A High-Precision Direct-Reading Loss and Phase Measuring Set for Carrier Frequencies

A set has been developed to measure the parameters of insertion loss and phase shift of communication systems components. The design effort has been directed toward achieving laboratory precision in measurement and at the same time maintaining the ease of use and speed necessary for a large volume of measurements. Accuracies of ±0.002 db, ±0.02 degree and ±1 cycle have been attained over the frequency range from 10 to 300 kc. The entire frequency range is covered without band switching by the use of a heterodyne signal oscillator which provides frequency accuracy by locking to a frequency standard. The principle of phase detection is based on measurement of the time interval corresponding to the displacement of sine wave zero crossings caused by the unknown. This method has the advantage of good accuracy inherent in the measurement of time by counting techniques and also the ease of automatic readout of phase shift by translation from time units. In measuring loss, use of a rapid sampling technique to compare the unknown with a standard eliminates errors caused by circuit drifts. T h e ever increasing complexity of communication systems and the demand for high-quality transmission have emphasized the need for close control of system components such as filters, equalizers, and repeaters. Prccise instrumentation to measure the parameters of loss and phase shift must be provided for use in both the development and production areas of these components. In the case of broadband carrier systems this need was met by development of a 3.6 mc phase measuring set.