A 5 to 50 MHz Direct-Reading Phase Meter with Hundredth-Degree Precision

The subject phase meter provides a direct, level-insensitive indication of the relative phase angle between two RF signals in the frequency range from 5 to 50 MHz. It has an inherent phase resolution capability of greater than 0.001°, although the present design is limited by stability, noise, and spurious responses to an accuracy of about ±0.01°. The instrument utilizes the well-known technique of measuring phase in terms of the time between the zero crossings of two sinusoidal signals, using an electronic counter for time-measuring and display. A considerable advance in angular resolution, accuracy, and operational ease over any known previous instrumentation has been achieved by a painstaking combination of such key factors as highly level-insensitive zero-crossing detectors, extremely linear RF/IF amplifiers and mixers, and multiperiod averaging of the numerical readout. Verification of the hundredth-degree accuracy for all phase angles, operating levels, and frequencies is a problem comparable in magnitude to the development of the meter itself. For cases where the signal level is essentially constant, a relatively simple verification procedure is described. Verification of meter insensitivity to signal level changes requires the availability of a phase-calibrated RF attenuator.