Single-Sideband Techniques in UHF Long-Range Communications

Several factors relevant to the design of uhf longrange communication systems are analyzed. In particular, singlesideband amplitude modulation is evaluated and compared to frequency modulation, with special regard to: a) spectrum conservation; b) performance in the presence of multipath; and c) realized channel signal-to-noise ratio vs total transmitted rf power. It is shown that: 1) SSB requires one-sixth to one-tenth of the spectrum width required by fm. 2) The useful bandwidth of the transmission medium in the presence of multipath is at least four times as great for SSB as for fm. 3) The average power required for a twenty-four channel SSB system is about 20 decibels less than that required for an equivalent fm system, providing equal usable communications. System design considerations are discussed for uhf single sideband, as well as the design parameters of a particular set of equipment operating in the 300 to 400-megacycle band. The linearity of high-power klystrons is discussed, and a promising technique for achieving highly efficient operation of such devices is described.