Transhorizon VHF TV signal propagation over mixed land-sea paths

摘要

The propagation characteristics of Rupavahini TV transmissions originating from Sri Lanka on channels 5 and 8 and monitored in southern India are studied. The receiving sites are chosen to provide mixed land-sea paths. The propagation characteristics of these mixed paths are influenced by sea-surface refractivity gradients and land-sea interactions. The analysis of the data indicates that different propagation mechanisms prevail for various percentages of time. Sometimes signal levels on the order of 10-dB below free space level are also observed, particularly in premonsoon months, which is due to the occurrence of ducting conditions prevailing in this region. Some observations of the distance dependence of the channel 5 signal show that the path loss increases by 10 dB for every 100 km of distance.