Phase Distortion in Telephone Apparatus

| ^ H E effects of amplitude distortion in the transmission of signals -L has been taken into consideration in t h e design of telephone systems for some time. Recently 1 increasing attention is being given to t h e phase changes which waves undergo in t h e process of their transmission. T h e necessity of this is, on the one hand, d u e chiefly to t h e use of long distance telephone systems involving greater lengths of loaded cable and numerous filters and repeaters in t a n d e m , and, on the other hand, due to t h e d e m a n d for improved performance. One place where b e t t e r quality has become particularly desirable is in circuits for interconnecting broadcasting stations. T h i s paper will present some general considerations of the relation between the phase characteristics 2 of telephone a p p a r a t u s and signal distortion, - ' show the types of phase characteristics t h a t most frequently require consideration and discuss the manner in which the a m o u n t of phase distortion is controlled. Brief reference will also be * Presented at New York Section, A. I. E. E., M a y 1930. At the end of this paper, a bibliography is given containing references to previous publications on this subject. 2 For a definition of phase characteristic see Appendix I. The " i n s e r t i o n " phase characteristic and " i m a g e t r a n s f e r " phase characteristic are defined there. 3 A companion paper by J. C. Steinberg deals specifically with t h e effects of phase distortion on the quality of speech and music.