Sec.  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  Sec. 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 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  Sec. 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]