Optimal Equalization of Wideband Coaxial Cable Channels Using 'Bump' Equalizers

The ideal communication channel exhibits a constant input-output gain characteristic over the entire transmission band. In the case of a 3/8-inch coaxial cable system, the cable loss varies from 4 dB/mile at 1 MHz, to 30 dB/mile at 60 MHz; and to compensate the cable loss, repeaters are required at periodic intervals. As is well known, the cascaded repeaters cannot exactly compensate the cable loss and this 1327 1328 THE BELL SYSTEM TECHNICAL JOURNAL, JULY-AUGUST 1972 mismatch results in the so-called "misalignment" of the cable system. In addition to the mismatch which is present initially, the channel misalignment is affected by the seasonal temperature variation and the aging of the components in the system. The objective of the main cable equalizers is that, after the equalization, the total input-output gain characteristic of the system should be, at all times, as nearly zero dB as possible over the entire message band. Since the transmission of amplitude information is of major importance in analog coaxial cable systems, various schemes of inputoutput "amplitude-only" equalization have been studied in the past. 1,2 It should be noted that the analog signal in the coaxial cable channel may contain either voice or digital information, and the transmission of voice-type information can be accomplished without phase equalization. For the transmission of high-speed digital information, the necessary phase equalization is usually furnished in the digital terminals and not in the main coaxial cable path.