An Analysis of Polyphase Envelope Detection

When the ratio of the frequency of the carrier to that of the modulating signal becomes less than approximately 10:1, AM detectors become unable to detect the impressed modulation in a satisfactory manner. Distortion due to transient charging and discharging phenomena in the diode circuit during detection of wide-band AM signals has imposed limitations on channel capacity in AM and FM wide-band multiplexing systems. This paper presents and analyzes polyphase envelope detection as a suitable method of solving the problem. This technique makes it possible to detect the envelope of the impressed AM signal to any desired degree of accuracy even when the ratio of the frequency of the carrier to that of the modulating signal approaches unity. The paper shows the results of an experiment that was carried out to verify the theory.