The Interpretation of Amplitude and Phase Distortion in Terms of Paired Echoes

In picture-transmission systems, such as television and facsimile, the signal transients are noticeably distorted by small amounts of amplitude and phase distortion. There has been developed a simple method of estimating the effects of such distortion from inspection of the amplitude and phase curves. The distortion is regarded as made up of a pattern of echoes, each echo corresponding to a small amount of distortion of both kinds. The separate interpretation of amplitude and phase distortion requires pairs of echoes, those of each pair being equally displaced in time before and after the signal output. This is called the "method of paired echoes." Amplitude distortion corresponds to symmetrical "positive" pairs whereas phase distortion corresponds to skew-symmetrical "negative" pairs. A complete and exact theory is presented on the basis of a small amount of distortion. The method of paired echoes is most useful in the interpretation of phase curves and the determination of the tolerance of phase distortion.