or right) stereophonic channel. The left (or right) signal as
electrically reproduced in reception of AM stereophonic broadcasts.
Main channel. The band of audio frequencies from 50 to 10,000 Hz
which amplitude modulates the carrier.
Maximum percentage of modulation. The greatest percentage of
modulation that may be obtained by a transmitter without producing in
its output, harmonics of the modulating frequency in excess of those
permitted by these regulations. (See Sec. 73.1570)
Maximum rated carrier power. The maximum power at which the
transmitter can be operated satisfactorily and is determined by the
design of the transmitter and the type and number of vacuum tubes or
other amplifier devices used in the last radio stage.
Model I facility. A station operating in the 1605-1705 kHz band
featuring fulltime operation with stereo, competitive technical quality,
10 kW daytime power, 1 kW nighttime power, non-directional antenna (or a
simple directional antenna system), and separated by 400-800 km from
other co-channel stations.
Model II facility. A station operating in the 535-1605 kHz band
featuring fulltime operation, competitive technical quality, wide area
daytime coverage with nighttime coverage at least 15% of the daytime
coverage.
Nighttime. The period of time between local sunset and local
sunrise.
Nominal power. The antenna input power less any power loss through a
dissipative network and, for directional antennas, without consideration
of adjustments specified in paragraphs (b)(1) and (b)(2) of Sec. 73.51
of the rules. However, for AM broadcast applications granted or filed
before June 3, 1985, nominal power is specified in a system of
classifications which include the following values: 50 kW, 25 kW, 10 kW,
5 kW, 2.5 kW, 1 kW, 0.5 kW, and 0.25 kW. The specified nominal power for
any station in this group of stations will be retained until action is
taken on or after June 3, 1985, which involves a
[[Page 11]]
change in the technical facilities of the station.
Percentage modulation (amplitude)
In a positive direction:
M = MAX-C x 100
----------------
c
In a negative direction:
M = C-MIN x 100
---------------
c
Where:
M = Modulation level in percent.
MAX = Instantaneous maximum level of the modulated radio frequency
envelope.
MIN = Instantaneous minimum level of the modulated radio frequency
envelope.
C = (Carrier) level of radio frequency envelope without modulation.
Plate modulation. The modulation produced by introduction of the
modulating wave into the plate circuit of any tube in which the carrier
frequency wave is present.
Primary service area. Means the service area of a broadcast station
in which the groundwave is not subject to objectionable interference or
objectionable fading.
Proof of performance measurements or antenna proof of performance
measurements. The measurements of field strengths made to determine the
radiation pattern or characteristics of an AM directional antenna
system.
Secondary service area. Means the service area of a broadcast
station served by the skywave and not subject to objectionable
interference and in which the signal is subject to intermittent
variations in strength.
Stereophonic channel. The band of audio frequencies from 50 to
10,000 Hz containing the stereophonic information which modulates the
radio frequency carrier.
Stereophonic crosstalk. An undesired signal occurring in the main
channel from modulation of the stereophonic channel or that occurring in
the stereophonic channel from modulation of the main channel.
Stereophonic pilot tone. An audio tone of fixed or variable
frequency modulating the carrier during the transmission of stereophonic
programs.
Stereophonic separation. The ratio of the electrical signal caused
in the right (or left) stereophonic channel to the electrical signal
caused in the left (or right) stereophonic channel by the transmission
of only a right (or left) signal.
Sunrise and sunset. For each particular location and during any
particular month, the time of sunrise and sunset as specified in the
instrument of authorization (See Sec. 73.1209).
White area. The area or population which does not receive
interference-free primary service from an authorized AM station or does
not receive a signal strength of at least 1 mV/m from an authorized FM
station.
[47 FR 8587, Mar. 1, 1982, as amended at 47 FR 13164, Mar. 29, 1982; 47
FR 13812, Apr. 1, 1982; 50 FR 18821, May 2, 1985; 50 FR 47054, Nov. 14,
1985; 56 FR 64856, Dec. 12, 1991]
Sec. 73.21 Classes of AM broadcast channels and stations.
(a) Clear channel. A clear channel is one on which stations are
assigned to serve wide areas. These stations are protected from
objectionable interference within their primary service areas and,
depending on the class of station, their secondary service areas.
Stations operating on these channels are classified as follows:
(1) Class A station. A Class A station is an unlimited time station
that operates on a clear channel and is designed to render primary and
secondary service over an extended area and at relatively long distances
from its transmitter. Its primary service area is protected from
objectionable interference from other stations on the same and adjacent
channels, and its secondary service area is protected from interference
from other stations on the same channel. (See Sec. 73.182). The
operating power shall not be less than 10 kW nor more than 50 kW. (Also
see Sec. 73.25(a)).
(2) Class B station. A Class B station is an unlimited time station
which is designed to render service only over a primary service area.
Class B stations are authorized to operate with a minimum power of 0.25
kW (or, if less than 0.25 kW, an equivalent RMS antenna field of at
least 141 mV/m at 1 km) and a maximum power of 50 kW, or 10 kW for
stations that are authorized to operate in the 1605-1705 kHz band.
[[Page 12]]
(3) Class D station. A Class D station operates either daytime,
limited time or unlimited time with nighttime power less than 0.25 kW
and an equivalent RMS antenna field of less than 141 mV/m at one km.
Class D stations shall operate with daytime powers not less than 0.25 kW
nor more than 50 kW. Nighttime operations of Class D stations are not
afforded protection and must protect all Class A and Class B operations
during nighttime hours. New Class D stations that had not been
previously licensed as Class B will not be authorized.
(b) Regional Channel. A regional channel is one on which Class B and
Class D stations may operate and serve primarily a principal center of
population and the rural area contiguous thereto.
Note: Until the North American Regional Broadcasting Agreement
(NARBA) is terminated with respect to the Bahama Islands and the
Dominican Republic, radiation toward those countries from a Class B
station may not exceed the level that would be produced by an
omnidirectional antenna with a transmitted power of 5 kW, or such lower
level as will comply with NARBA requirements for protection of stations
in the Bahama Islands and the Dominican Republic against objectionable
interference.
(c) Local channel. A local channel is one on which stations operate
unlimited time and serve primarily a community and the suburban and
rural areas immediately contiguous thereto.
(1) Class C station. A Class C station is a station operating on a
local channel and is designed to render service only over a primary
service area that may be reduced as a consequence of interference in
accordance with Sec. 73.182. The power shall not be less than 0.25 kW,
nor more than 1 kW. Class C stations that are licensed to operate with
0.1 kW may continue to do so.
[56 FR 64856, Dec. 12, 1991]
Sec. 73.23 AM broadcast station applications affected by international agreements.
(a) Except as provided in paragraph (b) of this section, no
application for an AM station will be accepted for filing if
authorization of the facilities requested would be inconsistent with
international commitments of the United States under treaties and other
international agreements, arrangements and understandings. (See list of
such international instruments in Sec. 73.1650(b)). Any such application
that is inadvertently accepted for filing will be dismissed.
(b) AM applications that involve conflicts only with the North
American Regional Broadcasting Agreement (NARBA), but that are in
conformity with the remaining treaties and other international
agreements listed in Sec. 73.1650(b) and with the other requirements of
this part 73, will be granted subject to such modifications as the FCC
may subsequently find appropriate, taking international considerations
into account.
(c) In the case of any application designated for hearing on issues
other than those related to consistency with international relationships
and as to which no final decision has been rendered, whenever action
under this section becomes appropriate because of inconsistency with
international relationships, the applicant involved shall,
notwithstanding the provisions Secs. 73.3522 and 73.3571, be permitted
to amend its application to achieve consistency with such relationships.
In such cases the provisions of Sec. 73.3605(c) will apply.
(d) In some circumstances, special international considerations may
require that the FCC, in acting on applications, follow procedures
different from those established for general use. In such cases,
affected applicants will be informed of the procedures to be followed.
[56 FR 64856, Dec. 12, 1991]
Sec. 73.24 Broadcast facilities; showing required.
An authorization for a new AM broadcast station or increase in
facilities of an existing station will be issued only after a
satisfactory showing has been made in regard to the following, among
others:
(a) That the proposed assignment will tend to effect a fair,
efficient, and equitable distribution of radio service among the several
states and communities.
(b) That a proposed new station (or a proposed change in the
facilities of an
[[Page 13]]
authorized station) complies with the pertinent requirements of
Sec. 73.37 of this chapter.
(c) That the applicant is financially qualified to construct and
operate the proposed station.
(d) That the applicant is legally qualified. That the applicant (or
the person or persons in control of an applicant corporation or other
organization) is of good character and possesses other qualifications
sufficient to provide a satisfactory public service.
(e) That the technical equipment proposed, the location of the
transmitter, and other technical phases of operation comply with the
regulations governing the same, and the requirements of good engineering
practice.
(f) That the facilities sought are subject to assignment as
requested under existing international agreements and the rules and
regulations of the Commission.
(g) That the population within the 1 V/m contour does not exceed 1.0
percent of the population within the 25 mV/m contour: Provided, however,
That where the number of persons within the 1 V/m contour is 300 or less
the provisions of this paragraph are not applicable.
(h) That, in the case of an application for a Class B or Class D
station on a clear channel, the proposed station would radiate, during
two hours following local sunrise and two hours preceding local sunset,
in any direction toward the 0.1 mV/m groundwave contour of a co-channel
United States Class A station, no more than the maximum value permitted
under the provisions of Sec. 73.187.
(i) That, for all stations, the daytime 5 mV/m contour encompasses
the entire principal community to be served. That, for stations in the
535-1605 kHz band, 80% of the principal community is encompassed by the
nighttime 5 mV/m contour or the nighttime interference-free contour,
whichever value is higher. That, for stations in the 1605-1705 kHz band,
50% of the principal community is encompassed by the 5 mV/m contour or
the nighttime interference-free contour, whichever value is higher.
That, Class D stations with nighttime authorizations need not
demonstrate such coverage during nighttime operation.
(j) That the public interest, convenience, and necessity will be
served through the operation under the proposed assignment.
[28 FR 13574, Dec. 14, 1963, as amended at 38 FR 5874, Mar. 5, 1973; 49
FR 43960, Nov. 1, 1984; 50 FR 40014, Oct. 1, 1985; 52 FR 11654, Apr. 10,
1987; 53 FR 1031, Jan. 15, 1988; 56 FR 64857, Dec. 12, 1991]
Sec. 73.25 Clear channels; Class A, Class B and Class D stations.
The frequencies in the following tabulations are designated as clear
channels and assigned for use by the Classes of stations given:
(a) On each of the following channels, one Class A station may be
assigned, operating with power of 50 kW: 640, 650, 660, 670, 700, 720,
750, 760, 770, 780, 820, 830, 840, 870, 880, 890, 1020, 1030, 1040,
1100, 1120, 1160, 1180, 1200, and 1210 kHz. In Alaska, these frequencies
can be used by Class A stations subject to the conditions set forth in
Sec. 73.182(a)(1)(ii). On the channels listed in this paragraph, Class B
and Class D stations may be assigned.
(b) To each of the following channels there may be assigned Class A,
Class B and Class D stations: 680, 710, 810, 850, 940, 1000, 1060, 1070,
1080, 1090, 1110, 1130, 1140, 1170, 1190, 1500, 1510, 1520, 1530, 1540,
1550, and 1560 kHz.
Note: Until superseded by a new agreement, protection of the Bahama
Islands shall be in accordance with NARBA. Accordingly, a Class A, Class
B or Class D station on 1540 kHz shall restrict its signal to a value no
greater than 5 V/m groundwave or 25 V/m-10% skywave at
any point of land in the Bahama Islands, and such stations operating
nighttime (i.e., sunset to sunrise at the location of the U.S. station)
shall be located not less than 650 miles from the nearest point of land
in the Bahama Islands.
(c) Class A, Class B and Class D stations may be assigned on 540,
690, 730, 740, 800, 860, 900, 990, 1010, 1050, 1220, 1540, 1570, and
1580 kHz.
[28 FR 13574, Dec. 14, 1963, as amended at 33 FR 4410, Mar. 12, 1968; 35
FR 18052, Nov. 25, 1970; 47 FR 27862, June 28, 1982; 49 FR 43960, Nov.
1, 1984; 50 FR 24520, June 11, 1985; 52 FR 47568, Dec. 15, 1987; 53 FR
1031, Jan. 15, 1988; 54 FR 39736, Sept. 28, 1989; 56 FR 64857, Dec. 12,
1991]
[[Page 14]]
Sec. 73.26 Regional channels; Class B and Class D stations.
(a) The following frequencies are designated as regional channels
and are assigned for use by Class B and Class D stations: 550, 560, 570,
580, 590, 600, 610, 620, 630, 790, 910, 920, 930, 950, 960, 970, 980,
1150, 1250, 1260, 1270, 1280, 1290, 1300, 1310, 1320, 1330, 1350, 1360,
1370, 1380, 1390, 1410, 1420, 1430, 1440, 1460, 1470, 1480, 1590, 1600,
1610, 1620, 1630, 1640, 1650, 1660, 1670, 1680, 1690, and 1700 kHz.
(b) Additionally, in Alaska, Hawaii, Puerto Rico, and the U.S.
Virgin Islands the frequencies 1230, 1240, 1340, 1400, 1450, and 1490
kHz are designated as Regional channels, and are assigned for use by
Class B stations. Stations formerly licensed to these channels in those
locations as Class C stations are redesignated as Class B stations.
[56 FR 64857, Dec. 12, 1991]
Sec. 73.27 Local channels; Class C stations.
Within the conterminous 48 states, the following frequencies are
designated as local channels, and are assigned for use by Class C
stations: 1230, 1240, 1340, 1400, 1450, and 1490 kHz.
[56 FR 64857, Dec. 12, 1991]
Sec. 73.28 Assignment of stations to channels.
(a) The Commission will not make an AM station assignment that does
not conform with international requirements and restrictions on spectrum
use that the United States has accepted as a signatory to treaties,
conventions, and other international agreements. See Sec. 73.1650 for a
list of pertinent treaties, conventions and agreements, and Sec. 73.23
for procedural provisions relating to compliance with them.
(b) Engineering standards now in force domestically differ in some
respects from those specified for international purposes. The
engineering standards specified for international purposes (see
Sec. 73.1650, International Agreements) will be used to determine:
(1) The extent to which interference might be caused by a proposed
station in the United States to a station in another country; and
(2) whether the United States should register an objection to any
new or changed assignment notified by another country. The domestic
standards in effect in the United States will be used to determine the
extent to which interference exists or would exist from a foreign
station where the value of such interference enters into a calculation
of:
(i) The service to be rendered by a proposed operation in the United
States; or
(ii) the permissible interfering signal from one station in the
United States to another United States station.
[28 FR 13574, Dec. 14, 1963, as amended at 29 FR 9499, July 11, 1964; 49
FR 32358, Aug. 14, 1984; 50 FR 18821, May 2, 1985; 54 FR 39736, Sept.
28, 1989; 56 FR 64857, Dec. 12, 1991]
Sec. 73.29 Class C stations on regional channels.
No license will be granted for the operation of a Class C station on
a regional channel.
[ 56 FR 64857, Dec. 12, 1991]
Sec. 73.30 Petition for authorization of an allotment in the 1605-1705 kHz band.
(a) Any party interested in operating an AM broadcast station on one
of the ten channels in the 1605-1705 kHz band must file a petition for
the establishment of an allotment to its community of license. Each
petition must include the following information:
(1) Name of community for which allotment is sought;
(2) Frequency and call letters of the petitioner's existing AM
operation; and
(3) Statement as to whether or not AM stereo operation is proposed
for the operation in the 1605-1705 kHz band.
(b) Petitions are to be filed during a filing period to be
determined by the Commission. For each filing period, eligible stations
will be allotted channels based on the following steps:
(1) Stations are ranked in descending order according to the
calculated improvement factor.
(2) The station with the highest improvement factor is initially
allotted the lowest available channel.
(3) Successively, each station with the next lowest improvement
factor, is allotted an available channel taking into account the
possible frequency
[[Page 15]]
and location combinations and relationship to previously selected
allotments. If a channel is not available for the subject station,
previous allotments are examined with respect to an alternate channel,
the use of which would make a channel available for the subject station.
(4) When it has been determined that, in accordance with the above
steps, no channel is available for the subject station, that station is
no longer considered and the process continues to the station with the
next lowest improvement factor.
(c) If awarded an allotment, a petitioner will have sixty (60) days
from the date of public notice of selection to file an application for
construction permit on FCC Form 301. (See Secs. 73.24 and 73.37(e) for
filing requirements). Unless instructed by the Commission to do
otherwise, the application shall specify Model I facilities. (See
Sec. 73.14). Upon grant of the application and subsequent construction
of the authorized facility, the applicant must file a license
application on FCC Form 302.
Note 1: Until further notice by the Commission, the filing of these
petitions is limited to licensees of existing AM stations (excluding
Class C stations) operating in the 535-1605 kHz band. First priority
will be assigned to Class D stations located within the primary service
contours of U.S. Class A stations that are licensed to serve communities
of 100,000 or more for which there exists no local fulltime aural
service.
Note 2: Selection among competing petitions will be based on
interference reduction. Notwithstanding the exception contained in Note
5 of this section, within each operational category, the station
demonstrating the highest value of improvement factor will be afforded
the highest priority for an allotment, with the next priority assigned
to the station with next lowest value, and so on, until available
allotments are filled.
