phase-modulation detector[′fāz ‚mäj·ə‚lā·shən di‚tek·tər]
A device which recovers or detects the modulating signal from a phase-modulated carder. Any frequency-modulation (FM) detector with minor modifications will detect phase-modulated waves. See Frequency-modulation detector
The only difference between FM and phase modulation (PM) is the manner in which the modulation index varies with the modulating frequency. The modulation index is independent of the modulating frequency in PM but is inversely proportional to the modulating frequency in FM. Therefore an FM detector, when used to detect a phase-modulated wave, produces an output voltage which is proportional to the modulating frequency, assuming the original modulating signal to be of constant amplitude. Consequently, a low-pass filter with a single reactive element, such as an RC (resistance-capacitance) filter, is needed in the output of the FM detector which is used to detect a phase-modulated wave.