Single sideband systems

Abstract

The everincreasing problem of the overcrowding of the wavebands calls for a more economical use of the very limited spectrum at our disposal. The conventional A. M. system which is by far the most popular system adopted for broadcasting is very wasteful in bandwidth, since the information being transmitted lies in each of the two sidebands. The adoption of single sideband systems seems to be the only logical way for dealing with the problem. However since conventional pure SSB cannot be detected by the ordinary A. M. receiver, its use has been up to now limited to point-to-point communication systems and amateur radio. Radio engineers have been trying to come up with a system which would have the bandwidth economy of a pure SSB system, and at the same time could be detected satisfactorily by a simple envelope detector. Thus the idea of Compatible Single Sideband was introduced. These systems, consist essentially of an A. M. system in which the carrier is not constant in frequency but is phase modulated by the audio in such a way that the sideband power lies on one side of the nominal carrier frequency instead of on both sides as in A. M. [...].