§ 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

   Note to paragraph (a)(1): These requirements above do not become effective
   until December 31, 2004 for commercial television licensees and December 31,
   2005 for noncommercial television licensees. Prior to those dates, the
   following minimum F(50,90) field strength in dB above one uV/m must be
   provided over the entire principal community to be served:
   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]

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