Note 3: The Commission will periodically evaluate the progress of
the movement of stations from the 535-1605 kHz band to the 1605-1705 kHz
band to determine whether the 1605-1705 kHz band should continue to be
administered on an allotment basis or modified to an assignment method.
If appropriate, the Commission will later develop further procedures for
use of the 1605-1705 kHz band by existing station licensees and others.
Note 4: Other than the exception specified in note 1 of this
section, existing fulltime stations are considered first for selection
as described in note 2 of this section. In the event that an allotment
availability exists for which no fulltime station has filed a relevant
petition, such allotment may be awarded to a licensed Class D station.
If more than one Class D station applies for this migration opportunity,
the following priorities will be used in the selection process: First
priority--a Class D station located within the 0.5 mV/m-50% contour of a
U.S. Class A station and licensed to serve a community of 100,000 or
more, for which there exists no local fulltime aural service; Second
priority--Class D stations ranked in order of improvement factor, from
highest to lowest, considering only those stations with improvement
factors greater than zero.
Note 5: The preference for AM stereo in the expanded band will be
administered as follows: when an allotment under consideration
(candidate allotment) conflicts with one or more previously selected
allotments (established allotments) and cannot be accommodated in the
expanded band, the candidate allotment will be substituted for the
previously established allotment provided that: the petitioner for the
candidate allotment has made a written commitment to the use of AM
stereo and the petitioner for the established allotment has not; the
difference between the ranking factors associated with the candidate and
established allotments does not exceed 10% of the ranking factor of the
candidate allotment; the substitution will not require the displacement
of more than one established allotment; and both the candidate allotment
and the established allotment are within the same priority group.
[58 FR 27949, May 12, 1993]
Sec. 73.31 Rounding of nominal power specified on applications.
(a) An application filed with the FCC for a new station or for an
increase in power of an existing station shall specify nominal power
rounded to two significant figures as follows:
------------------------------------------------------------------------
Rounded
down to
Nominal power (kW) nearest
figure
(kW)
------------------------------------------------------------------------
Below 0.25................................................... 0.001
0.25 to 0.99................................................. 0.01
1 to 9.9..................................................... 0.1
10 to 50..................................................... 1
------------------------------------------------------------------------
(b) In rounding the nominal power in accordance with paragraph (a)
of this section the RMS shall be adjusted accordingly. If rounding
upward to the nearest figure would result in objectionable interference,
the nominal power specified on the application is to
[[Page 16]]
be rounded downward to the next nearest figure and the RMS adjusted
accordingly.
[50 FR 18821, May 2, 1985, as amended at 53 FR 1031, Jan. 15, 1988]
73.33 Antenna systems; showing required.
(a) An application for authority to install a broadcast antenna
shall specify a definite site and include full details of the antenna
design and expected performance.
(b) All data necessary to show compliance with the terms and
conditions of the construction permit must be filed with the license
application. If the station is using a directional antenna, a proof of
performance must also be filed.
[28 FR 13574, Dec. 14, 1963, as amended at 37 FR 25840, Dec. 5, 1972]
Sec. 73.35 Calculation of improvement factors.
A petition for an allotment (See Sec. 73.30) in the 1605-1705 kHz
band filed by an existing fulltime AM station licensed in the 535-1605
kHz band will be ranked according to the station's calculated
improvement factor. (See Sec. 73.30). Improvement factors relate to both
nighttime and daytime interference conditions and are based on two
distinct considerations: (a) Service area lost by other stations due to
interference caused by the subject station, and (b) service area of the
subject station. These considerations are represented by a ratio. The
ratio consists, where applicable, of two separate additive components,
one for nighttime and one for daytime. For the nighttime component, to
determine the numerator of the ratio (first consideration), calculate
the RSS and associated service area of the stations (co- and adjacent
channel) to which the subject station causes nighttime interference.
Next, repeat the RSS and service area calculations excluding the subject
station. The cumulative gain in the above service area is the numerator
of the ratio. The denominator (second consideration) is the subject
station's interference-free service area. For the daytime component, the
composite amount of service lost by co-channel and adjacent channel
stations, each taken individually, that are affected by the subject
station, excluding the effects of other assignments during each study,
will be used as the numerator of the daytime improvement factor. The
denominator will consist of the actual daytime service area (0.5 mV/m
contour) less any area lost to interference from other assignments. The
value of this combined ratio will constitute the petitioner's
improvement factor. Notwithstanding the requirements of Sec. 73.153, for
uniform comparisons and simplicity, measurement data will not be used
for determining improvement factors and FCC figure M-3 ground
conductivity values are to be used exclusively in accordance with the
pertinent provisions of Sec. 73.183(c)(1).
[56 FR 64858, Dec. 12, 1991]
Sec. 73.37 Applications for broadcast facilities, showing required.
(a) No application will be accepted for a new station if the
proposed operation would involve overlap of signal strength contours
with any other station as set forth below in this paragraph; and no
application will be accepted for a change of the facilities of an
existing station if the proposed change would involve such overlap where
there is not already such overlap between the stations involved:
------------------------------------------------------------------------
Contour of
proposed
station Contour of any other
Frequency separation (kHz) (classes station (mV/m)
B, C and
D) (mV/m)
------------------------------------------------------------------------
0.............................. 0.005 0.100 (Class A).
0.025 0.500(Other classes).
0.500 0.025 (All classes).
10............................. 0.250 0.500(All classes).
0.500 0.250 (All classes).
20............................. 5 5 (All classes).
5 5 (All classes).
30............................. 25 25 (All classes).
------------------------------------------------------------------------
(b) In determining overlap received, an application for a new Class
C station with daytime power of 250 watts, or greater, shall be
considered on the assumption that both the proposed operation and all
existing Class C stations operate with 250 watts and utilize non-
directional antennas.
(c) If otherwise consistent with the public interest, an application
requesting an increase in the daytime power of an existing Class C
station on a local
[[Page 17]]
channel from 250 watts to a maximum of 1kW, or from 100 watts to a
maximum of 500 watts, may be granted notwithstanding overlap prohibited
by paragraph (a) of this section. In the case of a 100 watt Class C
station increasing daytime power, the provisions of this paragraph shall
not be construed to permit an increase in power to more than 500 watts,
if prohibited overlap would be involved, even if successive applications
should be tendered.
(d) In addition to demonstrating compliance with paragraphs (a),
and, as appropriate, (b), and (c) of this section, an application for a
new AM broadcast station, or for a major change (see Sec. 73.3571(a)(1))
in an authorized AM broadcast station, as a condition for its
acceptance, shall make a satisfactory showing, if new or modified
nighttime operation by a Class B station is proposed, that objectionable
interference will not result to an authorized station, as determined
pursuant to Sec. 73.182(1).
(e) An application for an authorization in the 1605-1705 kHz band
which has been selected through the petition process (See Sec. 73.30) is
not required to demonstrate compliance with paragraph (a), (b), (c), or
(d) of this section. Instead, the applicant need only comply with the
terms of the allotment authorization issued by the Commission in
response to the earlier petition for establishment of a station in the
1605-1705 kHz band. Within the allotment authorization, the Commission
will specify the assigned frequency and the applicable technical
requirements.
(f) Stations on 1580, 1590 and 1600 kHz. In addition to the rules
governing the authorization of facilities in the 535-1605 kHz band,
stations on these frequencies seeking facilities modifications must
protect assignments in the 1610-1700 kHz band. Such protection shall be
afforded in a manner which considers the spacings that occur or exist
between the subject station and a station within the range 1605-1700
kHz. The spacings are the same as those specified for stations in the
frequency band 1610-1700 kHz or the current separation distance,
whichever is greater. Modifications that would result in a spacing or
spacings that fails to meet any of the separations must include a
showing that appropriate adjustment has been made to the radiated signal
which effectively results in a site-to-site radiation that is equivalent
to the radiation of a station with standard Model I facilities (10 kW-D,
1 kW-N, non-DA, 90 degree antenna ht. & ground system) operating in
compliance with all of the above separation distances. In those cases
where that radiation equivalence value is already exceeded, a station
may continue to maintain, but not increase beyond that level.
Note 1: In the case of applications for changes in the facilities of
AM broadcast stations covered by this section, an application will be
accepted even though overlap of field strength contours as mentioned in
this section would occur with another station in an area where such
overlap does not already exist, if:
(1) The total area of overlap with that station would not be
increased;
(2) There would be no net increase in the area of overlap with any
other station; and
(3) There would be created no area of overlap with any station with
which overlap does not now exist.
Note 2: The provisions of this section concerning prohibited overlap
of field strength contours will not apply where:
(1) The area of overlap lies entirely over sea water: or
(2) The only overlap involved would be that caused to a foreign
station, in which case the provisions of the applicable international
agreement, as identified in Sec. 73.1650, will apply. When overlap would
be received from a foreign station, the provisions of this section will
apply, except where there would be overlap with a foreign station with a
frequency separation of 20 kHz, in which case the provisions of the
international agreement will apply in lieu of this section.
Note 3: In determining the number of ``authorized'' aural
transmission facilities in a given community, applications for that
community in hearing or otherwise having protected status under
specified ``cut-off'' procedures shall be considered as existing
stations. In the event that there are two or more mutually exclusive
protected applications seeking authorization for the proposed community
it will be assumed that only one is ``authorized.''
Note 4: A ``transmission facility'' for a community is a station
licensed to the community. Such a station provides a ``transmission
service'' for that community.
[56 FR 64858, Dec. 12, 1991; 57 FR 43290, Sept. 18, 1992]
[[Page 18]]
Sec. 73.44 AM transmission system emission limitations.
(a) The emissions of stations in the AM service shall be attenuated
in accordance with the requirements specified in paragraph (b) of this
section. Emissions shall be measured using a properly operated and
suitable swept-frequency RF spectrum analyzer using a peak hold duration
of 10 minutes, no video filtering, and a 300 Hz resolution bandwidth,
except that a wider resolution bandwidth may be employed above 11.5 kHz
to detect transient emissions. Alternatively, other specialized
receivers or monitors with appropriate characteristics may be used to
determine compliance with the provisions of this section, provided that
any disputes over measurement accuracy are resolved in favor of
measurements obtained by using a calibrated spectrum analyzer adjusted
as set forth above.
(b) Emissions 10.2 kHz to 20 kHz removed from the carrier must be
attenuated at least 25 dB below the unmodulated carrier level, emissions
20 kHz to 30 kHz removed from the carrier must be attenuated at least 35
dB below the unmodulated carrier level, emissions 30 kHz to 60 kHz
removed from the carrier must be attenuated at least [5 + 1 dB/kHz]
below the unmodulated carrier level, and emissions between 60 kHz and 75
kHz of the carrier frequency must be attenuated at least 65 dB below the
unmodulated carrier level. Emissions removed by more than 75 kHz must be
attenuated at least 43 + 10 Log (Power in watts) or 80 dB below the
unmodulated carrier level, whichever is the lesser attenuation, except
for transmitters having power less than 158 watts, where the attenuation
must be at least 65 dB below carrier level.
(c) Should harmful interference be caused to the reception of other
broadcast or non-broadcast stations by out of band emissions, the
licensee may be directed to achieve a greater degree of attentuation
than specified in paragraphs (a) and (b) of this section.
(d) Measurements to determine compliance with this section for
transmitter type acceptance are to be made using signals sampled at the
output terminals of the transmitter when operating into an artificial
antenna of substantially zero reactance. Measurements made of the
emissions of an operating station are to be made at ground level
approximately 1 kilometer from the center of the antenna system. When a
directional antenna is used, the carrier frequency reference field
strength to be used in order of preference shall be:
(1) The measure non-directional field strength.
(2) The RMS field strength determined from the measured directional
radiation pattern.
(3) The calculated expected field strength that would be radiated by
a non-directional antenna at the station authorized power.
(e) Licensees of stations complying with the ANSI/EIA-549-1988,
NRSC-1 AM Preemphasis/Deemphasis and Broadcast Transmission Bandwidth
Specifications (NRSC-1), prior to June 30, 1990 or from the original
commencement of operation will, until June 30, 1994, be considered to
comply with paragraphs (a) and (b) of this section, absent any reason
for the Commission to believe otherwise. Such stations are waived from
having to make the periodic measurements required in Sec. 73.1590(a)(6)
until June 30, 1994. However, licensees must make measurements to
determine compliance with paragraphs (a) and (b) of this section upon
receipt of an Official Notice of Violation or a Notice of Apparent
Liability alleging noncompliance with those provisions, or upon specific
request by the Commission.
[47 FR 8588, Mar. 1, 1982, as amended at 49 FR 3999, Feb. 1, 1984]
Sec. 73.45 AM antenna systems.
(a) All applicants for new, additional, or different AM station
facilities and all licensees requesting authority to change the
transmitting system site of an existing station must specify an antenna
system, the efficiency of which complies with the requirements for the
class and power of station. (See Secs. 73.186 and 73.189.)
(1) An application for authority to install an AM broadcast antenna
must specify a definite site and include full details of the antenna
system design and expected performance.
[[Page 19]]
(2) All data necessary to show compliance with the terms and
conditions of the construction permit must be filed with the application
for the station license to cover the construction. If the station has
constructed a directional antenna, a directional proof of performance
must be filed. See Secs. 73.150 through 73.157.
(b) The simultaneous use of a common antenna or antenna structure by
more than one AM station or by a station of any other type or service
may be authorized provided:
(1) Engineering data are submitted showing that satisfactory
operation of each station will be obtained without adversely affecting
the operation of the other station(s).
(2) The minimum field strength for each AM station complies with
Sec. 73.189(b).
(c) Should any changes be made or otherwise occur which would
possibly alter the resistance of the antenna system, the licensee must
commence the determination of the operating power by a method described
in Sec. 73.51(a)(1) or (d). (If the changes are due to the construction
of FM or TV transmitting facilities, see Secs. 73.316 and 73.685.) Upon
completion of any necessary repairs or adjustments, or upon completion
of authorized construction or modifications, the licensee must make a
new determination of the antenna resistance using the procedures
described in Sec. 73.54. Operating power should then be determined by a
direct method as described in Sec. 73.51. Notification of the value of
resistance of the antenna system must be filed with the FCC in
Washington, DC., as follows:
(1) Whenever the measurements show that the antenna or common point
resistance differs from that shown on the station authorization by more
than 2%, FCC Form 302 must be filed with the information and measurement
data specified in Sec. 73.54(d).
(2) Whenever AM stations use direct reading power meters pursuant to
Sec. 73.51, notification to the FCC in Washington, DC, must be filed in
accordance with Sec. 73.54(e).
[43 FR 53735, Nov. 17, 1978, as amended at 45 FR 28141, Apr. 28, 1980;
47 FR 8589, Mar. 1, 1982; 50 FR 32416, Aug. 12, 1985; 51 FR 2707; Jan.
21, 1986; 51 FR 26250, July 22, 1986]
Sec. 73.49 AM transmission system fencing requirements.
Antenna towers having radio frequency potential at the base (series
fed, folded unipole, and insulated base antennas) must be enclosed
within effective locked fences or other enclosures. Ready access must be
provided to each antenna tower base for meter reading and maintenance
purposes at all times. However, individual tower fences need not be
installed if the towers are contained within a protective property
fence.
[51 FR 2707, Jan. 21, 1986]
Sec. 73.51 Determining operating power.
(a) Except in those circumstances described in paragraph (d) of this
section, the operating power shall be determined by the direct method.
The direct method consists of either:
(1) using a suitable instrument for determining the antenna's input
power directly from the RF voltage, RF current, and phase angle; or
(2) calculating the product of the licensed antenna or common point
resistance at the operating frequency (see Sec. 73.54), and the square
of the indicated unmodulated antenna current at that frequency, measured
at the point where the resistance has been determined.
(b) The authorized antenna input power for each station shall be
equal to the nominal power for such station, with the following
exceptions:
(1) For stations with nominal powers of 5 kW, or less, the
authorized antenna input power to directional antennas shall exceed the
nominal power by 8 percent.
(2) For stations with nominal powers in excess of 5 kW, the
authorized antenna input power to directional antennas shall exceed the
nominal power by 5.3 percent.
(3) In specific cases, it may be necessary to limit the radiated
field to a level below that which would result if normal power were
delivered to the antenna. In such cases, excess power may be dissipated
in the antenna feed circuit, the transmitter may be operated with power
output at a level which is less than the rated carrier power, or a
combination of the two methods may
[[Page 20]]
be used, subject to the conditions given in paragraph (c) of this
section.
(i) Where a dissipative network is employed, the authorized antenna
current and resistance, and the authorized antenna input power shall be
determined at the input terminals of the dissipative network.
(ii) Where the authorized antenna input power is less than the
nominal power, subject to the conditions set forth in paragraph (c) of
this section, the transmitter may be operated at the reduced power level
necessary to supply the authorized antenna input power.
(c) Applications for authority to operate with antenna input power
which is less than nominal power and/or to employ a dissipative network
in the antenna system shall be made on FCC Form 302. The technical
information supplied on section II-A of this form shall be that applying
to the proposed conditions of operation. In addition, the following
information shall be furnished, as pertinent:
(1) Full details of any network employed for the purpose of
dissipating radio frequency energy otherwise delivered to the antenna
(see Sec. 73.54).
