Transmitter detecting apparatus

Details Transmitter detecting apparatus Transmitter detecting apparatus

1976-06-17

1978-11-28

Griffin, Robert L.

Electrical transmission or interconnection systems

Nonlinear reactor systems

Parametrons

307358, H04B 100

Patent

active

041278178

ABSTRACT:
An eavesdropping device having a microphone and a transmitter is detected by an apparatus including an antenna, a broad-band detector, a limiter-amplifier, and a loudspeaker. The apparatus establishes a regenerative feedback loop with the eavesdropping device and produces a revealing tone. The limiting amplifier shifts the level of the demodulated signal and amplifies all but a peak portion, and combines the signal thus limited with an unmodified signal in a differential amplifier, thus amplifying the peak portion, thus preventing amplifier saturation in an environment having interfering signals which are stronger than the signals transmitted by the eavesdropping device. Cascaded limiting amplifier stages can be used.

REFERENCES:
patent: 3473127 (1969-10-01), Williams et al.
patent: 3882272 (1975-05-01), Norian
patent: 3939420 (1976-02-01), Risberg et al.
patent: 3940699 (1976-02-01), Emgushov
patent: 3990011 (1976-11-01), Knight

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