Interference between Satellite Communication Systems and Common Carrier Surface Systems

Satellite systems will of necessity use ground transmitter powers of several thousand watts. Present microwave systems in the United States operating in the common carrier band utilize transmitters of the general 921 922 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1902 order of one watt output power and in this sense are consequently only about one-thousandth as interfering as a satellite ground transmitter. Furthermore, the inherent noise per cycle of bandwidth at the input of the satellite ground receiver will be about 20 db less than that of the present-day commerical common carrier receiver, thus making it correspondingly more sensitive to interference from other systems. Several general studies of interference 1,2 have used criteria of interference intended to encompass all varieties of ground radio relay systems, but inevitably the decision as to whether interference between particular sites is tolerable or intolerable must be made on the basis of the specific radio systems involved and the frequency bands in which they operate. The F.C.C., as a result of its studies, has recommended for consideration a number of bands between 3700 and 8400 mc, including the two common carrier bands .3700 to 4200 mc for the spacecrafts and 59256425 mc for the earth stations. 3 The experimental satellite equipment presently under construction by Bell Telephone Laboratories will operate in the top 100 megacycles of the 4- and 6-kmc common carrier frequency bands mentioned above and thus, potentially, interference may occur between the satellite system and the many ground commerical systems operating in these bands.