(2) A showing that the transmitter has been type accepted or
notified for operation at the proposed power output level, or, in lieu
thereof:
(i) A full description of the means by which transmitter output
power will be reduced.
(ii) Where the proposed transmitter power output level(s) is less
than 90% of the rated power of the transmitter, equipment performance
measurements must be made to confirm that the station transmissions
conform to the emission limitation specified in Sec. 73.44, under all
conditions of program operation.
(iii) A showing that, at the proposed power output level, means are
provided for varying the transmitter output within a tolerance of
plus-minus10 percent, to compensate for variations in line voltage
or other factors which may affect the power output level.
(d) When it is not possible or appropriate to use the direct method
of power determination due to technical reasons, the indirect method of
determining operating power (see paragraphs (e) and (f) of this section)
may be used on a temporary basis. A notation must be made in the station
log indicating the dates of commencement and termination of measurement
using the indirect method of power determination.
(e) The antenna input power is determined indirectly by applying an
appropriate factor to the input power to the last radio-frequency power
amplifier stage of the transmitter, using the following formula:
Antenna input power=Ep x Ip x F
Where:
Ep=DC input voltage of final radio stage.
Ip=Total DC input current of final radio stage.
F=Efficiency factor.
(1) If the above formula is not appropriate for the design of the
transmitter final amplifier, use a formula specified by the transmitter
manufacturer with other appropriate operating parameters.
(2) The value of F applicable to each mode of operation must be
determined and a record kept thereof with a notation as to its
derivation. This factor is to be established by one of the methods
described in paragraph (f) of this section and retained in the station
records.
(f) The value of F is to be determined by one of the following
procedures listed in order of preference:
(1) If the station had previously been authorized and operating by
determining the antenna input power by the direct method, the factor F
is the ratio of the antenna input power (determined by the direct
method) to the corresponding final radio frequency power amplifier input
power.
(2) If a station has not been previously in regular operation with
the power authorized for the period of indirect power determination, if
a new transmitter has been installed, or if, for any other reason, the
determination of the factor F by the method described in paragraph
(f)(1) of this section is impracticable:
(i) The factor F as shown in the transmitter manufacturer's test
report, if such a test report specifies a unique value of F for the
power level and frequently used; or
[[Page 21]]
(ii) The value determined by reference to the following table:
------------------------------------------------------------------------
Method of Maximum rated carrier Class of
Factor(F) modulation power amplifier
------------------------------------------------------------------------
0.70..... Plate.............. 1 kW or less.......... ................
.80...... Plate.............. 2.5 kW and over....... ................
.35...... Low level.......... 0.25 kW and over...... B.
.65...... Low level.......... 0.25 kW and over...... BC\1\.
.35...... Grid............... 0.25 kW and over...... ................
------------------------------------------------------------------------
\1\All linear amplifier operation where efficiency approaches that of
class C operation.
(Secs. 4, 5, 303, 48 Stat., as amended, 1066, as amended, 1068, 1082, as
amended; 47 U.S.C. 154, 155, 303. Interpret or apply secs. 301, 303,
307, 48 Stat. 1081, 1082, as amended, 47 U.S.C. 301, 303, 307)
[37 FR 7516, Apr. 15, 1972, as amended at 42 FR 36827, July 18, 1977; 42
FR 61863, Dec. 7, 1977; 44 FR 36036, June 20, 1979; 47 FR 28387, June
30, 1982; 48 FR 38477, Aug. 24, 1983; 48 FR 44805, Sept. 30, 1983; 49 FR
3999, Feb. 1, 1984; 49 FR 4210, Feb. 3, 1984; 49 FR 49850, Dec. 24,
1984; 50 FR 24521, June 11, 1985; 52 FR 10570, Apr. 2, 1987]
Sec. 73.53 Requirements for authorization of antenna monitors.
(a) General requirements. (1) Antenna monitors shall be type
approved or notifed by the FCC. Effective March 5, 1984, only grants of
notification will be issued for antenna monitors.
(2) Notification can be obtained by following the procedures
specified in subpart J of part 2 of the FCC's Rules.
(b) An antenna monitor eligible for authorization by the FCC shall
meet the following specifications:
(1) The monitor shall be designed to operate in the 535-1705 kHz
band.
(2) The monitor shall be capable of indicating any phase difference
between two RF voltages of the same frequency over a range of from 0 to
360 deg..
(3) The monitor shall be capable of indicating the relative
amplitude of two RF voltages.
(4) The device used to indicate phase differences shall indicate in
degrees, and shall be graduated in increments of 2 deg., or less. If a
digital indicator is provided, the smallest increment shall be 0.5 deg.,
or less.
(5) The device used to indicate relative amplitudes shall be
graudated in increments which are 1 percent, or less, of the full scale
value. If a digital indicator is provided, the smallest increment shall
be 0.1 percent, or less, of the full scale value.
(6) The monitor shall be equipped with means, if necessary, to
resolve ambiguities in indication.
(7) If the monitor is provided with more than one RF input terminal
in addition to a reference input terminal, appropriate switching shall
be provided in the monitor so that the signal at each of these RF inputs
may be selected separately for comparison with the reference input
signal.
(8) Each RF input of the monitor shall provide a termination of such
characteristics that, when connected to a sampling line of an impedance
specified by the manufacturer the voltage reflection coefficient shall
be 3 percent or less.
(9) The monitor, if intended for use by stations operating
directional antenna systems by remote control, shall be designed so that
the switching functions required by paragraph (b)(7) of this section may
be performed from a point external to the monitor, and phase and
amplitude indications be provided by external meters. The indications of
external meters furnished by the manufacturer shall meet the
specifications for accuracy and repeatability of the monitor itself, and
the connection of these meters to the monitor, or of other indicating
instruments with electrical characteristics meeting the specifications
of the monitor manufacturer shall not affect adversely the performance
of the monitor in any respect.
(10) The monitor must be accompanied by complete and correct
schematic diagrams and operating instructions when submitted for type
approval. When approved under notification, these materials shall be
retained by the applicant and not submitted unless otherwise requested
by the FCC. For the purpose of the equipment authorization, these
diagrams and instructions shall be considered as part of the monitor.
(11) When an RF signal of an amplitude within a range specified by
the manufacturer is applied to the reference RF input terminal of the
monitor, and another RF signal of the same frequency and of equal or
lower amplitude is applied to any other selected RF input terminal,
indications shall be
[[Page 22]]
provided meeting the following specifications.
(i) The accuracy with which any difference in the phases of the
applied signals is indicated shall be plus-minus1 deg.,or better,
for signal amplitude ratios of from 2:1 to 1:1, and
plus-minus2 deg.,or better, for signal amplitude ratios in excess
of 2:1 and up to 5:1.
(ii) The repeatability of indication of any difference in the phases
of the applied signals shall be plus-minus1 deg., or better.
(iii) The accuracy with which the relative amplitudes of the applied
signals is indicated, over a range in which the ratio of these
amplitudes is between 2:1 and 1:1, shall be plus-minus2 percent of
the amplitude ratio, or better, and for amplitude ratios in excess of
2:1 and up to 5:1, plus-minus5 percent of the ratio, or better.
(iv) The repeatability of indication of the relative amplitudes of
the applied signals, over a range where the ratio of these amplitudes is
between 5:1 and 1:1, shall be plus-minus2 percent of the amplitude
ratio, or better.
(v) The modulation of the RF signals by a sinusoidal wave of any
frequency between 100 and 10,000 Hz, at any amplitude up to 90 percent
shall cause no deviation in an indicated phase difference from its
value, as determined without modulation, greater than
plus-minus0.5 deg..
(12) The performance specifications set forth in paragraph (c)(13)
of this section, shall be met when the monitor is operated and tested
under the following conditions.
(i) After continuous operation for 1 hour, the monitor shall be
calibrated and adjusted in accordance with the manufacturer's
instructions.
(ii) The monitor shall be subjected to variations in ambient
temperature between the limits of 10 and 40 deg.C; external meters
furnished by the manufacturer will be subjected to variations between 15
and 30 deg.C.
(iii) Powerline supply voltage shall be varied over a range of from
10 percent below to 10 percent above the rated supply voltage.
(iv) The amplitude of the reference signal shall be varied over the
operating range specified by the manufacturer, and in any case over a
range of maximum to minimum values of 3 to 1.
(v) The amplitude of the comparison signal shall be varied from a
value which is 0.2 of the amplitude of the reference signal to a value
which is equal in amplitude to the reference signal.
(vi) Accuracy shall be determined for the most adverse combination
of conditions set forth above.
(vii) Repeatability shall be determined as that which may be
achieved under the specified test conditions over a period of 7 days,
during which no calibration or adjustment of the instrument, subsequent
to the initial calibration, shall be made.
(viii) The effects of modulation of the RF signal shall be
separately determined, and shall not be included in establishing values
for accuracy and repeatability.
(c) A station determined to have a critical directional antenna must
use an antenna monitor having high tolerance characteristics determined
on an individual basis, and specified on the station authorization. Such
monitors are not subject to the authorization of paragraph (a), however
they may be used only at the station for which they were specified.
Note: In paragraph (b)(1) of this section, the requirement that
monitors be capable of operation in the 535-1705 kHz band shall apply
only to equipment manufactured after July 1, 1992. Use of a monitor in
the 1605-1705 kHz band which is not approved for such operation will be
permitted pending the general availability of 535-1705 kHz band monitors
if a manufacturer can demonstrate, in the interim, that its monitor
performs in accordance with the standards in this section on these 10
channels.
(Secs. 4, 5, 303, 48 Stat., as amended, 1066, 1068, 1082 (47 U.S.C. 154,
155, 303))
[38 FR 1917, Jan. 19, 1973, as amended at 49 FR 3999, Feb. 1, 1984; 49
FR 29069, July 18, 1984; 50 FR 32416, Aug. 12, 1985; 50 FR 47054, Nov.
14, 1985; 51 FR 2707, Jan. 21, 1986; 56 FR 64859, Dec. 12, 1991; 57 FR
43290, Sept. 18, 1992; 60 FR 55480, Nov. 1, 1995]
Sec. 73.54 Antenna resistance and reactance measurements.
(a) The resistance of an omnidirectional series fed antenna is
measured at either the base of the antenna without intervening coupling
or tuning networks, or at the point the transmission line connects to
the output terminals of the transmitter. The resistance of a shunt
excited antenna may be measured at the point the radio
[[Page 23]]
frequency energy is transferred to the feed wire circuit or at the
output terminals of the transmitter.
(b) The resistance and reactance of a directional antenna shall be
measured at the point of common radiofrequency input to the directional
antenna system. The following conditions shall obtain:
(1) The antenna shall be finally adjusted for the required radiation
pattern.
(2) The reactance at the operating frequency and at the point of
measurement shall be adjusted to zero, or as near thereto as
practicable.
(c)(1) The resistance of an antenna shall be determined by the
following procedure: A series of discrete measurements shall be made
over a band of frequencies extending from approximately 25 kHz below the
operating frequency to approximately 25 kHz above that frequency, at
intervals of approximately 5 kHz. The measured values shall be plotted
on a linear graph, with frequency as the abscissa and resistance as the
ordinate. A smooth curve shall be drawn through the plotted values. The
resistance value corresponding to the point of intersection of the curve
and the ordinate representing the operating frequency of the station
shall be the resistance of the antenna.
(2) For a directional antenna, the reactance of the antenna shall be
determined by a procedure similar to that described in paragraph (c)(1)
of this section.
(d) Notification must be filed with the FCC in Washington, DC when
determining power by the direct method pursuant to Sec. 73.51 and must
specify the antenna or common point resistance at the operating
frequency. The following information must also be kept on file at the
station:
(1) A full description of the method used to make measurements.
(2) A schematic diagram showing clearly all components of coupling
circuits, the point of resistance measurement, the location of the
antenna ammeter, connections to and characteristics of all tower
lighting isolation circuits, static drains, and any other fixtures
connected to and supported by the antenna, including other antennas and
associated networks. Any network or circuit component used to dissipate
radio frequency power shall be specifically identified, and the
impedances of all components which control the level of power
dissipation, and the effective input resistance of the network must be
indicated.
(e) AM stations using direct reading power meters in accordance with
Sec. 73.51, can either submit the information required by paragraph (d)
of this section or submit a statement indicating that such a meter is
being used. Subsequent station licenses will indicate the use of a
direct reading power meter in lieu of the antenna resistance value in
such a situation.
[34 FR 18305, Nov. 15, 1969, as amended at 37 FR 7517, Apr. 15, 1972; 45
FR 26062, Apr. 17, 1980; 49 FR 49850, Dec. 24, 1984; 50 FR 32416, Aug.
12, 1985; 51 FR 2707, Jan. 21, 1986; 51 FR 26250, July 22, 1986]
Sec. 73.57 Remote reading antenna and common point ammeters.
Remote reading antenna and common point ammeters may be used without
further authority according to the following conditions:
(a) Remote reading antenna or common point ammeters may be provided
by:
(1) Inserting second radio frequency current sensing device directly
in the antenna circuit with remote leads to the indicating instruments.
(2) Inductive coupling to radio frequency current sensing device for
providing direct current to indicating instrument.
(3) Capacity coupling to radio frequency current sensing device for
providing direct current to indicating instrument.
(4) Current transformer connected to radio frequency current sensing
device for providing direct current to indicating instrument.
(5) Using transmission line current meter at transmitter as remote
reading ammeter. See paragraph (c) of this section.
(6) Using the indications of the antenna (phase) monitor, provided
that when the monitor is used to obtain remote reading indication of
non-directional antenna base current, the monitor calibration can be
independently
[[Page 24]]
made and maintained for each mode of operation.
(b) Devices used for obtaining remote reading antenna or common
point current indications, except antenna monitor coupling elements,
shall be located at the same point as, but below (transmitter side) the
associated main ammeter.
(c) In the case of shunt-excited antennas, the transmission line
current meter at the transmitter may be considered as the remote antenna
ammeter provided the transmission line is terminated directly into the
excitation circuit feed line, which shall employ series tuning only (no
shunt circuits of any type shall be employed) and insofar as
practicable, the type and scale of the transmission line meter should be
the same as those of the excitation circuit feed line meter (meter in
slant wire feed line or equivalent).
(d) Each remote reading ammeter shall be accurate to within 2
percent of the value read on its corresponding regular ammeter.
(e) All remote reading ammeters shall conform with the
specifications for regular antenna ammeters.
(f) Meters with arbitrary scale divisions may be used provided that
calibration charts or curves are provided at the transmitter control
point showing the relationship between the arbitrary scales and the
reading of the main meters.
(g) If a malfunction affects the remote reading indicators of the
antenna or common point ammeter, the operating power may be determined
by a method using alternative procedures as described in Sec. 73.51.
[41 FR 36817, Sept. 1, 1976, as amended at 48 FR 38477, Aug. 24, 1983;
49 FR 49850, Dec. 24, 1984; 50 FR 32416, Aug. 12, 1985; 60 FR 55480,
Nov. 1, 1995]
Sec. 73.58 Indicating instruments.
(a) Each AM broadcast station must be equipped with indicating
instruments which conform with the specifications described in
Sec. 73.1215 for determining power by the direct and indirect methods,
and with such other instruments as are necessary for the proper
adjustment, operation, and maintenance of the transmitting system.
However, auxiliary transmitters with a nominal power rating of 100 watts
or less are not required to be equipped with instruments to determine
power by the indirect method provided that the licensee can determine
the antenna input power at all times.
(b) A thermocouple type ammeter or other device capable of providing
an indication of radio frequency current, meeting the requirements of
Sec. 73.1215, shall be installed at the base of each antenna element. A
suitable jack and plug arrangement may be used to permit removal of the
meter from the antenna circuit thereby protecting it from damage by
lighting.
(c) Since it is usually impractical to measure the actual antenna
current of a shunt excited antenna system, the current measured at the
input of the excitation circuit feed line is accepted as the antenna
current.
(d) The function of each instrument shall be clearly and permanently
shown on the instrument itself or on the panel immediately adjacent
thereto.
(e) In the event that any one of these indicating instruments
becomes defective when no substitute which conforms with the required
specifications is available, the station may be operated without the
defective instrument pending its repair or replacement for a period not
in excess of 60 days without further authority of the Commission:
Provided, That:
(1) If the defective instrument is an antenna base current ammeter
of a directional antenna system, the indications may be obtained from
the antenna monitor pending the return to service of the regular meter,
provided other parameters are maintained at their normal values.
(2) If the defective instrument is the antenna current meter of a
non-directional station which does not employ a remote antenna ammeter,
or if the defective instrument is the common point meter of a station
which employs a directional antenna and does not employ a remote common
point meter, the operating power shall be determined by a method
described in Sec. 73.51(a)(1) or (d) during the entire time the station
is operated without the antenna current meter or common point
[[Page 25]]
meter. However, if a remote meter is employed and the antenna current
ammeter or common point meter becomes defective, the remote meter can be
used to determine operating power pending the return to service of the
regular meter.
(f) If conditions beyond the control of the licensee prevent the
restoration of the meter to service within the above allowed period,
information requested in accordance with Sec. 73.3549 may be filed with
the Engineer in Charge of the radio district in which the station is
located for such additional time as may be required to complete repairs
of the defective instrument.
