Interference between Satellite Communication Systems and Common Carrier Surface Systems

Abstract

Various published papers have discussed in quite general terms the problem of interference between satellite systems and ground systems. These studies have been largely qualitative, rather than quantitative, in nature. The magnitude of the interference between a satellite system and ground system, however, depends greatly on the frequency plans involved, the character and degree of modulation used, and the parameters of the equipment. Bell Telephone Laboratories has under construction experimental satellite equipment designed to operate in the heavily used 4- and 6-kmc common carrier bands, and the present paper is directed to the potential interference between this satellite equipment and ground point-to-point systems. Interference involving a satellite station and the TD-2 and TH systems is analyzed specifically, and it is shown that the separation between systems must be of the order of 100 to 120 miles or more when the antenna of the common carrier transmitter or receiver is pointed directly at the satellite ground station. If the antenna is beamed 90 degrees or more from the satellite site, the minimum distance may be of the order of 10 miles even when line-of-sight propagation exists between locations. This assumes the use of the Bell System's horn-reflector antenna on the terrestrial system. With a parabolic dish antenna the latter distance must be increased to about 40 miles and adequate blocking must exist in the interference path. These distances provide adequate freedom from mutual interference for both telephone and television modulating signals.