A Transversal Equalizer for Television Circuits

In tin ideal transmission system the received signal is an exact replica of the transmitted signal. In all practical systems the received signal differs from the transmitted signal, due to imperfections of the transmission media. The lack of uniform gain and delay over the frequency band of the system constitutes a common form of imperfection. These gain and delay distortions are usually so severe as to require some form of equalization.* The amount of equalization required depends upon the nature of the signal being transmitted. Fortunately, most communication signals have qualities that make perfect equalization unnecessary. For television transmission, the requirements are particularly stringent for both gain and delay equalization. Systems transmitting TV signals either as video circuits or carrier circuits usually use fixed gain and delay equalizers to correct the bulk of the system distortion and adjustable equalizers to correct the residual. The residual gain and delay distortions will vary with system aging and manufacturing variations; thus, an unpredictable amount of equalization is necessary. These distortion characteristics are arbitrary functions of frequency, and will change from time to time. This requires * A t h e o r y of equalization of complex systems is described in R e f . 1. 405