Goto Section: 73.315 | 73.317 | Table of Contents
Revised as of November 25, 2020
Goto Year:2020 |
§ 73.316 FM antenna systems.
(a) It shall be standard to employ horizontal polarization; however,
circular or elliptical polarization may be employed if desired.
Clockwise or counterclockwise rotation may be used. The supplemental
vertically polarized effective radiated power required for circular or
elliptical polarization shall in no event exceed the effective radiated
(b) Directional antennas. A directional antenna is an antenna that is
designed or altered for the purpose of obtaining a non-circular
(1) Applications for the use of directional antennas that propose a
ratio of maximum to minimum radiation in the horizontal plane of more
than 15 dB will not be accepted.
(2) Directional antennas used to protect short-spaced stations pursuant
to § 73.213 or § 73.215 of the rules, that have a radiation pattern which
varies more than 2 dB per 10 degrees of azimuth will not be authorized.
(c) Applications for directional antennas. (1) Applications for
construction permit proposing the use of directional antenna systems
must include a tabulation of the composite antenna pattern for the
proposed directional antenna. A value of 1.0 must be used to correspond
to the direction of maximum radiation. The pattern must be tabulated
such that 0¬° corresponds to the direction of maximum radiation or
alternatively, in the case of an asymmetrical antenna pattern, the
pattern must be tabulated such that 0¬° corresponds to the actual
azimuth with respect to true North. In the case of a composite antenna
composed of two or more individual antennas, the pattern required is
that for the composite antenna, not the patterns for each of the
individual antennas. Applications must include valuations tabulated at
intervals of not greater than ten (10) degrees. In addition, tabulated
values of all maximas and minimas, with their corresponding azimuths,
must be submitted.
(2) Applications for license upon completion of antenna construction
must include the following:
(i) A complete description of the antenna system, including the
manufacturer and model number of the directional antenna. It is not
sufficient to label the antenna with only a generic term such as
‚Äúdipole.‚ÄĚ In the case of individually designed antennas with no model
number, or in the case of a composite antenna composed of two or more
individual antennas, the antenna must be described as a ‚Äúcustom‚ÄĚ or
‚Äúcomposite‚ÄĚ antenna, as appropriate. A full description of the design
of the antenna must also be submitted.
(ii) A plot of the composite pattern of the directional antenna. A
value of 1.0 must be used to correspond to the direction of maximum
radiation. The plot of the pattern must be oriented such that 0¬°
corresponds to the direction of maximum radiation or alternatively, in
the case of an asymmetrical antenna pattern, the plot must be oriented
such that 0¬° corresponds to the actual azimuth with respect to true
North. The horizontal plane pattern must be plotted to the largest
scale possible on unglazed letter-size polar coordinate paper (main
engraving approximately 18 cm √ó 25 cm (7 inches √ó 10 inches)) using
only scale divisions and subdivisions of 1, 2, 2.5, or 5 times 10-nth.
Values of field strength less than 10% of the maximum field strength
plotted on that pattern must be shown on an enlarged scale. In the case
of a composite antenna composed of two or more individual antennas, the
composite antenna pattern should be provided, and not the pattern for
each of the individual antennas.
(iii) A tabulation of the measured relative field pattern required in
paragraph (c)(1) of this section. The tabulation must use the same zero
degree reference as the plotted pattern, and must contain values for at
least every 10 degrees. Sufficient vertical patterns to indicate
clearly the radiation characteristics of the antenna above and below
the horizontal plane. Complete information and patterns must be
provided for angles of ‚ąí10 deg. from the horizontal plane and
sufficient additional information must be included on that portion of
the pattern lying between + 10 deg. and the zenith and ‚ąí10 deg. and the
nadir, to conclusively demonstrate the absence of undesirable lobes in
these areas. The vertical plane pattern must be plotted on rectangular
coordinate paper with reference to the horizontal plane. In the case of
a composite antenna composed of two or more individual antennas, the
composite antenna pattern should be used, and not the pattern for each
of the individual antennas.
(iv) A statement that the antenna is mounted on the top of an antenna
tower recommended by the antenna manufacturer, or is side-mounted on a
particular type of antenna tower in accordance with specific
instructions provided by the antenna manufacturer.
(v) A statement that the directional antenna is not mounted on the top
of an antenna tower which includes a top-mounted platform larger than
the nominal cross-sectional area of the tower in the horizontal plane.
(vi) A statement that no other antenna of any type is mounted on the
same tower level as a directional antenna, and that no antenna of any
type is mounted within any horizontal or vertical distance specified by
the antenna manufacturer as being necessary for proper directional
(vii) A statement from an engineer listing such individual engineer's
qualifications and certifying that the antenna has been installed
pursuant to the manufacturer's instructions.
(viii) A statement from a licensed surveyor that the installed antenna
is properly oriented.
(ix)(A) For a station authorized pursuant to § 73.215 or Sec. § 73.509, a
showing that the root mean square (RMS) of the measured composite
antenna pattern (encompassing both the horizontally and vertically
polarized radiation components (in relative field)) is at least 85
percent of the RMS of the authorized composite directional antenna
pattern (in relative field). The RMS value, for a composite antenna
pattern specified in relative field values, may be determined from the
RMS = the square root of:
[(relative field value 1)2 + (relative field value 2)2 + .... + (last
relative field value)2]
total number of relative field values
(B) where the relative field values are taken from at least 36 evenly
spaced radials for the entire 360 degrees of azimuth. The application
for license must also demonstrate that coverage of the community of
license by the 70 dBu contour is maintained for stations authorized
pursuant to § 73.215 on Channels 221 through 300, as required by
§ 73.315(a), while noncommercial educational stations operating on
Channels 201 through 220 must show that the 60 dBu contour covers at
least a portion of the community of license.
(d) Applications proposing the use of FM transmitting antennas in the
immediate vicinity (i.e. 60 meters or less) of other FM or TV broadcast
antennas must include a showing as to the expected effect, if any, of
such approximate operation.
(e) Where an FM licensee or permittee proposes to mount its antenna on
or near an AM tower, as defined in § 1.30002, the FM licensee or
permittee must comply with § 1.30003 or § 1.30002, depending on whether
the antenna is proposed to be mounted on an AM tower (§ 1.30003) or near
an AM tower (§ 1.30002).
[ 28 FR 13623 , Dec. 14, 1963, as amended at 34 FR 14222 , Sept. 10, 1969;
37 FR 25841 , Dec. 5, 1972; 43 FR 53738 , Nov. 17, 1978; 48 FR 29508 ,
June 27, 1983; 51 FR 17028 , May 8, 1986; 54 FR 9804 , Mar. 8, 1989; 56 FR 57294 , Nov. 8, 1991; 62 FR 51058 , Sept. 30, 1997; 63 FR 70047 , Dec.
18, 1998; 78 FR 66298 , Nov. 5, 2013]
Goto Section: 73.315 | 73.317
Goto Year: 2020 |
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