[41 FR 36817, Sept. 1, 1976, as amended at 48 FR 38477, Aug. 24, 1983;
49 FR 49850, Dec. 24, 1984; 50 FR 32416, Aug. 12, 1985; 51 FR 2707, Jan.
21, 1986; 53 FR 2498, Jan. 28, 1988]
Sec. 73.61 AM directional antenna field strength measurements.
(a) Each AM station using a directional antenna must make field
strength measurements at the monitoring point locations specified in the
instrument of authorization, as often as necessary to ensure that the
field at those points does not exceed the values specified in the
station authorization. Additionally, stations not having an approved
sampling system must make the measurements once each calendar quarter at
intervals not exceeding 120 days. The provision of this paragraph
supersedes any schedule specified on a station license issued prior to
January 1, 1986. The results of the measurements are to be entered into
the station log pursuant to the provisions of Sec. 73.1820.
(b) Partial proof of performance measurements using the procedures
described in Sec. 73.154 must be made whenever the licensee has reason
to believe that the radiated field may be exceeding the limits for which
the station was most recently authorized to operate.
(c) A station may be directed to make a partial proof of performance
by the FCC whenever there is an indication that the antenna is not
operating as authorized.
[50 FR 47054, Nov. 14, 1985]
Sec. 73.62 Directional antenna system tolerances.
(a) Each AM station operating a directional antenna must maintain
the indicated relative amplitudes of the antenna base currents and
antenna monitor currents within 5% of the values specified therein.
Directional antenna relativephase currents must be maintained to within
3 deg. of the values specified on the instrument of
authorization, unless other tolerances are specified therein.
(b) Whenever the operating parameters of a directional antenna
cannot be maintained within the tolerances specified in paragraph (a) of
this section, the following procedures will apply:
(1) The licensee shall measure and log every monitoring point at
least once for each mode of directional operation. Subsequent variations
in operating parameters will require the remeasuring and logging of
every monitoring point to assure that the authorized monitoring point
limits are not being exceeded.
(2) Provided each monitoring point is within its specified limit,
operation may continue for a period up to 30 days before a request for
Special Temporary Authority (STA) must be filed, pursuant to paragraph
(b)(4) of this section, to operate with parameters at variance from the
provisions of paragraph (a) of this section.
(3) If any monitoring point exceeds its specified limit, the
licensee must either terminate operation within 3 hours or reduce power
in accordance with the applicable provisions of Sec. 73.1350(d), in
order to eliminate any possibility of interference or excessive
radiation in any direction.
(4) If operation pursuant to paragraph (b)(3) of this section is
necessary, or before the 30 day period specified in paragraph (b)(2) of
this section expires, the licensee must request a Special Temporary
Authority (STA) in accordance with Sec. 73.1635 to continue operation
with parameters at variance and/or with reduced power along with a
statement certifying that all monitoring points will be continuously
maintained within their specified limits.
(5) The licensee will be permitted 24 hours to accomplish the
actions specified in paragraph (b)(1) of this section;
[[Page 26]]
provided that, the date and time of the failure to maintain proper
operating parameters has been recorded in the station log.
(c) In any other situation in which it might reasonably be
anticipated that the operating parameters might vary out of tolerance
(such as planned array repairs or adjustment and proofing procedures),
the licensee shall, before such activity is undertaken, obtain an STA in
accordance with Sec. 73.1635 in order to operate with parameters at
variance and/or with reduced power as required to maintain all
monitoring points within their specified limits.
[50 FR 30946, July 31, 1985, as amended at 60 FR 55480, Nov. 1, 1995]
Sec. 73.68 Sampling systems for antenna monitors.
(a) Each AM station permittee authorized to construct a new
directional antenna system, must install the sampling system in
accordance with the following specifications:
(1) Devices used to extract or sample the current and the
transmission line connecting the sampling elements to the antenna
monitor must provide accurate and stable signals to the monitor (e.g.,
rigidly mounted and non-rotatable loops and all system components
protected from physical and environmental disturbances).
(2) Sampling lines for critical directional antennas (see
Sec. 73.14) must be of uniform length. Sampling lines for non-critical
directional antennas may be of different lengths provided the phase
difference of signals at the monitor are less than 0.5 deg. between the
shortest and longest cable lengths due to temperature variations to
which the system is exposed.
(3) Other configurations of sampling systems may be used upon
demonstration of stable operation to the FCC.
(b) A station having an antenna sampling system constructed
according to the specifications given in paragraph (a) of this section,
may obtain approval of that system by submitting an informal request to
the FCC in Washington, DC. The request for approval, signed by the
licensee or authorized representative, must contain sufficient
information to show that the sampling system is in compliance with all
requirements of paragraph (a) of this section.
Note: A public notice giving additional information on approval of
antenna sampling systems is available upon request from the FCC's
current copy contractor.
(c) In the event that the antenna monitor sampling system is
temporarily out of service for repair or replacement, the station may be
operated, pending completion of repairs or replacement, for a period not
exceeding 120 days without further authority from the FCC if all other
operating parameters and the field monitoring point values are within
the limits specified on the station authorization.
(d) If the antenna sampling system is modified or components of the
sampling system are replaced, the following procedure shall be followed:
(1) Temporary authority shall be requested and obtained from the
Commission in Washington to operate with parameters at variance with
licensed values pending issuance of a modified license specifying
parameters subsequent to modification or replacement of components.
(2) Immediately prior to modification or replacement of components
of the sampling system not on the towers, and after a verification that
all monitoring point values, base current ratios and operating
parameters are within the limits or tolerances specified in the
instrument of authorization or the pertinent rules, the following
indications must be read for each radiation pattern: Final plate current
and plate voltage, common point current, base currents and their ratios,
antenna monitor phase and current indications, and the field strength at
each monitoring point. Subsequent to these modifications or changes the
above procedure must be repeated.
(3) If that portion of the sampling system above the base of the
towers is modified or components replaced, a partial proof of
performance shall be executed in accordance with Sec. 73.154 subsequent
to these changes. The partial proof of performance shall be accompanied
by common point impedance measurements made in accordance with
Sec. 73.54.
(4) Request for modification of license shall be submitted to the
FCC in
[[Page 27]]
Washington, DC, within 30 days of the date of sampling system
modification or replacement. Such request shall specify the transmitter
plate voltage and plate current, common point current, base currents and
their ratios, antenna monitor phase and current indications, and all
other data obtained pursuant to this paragraph.
(e) If an existing sampling system is found to be patently of
marginal construction, or where the performance of a directional antenna
is found to be unsatisfactory, and this deficiency reasonably may be
attributed, in whole or in part, to inadequacies in the antenna
monitoring system, the FCC may require the reconstruction of the
sampling system in accordance with requirements specified above.
[41 FR 7405, Feb. 18, 1976, as amended at 42 FR 24056, May 12, 1977; 44
FR 58731, Oct. 11, 1979; 46 FR 35462, July 8, 1981; 48 FR 38478, Aug.
24, 1983; 48 FR 44805, Sept. 30, 1983; 49 FR 32358, Aug. 14, 1984; 50 FR
47054, Nov. 14, 1985; 51 FR 9965, Mar. 24, 1986; 51 FR 40435, Nov. 7,
1986; 56 FR 64859, Dec. 12, 1991]
Sec. 73.69 Antenna monitors.
(a) Each station using a directional antenna must have in operation
at the transmitter site an FCC authorized antenna monitor. However, if
the station authorization sets specific tolerances within which the
phase and amplitude relationships must be maintained, or requires the
use of a monitor of specified repeatability, resolution or accuracy, the
antenna monitor used will be authorized on an individual basis.
(1) Normally, the antenna monitor is to be installed immediately
adjacent to the transmitter and antenna phasing equipment. However, the
monitor may be located elsewhere provided that its environment is
maintained at all times within those limits under which the monitor was
type-approved.
(2) The antenna monitor installed at a station operating a
directional antenna by remote control or when the monitor is installed
in the antenna field at a distance from the transmitter, must be
designed and authorized for such use in accordance with the provisions
of Sec. 73.53(b)(9).
(b) In the event that the antenna monitor sampling system is
temporarily out of service for repair or replacement, the station may be
operated, pending completion of repairs or replacement, for a period not
exceeding 120 days without further authority from the FCC if all other
operating parameters, and the field monitoring point values are within
the limits specified on the station authorization.
(c) If conditions beyond the control of the licensee prevent the
restoration of the monitor to service within the allowed period,
informal request in accordance with Sec. 73.3549 of the Commission's
rules must be filed with the Engineer in Charge of the radio district in
which the station is located for such additional time as may be required
to complete repairs of the defective instrument.
(d) If an authorized antenna monitor is replaced by another antenna
monitor, the following procedure shall be followed:
(1) Temporary authority shall be requested and obtained from the
Commission in Washington to operate with parameters at variance with
licensed values, pending issuance of a modified license specifying new
parameters.
(2) Immediately prior to the replacement of the antenna monitor,
after a verification that all monitoring point values and base current
ratios are within the limits or tolerances specified in the instrument
of authorization or the pertinent rules, the following indications must
be read for each radiation pattern: Final plate current and plate
voltage, common point current, base currents, antenna monitor phase and
current indications, and the field strength at each monitoring point.
(3) With the new monitor substituted for the old, all indications
specified in paragraph (d)(2) of this section, again must be read. If no
change has occurred in the indication for any parameter other than the
indications of the antenna monitor, the new antenna monitor indications
must be deemed to be those reflecting correct array adjustments.
(4) If it cannot be established by the observations required in
paragraph (d)(2) of this section that base current ratios and monitoring
point values are within the tolerances or limits prescribed by the rules
and the instrument of authorization, or if the substitution
[[Page 28]]
of the new antenna monitor for the old results in changes in these
parameters, a partial proof of performance shall be executed and
analyzed in accordance with Sec. 73.154.
(5) An informal request for modification of license shall be
submitted to the Commission in Washington, DC, within 30 days of the
date of monitor replacement. Such request shall specify the make, type,
and serial number of the replacement monitor, phase and sample current
indications, and other data obtained pursuant to this paragraph (d) of
this section.
(e) The antenna monitor must be calibrated according to the
manufacturer's instructions as often as necessary to ensure its proper
operation.
(Secs. 4, 5, 303, 48 Stat., as amended, 1066, 1068, as amended, 1082, as
amended; 47 U.S.C. 154, 303. Interpret or apply secs. 301, 303, 307, 48
Stat. 1081, 1082, as amended, 1083, as amended, 47 U.S.C. 301, 303, 307)
[38 FR 1918, Jan. 19, 1973, as amended at 40 FR 15884, Apr. 8, 1975; 40
FR 25459, June 16, 1975; 40 FR 27939, July 2, 1975; 41 FR 22942, June 8,
1976; 41 FR 32892, Aug. 6, 1976; 43 FR 4022, Jan. 31, 1978; 45 FR 26062,
Apr. 17, 1980; 48 FR 38478, Aug. 24, 1983; 49 FR 3999, Feb. 1, 1984; 50
FR 47054, Nov. 14, 1985; 51 FR 9965, Mar. 24, 1986; 56 FR 64859, Dec.
12, 1991; 60 FR 55480, Nov. 1, 1995]
Sec. 73.72 Operating during the experimental period.
(a) An AM station may operate during the experimental period (the
time between midnight and sunrise, local time) on its assigned frequency
and with its authorized power for the routine testing and maintenance of
its transmitting system, and for conducting experimentation under an
experimental authorization, provided no interference is caused to other
stations maintaining a regular operating schedule within such period.
(b) No station licensed for ``daytime'' or ''specified hours'' of
operation may broadcast any regular or scheduled program during this
period.
(c) The licensee of an AM station shall operate or refrain from
operating its station during the experimental period as directed by the
FCC to facilitate frequency measurements or for the determination of
interference.
[43 FR 32780, July 28, 1978, as amended at 56 FR 64859, Dec. 12, 1991]
Sec. 73.88 Blanketing interference.
The licensee of each broadcast station is required to satisfy all
reasonable complaints of blanketing interference within the 1 V/m
contour.
Note: For more detailed instructions concerning operational
responsibilities of licensees and permittees under this section, see
Sec. 73.318 (b), (c) and (d).
[28 FR 13574, Dec. 14, 1963, as amended at 56 FR 64859, Dec. 12, 1991]
Sec. 73.99 Presunrise service authorization (PSRA) and postsunset service authorization (PSSA).
(a) To provide maximum uniformity in early morning operation
compatible with interference considerations, and to provide for
additional service during early evening hours for Class D stations,
provisions are made for presunrise service and postsunset service. The
permissible power for presunrise or postsunset service authorizations
shall not exceed 500 watts, or the authorized daytime or critical hours
power (whichever is less). Calculation of the permissible power shall
consider only co-channel stations for interference protection purposes.
(b) Presunrise service authorizations (PSRA) permit:
(1) Class D stations operating on Mexican, Bahamian, and Canadian
priority Class A clear channels to commence PSRA operation at 6 a.m.
local time and to continue such operation until the sunrise times
specified in their basic instruments of authorization.
(2) Class D stations situated outside 0.5 mV/m-50% skywave contours
of co-channel U.S. Class A stations to commence PSRA operation at 6 a.m.
local time and to continue such operation until sunrise times specified
in their basic instruments of authorization.
(3) Class D stations located within co-channel 0.5 mV/m-50% skywave
contours of U.S. Class A stations, to commence PSRA operation either at
6 a.m. local time, or at sunrise at the nearest Class A station located
east of the
[[Page 29]]
Class D station (whichever is later), and to continue such operation
until the sunrise times specified in their basic instruments of
authorization.
(4) Class B and Class D stations on regional channels to commence
PSRA operation at 6 a.m. local time and to continue such operation until
local sunrise times specified in their basic instruments of
authorization.
(c) Extended Daylight Saving Time Pre-Sunrise Authorizations:
(1) Between the first Sunday in April and the end of the month of
April, Class D stations will be permitted to conduct pre-sunrise
operation beginning at 6 a.m. local time with a maximum power of 500
watts (not to exceed the station's regular daytime or critical hours
power), reduced as necessary to comply with the following requirements:
(i) Full protection is to be provided as specified in applicable
international agreements.
(ii) Protection is to be provided to the 0.5 mV/m groundwave signals
of co-channel U.S. Class A stations; protection to the 0.5 mV/m-50%
skywave contours of these stations is not required.
(iii) In determining the protection to be provided, the effect of
each interfering signal will be evaluated separately. The presence of
interference from other stations will not reduce or eliminate the
required protection.
(iv) Notwithstanding the requirements of paragraph (c)(1) (ii) and
(iii) of this section, the stations will be permitted to operate with a
minimum power of 10 watts unless a lower power is required by
international agreement.
(2) The Commission will issue appropriate authorizations to Class D
stations not previously eligible to operate during this period. Class D
stations authorized to operate during this presunrise period may
continue to operate under their current authorization.
(d) Postsunset service authorizations (PSSA) permit:
(1) Class D stations located on Mexican, Bahamian, and Canadian
priority Class A clear channels to commence PSSA operation at sunset
times specified in their basic instruments of authorization and to
continue for two hours after such specified times.
(2) Class D stations situated outside 0.5 mV/m-50% skywave contours
of co-channel U.S. Class A stations to commence PSSA operations at
sunset times specified in their basic instruments of authorization and
to continue for two hours after such specified times.
(3) Class D stations located within co-channel 0.5 mV/m-50% skywave
contours of U.S. Class A stations to commence PSSA operation at sunset
times specified in their basic instruments of authorization and to
continue such operation until two hours past such specified times, or
until sunset at the nearest Class A station located west of the Class D
station, whichever is earlier. Class D stations located west of the
Class A station do not qualify for PSSA operation.
(4) Class D stations on regional channels to commence PSSA operation
at sunset times specified on their basic instruments of authorization
and to continue such operation until two hours past such specified
times.
(e) Procedural Matters. (1) Applications for PSRA and PSSA operation
are not required. Instead, the FCC will calculate the periods of such
operation and the power to be used pursuant to the provisions of this
section and the protection requirements contained in applicable
international agreements. Licensees will be notified of permissible
power and times of operation. Presunrise and Postsunset service
authority permits operation on a secondary basis and does not confer
license rights. No request for such authority need be filed. However,
stations intending to operate PSRA or PSSA shall submit by letter,
signed as specified in Sec. 73.3513, the following information:
(i) Licensee name, station call letters and station location,
(ii) Indication as to whether PSRA operation, PSSA operation, or
both, is intended by the station,
(iii) A description of the method whereby any necessary power
reduction will be achieved.
(2) Upon submission of the required information, such operation may
begin without further authority.
[[Page 30]]
(f) Technical Criteria. Calculations to determine whether there is
objectionable interference will be determined in accordance with the AM
Broadcast Technical Standards, Secs. 73.182 through 73.190, and
applicable international agreements. Calculations will be performed
using daytime antenna systems, or critical hours antenna systems when
specified on the license. In performing calculations to determine
assigned power and times for commencement of PSRA and PSSA operation,
the following standards and criteria will be used:
(1) Class D stations operating in accordance with paragraphs (b)(1),
(b)(2), (d)(1), and (d)(2) of this section are required to protect the
nighttime 0.5 mV/m-50% skywave contours of co-channel Class A stations.
Where a 0.5 mV/m-50% skywave signal from the Class A station is not
produced, the 0.5 mV/m groundwave contour shall be protected.
