Equalization of Cables for Local Television Transmission

Television transmission places stringent requirements on equalization of the transmission medium. This is particularly true on short-haul intracity circuits. A large number of these short-haul links may be connected in tandem for overall long distance television service. Because the arrangement of circuits is subject to frequent change, each link must be independently equalized to close limits. In contrast with the fixed repeater spacings used in long-haul coaxial systems, the lengths of these individual short-haul circuits range from a fraction of a mile to ten or more miles. This requires an equalization system sufficiently flexible to handle all of the circuit lengths encountered in the field. Transmission over these local circuits is handled at video frequencies using special balanced cables. The video band is logarithmically very wide, extending from 30 cps to 4.5 mc --· a span of over 17 octaves in frequency. This wide band adds to the complexity of the equalizers and makes necessarj r the use of special impedance networks for terminating the cable. In connection with the A2A system described in a companion paper, 1 improved equalizers have been developed for video cable. The design of these equalizers is based on an analysis of the cable performance, which 713