The Measurement of Delay Distortion in Microwave Repeaters

HE successful transmission of broadband television and pulse signals over any communication circuit depends upon the preservation of the complex wave shapes of the original transmitted signals. Fourier analysis tells us that a complex signal wave can be resolved into a spectrum of frequencies with certain amplitude and phase relationships. It is well known that the amplitude relationships of all essential frequencies in this spectrum must be substantially preserved. It is equally important that the phase relationships of the essential frequencies should be preserved. The instantaneous value of the received signal is the vector sum of the instantaneous amplitudes of all the component frequencies. Therefore, if the relative phase of some frequency component is changed by 180° the sign of its contribution to the o u t p u t is reversed, and it is clear that a closer approximation to the original signal could be obtained by suppressing this frequency component rather than permitting it to contribute negatively to the output. It can be shown 1 that the relative phase relations of the component frequencies in a complex signal wave will be preserved if the phase shift in passing through a circuit is a linear function of the angular frequency. T h a t is 0 = Toco + «7T . · (1)