Electrical transmission or interconnection systems – Nonlinear reactor systems – Parametrons
Patent
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
Dektor Counterintelligence & Security, Inc.
Griffin Robert L.
Psitos Aristotelis M.
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