Narrow band interference suppression circuit with controlled oscillator - offsets intermediate-frequency signals by amt. dependent on frequency of interfering signal before application to notch filter

摘要

Switching (16) between a search mode and a control mode is controlled by a band-pass filter (19) tuned to the centre frequency of the notch filter, an amplitude demodulator (20) and a threshold circuit (24). For control of the oscillator frequency two band-pass filters (26,27) are tuned to higher and lower frequencies respectively with offsets equal to half of the notch bandwidth, and followed by amplitude demodulators (28,29) whose outputs are subtracted (30) one from the other. USE/ADVANTAGE - Esp. in FM car radio, frequency measurement on interference is possible even when useful signal is transiently at lower level.