Transequatorial Propagation of TV Signals via Sporadic-E

Abstract

Field Strengths of video signals by Transequatorial propagation between Kokavil (Sri Lanka) & Madras (India); and Pidurutalagala (Sri Lanka) & Madras (India) were recorded daring March 1982 to June 1983 on VHF band III channels 5 and 8 ie picture carriers frequencies of 175.25 MHz and 196.25 MHz respectively. The observed signal strength on both of these channels indicated strong dependence on the occurrence of blanketing sporadic E layers (E_s-b) of the ionosphere near the magnetic equator. A comparison between the video field strengths and critical frequency blanketing sporadic-E, fbE_s, led to the conclusion that the transequatorial propagation is mainly due to the presence of sporadic-E rather than the actual values of f_bE_s The observed video signal strengths plotted vs f_oE_s, critical frequency of sporadic E show better correlation in distinct frequency ranges 3–5 MH_z and 7–11 MH_z. On the otherhand, there is no evidence of the influence of the F-region (f_oF₂, the critical frequency of the F₂ layer and spread-F) of the ionosphere on the transequatorial propagation of the VHF signals.