UHF Long-Range Communication Systems

Recent discoveries about long-range propagation of uhf radio waves, together with careful utilization of high-powered transmitters and large antennas, have made possible reliable multichannel point-to-point uhf radio communication systems which operate over distances of 200 miles or more beyond the horizon. Measurements by various investigators have shown that transmission losses on such paths have median values of the order of 80 db below free-space levels. A program of investigation at Lincoln Laboratory, MIT, has yielded detailed propagation data necessary for the design of long-distance multichannel uhf radio communication circuits. This has also led to the design of specialized equipment for this application. These circuits employ antennas having transmitting and receiving gains of 25-40 db; high-power FM transmitters of up to 10-kw output; sensitive FM receivers having low-noise input circuits, and excellent selectivity; and space-diversity reception. A procedure for system design is outlined.