Goto Section: 73.624 | 73.626 | Table of Contents

FCC 73.625
Revised as of December 6, 2018
Goto Year:2018 | 2020
  § 73.625   DTV coverage of principal community and antenna system.

   (a) Transmitter location. (1) The DTV 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
   F(50,90) field strength in dB above one uV/m will be provided over the
   entire principal community to be served:
   Channels 2-6   35 dBu
   Channels 7-13  43 dBu
   Channels 14-69 48 dBu
   Channels 2-6   28 dBu
   Channels 7-13  36 dBu
   Channels 14-69 41 dBu

   (2) The location of the antenna must be so chosen that there is not a
   major obstruction in the path over the principal community to be
   served.

   (3) For the purposes of this section, coverage is to be determined in
   accordance with paragraph (b) of this section. Under actual conditions,
   the true coverage may vary from these estimates because the terrain
   over any specific path is expected to be different from the average
   terrain on which the field strength charts were based. Further, the
   actual extent of service will usually be less than indicated by these
   estimates due to interference from other stations. Because of these
   factors, the predicted field strength contours give no assurance of
   service to any specific percentage of receiver locations within the
   distances indicated.

   (b) Determining coverage. (1) In predicting the distance to the field
   strength contours, the F (50,50) field strength charts (Figures 9, 10
   and 10b of § 73.699 of this part) and the F (50,10) field strength
   charts (Figures 9a, 10a and 10c of § 73.699 of this part) shall be used.
   To use the charts to predict the distance to a given F (50,90) contour,
   the following procedure is used: Convert the effective radiated power
   in kilowatts for the appropriate azimuth into decibel value referenced
   to 1 kW (dBk). Subtract the power value in dBk from the contour value
   in dBu. Note that for power less than 1 kW, the difference value will
   be greater than the contour value because the power in dBk is negative.
   Locate the difference value obtained on the vertical scale at the left
   edge of the appropriate F (50,50) chart for the DTV station's channel.
   Follow the horizontal line for that value into the chart to the point
   of intersection with the vertical line above the height of the antenna
   above average terrain for the appropriate azimuth located on the scale
   at the bottom of the chart. If the point of intersection does not fall
   exactly on a distance curve, interpolate between the distance curves
   below and above the intersection point. The distance values for the
   curves are located along the right edge of the chart. Using the
   appropriate F (50,10) chart for the DTV station's channel, locate the
   point where the distance coincides with the vertical line above the
   height of the antenna above average terrain for the appropriate azimuth
   located on the scale at the bottom of the chart. Follow a horizontal
   line from that point to the left edge of the chart to determine the F
   (50,10) difference value. Add the power value in dBk to this difference
   value to determine the F (50,10) contour value in dBu. Subtract the F
   (50,50) contour value in dBu from this F (50,10) contour value in dBu.
   Subtract this difference from the F (50,50) contour value in dBu to
   determine the F (50,90) contour value in dBu at the pertinent distance
   along the pertinent radial.

   (2) The effective radiated power to be used is that radiated at the
   vertical angle corresponding to the depression angle between the
   transmitting antenna center of radiation and the radio horizon as
   determined individually for each azimuthal direction concerned. In
   cases where the relative field strength at this depression angle is 90%
   or more of the maximum field strength developed in the vertical plane
   containing the pertaining radial, the maximum radiation shall be used.
   The depression angle is based on the difference in elevation of the
   antenna center of radiation above the average terrain and the radio
   horizon, assuming a smooth spherical earth with a radius of 8,495.5
   kilometers (5,280 miles) and shall be determined by the following
   equation:

   A = 0.0277 square root of H

   Where:

   A is the depression angle in degrees.

   H is the height in meters of the transmitting antenna radiation center
   above average terrain of the 3.2-16.1 kilometers (2-10 miles) sector of
   the pertinent radial.

   This formula is empirically derived for the limited purpose specified
   here. Its use for any other purpose may be inappropriate.

   (3) Applicants for new DTV stations or changes in the facilities of
   existing DTV stations must submit to the FCC a showing as to the
   location of their stations' or proposed stations' contour. This showing
   is to include a map showing this contour, except where applicants have
   previously submitted material to the FCC containing such information
   and it is found upon careful examination that the contour locations
   indicated therein would not change, on any radial, when the locations
   are determined under this section. In the latter cases, a statement by
   a qualified engineer to this effect will satisfy this requirement and
   no contour maps need be submitted.

