Residual attenuation equalisation of broadband systems by generalised transversal networks

Residual attenuation equalisation of broadband coaxial-cable systems has been achieved elsewhere by a set of harmonic cosine characteristics based on an almost linear frequency scale. This method is, however, not efficient for systems which exhibit high distortion near the bandedges. A simple analysis of measured characteristics yields the requirements for suitably transforming, or `warping¿, the frequency scale. Generalisations of the transversal-equaliser principle offer the realisation of cosine characteristics with frequency scales which match particular problems. The investigation on which the paper is based was concerned with the coaxial-cable network of the British Post Office, and led to novel designs, of which the `twin cosine equaliser¿ has been accepted for service use. This device enables residual distortion of up to 6dB to be reduced to rather less than 1dB, with a minimum of auxiliary instrumentation.