Goto Section: 73.684 | 73.686 | Table of Contents
Revised as of October 1, 2020
Goto Year:2019 |
§ 73.685 Transmitter location and antenna system.
(a) The transmitter location shall be chosen so that, on the basis of
the effective radiated power and antenna height above average terrain
employed, the following minimum field strength in dB above one uV/m
will be provided over the entire principal community to be served:
Channels 2-6 Channels 7-13 Channels 14-69
74 dBu 77 dBu 80 dBu
(b) Location of the antenna at a point of high elevation is necessary
to reduce to a minimum the shadow effect on propagation due to hills
and buildings which may reduce materially the strength of the station's
signals. In general, the transmitting antenna of a station should be
located at the most central point at the highest elevation available.
To provide the best degree of service to an area, it is usually
preferable to use a high antenna rather than a low antenna with
increased transmitter power. The location should be so chosen that
line-of-sight can be obtained from the antenna over the principal
community to be served; in no event should there be a major obstruction
in this path. The antenna must be constructed so that it is as clear as
possible of surrounding buildings or objects that would cause shadow
problems. It is recognized that topography, shape of the desired
service area, and population distribution may make the choice of a
transmitter location difficult. In such cases, consideration may be
given to the use of a directional antenna system, although it is
generally preferable to choose a site where a nondirectional antenna
may be employed.
(c) In cases of questionable antenna locations it is desirable to
conduct propagation tests to indicate the field strength expected in
the principal community to be served and in other areas, particularly
where severe shadow problems may be expected. In considering
applications proposing the use of such locations, the Commission may
require site tests to be made. Such tests should be made in accordance
with the measurement procedure in § 73.686, and full data thereon must
be supplied to the Commission. Test transmitters should employ an
antenna having a height as close as possible to the proposed antenna
height, using a balloon or other support if necessary and feasible.
Information concerning the authorization of site tests may be obtained
from the Commission upon request.
(d) Present information is not sufficiently complete to establish
"blanket areas" of television broadcast stations. A "blanket area" is
that area adjacent to a transmitter in which the reception of other
stations is subject to interference due to the strong signal from this
station. The authorization of station construction in areas where
blanketing is found to be excessive will be on the basis that the
applicant will assume full responsibility for the adjustment of
reasonable complaints arising from excessively strong signals of the
applicant's station or take other corrective action.
(e) An antenna designed or altered to produce a noncircular radiation
pattern in the horizontal plane is considered to be a directional
antenna. Antennas purposely installed in such a manner as to result in
the mechanical beam tilting of the major vertical radiation lobe are
included in this category. Directional antennas may be employed for the
purpose of improving service upon an appropriate showing of need.
Stations operating on Channels 2-13 will not be permitted to employ a
directional antenna having a ratio of maximum to minimum radiation in
the horizontal plane in excess of 10 dB. Stations operating on Channels
14-69 with transmitters delivering a peak visual power output of more
than 1 kW may employ directive transmitting antennas with a maximum to
minimum radiation in the horizontal plane of not more than 15 dB.
Stations operating on Channels 14-69 and employing transmitters
delivering a peak visual power output of 1 kW or less are not limited
as to the ratio of maximum to minimum radiation.
(f) Applications proposing the use of directional antenna systems must
be accompanied by the following:
(1) Complete description of the proposed antenna system, including the
manufacturer and model number of the proposed directional antenna.
(2) Relative field horizontal plane pattern (horizontal polarization
only) of the proposed directional antenna. A value of 1.0 should be
used for the maximum radiation. The plot of the pattern should be
oriented so that 0° corresponds to true North. Where mechanical beam
tilt is intended, the amount of tilt in degrees of the antenna vertical
axis and the orientation of the downward tilt with respect to true
North must be specified, and the horizontal plane pattern must reflect
the use of mechanical beam tilt.
(3) A tabulation of the relative field pattern required in paragraph
(b)(2), of this section. The tabulation should use the same zero degree
reference as the plotted pattern, and be tabulated at least every 10°.
In addition, tabulated values of all maxima and minima, with their
corresponding azimuths, should be submitted.
(4) Horizontal and vertical plane radiation patterns showing the
effective radiated power, in dBk, for each direction. Sufficient
vertical plane patterns must be included to indicate clearly the
radiation characteristics of the antenna above and below the horizontal
plane. In cases where the angles at which the maximum vertical
radiation varies with azimuth, a separate vertical radiation pattern
must be provided for each pertinent radial direction.
(5) All horizontal plane patterns must be plotted to the largest scale
possible on unglazed letter-size polar coordinate paper (main engraving
approximately 18 cm × 25 cm (7 inches × 10 inches)) using only scale
divisions and subdivisions of 1, 2, 2.5 or 5 times 10-nth. All vertical
plane patterns must be plotted on unglazed letter-size rectangular
coordinate paper. Values of field strength on any pattern less than 10%
of the maximum field strength plotted on that pattern must be shown on
an enlarged scale.
(6) The horizontal and vertical plane patterns that are required are
the patterns for the complete directional antenna system. In the case
of a composite antenna composed of two or more individual antennas,
this means that the patterns for the composite antenna, not the
patterns for each of the individual antennas, must be submitted.
(g) Applications proposing the use of television broadcast antennas
within 61.0 meters (200 feet) of other television broadcast antennas
operating on a channel within 20 percent in frequency of the proposed
channel, or proposing the use of television broadcast antennas on
Channels 5 or 6 within 61.0 meters (200 feet) of FM broadcast antennas,
must include a showing as to the expected effect, if any, of such
(h) Where the TV licensee or permittee proposes to mount its antenna on
or near an AM tower, as defined in § 1.30002, the TV licensee or
permittee must comply with § 1.30003 or § 1.30002.
(Secs. 4, 5, 303, 48 Stat., as amended, 1066, 1068, 1082 (47 U.S.C.
154, 155, 303))
[ 28 FR 13660 , Dec. 14, 1963, as amended at 35 FR 5693 , Apr. 8, 1970; 40 FR 25461 , June 16, 1975; 43 FR 53740 , Nov. 17, 1978; 44 FR 22740 , Apr.
17, 1979; 45 FR 26065 , Apr. 17, 1980; 47 FR 35990 , Aug. 18, 1982; 48 FR 21486 , May 12, 1983; 50 FR 23701 , June 5, 1985; 58 FR 44951 , Aug. 25,
1993; 62 FR 51059 , Sept. 30, 1997; 78 FR 66298 , Nov. 5, 2013]
Goto Section: 73.684 | 73.686
Goto Year: 2019 |
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