(2) Class D stations are required to fully protect foreign Class B
and Class C stations when operating PSRA and PSSA; Class D stations
operating PSSA are required to fully protect U.S. Class B stations. For
purposes of determining protection, the nighttime RSS limit will be used
in the determination of maximum permissible power.
(3) Class D stations operating in accordance with paragraphs (d)(2)
and (d)(3) of this section are required to restrict maximum 10% skywave
radiation at any point on the daytime 0.1 mV/m groundwave contour of a
co-channel Class A station to 25 V/m. The location of the 0.1
mV/m contour of the Class A station will be determined by use of Figure
M3, Estimated Ground Conductivity in the United States. When the 0.1 mV/
m contour extends beyond the national boundary, the international
boundary shall be considered the 0.1 mV/m contour.
(4) Class B and Class D stations on regional channels operating PSRA
and PSSA (Class D only) are required to provide full protection to co-
channel foreign Class B and Class C stations.
(5) Class D stations on regional channels operating PSSA beyond 6
p.m. local time are required to fully protect U.S. Class B stations.
(6) The protection that Class D stations on regional channels are
required to provide when operating PSSA until 6 p.m. local time is as
follows.
(i) For the first half-hour of PSSA operation, protection will be
calculated at sunset plus 30 minutes at the site of the Class D station;
(ii) For the second half-hour of PSSA operation, protection will be
calculated at sunset plus one hour at the site of the Class D station;
(iii) For the second hour of PSSA operation, protection will be
calculated at sunset plus two hours at the site of the Class D station;
(iv) Minimum powers during the period until 6 p.m. local time shall
be permitted as follows:
------------------------------------------------------------------------
Calculated power Adjusted minimum power
------------------------------------------------------------------------
From 1 to 45 watts.................... 50 watts.
Above 45 to 70 watts.................. 75 watts.
Above 70 to 100 watts................. 100 watts.
------------------------------------------------------------------------
(7) For protection purposes, the nighttime 25% RSS limit will be
used in the determination of maximum permissible power.
(g) Calculations made under paragraph (d) of this section may not
take outstanding PSRA or PSSA operations into account, nor will the
grant of a PSRA or PSSA confer any degree of interference protection on
the holder thereof.
(h) Operation under a PSRA or PSSA is not mandatory, and will not be
included in determining compliance with the requirements of
Sec. 73.1740. To the extent actually undertaken, however, presunrise
operation will be considered by the FCC in determining overall
compliance with past programming representations and station policy
concerning commercial matter.
(i) The PSRA or PSSA is secondary to the basic instrument of
authorization with which it is to be associated. The PSRA or PSSA may be
suspended, modified, or withdrawn by the FCC without prior notice or
right to hearing, if necessary to resolve interference conflicts, to
implement agreements with foreign governments, or in other circumstances
warranting such action. Moreover, the PSRA or PSSA does not extend
beyond the term of the basic authorization.
(j) The Commission will periodically recalculate maximum permissible
power and times for commencing PSRA
[[Page 31]]
and PSSA for each Class D station operating in accordance with paragraph
(c) of this section. The Commission will calculate the maximum power at
which each individual station may conduct presunrise operations during
extended daylight saving time and shall issue conforming authorizations.
These original notifications and subsequent notifications should be
associated with the station's authorization. Upon notification of new
power and time of commencing operation, affected stations shall make
necessary adjustments within 30 days.
(k) A PSRA and PSSA does not require compliance with Secs. 73.45,
73.182 and 73.1560 where the operation might otherwise be considered as
technically substandard. Further, the requirements of paragraphs (a)(5),
(b)(2), (c)(2), and (d)(2) of Sec. 73.1215 concerning the scale ranges
of transmission system indicating instruments are waived for PSRA and
PSSA operation except for the radio frequency ammeters used in
determining antenna input power.
(1) A station having an antenna monitor incapable of functioning at
the authorized PSRA and PSSA power when using a directional antenna
shall take the monitor reading using an unmodulated carrier at the
authorized daytime power immediately prior to commencing PSRA or PSSA
operations. Special conditions as the FCC may deem appropriate may be
included for PSRA or PSSA to insure operation of the transmitter and
associated equipment in accordance with all phases of good engineering
practice.
[56 FR 64860, Dec. 12, 1991; 57 FR 43290, Sept. 18, 1992, as amended at
58 FR 27950, May 12, 1993]
Sec. 73.127 Use of multiplex transmission.
The licensee of an AM broadcast station may use its AM carrier to
transmit signals not audible on ordinary consumer receivers, for both
broadcast and non-broadcast purposes subject to the following
requirements:
(a) Such use does not disrupt or degrade the station's own programs
or the programs of other broadcast stations.
(b) AM carrier services that are common carrier in nature are
subject to common carrier regulation. Licensees operating such services
are required to apply to the FCC for the appropriate authorization and
to comply with all policies and rules applicable to the service.
Responsibility for making the initial determinations of whether a
particular activity is common carriage rests with the AM station
licensee. Initial determinations by licensees are subject to FCC
examination and may be reviewed at the FCC's discretion. AM carrier
services that are private carrier in nature must notify the Licensing
Division of the Private Radio Bureau at Gettysburg, Pennsylvania 17325,
by letter, prior to initiating service certifying compliance with 47 CFR
parts 90 and 94.
(c) AM carrier services are of a secondary nature under the
authority of the AM station authorization, and the authority to provide
such communications services may not be retained or transferred in any
manner separate from the station's authorization. The grant or renewal
of an AM station permit or license is not furthered or promoted by
proposed or past service. The permittee or licensee must establish that
the broadcast operation is in the public interest wholly apart from the
subsidiary communications services provided.
(d) The station identification, delayed recording, and sponsor
identification announcements required by Secs. 73.1201, 73.1208, and
73.1212 are not applicable to leased communications services transmitted
via services that are not of a general broadcast program nature.
(e) The licensee or permittee must retain control over all material
transmitted in a broadcast mode via the station's facilities, with the
right to reject any material that it deems inappropriate or undesirable.
(f) Installation of the multiplex transmitting equipment must
conform with the requirements of Sec. 73.1690(e).
[47 FR 25345, June 11, 1982, as amended at 49 FR 34015, Aug. 28, 1984;
51 FR 41629, Nov. 18, 1986; 51 FR 44478, Dec. 10, 1986]
Sec. 73.128 AM Stereophonic Broadcasting.
(a) An Am broadcast station may, without specific authority from the
FCC, transmit stereophonic programs
[[Page 32]]
upon installation of type accepted stereophonic transmitting equipment
and the necessary measuring equipment to determine that the stereophonic
transmissions conform to the modulation characteristics specified in
paragraphs (b) and (c) of this section. Stations transmitting
stereophonic programs prior to March 21, 1994 may continue to do so
until March 21, 1995 as long as they continue to comply with the rules
in effect prior to March 21, 1994.
(b) The following limitations on the transmitted wave must be met to
insure compliance with the occupied bandwidth limitations, compatibility
with AM receivers using envelope detectors, and any applicable
international agreements to which the FCC is a party:
(1) The transmitted wave must meet the occupied bandwidth
specifications of Sec. 73.44 under all possible conditions of program
modulation. Compliance with requirement shall be demonstrated either by
the following specific modulation tests or other documented test
procedures that are to be fully described in the application for type
acceptance and the transmitting equipment instruction manual. (See
Sec. 2.983(d)(8) and (j)).
(i) Main channel (L+R) under all conditions of amplitude modulations
for the stereophonic system but not exceeding amplitude modulation on
negative peaks of 100%.
(ii) Stereophonic (L-R) modulated with audio tones of the same
amplitude at the transmitter input terminals as in paragraph (b)(i) of
this section but with the phase of either the L or R channel reversed.
(iii) Left and Right Channel only, under all conditions of
modulation for the stereophonic system in use but not exceeding
amplitude modulation on negative peaks of 100%.
(c) Effective on December 20, 1994, stereophonic transmissions shall
conform to the following additional modulation characteristics:
(1) The audio response of the main (L+R) channel shall conform to
the requirements of the ANSI/EIA-549-1988, NRSC-1 AM Preemphasis/
Deemphasis and Broadcast Transmission Bandwidth Specifications (NRSC-1).
(2) The left and right channel audio signals shall conform to
frequency response limitations dictated by ANSI/EIA-549-1988.
(3) The stereophonic difference (L-R) information shall be
transmitted by varying the phase of the carrier in accordance with the
following relationship:
[GRAPHIC] [TIFF OMITTED] TR20DE93.000
where:
L(t)=audio signal left channel,
R(t)=audio signal right channel,
m=modulation factor, and
mpeak(L(t)+R(t))=1 for 100% amplitude modulation,
mpeak(L(t)-R(t))=1 for 100% phase modulation.
(4) The carrier phase shall advance in a positive direction when a
left channel signal causes the transmitter envelope to be modulated in a
positive direction. The carrier phase shall likewise retard (negative
phase change) when a right channel signal causes the transmitter
envelope to be modulated in a positive direction. The phase modulation
shall be symmetrical for the condition of difference (L-R) channel
information sent without the presence of envelope modulation.
(5) Maximum angular modulation, which occurs on negative peaks of
the left or right channel with no signal present on the opposite channel
(L(t)=-0.75, R(t)=0, or R(t)=-0.75, L(t)=0) shall not exceed 1.25
radians.
(6) A peak phase modulation of +/-0.785 radians under the condition
of difference (L-R) channel modulation
[[Page 33]]
and the absence of envelope (L+R) modulation and pilot signal shall
represent 100% modulation of the difference channel.
(7) The composite signal shall contain a pilot tone for indication
of the presence of stereophonic information. The pilot tone shall
consist of a 25 Hz tone, with 3% or less total harmonic distortion and a
frequency tolerance of +/- 0.1 H2, which modulates the carrier
phase +/- 0.05 radians peak, corresponding to 5% L-R modulation when no
other modulation is present. The injection level shall be 5%, with a
tolerance of +1, -1%.
(8) The composite signal shall be described by the following
expression:
[GRAPHIC] [TIFF OMITTED] TR20DE93.001
where:
A=the unmodulated carrier voltage
m=the modulation index
Csn=the magnitude of the nth term of the sum signal
Cdn=the magnitude of the nth term of the difference signal
sn=the nth order angular velocity of the sum signal
dn=the nth order angular velocity of the difference
signal
c=the angular velocity of the carrier
[GRAPHIC] [TIFF OMITTED] TR20DE93.002
Asn and Bsn are the nth sine and cosine coefficients of
Csn
Adn and Bdn are the nth sine and cosine coefficients of
Cdn
[58 FR 66301, Dec. 20, 1993]
Sec. 73.132 Territorial exclusivity.
No licensee of an AM broadcast station shall have any arrangement
with a network organization which prevents
[[Page 34]]
or hinders another station serving substantially the same area from
broadcasting the network's programs not taken by the former station, or
which prevents or hinders another station serving a substantially
different area from broadcasting any program of the network
organization: Provided, however, That this section does not prohibit
arrangements under which the station is granted first call within its
primary service area upon the network's programs. The term ``network
organization'' means any organization originating program material, with
or without commercial messages, and furnishing the same to stations
interconnected so as to permit simultaneous broadcast by all or some of
them. However, arrangements involving only stations under common
ownership, or only the rebroadcast by one station or programming from
another with no compensation other than a lump-sum payment by the
station rebroadcasting, are not considered arrangements with a network
organization. The term ``arrangement'' means any contract, arrangement
or understanding, expressed or implied.
[42 FR 16422, Mar. 28, 1977]
Sec. 73.150 Directional antenna systems.
(a) For each station employing a directional antenna, all
determinations of service provided and interference caused shall be
based on the inverse distance fields of the standard radiation pattern
for that station. (As applied to nighttime operation the term ``standard
radiation pattern'' shall include the radiation pattern in the
horizontal plane, and radiation patterns at angles above this plane.)
(1) Parties submitting directional antenna patterns pursuant to this
section and Sec. 73.152 (Modified standard pattern) must submit patterns
which are tabulated and plotted in units of millivolts per meter at 1
kilometer.
Note: Applications for new stations and for changes (both minor and
major) in existing stations must use a standard pattern.
(b) The following data shall be submitted with an application for
authority to install a directional antenna:
(1) The standard radiation pattern for the proposed antenna in the
horizontal plane, and where pertinent, tabulated values for the
azimuthal radiation patterns for angles of elevation up to and including
60 degrees, with a separate section for each increment of 5 degrees.
(i) The standard radiation pattern shall be based on the theoretical
radiation pattern. The theoretical radiation pattern shall be calculated
in accordance with the following mathematical expression:
[GRAPHIC] [TIFF OMITTED] TC01MR91.062
(Eq. 1)
where:
E(,)th! Represents the theoretical inverse
distance fields at one kilometer for the given azimuth and elevation....
k Represents the multiplying constant which determines the basic
pattern size. It shall be chosen so that the effective field (RMS) of
the theoretical pattern in the horizontal plane shall be no greater than
the value computed on the assumption that nominal station power (see
Sec. 73.14) is delivered to the directional array, and that a lumped
loss resistance of one ohm exists at the current loop of each element of
the array, or at the base of each element of electrical height lower
than 0.25 wavelength, and no less than the value required by
Sec. 73.189(b)(2) of this part for a station of the class and nominal
power for which the pattern is designed.................................
n Represents the number of elements (towers) in the directional array..
i Represents the ith element in the array.........................
Fi Represents the field ratio of the ith element in the
array...................................................................
i (th antenna. This value depends on the tower
height, as well as whether the tower is top-loaded or sectionalized. The
various formulas for computing fi (i Represents the electrical spacing of the ith tower from
the reference point.....................................................
i Represents the orientation (with respect to true
north) of the ith tower............................................
Represents the azimuth (with respect to true north).........
i Represents the electrical phase angle of the current
in the ith tower...................................................
[[Page 35]]
The standard radiation pattern shall be constructed in accordance
with the following mathematical expression:
[GRAPHIC] [TIFF OMITTED] TC01MR91.063
where:
E(,)std represents the inverse distance
fields at one kilometer which are produced by the directional antenna in
the horizontal and vertical planes. E(,)th
represents the theoretical inverse distance fields at one kilometer as
computed in accordance with Eq. 1, above.
Q is the greater of the following two quantities: 0.025g()
Erss or 10.0g() PkW
where:
g() is the vertical plane distribution factor,
f(), for the shortest element in the array (see Eq. 2, above;
also see Sec. 73.190, Figure 5). If the shortest element has an
electrical height in excess of 0.5 wavelength, g() shall be
computed as follows:
[GRAPHIC] [TIFF OMITTED] TC01MR91.064
Erss is the root sum square of the amplitudes of the inverse
fields of the elements of the array in the horizontal plane, as used in
the expression for E(,)th (see Eq. 1, above),
and is computed as follows:
[GRAPHIC] [TIFF OMITTED] TC01MR91.065
PkW is the nominal station power expressed in kilowatts, see
Sec. 73.14. If the nominal power is less than one kilowatt, PkW=1.
(ii) Where the orthogonal addition of the factor Q to
E(,)th results in a standard pattern whose
minimum fields are lower than those found necessary or desirable, these
fields may be increased by appropriate adjustment of the parameters of
E(,)th.
(2) All patterns shall be computed for integral multiples of five
degrees, beginning with zero degrees representing true north, and, shall
be plotted to the largest scale possible on unglazed letter-size paper
(main engraving approximately 7'' x 10'') using only scale divisions
and subdivisions of 1,2,2.5, or 5 times 10nth. The horizontal plane
pattern shall be plotted on polar coordinate paper, with the zero degree
point corresponding to true north. Patterns for elevation angles above
the horizontal plane may be plotted in polar or rectangular coordinates,
with the pattern for each angle of elevation on a separate page.
Rectangular plots shall begin and end at true north, with all azimuths
labelled in increments of not less than 20 degrees. If a rectangular
plot is used, the ordinate showing the scale for radiation may be
logarithmic. Such patterns for elevation angles above the horizontal
plane need be submitted only upon specific request by Commission staff.
Minor lobe and null detail occurring between successive patterns for
specific angles of elevation need not be submitted. Values of field
strength on any pattern less than ten percent of the maximum field
strength plotted on that pattern shall be shown on an enlarged scale.
Rectangular plots with a logarithmic ordinate need not utilize an
expanded scale unless necessary to show clearly the minor lobe and null
detail.
(3) The effective (RMS) field strength in the horizontal plane of
E(,)std, E(,)th and
the root-sum-square (RSS) value of the inverse distance fields of the
array elements at 1 kilometer, derived from the equation for
E(,)th. These values shall be tabulated on the
page on which the horizontal plane pattern is plotted, which shall be
specifically labelled as the Standard Horizontal Plane Pattern.
(4) Physical description of the array, showing:
(i) Number of elements.
(ii) Type of each element (i.e., guyed or self-supporting, uniform
cross section or tapered (specifying base dimensions), grounded or
insulated, etc.)
(iii) Details of top loading, or sectionalizing, if any.
(iv) Height of radiating portion of each element in feet (height
above base insulator, or base, if grounded).
(v) Overall height of each element above ground.
(vi) Sketch of antenna site, indicating its dimensions, the location
of the
[[Page 36]]
antenna elements, thereon, their spacing from each other, and their
orientation with respect to each other and to true north, the number and
length of the radials in the ground system about each element, the
dimensions of ground screens, if any, and bonding between towers and
between radial systems.
