§  80.767   Propagation curve.

   The propagation graph, §  80.767 Graph 1, must be used in computing the
   service area contour. The graph provides data for field strengths in
   dBu for an effective radiated power of 1 kW, over sea water, fresh
   water or land (smooth earth); transmitting antena heights of 4,800,
   3,200, 1,600, 800, 400, 200, and 100 feet; based on a receiving antenna
   height of 9 meters (30 feet), for the 156-162 MHz band. The use of this
   is described in this section.

   (a) Calculate the effective radiated power of the coast station, Ps in
   dB referred to 1 kW (dBk), as follows:
   eCFR graphic ec02ap91.005.gif

   where,

   Pt=Transmitter output power in dB referred to 1 kW: Transmitter output
   power in watts is converted to dBk by Pt=10 [log10 (Power in
   watts)]−30. Also see §  80.761 Graph 1 for a conversion graph.

   G=Antenna gain in dB referred to a standard half-wave dipole, in the
   direction of each plotted radial, and

   L=Line losses between the transmitter and the antenna, in dB.

   Notes: 1. To determine field strengths where the distance is known, for
   effective radiated powers other than 1kW (0 dBk): Enter the graph from
   the “statute miles” scale at the known distance, read up to
   intersection with the curve for the antenna height, read left to the
   “dBu for 1 kW radiated” scale and note the referenced field strength
   (Fe). The value of the actual field strength (F) in dBu will be F=Fe+Ps
   where Ps is the effective radiated power calculated above.

   2. To determine distance, where the actual field strength is specified,
   for effective radiated powers other than 0 dBk: The value of the field
   referenced strength will be Fe=F−Ps in dBu. Enter the graph, from the
   “dBu for 1 kW radiated” scale at the corrected value of Fe, read right
   to intersection with the antenna height, read down to “statute miles”
   scale.

   (b) Determine the antenna height. For antenna heights between the
   heights for which this graph is drawn, use linear interpolation; assume
   linear height-gain for antennas higher than 4,800 feet.

   (c) For receiver antenna heights lower than 9 meters (30 feet), assume
   that the field strength is the same as at 9 meters (30 feet).

   (d) Assume that propagation over fresh water or over land is the same
   as that over sea water.
   eCFR graphic ec02ap91.006.gif

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