Phase Distortion and Phase Distortion Correction

The importance of the role played by the steady state phase characteristics of long cable circuits has recently been emphasized in telephone and telegraph transmission. In this paper an analytical exposition of the theory of phase distortion is followed by a consideration of various methods of phase distortion correction with particular reference to terminal phase compensating networks and to the application of the lattice network to the loaded line as a terminal phase corrector. 1. INTRODUCTION F ROM the standpoint of ideal quality, a transmission system must be so designed t h a t the received currents, which represent the transmitted signal, shall be a faithful copy of the corresponding currents which enter the transmission system at the sending end; t h a t is, the transmission system must be distortionless. For relatively short distances the deleterious effects of phase distortion are not appreciable but as the range of transmission is increased a point may be reached where the impairment of quality becomes so serious as to reduce the commercial efficiency of the circuits. This fact was first recognized on long submarine telegraph circuits. With regard to telephony, the importance of the question of the quality of received speech was initially emphasized by the advent of the efficient telephone repeater, 1 making possible the increased length of the modern telephone system. This increased length, involving the necessity for circuits of higher quality, led to the development of improved loading designs.