An Instrument for Short-Period Frequency Comparisons of Great Accuracy

The instrument is intended for use, in conjunction with an accurate chronometer, in short-period comparisons of the frequencies of high-grade 100-kc/s oscillators. The phases of the two inputs are compared in a discriminator, the output of which controls a trigger circuit. Pulses from the trigger control the starting and stopping of the chronometer, which measures the periods of beats between the signals. Comparisons of frequencies differing by about 1 part in 106 can be made to an accuracy of 1 part in 1011 over the period of a single beat, i.e. about 10 sec.