Effect of the Quadrature Component in Single Sideband Transmission

A P R E V I O U S article 1 gives an analysis of single sideband transmission. Since that article was written this subject, particularly in its application to picture transmission and television, has assumed considerable importance. For this reason it now seems desirable to amplify the previous theoretical treatment and to indicate certain experimental results which have been obtained in the meantime. The present article gives experimental evidence that, for a given bandwidth, single sideband transmission is distinctly superior to double sideband in picture transmission. 2 It also gives a theoretical discussion which indicates that this is not inconsistent with the observed fact that oscillograms with single sideband transmission show considerable distortion. As described in the previous article distortion to be considered in single sideband transmission as compared with double sideband transmission arises in three ways. 1. There may be present a slowly varying in-phase component due principally to the inaccurate location of the carrier frequency with respect to the edge of the filter characteristic. 2. The edge of the filter characteristic where the carrier is located may be so designed that there is a net distortion due to failure of the vestigial sideband to be accurately complementary to the principal sideband. 3. There is present a quadrature component which results in considerable distortion of the envelope of the received wave under ordinary conditions. By in-phase component is meant a component whose carrier is in phase with the steady state carrier; by quadrature component is meant a component whose carrier is in quadrature with the steady state carrier.