   (4) The antenna height to be used with these charts is the height of
   the radiation center of the antenna above the average terrain along the
   radial in question. In determining the average elevation of the
   terrain, the elevations between 3.2-16.1 kilometers (2-10 miles) from
   the antenna site are employed. Profile graphs shall be drawn for 8
   radials beginning at the antenna site and extending 16.1 kilometers (10
   miles) therefrom. The radials should be drawn for each 45 degrees of
   azimuth starting with True North. At least one radial must include the
   principal community to be served even though such community may be more
   than 16.1 kilometers (10 miles) from the antenna site. However, in the
   event none of the evenly spaced radials include the principal community
   to be served and one or more such radials are drawn in addition to the
   8 evenly spaced radials, such additional radials shall not be employed
   in computing the antenna height above average terrain. Where the
   3.2-16.1 kilometers (2-10 mile) portion of a radial extends in whole or
   in part over large bodies of water (such as ocean areas, gulfs, sounds,
   bays, large lakes, etc., but not rivers) or extends over foreign
   territory but the contour encompasses land area within the United
   States beyond the 16.1 kilometers (10 mile) portion of the radial, the
   entire 3.2-16.1 kilometers (2-10 mile) portion of the radial shall be
   included in the computation of antenna height above average terrain.
   However, where the contour does not so encompass United States land
   area and (1) the entire 3.2-16.1 kilometers (2-10 mile) portion of the
   radial extends over large bodies of water or foreign territory, such
   radial shall be completely omitted from the computation of antenna
   height above average terrain, and (2) where a part of the 3.2-16.1
   kilometers (2-10 mile) portion of a radial extends over large bodies of
   water or over foreign territory, only that part of the radial extending
   from the 3.2 kilometer (2 mile) sector to the outermost portion of land
   area within the United States covered by the radial shall be employed
   in the computation of antenna height above average terrain. The profile
   graph for each radial should be plotted by contour intervals of from
   12.2-30.5 meters (40-100 feet) and, where the data permits, at least 50
   points of elevation (generally uniformly spaced) should be used for
   each radial. In instances of very rugged terrain where the use of
   contour intervals of 30.5 meters (100 feet) would result in several
   points in a short distance, 61.0-122.0 meter (200-400 foot) contour
   intervals may be used for such distances. On the other hand, where the
   terrain is uniform or gently sloping the smallest contour interval
   indicated on the topographic map (see paragraph (b)(5) of this section)
   should be used, although only relatively few points may be available.
   The profile graphs should indicate the topography accurately for each
   radial, and the graphs should be plotted with the distance in
   kilometers as the abscissa and the elevation in meters above mean sea
   level as the ordinate. The profile graphs should indicate the source of
   the topographical data employed. The graph should also show the
   elevation of the center of the radiating system. The graph may be
   plotted either on rectangular coordinate paper or on special paper
   which shows the curvature of the earth. It is not necessary to take the
   curvature of the earth into consideration in this procedure, as this
   factor is taken care of in the charts showing signal strengths. The
   average elevation of the 12.9 kilometer (8 miles) distance between
   3.2-16.1 kilometers (2-10 miles) from the antenna site should then be
   determined from the profile graph for each radial. This may be obtained
   by averaging a large number of equally spaced points, by using a
   planimeter, or by obtaining the median elevation (that exceeded for 50%
   of the distance) in sectors and averaging those values. In directions
   where the terrain is such that negative antenna heights or heights
   below 30.5 meters (100 feet) for the 3.2 to 16.1 kilometers (2 to 10
   mile) sector are obtained, an assumed height of 30.5 meters (100 feet)
   shall be used for the prediction of coverage. However, where the actual
   contour distances are critical factors, a supplemental showing of
   expected coverage must be included together with a description of the
   method employed in predicting such coverage. In special cases, the
   Commission may require additional information as to terrain and
   coverage.

