Abstract: A pilot signal cancelling circuit for an FM multiplex demodulator wherein the amplitude of the cancelling signal tracks that of the pilot signal contained in or mixed into the composite signal. The amplified composite signal is synchronously detected with the fixed amplitude 19 KHz pilot signal extracted by a phase lock loop 2, and the detector output is filtered to remove high frequency components and then converted to a current variation in a d.c. amplifier 13. The output of the latter is fed to a current controlled attenuator 14 together with the fixed amplitude pilot signal, and the level adjusted attenuator output is then inverted, divided into left and right channel components by the 38 KHz sub-carrier signals, and fed to adders in the multiplex demodulator outputs to cancel the pilot signal components therein.

Abstract: Unwanted pilot signal components in the "L" and "R" outputs of a stereophonic FM multiplex demodulator are cancelled by inverting the 19KHz pilot signal, separately multiplying or gating it with the opposite phase 38KHz subcarrier signals, and adding the multiplier or gate outputs to the "L" and "R" demodulator outputs. The multiplication produces signals equal in amplitude but opposite in phase to the contaminating pilot signal components, whereby the latter are effectively cancelled by the addition function.