Noise limiting circuit for FM stereo receiver

Details Noise limiting circuit for FM stereo receiver Noise limiting circuit for FM stereo receiver

1977-03-29

1978-05-02

Britton, Howard W.

325319, 325348, 325457, 325477, 325480, H04H 500

Patent

active

040876411

ABSTRACT:
A noise limiting circuit for an FM stereo receiver comprises a filter circuit 13 for grounding high frequency components in the detector output signal through a transistor switch 14 in response to a low field strength signal supplied by the IF amplifier. The filter circuit, when activated, also grounds the 19 KHz pilot signal to automatically switch from a stereo to monaural mode, which further improves the S/N ratio. The pilot signal grounding effect may be enhanced by including an inductor in the filter circuit which, in combination with the filter capacitor, is tuned to the pilot signal frequency. The transistor 14 is switched in a rapid on -- slow off mode by providing a storage capacitor 20 and discharge resistors 17, 19 in the base control circuit of the transistor, and the filter switching or squelch level may be adjusted by a variable resistor 22.

REFERENCES:
patent: 3569633 (1971-03-01), Brahman
patent: 3707603 (1972-12-01), Limberg
patent: 3790714 (1974-02-01), Ohsawa

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