A Fundamental Suppression Type Harmonic Analyzer

The principles and design of an harmonic analyzer of novel form are described. The analyzer operates by suppressing the fundamental and passing the harmonics through an amplifier with a calibrated gain control to a cathode-ray oscillograph or vacuum tube voltmeter. The apparatus is designed for analysis of audio-frequency oscillations but could be used with frequencies of a much higher order if the curve of frequency against gain were plotted for the amplifier. The power required for operation is small, an input impedance of the analyzer being of the order of 500,000 ohms. In practice it was found that the instrument was capable of giving a fairly accurate estimate of the total harmonic content for values as low as 0.2 per cent. Using a cathode-ray oscillograph it is possible to separate two or more harmonics, but the instrument is chiefly useful for estimating total harmonic distortion of a wave. The instrument should be useful as a distortion meter for power supply systems, giving a reading of the total harmonic distortion with the aid of a vacuum tube voltmeter.