A Regenerated Sideband Demodulator for Television

A vestigial sideband system of TV transmission has inherent phase and quadrature distortion. Phase distortion is caused by nonlinearity of the phase vs. frequency characteristic of the system; quadrature distortion is caused by the transmission of sidebands which are not symmetrical about the carrier. The nonlinearity of the phase characteristic is particularly troublesome at frequencies near the picture carrier where most of the energy is concentrated. At present, techniques exist for equalizing for phase distortion or its derivative envelope delay distortion at video frequencies, but these are only partially effective because there is quadrature distortion still present. If it were possible to recreate the missing sidebands from the existing sidebands, a double sideband signal would be presented to the detector and quadrature distortion would be eliminated. Also, by adding existing and regenerated signals in a way such that their respective picture carriers are not in phase, a very substantial improvement in the linearity of the phase vs. frequency of the overall system, including the transmitter if desired, can be effected, and waveform distortions are practically eliminated. A brief mathematical analysis of the distortions in the vestigial sideband system and a description of the apparatus are given, with photographs to show the possible results.

Print ISSN

0361-4573

Published

1967-09

Content type

Original Research

DOI

10.5594/J10944