Electronic Indicator for Low Audio Frequencies

An instrument which indicates the frequencies of the components in a periodic complex electrical waveform is described. The frequencies are displayed on four parallel linear scales on a cathode-ray tube. The scales can be set up, without frequency calibration and with an accuracy of 3 per cent, from design equations developed in this paper. The range of indication is from 1 cycle to 1 kilocycle per second. The performance is described, and limitations on the rate of sweeping the frequency bands and the effects of transients are discussed.