Group-delay distortion-measuring equipment

The paper describes equipment used to measure changes in the slope of the phase/frequency characteristic of a transmission system over a frequency range extending from 200 kc/s to 5 Mc/s. The equipment can be used equally well to determine the distortion characteristic of a system of which the input and output terminals are available in one place or under the conditions common in an installed system with remote transmitting and receiving terminals. In common with nearly all schemes of group-delay measurement, the basic principle is due to Nyquist. The equipment represents an advance in current technique in replacing laborious operating procedure with the facility of direct reading. When the transmitter test frequency is varied from a datum frequency over the range desired, direct readings of group-delay distortion are given by a cathode-ray-tube display calibrated in intervals of 10 millimicrosec.