Notes on Cable Equalizers

Coaxial and twisted-pair cables have the frequen-cy-dependent behavior of increasing loss with increas-ing frequency. The primary mechanism for this char-acteristic is skin effect, which progressively reduces the effective cross-section of the current-carrying por-tion of the cable’s conductors at higher frequencies. In channelized broadband systems such as cable television, the problem is handled with equalized line amplifiers. These amplifiers have a highpass response that is approximately the opposite of the cable loss characteristic. These amplifiers do not need to be par-ticularly accurate in their correction factor because each channel occupies a small portion of the total spec- trum and will have little gain deviation. The main purpose of the equalizers is to maintain signal levels at the highest frequency channels—which eventually are limited by the increased noise, which is amplified along with the signals.