A precision phase comparator for use at low radio frequencies

The design and construction of a precision phase comparator for operation at a frequency of 87.5 kc/s is described. It consists essentially of a phase-multiplier unit, a calibrated phase-shifting goniometer and a cathode-ray-tube indicator. The phase angle between two sinusoidal signals is determined by measuring the phase shift required to bring each signal into the same phase relationship with a reference signal. A coarse measurement of phase, which is necessary in order to eliminate ambiguities due to the high multiplication factor, can be obtained by switching the multiplier out of circuit. Under ideal conditions measurements to an accuracy of about 0.01° can be made. Data showing the effect on accuracy of various parameters, such as random noise and changes in input signal level, are given.