Transhorizon propagation over the sea: Observations and predictions

Measurements of signal strength are reported for a study of UHF propagation on transhorizon sea paths in the British Channel Islands. Enhancements of up to 30 dB from the mean are seen for periods of hours or days, especially in the summer, and are present for up to 12% of the time overall. The probability distribution of received power is shown for the three paths and various antenna heights., and is compared with predictions of signal strength using ITU-R Recommendation P1546. Most notably, the median observed signal exceeds the median prediction by about 10 - 15 dB. The upper decile, however, is in reasonable agreement.