47 CFR 80.771 - Method of computing coverage.
Compute the 17 dBu contour as follows:
(a) Determine the effective antenna height above mean sea level according to the procedures in §§ 80.757-80.761.
(b) Determine the effective radiated power according to § 80,765. Determine for each radial the distance from the antenna site to the 17 dBu point of field strength using procedures of §§ 80.765 and 80.767.
(c) Plot on a suitable map each point of 17 dBu field strength for all radials and draw the contour by connecting the adjacent points by a smooth curve.