Sec. 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..................................................   L28 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 Sec. 73.699 of this part) and the F (50,10) field strength 
charts (Figures 9a, 10a and 10c of Sec. 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

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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

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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 x 25 cm (7 inches x 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

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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.

[ 62 FR 26990 , May 16, 1997]