Method of and apparatus for transmitting clandestine radio signals
First Claim
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1. A method of transmitting clandestine signals from a first to a second location which comprises the following steps:
- at said first location,(a) amplitude modulating the output of a first continuous wave oscillator with a periodic pulse train;
(b) dispersing the frequency spectrum of said modulated output in a first acoustic surface wave device;
(c) pulse modulating the input to said acoustic surface wave device with the signal to be transmitted;
(d) transmitting said dispersed spectrum to said second location, andat said second location,(e) mixing the incoming signal from said first location with the output of a second continuous wave oscillator having the identical frequency as said first continuous wave oscillator;
(f) applying the resultant IF signal to a second acoustic surface wave device to contract and restore the pulse modulated signal spectrum, said spectrum includng noise and pulse levels above said noise;
(g) detecting the output pulses from said second acoustic surface wave device exceeding said noise levels to recover the clandestine signal from the noise; and
(h) applying the signal output to an output device.
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Abstract
Clandestine signals are transmitted by using a surface wave acoustic device to disperse the spectrum of a pulse-modulated CW carrier. The dispersed signal is itself modulated and then transmitted to a remote location, at low level. At the remote location, an acoustic device of conjugate characteristics is used to recover the dispersed signal from out of the background noise.
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Citations
9 Claims
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1. A method of transmitting clandestine signals from a first to a second location which comprises the following steps:
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at said first location, (a) amplitude modulating the output of a first continuous wave oscillator with a periodic pulse train; (b) dispersing the frequency spectrum of said modulated output in a first acoustic surface wave device; (c) pulse modulating the input to said acoustic surface wave device with the signal to be transmitted; (d) transmitting said dispersed spectrum to said second location, and at said second location, (e) mixing the incoming signal from said first location with the output of a second continuous wave oscillator having the identical frequency as said first continuous wave oscillator; (f) applying the resultant IF signal to a second acoustic surface wave device to contract and restore the pulse modulated signal spectrum, said spectrum includng noise and pulse levels above said noise; (g) detecting the output pulses from said second acoustic surface wave device exceeding said noise levels to recover the clandestine signal from the noise; and (h) applying the signal output to an output device. - View Dependent Claims (2, 3, 4)
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5. A clandestine transmitter which comprises:
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a continuous wave oscillator; a source of a periodic train of pulses; means for amplitude modulating the output of said oscillator with the output of said pulse train source; an acoustic surface wave device for dispersing the frequency spectrum of the output signal from said modulating means; first means for transmitting the dispersed frequency spectrum to a second location; a low frequency continuous wave source; means for triggering said periodic pulse train source with the output of said low frequency continuous wave source; and second means for transmitting said low frequency signal to said second location over a different transmission path than that used to transmit the output of said frequency dispersing means.
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6. A clandestine transmitter which comprises:
- a continuous wave oscillator;
a source of a periodic train of pulses;
means for amplitude modulating the output of said oscillator with the output of said pulse train source;
means for supplying an audio-frequency signal to be transmitted;
means for pulse-position-modulating said audio frequency signal;
means for triggering said periodic pulse train source with the output of said pulse-position-modulating means;
an acoustic surface wave device for dispersing the frequency spectrum of the output signal from said amplitude modulating means; and
means for transmitting the dispersed frequency spectrum to a second location.
- a continuous wave oscillator;
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7. A clandestine receiver, which comprises:
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means for receiving a clandestine signal transmitted from a remote location; a source of continuous wave oscillations; means for mixing said continuous wave oscillations with said received signal thereby to generate an intermediate frequency signal; an acoustic surface wave device for contracting the frequency spectrum of said intermediate frequency signal; means for detecting the signal output from said frequency spectrum contracting device; a threshold detector connected to the output of said detecting means for discriminating between said detected signal and the ambient noise; output means connected to the output of said threshold detector; means for receiving a low frequency signal transmitted from said remote location over a transmission path which differs from the transmission path used to transmit said clandestine signal; and a phase-lock loop circuit having an input connected to said low frequency signal receiving means, an output connected to said output means, and a reference signal input connected to said detecting means.
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8. Apparatus for transmitting clandestine signals from a first to a second location comprising:
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a first continuous wave oscillator; a pulse source generating a periodic pulse train; means for amplitude modulating the output of said first oscillator with said periodic pulse train; a first acoustic surface wave device dispersing the frequency spectrum of the amplitude modulated output; means for pulse modulating the input to said acoustic surface wave device with the signal to be transmitted; means for transmitting the dispersed spectrum to said second location; a second continuous wave oscillator at said second location having the same frequency as said first oscillator; means at said second location for mixing the incoming dispersed spectrum with the output of said second oscillator to provide an IF signal; a second acoustic surface wave device receiving said IF signal and contracting and restoring the pulse modulated signal spectrum, said spectrum including noise and pulse levels above said noise; and means for detecting the output pulses from said second acoustic surface wave device exceeding said noise levels to recover the clandestine signal from the noise. - View Dependent Claims (9)
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Specification