(5) Electrical description of the array, showing:
(i) Relative amplitudes of the fields of the array elements.
(ii) Relative time phasing of the fields of the array elements in
degrees leading [+] or lagging [-].
(iii) Space phasing between elements in degrees.
(iv) Where waiver of the content of this section is requested or
upon request of the Commission staff, all assumptions made and the basis
therefor, particularly with respect to the electrical height of the
elements, current distribution along elements, efficiency of each
element, and ground conductivity.
(v) Where waiver of the content of this section is requested, or
upon request of the Commission staff, those formulas used for computing
E(,)th and E(,)std.
Complete tabulation of final computed data used in plotting patterns,
including data for the determination of the RMS value of the pattern,
and the RSS field of the array.
(6) The values used in specifying the parameters which describe the
array must be specified to no greater precision than can be achieved
with available monitoring equipment. Use of greater precision raises a
rebuttable presumption of instability of the array. Following are
acceptable values of precision; greater precision may be used only upon
showing that the monitoring equipment to be installed gives accurate
readings with the specified precision.
(i) Field Ratio: 3 significant figures.
(ii) Phasing: to the nearest 0.1 degree.
(iii) Orientation (with respect to a common point in the array, or
with respect to another tower): to the nearest 0.1 degree.
(iv) Spacing (with respect to a common point in the array, or with
respect to another tower): to the nearest 0.1 degree.
(v) Electrical Height (for all parameters listed in Section 73.160):
to the nearest 0.1 degree.
(vi) Theoretical RMS (to determine pattern size): 4 significant
figures.
(vii) Additional requirements relating to modified standard patterns
appear in Sec. 73.152(c)(3) and (c)(4).
(7) Any additional information required by the application form.
(c) Sample calculations for the theoretical and standard radiation
follow. Assume a five kilowatt (nominal power) station with a
theoretical RMS of 685 mV/m at one kilometer. Assume that it is an in-
line array consisting of three towers. Assume the following parameters
for the towers:
------------------------------------------------------------------------
Field Relative Relative Relative
Tower ratio phasing spacing orientation
------------------------------------------------------------------------
1............................. 1.0 -128.5 0.0 0.0
2............................. 1.89 0.0 110.0 285.0
3............................. 1.0 128.5 220.0 285.0
------------------------------------------------------------------------
Assume that tower 1 is a typical tower with an electrical height of
120 degrees. Assume that tower 2 is top-loaded in accordance with the
method described in Sec. 73.160(b)(2) where A is 120 electrical degrees
and B is 20 electrical degrees. Assume that tower 3 is sectionalized in
accordance with the method described in Sec. 73.160(b)(3) where A is 120
electrical degrees, B is 20 electrical degrees, C is 220 electrical
degrees, and D is 15 electrical degrees.
The multiplying constant will be 323.6.
Following is a tabulation of part of the theoretical pattern:
------------------------------------------------------------------------
Vertical
Azimuth 0 30 60 angle
------------------------------------------------------------------------
0........................... 15.98 62.49 68.20
105......................... 1225.30 819.79 234.54
235......................... 0.43 18.46 34.56
247......................... 82.62 51.52 26.38
------------------------------------------------------------------------
If we further assume that the station has a standard pattern, we
find that Q, for
Sec. 73.151 Field strength measurements to establish performance of directional antennas.
(a) In addition to the information required by the license
application form, the following showing must be submitted to establish
for each mode of directional operation, that the effective measured
field strength (RMS) at 1 mile is not less than 85 percent of the
effective field strength specified for the standard radiation pattern
for that mode of directional operation, or less than that specified in
Sec. 73.189(b) for the class of station involved, whichever is the
higher value, and that the measured field strength at 1 mile in any
direction does not exceed the field shown in that direction on the
standard radiation pattern for that mode of directional operation:
(1) A tabulation of inverse field strengths in the horizontal plane
at 1 mile, as determined from field strength measurements taken and
analyzed in accordance with Sec. 73.186, and a statement of the
effective field strength (RMS), based on these measurements.
Measurements shall be made in at least the following directions:
(i) Those specified in the instrument of authorization.
(ii) In major lobes. Generally at least three radials are necessary
to establish a major lobe; however, additional radials may be required.
(iii) Along sufficient number of other radials to establish the
effective field. In the case of a relatively simple directional antenna
pattern, approximately five radials in addition to those in paragraphs
(a)(1) (i) and (ii) of this section are sufficient. However, when more
complicated patterns are involved, that is, patterns having several or
sharp lobes or nulls, measurements shall be taken along as many radials
as may be necessary, to definitely establish the pattern(s).
(2) A tabulation of:
(i) The phase difference of the current in each other element with
respect to the reference element, and whether the current leads (+) or
lags (-) the current in the reference element, as indicated by the
station's antenna monitor.
(ii) The ratio of the amplitude of the radio frequency current in
each other element to the current in the reference element, as indicated
on the station's antenna monitor.
(iii) The value of the radio frequency current at the base of each
element, and the ratio of the current in each other element to the base
current in the reference element. If there are substantial differences
between the ratios established in paragraph (a)(2)(ii) of this section
and the ratios computed in this paragraphs (a)(2)(iii) and/or if there
are substantial differences between the parameters established in
paragraphs (a)(2) (i) and (ii) of this section and this paragraph
(a)(2)(iii), and those used in the design of the standard radiation
pattern, a full explanation of the reasons for these differences shall
be given.
(3) The actual field strength measured at each monitoring point
established in the various directions for which a limiting field was
specified in the instrument of authorization together with accurate and
detailed description of each monitoring point together with ordinary
snapshots, clear and sharp, taken with the field strength meter in its
measuring position and with the camera so located that its field of view
takes in as many pertinent landmarks as possible. In addition, the
directions for proceeding to each monitoring point together with a rough
sketch or map upon which has been indicated the most accessible
approaches to the monitoring points should be submitted.
(b) For stations authorized to operate with simple directional
antenna systems (e.g., two towers) in the 1605-1705 kHz band, the
measurements to support pattern RMS compliance referred to in paragraphs
(a)(1)(ii) and (a)(1)(iii)
[[Page 38]]
of this section are not required. In such cases, measured radials are
required only in the direction of short-spaced allotments, or in
directions specifically identified by the Commission.
[36 FR 919, Jan. 20, 1971, as amended at 42 FR 36828, July 18, 1977; 49
FR 23348, June 6, 1984; 50 FR 32416, Aug. 12, 1985; 56 FR 64862, Dec.
12, 1991]
Sec. 73.152 Modification of directional antenna data.
(a) If, after construction and final adjustment of a directional
antenna, a measured inverse distance field in any direction exceeds the
field shown on the standard radiation pattern for the pertinent mode of
directional operation, an application shall be filed, specifying a
modified standard radiation pattern and/or such changes as may be
required in operating parameters so that all measured effective fields
will be contained within the modified standard radiation pattern.
(b) Normally, a modified standard pattern is not acceptable at the
initial construction permit stage, before a proof-of-performance has
been completed. However, in certain cases, where it can be shown that
modification is necessary, a modified standard pattern will be
acceptable at the initial construction permit stage. Following is a non-
inclusive list of items to be considered in determining whether a
modification is acceptable at the initial construction permit stage:
(1) When the proposed pattern is essentially the same as an existing
pattern at the same antenna site. (e.g., A DA-D station proposing to
become a DA-1 station.)
(2) Excessive reradiating structures, which should be shown on a
plat of the antenna site and surrounding area.
(3) Other environmental factors; they should be fully described.
(4) Judgment and experience of the engineer preparing the
engineering portion of the application. This must be supported with a
full discussion of the pertinent factors.
(c) The following general principles shall govern the situations in
paragraphs (a) and (b) in this section:
(1) Where a measured field in any direction will exceed the
authorized standard pattern, the license application may specify the
level at which the input power to the antenna shall be limited to
maintain the measured field at a value not in excess of that shown on
the standard pattern, and shall specify the common point current
corresponding to this power level. This value of common point current
will be specified on the license for that station.
(2) Where any excessive measured field does not result in
objectionable interference to another station, a modification of
construction permit application may be submitted with a modified
standard pattern encompassing all measured fields. The modified standard
pattern shall supersede the previously submitted standard radiation
pattern for that station in the pertinent mode of directional operation.
Following are the possible methods of creating a modified standard
pattern:
(i) The modified pattern may be computed by making the entire
pattern larger than the original pattern (i.e., have a higher RMS value)
if the measured fields systematically exceed the confines of the
original pattern. The larger pattern shall be computed by using a larger
multiplying constant, k, in the theoretical pattern equation (Eq. 1) in
Sec. 73.150(b)(1).
(ii) Where the measured field exceeds the pattern in discrete
directions, but objectionable interference does not result, the pattern
may be expanded over sectors including these directions. When this
``augmentation'' is desired, it shall be achieved by application of the
following equation:
E(,aug =
{E(,std} 2+ A{g(A/S }2
where:
E(,std!is the standard pattern field
at some particular azimuth and elevation angle, before augmentation,
computed pursuant to Eq. 2, Sec. 73.150(b)(1)(i).
[[Page 39]]
E(,aug.!is the field in the direction
specified above, after augmentation.
A=E(',O)2aug-E(',O)2s
td!in which '!is the central azimuth of augmentation.
E(',O)aug!and E(',O)std!are the
fields in the horizontal plane at the central azimuth of augmentation.
Note: ``A'' must be positive, except during the process of
converting non-standard patterns to standard patterns pursuant to the
Report and Order in Docket No. 21473, and in making minor changes to
stations with patterns developed during the conversion. However, even
when ``A'' is negative, ``A'' cannot be so negative that
E(,aug!is less than
E(,th!at any azimuth or vertical elevation
angle.
g(A!is the absolute horizontal angle between the azimuth at
which the augmented pattern value is being computed and the central
azimuth of augmentation. (DA!cannot exceed 1/2 S.)
In the case where there are spans which overlap, the above formula
shall be applied repeatedly, once for each augmentation, in ascending
order of central azimuth of augmentation, beginning with zero degrees
representing true North. Note that, when spans overlap, there will be,
in effect, an augmentation of an augmentation. And, if the span of an
earlier augmentation overlaps the central azimuth of a later
augmentation, the value of ``A'' for the later augmentation will be
different than the value of ``A'' without the overlap of the earlier
span.
(iii) A combination of paragraphs (c)(2) (i) and (ii), of this
section, with (i) being applied before (ii) is applied.
(iv) Where the measured inverse distance field exceeds the value
permitted by the standard pattern, and augmentation is allowable under
the terms of this section, the requested amount of augmentation shall be
centered upon the azimuth of the radial upon which the excessive
radiation was measured and shall not exceed the following:
(A) The actual measured inverse distance field value, where the
radial does not involve a required monitoring point.
(B) 120% of the actual measured inverse field value, where the
radial has a monitoring point required by the instrument of
authorization.
Whereas some pattern smoothing can be accommodated, the extent of the
requested span(s) shall be minimized and in no case shall a requested
augmentation span extend to a radial azimuth for which the analyzed
measurement data does not show a need for augmentation.
(3) A Modified Standard Pattern shall be specifically labeled as
such, and shall be plotted in accordance with the requirements of
paragraph (b)(2) of Sec. 73.150. The effective (RMS) field strength in
the horizontal plane of E(,std,
!E(,th, and the root sum square (RSS)
value of the inverse fields of the array elements (derived from the
equation for E(,th), shall be tabulated on
the page on which the horizontal plane pattern is plotted. Where sector
augmentation has been employed in designing the modified pattern, the
direction of maximum augmentation (i.e., the central azimuth of
augmentation) shall be indicated on the horizontal plane pattern for
each augmented sector, and the limits of each sector shall also be
shown. Field values within an augmented sector, computed prior to
augmentation, shall be depicted by a broken line.
(4) There shall be submitted, for each modified standard pattern,
complete tabulations of final computed data used in plotting the
pattern. In addition, for each augmented sector, the central azimuth of
augmentation, span, and radiation at the central azimuth of augmentation
(E(,aug) shall be tabulated.
(5) The parameters used in computing the modified standard pattern
shall be specified with realistic precision. Following is a list of the
maximum acceptable precision:
(i) Central Azimuth of Augmentation: to the nearest 0.1 degree.
(ii) Span: to the nearest 0.1 degree.
(iii) Radiation at Central Azimuth of Augmentation: 4 significant
figures.
(d) Sample calculations for a modified standard pattern follow.
First, assume the existing standard pattern in Sec. 73.150(c). Then,
assume the following augmentation parameters:
[[Page 40]]
------------------------------------------------------------------------
Radiation
Central at
Augmentation number azimuth Span central
azimuth
------------------------------------------------------------------------
1.......................................... 110 40 1,300
2.......................................... 240 50 52
3.......................................... 250 10 130
------------------------------------------------------------------------
Following is a tabulation of part of the modified standard pattern:
------------------------------------------------------------------------
Vertical
Azimuth 0 30 60 angle
------------------------------------------------------------------------
0........................... 28.86 68.05 72.06 .........
105......................... 1,299.42 872.14 254.21 .........
235......................... 39.00 35.74 38.71 .........
247......................... 100.47 66.69 32.78 .........
------------------------------------------------------------------------
[46 FR 11992, Feb. 12, 1981, as amended at 56 FR 64862, Dec. 12, 1991]
Sec. 73.153 Field strength measurements in support of applications or evidence at hearings.
In the determination of interference, groundwave field strength
measurements will take precedence over theoretical values, provided such
measurements are properly taken and presented. When measurements of
groundwave signal strength are presented, they shall be sufficiently
complete in accordance with Sec. 73.186 to determine the field strength
at 1 mile in the pertinent directions for that station. The antenna
resistance measurements required by Sec. 73.186 need not be taken or
submitted.
[44 FR 36037, June 20, 1979, as amended at 56 FR 64862, Dec. 12, 1991]
Sec. 73.154 AM directional antenna partial proof of performance measurements.
(a) A partial proof of performance consists of at least 10 field
strength measurements made on each of the radials established in the
latest complete proof of performance of the directional antenna system.
(b) The measurements are to be made within 2 to 10 miles (3 to 16
kilometers) from the center of the antenna array. When a monitoring
point as designated on the station authorization is on a particular
radial, one of the radial measurements must be made at that point.
(c) The results of the measurements are to be analyzed in either of
two methods. Either the arithmetic average or the logarithmic average of
the ratios of the field strength at each measurement point along each
radial to the corresponding field strength in the most recent complete
proof of performance may be used to establish the inverse distance
fields. (The logarithmic average for each radial is the antilogarithm of
the mean of the logarithms of the ratios of field strength (new to old)
for each measurement location along a given radial).
(d) The result of the most recent partial proof of performance
measurements and analysis is to be retained in the station records
available to the FCC upon request.
[50 FR 47054, Nov. 14, 1985]
Sec. 73.157 Antenna testing during daytime.
(a) The licensee of a station using a directional antenna during
daytime or nighttime hours may, without further authority, operate
during daytime hours with the licensed nighttime directional facilities
or with a nondirectional antenna when conducting monitoring point field
strength measurements or antenna proof of performance measurements.
(b) Operation pursuant to this section is subject to the following
conditions:
(1) No harmful interference will be caused to any other station.
(2) The FCC may notify the licensee to modify or cease such
operation to resolve interference complaints or when such action may
appear to be in the public interest, convenience and necessity.
(3) Such operation shall be undertaken only for the purpose of
taking monitoring point field strength measurements or antenna proof of
performance measurements, and shall be restricted to the minimum time
required to accomplish the measurements.
(4) Operating power in the nondirectional mode shall be adjusted to
the same power as was utilized for the most recent nondirectional proof
of performance covering the licensed facilities.
[50 FR 30947, July 31, 1985]
[[Page 41]]
Sec. 73.158 Directional antenna monitoring points.
(a) When a licensee of a station using a directional antenna system
finds that a field monitoring point, as specified on the station
authorization, is no longer accessible for use or is unsuitable because
of nearby construction or other disturbances to the measured field, an
informal application to change the monitoring point location is to be
promptly submitted to the FCC in Washington, DC. The application must
include the following information:
(1) A partial proof of performance conducted on the radial
containing the monitoring point to be changed.
(2) A written description of the routing to the new selected
monitoring point.
(3) A map showing the location and routing to the new selected
monitoring point.
(4) A photograph showing the new monitoring point in relation to
nearby permanent landmarks that can be used in locating the point
accurately at all times throughout the year. Do not use seasonal or
temporary features in either the written descriptions or photographs as
landmarks for locating field points.
(b) When the descriptive routing to reach any of the monitoring
points as shown on the station license is no longer correct due to road
or building construction or other changes, the licensee must prepare and
file with the FCC, in Washington, DC, a request for a corrected station
license showing the new routing description. A copy of the description
is to be posted with the existing station license. The notification is
to include the information specified in paragraphs (a) (2) and (3) of
this section.
[47 FR 28387, June 30, 1982]
Sec. 73.160 Vertical plane radiation characteristics, f(,!is
0 degrees in the horizontal plane, and 90 degrees when perpendicular to
the horizontal plane. The vertical plane radiation characteristic is
referred to as f(.
E(O) is the radiation from the tower in the horizontal plane.
(b) Listed below are formulas for f() - cos G
f() = ------------------------
(1 - cos G) cos
where:
G is the electrical height of the tower, not including the base
insulator and pier. (In the case of a folded unipole tower, the entire
radiating structure's electrical height is used.)
