§ 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:

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.

(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.