A Method for Calibrating Microwave Wavemeter

A method of calibrating wavemeters in the microwave range is described in which the frequency of a calibrating oscillator having sufficient power to drive a wavemeter is continually checked against the harmonics of a crystal-controlled reference oscillator by visual means. The two frequencies being compared are separately heterodyned with that of a third oscillator, which is frequency-modulated. The modulation products then pass through a narrow-band receiver to an oscilloscope whose sweep is synchronized with the saw-tooth modulation voltage. Whenever the difference between the instaneous frequency of the modulated signal and the output of one of the generators equals the frequency to which the receiver is tuned, a pulse of energy is transmitted through the receiver and appears as a pip on the oscilloscope. Pips will appear corresponding to the moments when the instantaneous frequency is greater or less than that of each of the fixed frequencies. The oscillographic pattern then comprises two fixed pulses due to the reference oscillator, and another pair which can be shifted by changing the frequency of the calibrating oscillator. When the two pairs are superimposed, the frequency of the power oscillator matches that of the crystal harmonic. By superimposing the higher-frequency pulse of one pair on the lower-frequency pulse of the other pair, and vice versa, additional adjustments of the power oscilator can be made to differ from the standard by ± twice the frequency of the receiver.