   (5) In the preparation of the profile graph previously described, and
   in determining the location and height above sea level of the antenna
   site, the elevation or contour intervals shall be taken from the United
   States Geological Survey Topographic Quadrangle Maps, United States
   Army Corps of Engineers' maps or Tennessee Valley Authority maps,
   whichever is the latest, for all areas for which such maps are
   available. If such maps are not published for the area in question, the
   next best topographic information should be used. Topographic data may
   sometimes be obtained from State and Municipal agencies. Data from
   Sectional Aeronautical Charts (including bench marks) or railroad depot
   elevations and highway elevations from road maps may be used where no
   better information is available. In cases where limited topographic
   data is available, use may be made of an altimeter in a car driven
   along roads extending generally radially from the transmitter site.
   United States Geological Survey Topographic Quadrangle Maps may be
   obtained from the United States Geological Survey, Department of the
   Interior, Washington, D.C. 20240. Sectional Aeronautical Charts are
   available from the United States Coast and Geodetic Survey, Department
   of Commerce, Washington, D.C. 20235. In lieu of maps, the average
   terrain elevation may be computer generated, except in the cases of
   dispute, using elevations from a 30 second point or better topographic
   data file. The file must be identified and the data processed for
   intermediate points along each radial using linear interpolation
   techniques. The height above mean sea level of the antenna site must be
   obtained manually using appropriate topographic maps.

   (c) Antenna system. (1) The antenna system shall be designed so that
   the effective radiated power at any angle above the horizontal shall be
   as low as the state of the art permits, and in the same vertical plane
   may not exceed the effective radiated power in either the horizontal
   direction or below the horizontal, whichever is greater.

   (2) 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.

   (3) Applications proposing the use of directional antenna systems must
   be accompanied by the following:

   (i) Complete description of the proposed antenna system, including the
   manufacturer and model number of the proposed directional antenna.

   (ii) 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 degrees 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.

   (iii) A tabulation of the relative field pattern required in paragraph
   (c)(3)(ii) of this section. The tabulation should use the same zero
   degree reference as the plotted pattern, and be tabulated at least
   every 10 degrees. In addition, tabulated values of all maxima and
   minima, with their corresponding azimuths, should be submitted.

   (iv) 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.

   (v) 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 percent of the maximum field strength plotted on that
   pattern must be shown on an enlarged scale.

   (vi) 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.

   (4) Where simultaneous use of antennas or antenna structures is
   proposed, the following provisions shall apply:

   (i) In cases where it is proposed to use a tower of an AM broadcast
   station as a supporting structure for a DTV broadcast antenna, an
   appropriate application for changes in the radiating system of the AM
   broadcast station must be filed by the licensee thereof. A formal
   application (FCC Form 301, or FCC Form 340 for a noncommercial
   educational station) will be required if the proposal involves
   substantial change in the physical height or radiation characteristics
   of the AM broadcast antennas; otherwise an informal application will be
   acceptable. (In case of doubt, an informal application (letter)
   together with complete engineering data should be submitted.) An
   application may be required for other classes of stations when the
   tower is to be used in connection with a DTV station.

   (ii) When the proposed DTV antenna is to be mounted on a tower in the
   vicinity of an AM station directional antenna system and it appears
   that the operation of the directional antenna system may be affected,
   an engineering study must be filed with the DTV application concerning
   the effect of the DTV antenna on the AM directional radiation pattern.
   Field measurements of the AM stations may be required prior to and
   following construction of the DTV station antenna, and readjustments
   made as necessary.

   (5) Applications proposing the use of electrical beam tilt pursuant to
   section 73.622(f)(4) must be accompanied by the following:

   (i) Complete description of the proposed antenna system, including the
   manufacturer and model number. Vertical plane radiation patterns
   conforming with paragraphs (c)(3)(iv), (c)(3)(v) and (c)(3)(vi) of this
   section.

   (ii) For at least 36 evenly spaced radials, including 0 degrees
   corresponding to true North, a determination of the depression angle
   between the transmitting antenna center of radiation and the radio
   horizon using the formula in paragraph (b)(2) of this section.

   (iii) For each such radial direction, the ERP at the depression angle,
   taking into account the effect of the electrical beam tilt, mechanical
   beam tilt, if used, and directional antenna pattern if a directional
   antenna is specified.

   (iv) The maximum ERP toward the radio horizon determined by this
   process must be clearly indicated. In addition, a tabulation of the
   relative fields representing the effective radiation pattern toward the
   radio horizon in the 36 radial directions must be submitted. A value of
   1.0 should be used for the maximum radiation.

   [ 62 FR 26990 , May 16, 1997, as amended at  63 FR 13562 , Mar. 20, 1998;
    66 FR 9985 , Feb. 13, 2001;  66 FR 65135 , Dec. 18, 2001;  83 FR 5544 , Feb.
   8, 2018]

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Goto Section: 73.624 | 73.626

Goto Year: 2018 | 2020
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