A Low-Power FM Transmitter a Village Can Afford: Coverage by Power and Antenna Height, and the Cost per Listener Reached

A community FM station is usually specified by its transmitter power, but the people it serves live or do not live inside a coverage contour that power alone does not determine. This paper computes that contour from stated assumptions: the Okumura-Hata propagation model with its rural correction at 100 MHz, a 3 dBi transmit antenna with 2 dB of feeder loss, and a reception criterion of 45 dB microvolts per metre at the receiver (a received power of -72.2 dBm with a 0 dBi antenna), over a district of 20 people per km². A 10 W transmitter on a 30 m mast covers a radius of 10.40 km and reaches 6795 people for a complete station cost of USD 2945.45, or USD 0.433 per person reached; the largest station tabulated, 30 W on a 45 m mast, reaches 21085 people over 18.32 km at USD 0.212 per person. Doubling power from 10 W to 20 W multiplies the radius by 1.217, while doubling antenna height from 30 m to 60 m multiplies it by 1.533 — a margin equivalent to multiplying transmitter power by 4.50. A 20 W station broadcasting 12 hours a day needs a solar panel of 146.7 W and a battery of 1980.4 Wh (82.5 Ah at 24 V), a solar system costing USD 939.50. Height, not wattage, is the cheaper direction in which to grow a village station. SIMULATED, NOT MEASURED.