Tropospheric scatter observations at 3 480 Mc/s with aerials of variable spacing

Short-term measurements are described of signal amplitude, fading characteristics, correlation distances and height gain at three ranges (130, 258 and 398km) from a transmitting system radiating horizontally polarized waves. Although the results were variable and at times difficult to interpret, it is considered that 150¿ should be an adequate horizontal spacing, even at the shortest ranges, for directional receiving aerials operated in diversity, with a tendency towards smaller values for vertical spacing. Fading rates lying generally between 1 and 10 per second are found, with Rayleigh-type fading tending to occur at the longer ranges. No consistent relationship between signal amplitude, fading and correlation distance is found, although the highest fading rates are often accompanied by low correlation distances. Cross-correlation measurements show definite evidence of the steady drifting of scattering centres. Diffraction effects leading to height gain are found, and there is some indication of standing waves due to ground reflections. Aerial siting is discussed and the transportable equipment which was developed for the tests is briefly described.