Apparatus for detecting an electronic surveillance device
First Claim
1. A device for detecting a covert electronic surveillance apparatus of the type which senses information in the audio frequency range and which includes a covert transmittter for generating electromagnetic signals modulated by said information, comprising:
- a microphone for receiving audio signals in an area to be searched;
first means for passing signals in a predetermined bandwidth from said microphone;
a radio receiver for receiving and demodulating said elecromagnetic signals from said covert electronic surveillance apparatus;
second means for passing signals in said predetermined bandwidth from said receiver; and
means for comparing the outputs of said first and second passing means to detect coincident outputs indicative of the presence of said covert electronic surveillance apparatus.
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Accused Products
Abstract
A method and apparatus for detecting a covert audio transmitter in which a microphone which picks up audio frequencies in the room and a radio receiver tuned to an unidentified audio signal are compared to determine if a "bug" is in the room being searched. An innocuous type of noise is introduced into the area to be searched by having persons converse or by turning on a radio, and these audio frequency signals are picked up directly by a microphone associated with the bug. The signal received by the bug causes the bug'"'"'s RF carrier to be modulated, and this is picked up by the bug detector'"'"'s radio receiver. The received signal is demodulated and is compared with the audio signal picked up by the bug detector'"'"'s microphone to determine if the demodulated radio signal corresponds to the sounds in the room. If the demodulated signal from the detector'"'"'s radio receiver matches the audio information picked up by the detector'"'"'s microphone, an indicator light is lit to inform the operator that a bug is present.
19 Citations
23 Claims
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1. A device for detecting a covert electronic surveillance apparatus of the type which senses information in the audio frequency range and which includes a covert transmittter for generating electromagnetic signals modulated by said information, comprising:
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a microphone for receiving audio signals in an area to be searched; first means for passing signals in a predetermined bandwidth from said microphone; a radio receiver for receiving and demodulating said elecromagnetic signals from said covert electronic surveillance apparatus; second means for passing signals in said predetermined bandwidth from said receiver; and means for comparing the outputs of said first and second passing means to detect coincident outputs indicative of the presence of said covert electronic surveillance apparatus. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A device for detecting a covert electronic surveillance apparatus of the type which senses information in the audio frequency range and which includes a covert transmitter for generating electromagnetic signals modulated by said information, said detecting device comprising:
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a microphone for receiving audio signals in an area to be searched; a radio receiver for receiving and demodulating said electromagnetic signals from said covert electronic surveillance apparatus; a clock generator; first and second switched capacitor filters tuned to the same frequency and controlled by said clock generator, said first switched capacitor filter receiving said audio signals from said microphone as an input and said second switched capacitor filter receiving said demodulated electromagnetic signals from said radio receiver as an input; first and second monostable multivibrators responsive to the output of said first and second switched capacitor filters, respectively, said first and second monostable multivibrators respectively producing an output pulse of a first predetermined duration when an input signal is received; and pulse stretching means for outputting a pulse of a second predetermined duration when output pulses from said first and second monostable multivibrators are both of a predetermined logic level, said pulse of said second predetermined duration indicating that a signal received by said radio receiver is being outputted by said covert electronic surveillance apparatus.
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15. A method of detecting the presence of a covert audio transmitter in an area, comprising the steps of:
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(a) detecting an unidentified radio signal; (b) demodulating said unidentified radio signal in a radio receiver; (c) receiving audio frequency signals from a microphone in the area to be searched; (d) selectively bandpass filtering said unidentified radio signal and said received audio frequency signals over the same frequency range; (e) comparing the filtered unidentified radio signal and the filtered received audio frequency signals; and (f) indicating coincidence of the filtered signals when said comparing step produces a favorable comparison. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23)
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Specification