A System for Frequency Measurements Based on a Single Frequency

The method here described is suitable for calibration of either piezo oscillators or frequency meters in terms of an accurately standardized temperature controlled piezo oscillator. A radio-frequency generator is adjusted and maintained at 10 kc in terms of the standard piezo oscillator. The correct adjustment of this generator is shown by a special form of beat indicator which gives both visible and audible indication of the frequency difference between the piezo oscillator afnd a harmonic of the 10-kc generating set. A second auxiliary generator may then be set to a harmonic of the 10-kc generating set, such as some frequency assignment in the broadcasting band. The correct setting of the auxiliary generator is also determined by means of the special beat indicator. The piezo oscillator to be tested will usually be found to give an audible note in the telephone receivers connected to it. The audible note represents the difference in frequency between the piezo oscillator and the auxiliary generating set. The frequency difference is determined by comparison with a calibrated audio-frequency generator.