BBC R&D

Abstract

On oversea paths within the horizon, the received field strength is the vector sum of a direct component and a component reflected from the surface of the sea. If the level of the sea varies, the relative phase of the reflected component alters and causes field strength variations. To determine the effect of these variations on UHF television reception, a series of measurements and subjective assessments have been made in various areas of the United Kingdom.

It is concluded that, for horizontally polarised signals, field strength changes of more than 40 dB can occur at unobstructed locations. The range of fading is reduced in built-up and diffracted-field areas. It is also reduced by using vertical polarization. The variation of signal level is generally accompanied by multipath propagation and frequency-selective effects, which cause severe degradation of the television service in certain coastal areas. Areas likely to suffer such degradation are detailed.