§  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 0DEG 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
   10DEG. 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
   proximate operation.

   (h) Where a TV licensee or permittee proposes to mount an antenna on an
   AM antenna tower, or locate within 3.2 km of an AM antenna tower, the
   TV licensee or permittee must comply with §  73.1692.

   (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]

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