Signal to noise ratio indicating circuit

Details Signal to noise ratio indicating circuit Signal to noise ratio indicating circuit

1975-12-15

1977-07-26

Safourek, Benedict V.

325348, 325478, 325403, 325474, H04B 110

Patent

active

040386040

ABSTRACT:
A radio receiver squelch circuit responds to an IF carrier modulated by any of AM voice, AM pulse, CW, interrupted CW, or angle modulated signals. After the IF carrier is amplitude normalized it is supplied to a network for deriving a D.C. voltage having an amplitude indicative of the signal to noise level of the normalized IF. The signal to noise level indicating circuit includes a detector for deriving a waveform that is a replica of the envelope of the normalized IF. In response to the envelope amplitude being above a predetermined threshold level, indicative of the presence of a signal, a capacitor is discharged by a constant current source. In response to the envelope being below the predetermined level for an initial predetermined time, the capacitor is charged by a constant current source. In response to the envelope amplitude being below the predetermined level for in excess of the initial predetermined time, the capacitor is charged by a much smaller current. Thereby, the capacitor voltage level is indicative of the signal to noise ratio of the IF signal. The voltage across the capacitor is monitored with an amplitude comparison including amplitude hysteresis to derive a squelch control signal.

REFERENCES:
patent: 2942105 (1960-06-01), Hargreaves, Jr.
patent: 3196354 (1965-06-01), Engelbrecht
patent: 3217258 (1965-11-01), Arlin et al.
patent: 3238457 (1966-03-01), Boymel et al.
patent: 3626294 (1971-12-01), Dancy
patent: 3699457 (1972-10-01), Wright
patent: 3747703 (1973-07-01), Knowd et al.

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