(2) For a top-loaded tower, the following formula shall be used:
cos B cos (A sin ) - sin sin B sin (A sin ) - cos (A + B)
f() =
cos (cos B - cos (A + B))
where:
A is the physical height of the tower, in electrical degrees, and
B is the difference, in electrical degrees, between the apparent
electrical height (G, based on current distribution) and the actual
physical height.
G is the apparent electrical height: the sum of A and B; A+B.
See Figure 1 of this section.
[[Page 42]]
[GRAPHIC] [TIFF OMITTED] TC01MR91.066
[[Page 43]]
(3) For a sectionalized tower, the following formula shall be used:
{sin [cos B cos (A sin ) - cos G] +
sin B [cos D cos(C sin ) - sin sin D sin(C sin ) - cos cos(A
sin )]}
f() = ----------------------------------------------------------------------------
cos [sin (cos B - cos G) + sin B (cos D - cos )]
where:
A is the physical height, in electrical degrees, of the lower
section of the tower.
B is the difference between the apparent electrical height (based on
current distribution) of the lower section of the tower and the physical
height of the lower section of the tower.
C is the physical height of the entire tower, in electrical degrees.
D is the difference between the apparent electrical height of the
tower (based on current distribution of the upper section) and the
physical height of the entire tower. D will be zero if the sectionalized
tower is not top-loaded.
G is the sum of A and B; A+B.
H is the sum of C and D; C+D.
is the difference between H and A; H-A.
See Figure 2 of this section.
[[Page 44]]
[GRAPHIC] [TIFF OMITTED] TC01MR91.067
[[Page 45]]
(c) One of the above f(=115
electrical degrees (235-120):
------------------------------------------------------------------------
Sec. 73.182 Engineering standards of allocation.
(a) Sections 73.21 to 73.37, inclusive, govern allocation of
facilities in the AM broadcast band 535-1705 kHz. Sec. 73.21 establishes
three classes of channels in this band, namely, clear, regional and
local. The classes and power of AM broadcast stations which will be
assigned to the various channels are set forth in Sec. 73.21. The
classifications of the AM broadcast stations are as follows:
(1) Class A stations operate on clear channels with powers no less
than 10kW nor greater than 50 kW. These stations are designed to render
primary and secondary service over an extended area, with their primary
services areas protected from objectionable interference from other
stations on the same and adjacent channels. Their secondary service
areas are protected from objectionable interference from co-channel
stations. For purposes of protection, Class A stations may be divided
into two groups, those located in any of the contiguous 48 States and
those located in Alaska in accordance with Sec. 73.25.
(i) The mainland U.S. Class A stations are those assigned to the
channels allocated by Sec. 73.25. The power of these stations shall be
50 kW. The Class A stations in this group are afforded protection as
follows:
(A) Daytime. To the 0.1 mV/m groundwave contour from stations on the
same channel, and to the 0.5 mV/m groundwave contour from stations on
adjacent channels.
(B) Nighttime. To the 0.5 mV/m-50% skywave contour from stations on
the same channels.
(ii) Class A stations in Alaska operate on the channels allocated by
Sec. 73.25 with a minimum power of 10 kW, a maximum power of 50 kW, and
an antenna efficiency of 282 mV/m/kW at 1 kilometer. Stations operating
on these channels in Alaska which have not been designated as Class A
stations in response to licensee request will continue to be considered
as Class B stations. During daytime hours a Class A station in Alaska is
protected to the 100 V/m groundwave contour from co-channel
stations. During nighttime hours, a Class A station in Alaska is
protected to the 100 V/m-50 percent skywave contour from co-
channel stations. The 0.5 mV/m groundwave contour is protected both
daytime and nighttime from stations on adjacent channels.
[[Page 46]]
Note: In the Report and Order in MM Docket No. 83-807, the
Commission designated 15 stations operating on U.S. clear channels as
Alaskan Class A stations. Eleven of these stations already have Alaskan
Class A facilities and are to be protected accordingly. Permanent
designation of the other four stations as Alaskan Class A is conditioned
on their constructing minimum Alaskan Class A facilities no later than
December 31, 1989. Until that date or until such facilities are
obtained, these four stations shall be temporarily designated as Alaskan
Class A stations, and calculations involving these stations should be
based on existing facilities but with an assumed power of 10 kW.
Thereafter, these stations are to be protected based on their actual
Alaskan Class A facilities. If any of these stations does not obtain
Alaskan Class A facilities in the period specified, it is to be
protected as a Class B station based on its actual facilities. These
four stations may increase power to 10 kW without regard to the impact
on co-channel Class B stations. However, power increases by these
stations above 10 kW (or by existing Alaskan Class A stations beyond
their current power level) are subject to applicable protection
requirements for co-channel Class B stations. Other stations not on the
original list but which meet applicable requirements may obtain Alaskan
Class A status by seeking such designation from the Commission. If a
power increase or other change in facilities by a station not on the
original list is required to obtain minimum Alaskan Class A facilities,
any such application shall meet the interference protection requirements
applicable to an Alaskan Class A proposal on the channel.
(2) Class B stations are stations which operate on clear and
regional channels with powers not less than 0.25 kW nor more than 50 kW.
These stations render primary service only, the area of which depends on
their geographical location, power, and frequency. It is recommended
that Class B stations be located so that the interference received from
other stations will not limit the service area to a groundwave contour
value greater than 2.0 mV/m nighttime and to the 0.5 mV/m groundwave
contour daytime, which are the values for the mutual protection between
this class of stations and other stations of the same class.
Note: See Secs. 73.21(b)(1) and 73.26(b) concerning power
restrictions and classifications relative to Class B, Class C, and Class
D stations in Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands.
Stations in the above-named places that are reclassified from Class C to
Class B stations under Sec. 73.26(b) shall not be authorized to increase
power to levels that would increase the nighttime interference-free
limit of co-channel Class C stations in the conterminous United States.
(3) Class C stations operate on local channels, normally rendering
primary service to a community and the suburban or rural areas
immediately contiguous thereto, with powers not less than 0.25 kW, nor
more than 1 kW, except as provided in Sec. 73.21(c)(1). Such stations
are normally protected to the daytime 0.5 mV/m contour. On local
channels the separation required for the daytime protection shall also
determine the nighttime separation. Where directional antennas are
employed daytime by Class C stations operating with more than 0.25 kW
power, the separations required shall in no case be less than those
necessary to afford protection, assuming nondirectional operation with
0.25 kW. In no case will 0.25 kW or greater nighttime power be
authorized to a station unable to operate nondirectionally with a power
of 0.25 kW during daytime hours. The actual nighttime limitation will be
calculated. For nighttime protection purposes, Class C stations in the
48 contiguous United States may assume that stations in Alaska, Hawaii,
Puerto Rico, and the U.S. Virgin Islands operating on 1230, 1240, 1340,
1400, 1450, and 1490 kHz are Class C stations.
(4) Class D stations operate on clear and regional channels with
daytime powers of not less than 0.25 kW (or equivalent RMS field of 141
mV/m at one kilometer if less than 0.25 kW) and not more than 50 kW.
Class D stations that have previously received nighttime authority
operate with powers of less than 0.25 kW (or equivalent RMS fields of
less than 141 mV/m at one kilometer) are not required to provide
nighttime coverage in accordance with Sec. 73.24(j) and are not
protected from interference during nighttime hours. Such nighttime
authority is permitted on the basis of full nighttime protection being
afforded to all Class A and Class B stations.
(b) When a station is already limited by interference from other
stations to
[[Page 47]]
a contour value greater than that normally protected for its class, the
individual received limits shall be the established standard for such
station with respect to interference from each other station.
(c) The four classes of AM broadcast stations have in general three
types of service areas, i.e., primary, secondary and intermittent. (See
Sec. 73.14 for the definitions of primary, secondary, and intermittent
service areas.) Class A stations render service to all three areas.
Class B stations render service to a primary area but the secondary and
intermittent service areas may be materially limited or destroyed due to
interference from other stations, depending on the station assignments
involved. Class C and Class D stations usually have only primary service
areas. Interference from other stations may limit intermittent service
areas and generally prevents any secondary service to those stations
which operate at night. Complete intermittent service may still be
obtained in many cases depending on the station assignments involved.
(d) The groundwave signal strength required to render primary
service is 2 mV/m for communities with populations of 2,500 or more and
0.5 mV/m for communities with populations of less than 2,500. See
Sec. 73.184 for curves showing distance to various groundwave field
strength contours for different frequencies and ground conductivities,
and also see Sec. 73.183, ``Groundwave signals.''
(e) A Class C station may be authorized to operate with a
directional antenna during daytime hours providing the power is at least
0.25 kW. In computing the degrees of protection which such antenna will
afford, the radiation produced by the directional antenna system will be
assumed to be no less, in any direction, than that which would result
from non-directional operation using a single element of the directional
array, with 0.25 kW.
(f) All classes of broadcast stations have primary service areas
subject to limitation by fading and noise, and interference from other
stations to the contours set out for each class of station.
(g) Secondary service is provided during nighttime hours in areas
where the skywave field strength, 50% or more of the time, is 0.5 mV/m
or greater (0.1 mV/m in Alaska). Satisfactory secondary service to
cities is not considered possible unless the field strength of the
skywave signal approaches or exceeds the value of the groundwave field
strength that is required for primary service. Secondary service is
subject to some interference and extensive fading whereas the primary
service area of a station is subject to no objectionable interference or
fading. Only Class A stations are assigned on the basis of rendering
secondary service.
Note: Standards have not been established for objectionable fading
because of the relationship to receiver characteristics. Selective
fading causes audio distortion and signal strength reduction below the
noise level, objectionable characteristics inherent in many modern
receivers. The AVC circuits in the better designed receivers generally
maintain the audio output at a sufficiently constant level to permit
satisfactory reception during most fading conditions.
(h) Intermittent service is rendered by the groundwave and begins at
the outer boundary of the primary service area and extends to a distance
where the signal strength decreases to a value that is too low to
provide any service. This may be as low as a few V/m in certain
areas and as high as several millivolts per meter in other areas of high
noise level, interference from other stations, or objectionable fading
at night. The intermittent service area may vary widely from day to
night and generally varies over shorter intervals of time. Only Class A
stations are protected from interference from other stations to the
intermittent service area.
(i) Broadcast stations are licensed to operate unlimited time,
limited time, daytime, share time, and specified hours. (See
Secs. 73.1710, 73.1725, 73.1720, 73.1715, and 73.1730.) Applications for
new stations shall specify unlimited time operation only.
(j) Section 73.24 sets out the general requirements for modifying
the facilities of a licensed station and for establishing a new station.
Sections 73.24(b) and 73.37 include interference related
[[Page 48]]
provisions that be considered in connection with an application to
modify the facilities of an existing station or to establish a new
station. Section 73.30 describes the procedural steps required to
receive an authorization to operate in the 1605-1705 kHz band.
(k) Objectionable nighttime interference from a broadcast station
occurs when, at a specified field strength contour with respect to the
desired station, the field strength of an undesired station (co-channel
or first adjacent channel, after application of proper protection ratio)
exceeds for 10% or more of the time the values set forth in these
standards. The value derived from the root-sum-square of all
interference contributions represents the extent of a station's
interference-free coverage.
(1) With respect to the root-sum-square (RSS) values of interfering
field strengths referred to in this section, calculation of nighttime
interference-free service is accomplished by considering the signals on
the three channels of concern (co- and first adjacencies) in order of
decreasing magnitude, adding the squares of the values and extracting
the square root of the sum, excluding those signals which are less than
50% of the RSS values of the higher signals already included.
(2) With respect to the root-sum-square values of interfering field
strengths referred to in this section, calculation of nighttime
interference for non-coverage purposes is accomplished by considering
the signals on the three channels of concern (co- and first adjacencies)
in order of decreasing magnitude, adding the squares of the values and
extracting the square root of the sum, excluding those signals which are
less than 25% of the RSS values of the higher signals already included.
(3) With respect to the root-sum-square values of interfering field
strengths referred to in this section, calculation is accomplished by
considering the signals on the three channels of concern (co- and first
adjacencies) in order of decreasing magnitude, adding the squares of the
values and extracting the square root of the sum. The 0% exclusion
method applies only to the determination of an improvement factor value
for evaluating a station's eligibility for migration to the band 1605-
1705 kHz.
(4) The RSS value will not be considered to be increased when a new
interfering signal is added which is less than the appropriate exclusion
percentage as applied to the RSS value of the interference from existing
stations, and which at the same time is not greater than the smallest
signal included in the RSS value of interference from existing stations.
(5) It is recognized that application of the above ``50% exclusion''
method (or any exclusion method using a per cent value greater than
zero) of calculating the RSS interference may result in some cases in
anomalies wherein the addition of a new interfering signal or the
increase in value of an existing interfering signal will cause the
exclusion of a previously included signal and may cause a decrease in
the calculated RSS value of interference. In order to provide the
Commission with more realistic information regarding gains and losses in
service (as a basis for determination of the relative merits of a
proposed operation) the following alternate method for calculating the
proposed RSS values of interference will be employed wherever
applicable.
(6) In the cases where it is proposed to add a new interfering
signal which is not less than 50% (or 25%, depending on which study is
being performed) of the RSS value of interference from existing stations
or which is greater that the smallest signal already included to obtain
this RSS value, the RSS limitation after addition of the new signal
shall be calculated without excluding any signal previously included.
Similarly, in cases where it is proposed to increase the value of one of
the existing interfering signals which has been included in the RSS
value, the RSS limitation after the increase shall be calculated without
excluding the interference from any source previously included.
(7) If the new or increased signal proposed in such cases is
ultimately authorized, the RSS values of interference to other stations
affected will thereafter be calculated by the ``50% exclusion'' (or 25%
exclusion, depending on which study is being performed)
[[Page 49]]
method without regard to this alternate method of calculation.
(8) Examples of RSS interference calculations:
(i) Existing interferences:
Station No. 1--1.00 mV/m.
Station No. 2--0.60 mV/m.
Station No. 3--0.59 mV/m.
Station No. 4--0.58 mV/m.
The RSS value from Nos. 1, 2 and 3 is 1.31 mV/m; therefore interference
from No. 4 is excluded for it is less than 50% of 1.31 mV/m.
(ii) Station A receives interferences from:
Station No. 1--1.00 mV/m.
Station No. 2--0.60 mV/m.
Station No. 3--0.59 mV/m.
It is proposed to add a new limitation, 0.68 mV/m. This is more than 50%
of 1.31 mV/m, the RSS value from Nos. 1, 2 and 3. The RSS value of
Station No. 1 and of the proposed station would be 1.21 m/Vm which is
more than twice as large as the limitation from Station No. 2 or No. 3.
However, under the above provision the new signal and the three existing
interferences are nevertheless calculated for purposes of comparative
studies, resulting in an RSS value of 1.47 mV/m. However, if the
proposed station is ultimately authorized, only No. 1 and the new signal
are included in all subsequent calculations for the reason that Nos. 2
and 3 are less than 50% of 1.21 mV/m, the RSS value of the new signal
and No. 1.
(iii) Station A receives interferences from:
Station No. 1--1.00 mV/m.
Station No. 2--0.60 mV/m.
Station No. 3--0.59 mV/m.
No. 1 proposes to increase the limitation it imposes on Station A to
1.21 mV/m. Although the limitations from stations Nos. 2 and 3 are less
than 50% of the 1.21 mV/m limitation, under the above provision they are
nevertheless included for comparative studies, and the RSS limitation is
calculated to be 1.47 mV/m. However, if the increase proposed by Station
No. 1 is authorized, the RSS value then calculated is 1.21 mV/m because
Stations Nos. 2 and 3 are excluded in view of the fact that the
limitations they impose are less than 50% of 1.21 mV/m.
Note: The principles demonstrated in the previous examples for the
calculation of the 50% exclusion method also apply to calculations using
the 25% exclusion method after appropriate adjustment.
(l) Objectionable nighttime interference from a station shall be
considered to exist to a station when, at the field strength contour
specified in paragraph (q) of this section with respect to the class to
which the station belongs, the field strength of an interfering station
operating on the same channel or on a first adjacent channel after
signal adjustment using the proper protection ratio, exceeds for 10% or
more of the time the value of the permissible interfering signal set
forth opposite such class in paragraph (q) of this section.
(m) For the purpose of estimating the coverage and the interfering
effects of stations in the absence of field strength measurements, use
shall be made of Figure 8 of Sec. 73.190, which describes the estimated
effective field (for 1 kW power input) of simple vertical
omnidirectional antennas of various heights with ground systems having
at least 120 quarter-wavelength radials. Certain approximations, based
on the curve or other appropriate theory, may be made when other than
such antennas and ground systems are employed, but in any event the
effective field to be employed shall not be less than the following:
------------------------------------------------------------------------
Class of station Effective field (at 1 km)
------------------------------------------------------------------------
All Class A (except Alaskan)............... 362 mV/m.
Class A (Alaskan), B and D................. 282 mV/m.
Class C.................................... 241 mV/m.
------------------------------------------------------------------------
Note (1): When a directional antenna is employed, the radiated signal of
a broadcasting station will vary in strength in different directions,
possibly being greater than the above values in certain directions and
less in other directions depending upon the design and adjustment of
the directional antenna system. To determine the interference in any
direction, the measured or calculated radiated field (unattenuated
field strength at 1 kilometer from the array) must be used in
conjunction with the appropriate propagation curves. (See Sec. 73.185
for further discussion and solution of a typical directional antenna
case.)
Note (2): For Class B stations in Alaska, Hawaii, Puerto Rico and the
U.S. Virgin Islands, 241 mV/m shall be used.
(n) The existence or absence of objectionable groundwave
interference from stations on the same or adjacent channels shall be
determined by actual measurements made in accordance with the method
described in Sec. 73.186, or in the absence of such measurements, by
reference to the propagation curves of Sec. 73.184. The existence or
absence of objectionable interference due to skywave propagation shall
be determined by reference to Formula 2 in Sec. 73.190.
(o) Computation of Skywave Field Strength Values:
[[Page 50]]
(1) Fifty Percent Skywave Field Strength Values (Clear Channel). In
computing the fifty percent skywave field strength values of a Class A
clear channel station, use shall be made of Formula 1 of Sec. 73.190,
entitled ``Skywave Field Strength'' for 50 percent of the time.
(2) Ten Percent Skywave Field Strength Values. In computing the 10%
skywave field strength for stations on a single signal or an RSS basis,
Formula 2 in Sec. 73.190 shall be used.
(3) Determination of Angles of Departure. In calculating skywave
field strength for stations on all channels, the pertinent vertical
angle shall be determined by use of the formula in Sec. 73.190(d).
(p) The distance to any specified groundwave field strength contour
for any frequency may be determined from the appropriate curves in
Sec. 73.184 entitled ``Ground Wave Field Strength vs. Distance.''
(q) Normally protected service contours and permissible interference
signals for broadcast stations are as follows (for Class A stations, see
also paragraph (a) of this section):
----------------------------------------------------------------------------------------------------------------
Signal strength contour of area Permissible interfering signal
protected from objectionable (V/m)
Class of station Class of channel interference \1\(V/m) ---------------------------------
used ---------------------------------------
Day \2\ Night Day \2\ Night \3\
----------------------------------------------------------------------------------------------------------------
A.................. Clear............. SC 100 SC 500 50% SW SC 5 SC 25
AC 500 AC 500 GW AC 250 AC 250
A (Alaskan)........ ......do.......... SC 100 SC 100 50% SW SC 5 SC 5
AC 500 AC 500 GW AC 250 AC 250
B.................. Clear............. 500 2000 \2\ 25 25
Regional.......... ................ ................... AC 250 250
C.................. Local............. 500 No presc.\4\ SC25 Not presc.
D.................. Clear............. 500 Not presc SC 25 Not presc.
Regional.......... ................ ................... AC 250 ...............
----------------------------------------------------------------------------------------------------------------
\1\ When a station is already limited by interference from other stations to a contour of higher value than that
normally protected for its class, this higher value contour shall be the established protection standard for
such station. Changes proposed by Class A and B stations shall be required to comply with the following
restrictions. Those interferers that contribute to another station's RSS using the 50% exclusion method are
required to either reduce their contributions to that RSS by 10%, or to a level at which their contributions
no longer enter into the 50% RSS value, whichever is the lesser amount of reduction. Those interferers that
contribute to a station's RSS using the 25% exclusion method but do not contribute to that station's RSS using
the 50% exclusion method may make changes not to exceed their present contribution. Interferers not included
in a station's RSS using the 25% exclusion method are permitted to increase radiation as long as the 25%
exclusion threshold is not equalled or exceeded. In no case will a reduction be required that would result in
a contributing value that is below the pertinent value specified in the table. This note does not apply to
Class C stations; or to the protection of Class A stations which are normally protected on a single signal,
non-RSS basis.
\2\ Groundwave.
\3\ Skywave field strength for 10 percent or more of the time.
\4\ During nighttime hours, Class C stations in the contiguous 48 States may treat all Class B stations assigned
to 1230, 1240, 1340, 1400, 1450 and 1490 kHz in Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands as if
they were Class C stations.
Note: SC=Same channel; AC=Adjacent channel; SW=Skywave; GW=Groundwave
(r) The following table of logarithmic expressions is to be used as
required for determining the minimum permissible ratio of the field
strength of a desired to an undesired signal. This table shall be used
in conjunction with the protected contours specified in paragraph (q) of
this section.
----------------------------------------------------------------------------------------------------------------
Desired Groundwave to:
Frequency separation of desired to -------------------------------------------------- Desired 50% Skywave to
undesired signals (kHz) Undesired groundwave Undesired 10% Skywave Undesired 10% Skywave
(dB) (dB) (dB)
----------------------------------------------------------------------------------------------------------------
0.................................... 26 26 26
10................................... 6 6 not presc.
----------------------------------------------------------------------------------------------------------------
(s) Two stations, one with a frequency twice of the other, should
not be assigned in the same groundwave service area unless special
precautions are taken to avoid interference from the second harmonic of
the station operating on the lower frequency. Additionally, in selecting
a frequency, consideration should be given to the fact that occasionally
the frequency assignment of two stations in the same area may bear such
a relation to the intermediate frequency of some broadcast
[[Page 51]]
receivers as to cause ``image'' interference, However, since this can
usually be rectified by readjustment of the intermediate frequency of
such receivers, the Commission, in general, will not take this kind of
interference into consideration when authorizing stations.
(t) The groundwave service of two stations operating with
synchronized carriers and broadcasting identical programs will be
subject to some distortion in areas where the signals from the two
stations are of comparable strength. For the purpose of estimating
coverage of such stations, areas in which the signal ratio is between
1:2 and 2:1 will not be considered as receiving satisfactory service.
Note: Two stations are considered to be operated synchronously when
the carriers are maintained within 0.2 Hz of each other and they
transmit identical program s.
[56 FR 64862, Dec. 12, 1991; 57 FR 43290, Sept. 18, 1992, as amended at
58 FR 27950, May 12, 1993]
Sec. 73.183 Groundwave signals.
(a) Interference that may be caused by a proposed assignment or an
existing assignment during daytime hours should be determined, when
possible, by measurements on the frequency involved or on another
frequency over the same terrain and by means for the curves in
Sec. 73.184 entitled ``Ground Wave Field Strength versus Distance.''
Note: Groundwave field strength measurements will not be accepted or
considered for the purpose of establishing that interference to a
station in a foreign country other than Canada, or that the field
strength at the border thereof, would be less than indicated by the use
of the ground conductivity maps and engineering standards contained in
this part and applicable international agreements. Satisfactory
groundwave measurements offered for the purpose of demonstrating values
of conductivity other than those shown by Figure M3 in problems
involving protection of Canadian stations will be considered only if,
after review thereof, the appropriate agency of the Canadian government
notifies the Commission that they are acceptable for such purpose.
(b)(1) In all cases where measurements taken in accordance with the
requirements are not available, the groundwave strength must be
determined by means of the pertinent map of ground conductivity and the
groundwave curves of field strength versus distance. The conductivity of
a given terrain may be determined by measurements of any broadcast
signal traversing the terrain involved. Figure M3 (See Note 1) shows the
conductivity throughout the United States by general areas of reasonably
uniform conductivity. When it is clear that only one conductivity value
is involved, Figure R3 of Sec. 73.190, may be used. It is a replica of
Figure M3, and is contained in these standards. In all other situations
Figure M3 must be employed. It is recognized that in areas of limited
size or over a particular path, the conductivity may vary widely from
the values given; therefore, these maps are to be used only when
accurate and acceptable measurements have not been made.
(2) For determinations of interference and service requiring a
knowledge of ground conductivities in other countries, the ground
conductivity maps comprising Appendix 1 to Annex 2 of each of the
following international agreements may be used:
(i) For Canada, the U.S.-Canada AM Agreement, 1984;
(ii) For Mexico, the U.S.-Mexico AM Agreement, 1986; and
(iii) For other Western Hemisphere countries, the Regional Agreement
for the Medium Frequency Broadcasting Service in Region 2.
Where different conductivities appear in the maps of two countries
on opposite sides of the border, such differences are to be considered
as real, even if they are not explained by geophysical cleavages.
(c) Example of determining interference by the graphs in
Sec. 73.184:
It is desired to determine whether objectionable interference exists
between a proposed 5 kW Class B station on 990 kHz and an existing 1 kW
Class B station on first adjacent channel, 1000 kHz. The distance
between the two stations is 260 kilometers and both stations operate
nondirectionally with antenna systems that produce a horizontal
effective field of 282 in mV/m at one kilometer. (See Sec. 73.185
regarding use of directional antennas.) The ground conductivity at the
site of each station and along the intervening terrain is 6 mS/m. The
protection to Class B stations during daytime is to the 500 V/m
(0.5 Vm) contour using a 6 dB protection factor. The distance to the 500
V/m groundwave contour of the 1 kW station is
[[Page 52]]
determined by the use of the appropriate curve in Sec. 73.184. Since the
curve is plotted for 100 mV/m at a 1 kilometer, to find the distance of
the 0.5 mV/m contour of the 1 kw station, it is necessary to determine
the distance to the 0.1773 m/Vm contour.
(100 x 0.5/282=0.1773)
Using the 6 mS/m curve, the estimated radius of the 0.5 mV/m contour is
62.5 kilometers. Subtracting this distance from the distance between the
two stations leaves 197.5 kilometers. Using the same propagation curve,
the signal from the 5 kW station at this distance is seen to be 0.059
mV/m. Since a protection ratio of 6 dB, desired to undesired signal,
applies to stations separated by 10 kHz, the undesired signal could have
had a value of up to 0.25 mV/m without causing objectionable
interference. For co-channel studies, a desired to undesired signal
ratio of no less than 20:1 (26 dB) is required to avoid causing
objectionable interference.
(d) Where a signal traverses a path over which different
conductivities exist, the distance to a particular groundwave field
strength contour shall be determined by the use of the equivalent
distance method. Reasonably accurate results may be expected in
determining field strengths at a distance from the antenna by
application of the equivalent distance method when the unattenuated
field of the antenna, the various ground conductivities and the location
of discontinuities are known. This method considers a wave to be
propagated across a given conductivity according to the curve for a
homogeneous earth of that conductivity. When the wave crosses from a
region of one conductivity into a region of a second conductivity, the
equivalent distance of the receiving point from the transmitter changes
abruptly but the field strength does not. From a point just inside the
second region the transmitter appears to be at that distance where, on
the curve for a homogeneous earth of the second conductivity, the field
strength equals the value that occurred just across the boundary in the
first region. Thus the equivalent distance from the receiving point to
the transmitter may be either greater or less than the actual distance.
An imaginary transmitter is considered to exist at that equivalent
distance. This technique is not intended to be used as a means of
evaluating unattenuated field or ground conductivity by the analysis of
measured data. The method to be employed for such determinations is set
out in Sec. 73.186.
(e) Example of the use of the equivalent distance method;
It is desired to determine the distance to the 0.5 mV/m and 0.025
mV/m contours of a station on a frequency of 1000 kHz with an inverse
distance field of 100 mV/m at one kilometer being radiated over a path
having a conductivity of 10 mS/m for a distance of 20 kilometers, 5 mS/m
for the next 30 kilometers and 15 mS/m thereafter. Using the appropriate
curve in Sec. 73.184, Graph 12, at a distance of 20 kilometers on the
curve for 10 mS/m, the field strength is found to be 2.84 mV/m. On the
5mS/m curve, the equivalent distance to this field strength is 14.92
kilometers, which is 5.08 (20-14.92 kilometers nearer to the
transmitter. Continuing on the propagation curve, the distance to a
field strength of 0.5 mV/m is found to be 36.11 kilomteres.
The actual length of the path travelled, however, is 41.19
(36.11+5.08) kilometers. Continuing on this propagation curve to the
conductivity change at 44.92 (50.00-5.08) kilometers, the field strength
is found to be 0.304 mV/m. On the 15 mS/m propagation curve, the
equivalent distance to this field strength is 82.94 kilometers, which
changes the effective path length by 38.02 (82.94-44.92) kilometers.
Continuing on this propagation curve, the distance to a field strength
of 0.025 mV/m is seen to be 224.4 kilometers. The actual length of the
path travelled, however, is 191.46 (224.4+5.08-38.02) kilometers.
[28 FR 13574, Dec. 14, 1963, as amended at 44 FR 36037, June 20, 1979;
48 FR 9011, Mar. 3, 1983; 50 FR 18822, May 2, 1985; 50 FR 24522, June
11, 1985; 51 FR 9965, Mar. 24, 1986; 54 FR 39736, Sept. 28, 1989; 56 FR
64866, Dec. 12, 1991; 57 FR 43290, Sept. 18, 1992]
Sec. 73.184 Groundwave field strength graphs.
(a) Graphs 1 to 20 show, for each of 20 frequencies, the computed
values of groundwave field strength as a function of groundwave
conductivity and distance from the source of radiation. The groundwave
field strength is considered to be that part of the vertical component
of the electric field which has not been reflected from the ionosphere
nor from the troposphere. These 20 families of curves are plotted on
log-log graph paper and each is to be used for the range of frequencies
shown thereon. Computations are based on a
[[Page 53]]
dielectric constant of the ground (referred to air as unity) equal to 15
for land and 80 for sea water and for the ground conductivities
(expressed in mS/m) given on the curves. The curves show the variation
of the groundwave field strength with distance to be expected for
transmission from a vertical antenna at the surface of a uniformly
conducting spherical earth with the groundwave constants shown on the
curves. The curves are for an antenna power of such efficiency and
current distribution that the inverse distance (unattenuated) field is
100 mV/m at 1 kilometer. The curves are valid for distances that are
large compared to the dimensions of the antenna for other than short
vertical antennas.
(b) The inverse distance field (100 mV/m divided by the distance in
kilometers) corresponds to the groundwave field intensity to be expected
from an antenna with the same radiation efficiency when it is located
over a perfectly conducting earth. To determine the value of the
groundwave field intensity corresponding to a value of inverse distance
field other than 100 mV/m at 1 kilometer, multiply the field strength as
given on these graphs by the desired value of inverse distance field at
1 kilometer divided by 100; for example, to determine the groundwave
field strength for a station with an inverse distance field of 2700 mV/m
at 1 kilometer, simply multiply the values given on the charts by 27.
The value of the inverse distance field to be used for a particular
antenna depends upon the power input to the antenna, the nature of the
ground in the neighborhood of the antenna, and the geometry of the
antenna. For methods of calculating the interrelations between these
variables and the inverse distance field, see ``The Propagation of Radio
Waves Over the Surface of the Earth and in the Upper Atmosphere,'' Part
II, by Mr. K.A. Norton, Proc. I.R.E., Vol. 25, September 1937, pp. 1203-
1237.
Note: The computed values of field strength versus distance used to
plot Graphs 1 to 20 are available in tabular form. For information on
obtaining copies of these tabulations call or write the Consumer Affairs
Office, Federal Communications Commission, Washington, DC 20554, (202)
632-7000.
(c) Provided the value of the dielectric constant is near 15, the
ground conductivity curves of Graphs 1 to 20 may be compared with actual
field strength measurement data to determine the appropriate values of
the ground conductivity and the inverse distance field strength at 1
kilometer. This is accomplished by plotting the measured field strengths
on transparent log-log graph paper similar to that used for Graphs 1 to
20 and superimposing the plotted graph over the Graph corresponding to
the frequency of the station measured. The plotted graph is then shifted
vertically until the plotted measurement data is best aligned with one
of the conductivity curves on the Graph; the intersection of the inverse
distance line on the Graph with the 1 kilometer abscissa on the plotted
graph determines the inverse distance field strength at 1 kilometer. For
other values of dielectric constant, the following procedure may be used
to determine the dielectric constant of the ground, the ground
conductivity and the inverse distance field strength at 1 kilometer.
Graph 21 gives the relative values of groundwave field strength over a
plane earth as a function of the numerical distance p and phase angle b.
On graph paper with coordinates similar to those of Graph 21, plot the
measured values of field strength as ordinates versus the corresponding
distances from the antenna in kilometers as abscissae. The data should
be plotted only for distances greater than one wavelength (or, when this
is greater, five times the vertical height of the antenna in the case of
a nondirectional antenna or 10 times the spacing between the elements of
a directional antenna) and for distances less than 80f\1\/\3\MHz
kilometers (i.e., 80 kilometers at 1 MHz). Then, using a light box,
place the plotted graph over Graph 21 and shift the plotted graph
vertically and horizontally (making sure that the vertical lines on both
sheets are parallel) until the best fit with the data is obtained with
one of the curves on Graph 21. When the two sheets are properly lined
up, the value of the field strength corresponding to the intersection of
the inverse distance line of Graph 21 with the 1 kilometer
[[Page 54]]
abscissa on the data sheet is the inverse distance field strength at 1
kilometer, and the values of the numerical distance at 1 kilometer,
p1, and of b are also determined. Knowing the values of b and
p1 (the numerical distance at one kilometer), we may substitute in
the following approximate values of the ground conductivity and
dielectric constant.
R
x ----------- <3-ln (> ----------- <3-ln )>1 cos b (Eq. 1)
p
(R/)1= Number of wavelengths in 1 kilometer,
* * * * *
fMHz=frequency expressed in megahertz,
tan b-
1 (Eq. 3)
=dielectric constant on the ground referred to air as unity.
First solve for by substituting the known values of
p1, (R/