Privacy communication method and system

• US 4,244,053 A
• Filed: 09/10/1970
• Issued: 01/06/1981
• Est. Priority Date: 09/10/1970
• Status: Expired due to Term

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Martin, Paul E., Clinch, Marvin R., Fenwick, Robert B., Graf, Calvin R.
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/073,812
• Time in Patent Office: 3,771 Days
• Field of Search: 325/32, 179/1.5 R, 179/1.5 F, 331/177, 331/178, 331/179, 375/1, 455/26, 455/29
• US Class Current: 380/34
• CPC Class Codes: H04K 1/003 by varying carrier frequency at or within predetermined or random intervals H04K1/04 takes precedence

Abstract

A privacy communication method and system which utilizes coherent, continuously changing frequencies for keyed, pulsed, and voice communications. A synthesized swept frequency or "chirp" signal imparts a privacy or secure communications capability to the communications signal by virtue of the random or pseudo-random nature of the transmitted signals which is programmed.

Claims

1. A privacy communication system comprising means of generating a signal continuously changing frequency with time in accordance with a preset relationship, said generating means being composed of a first frequency synthesizing means, a first digital computer connected to said frequency synthesizing means, said digital computer having the ability to very rapidly read memory storage to determine the increment of frequency change at any instant of time and also being preprogrammed in accordance with the preset relationship in frequency and in time, a first frequency standard serving as a frequency base for said frequency synthesizer means, said frequency standard maintaining frequency stability over an extended period of time, means to selectively impress intelligence upon said generated signal, means to transmit said signal impressed with said intelligence, means to receive the transmitted signal, said receiving means being physically displaced from said transmitting means, a mixer being fed the received signal as a first input signal, a second frequency synthesizing means identical to said first frequency synthesizing means, a second digital computer connected to said second frequency synthesizing means and identical in capability and preprogramming to said first digital computer, a second frequency standard also connected to said second frequency synthesizer means and identical to said first frequency standard, said first and second frequency standard initially being synchronized, said second frequency synthesizer providing a second input signal for said mixer, a receiver being fed the output signal from said mixer, said receiver being utilized as an intermediate frequency amplifier and detector, a post detection device receiving the output signal from said receiver for conversion to the initially impressed intelligence, and a threshold detector also receiving the output signal of said receiver and providing a control signal to said second digital computer.

2. A privacy communication system as described in claim 1 further including amplifier means interconnecting said receiving means and said mixer.

3. A privacy communication system having a first transmitter with a first receiver physically displaced therefrom comprising at said first transmitter a first frequency synthesizing means, a first digital computer connected to said first frequency synthesizing means, said first digital computer having the ability to very rapidly read memory storage to determine the increment of frequency change at any instant of time and also being preprogrammed in accordance with a preset relationship in frequency and time to provide a sweeping signal at predetermined varying rates to said first frequency synthesizing means, a first frequency standard serving as a preselected frequency base for said first frequency synthesizer means, said frequency standard maintaining frequency stability over an extended period of time, modulating means for impressing intelligence selectively upon the output signal from said first frequency synthesizing means, means for transmitting the signal from said modulating means, at said first receiver, antenna means for receiving the transmitted signal, mixer means being fed a first input signal the received signal, second frequency synthesizer means identical to said first frequency synthesizer means, a second digital computer connected to said second frequency synthesizing means and identical in capability and preprogramming to said first digital computer, said first and second digital computers providing sweeping signals at predetermined varying rates allowing said first transmitter and said receiver to be provided with an identical coded arrangement of various swept characters, a second frequency standard connected to said second frequency synthesizer, said first and second frequency standards being identical and initially being synchronized, said second frequency synthesizer providing a a second input signal for said mixer means, receiver means being fed the output signal from said mixer means, a post detection device receiving the output signal from said receiver means for conversion to said impressed intelligence, and threshold detector means set at a predetermined level, said threshold detector also receiving the output signal from said receiver means and providing in response thereto a control signal to said second digital computer to determine those frequencies providing acceptable quality of communications.

4. A privacy communication system as described in claim 3 further including, at said first transmitter, a second receiver identical to said first receiver and first means to alternately transmit and receive thereat, at said first receiver, a second transmitter identical to said first transmitter and second means to alternately receive and transmit thereat.

5. A privacy communication system having a transmitter with a receiver physically displaced therefrom for sounding being comprised of at said transmitter first frequency synthesizing means, first digital computer connected to said first frequency synthesizing means, said first digital computer having the ability to very rapidly read memory storage to determine the increment of frequency change at any instant of time and also being preprogrammed in accordance with a preset relationship in frequency and time to provide a sweeping signal at predetermined varying rates to said first frequency synthesizing means to provide therefrom a continuous wave linearly swept signal, first frequency standard serving as a preselected frequency base for said first frequency synthesizer and said first digital computer, means for transmitting the output from said first synthesizing means for transmission to said receiver by way of the ionosphere, at said receiver, antenna means receiving the transmitted signal, means to receive said transmitted signal, second frequency synthesizer means identical to said first frequency synthesizer means, a second digital computer connected to said second frequency synthesizing means and identical in capability and preprogramming to said first digital computer, said first and second digital computers providing linear sweeping signals with frequency changes being made at a point of a sine wave where both old and the new frequencies are identical in phase, a second frequency standard connected to said second frequency synthesizer and said second digital computer, said first and second frequency standards being identical and initially being synchronized, said second frequency synthesizer providing an injection signal to said receive means, and a spectrum analyzer receiving the output signal from said receive means to precisely determine signal delay and path length.

6. A privacy communication system for simplex operation comprising at a first site, and also at a second site physically displaced from said first site, antenna receiving means, a first broadband amplifier connected to said antenna receiving means, modulation generator means, a broadband mixer, a sweep frequency synthesizer connected to said broadband mixer, a digital computer connected to said sweep frequency synthesizer, said digital computer having the capability to very rapidly read memory storage to determine the increment of frequency change at any instant of time and also being preprogrammed in accordance with a preset relationship in frequency and time to provide a sweeping signal at predetermined varying rates to said sweep frequency synthesizer, detector means, a second broadband amplifier, means to key said second broadband amplifier, transmitting antenna means connected to said second broadband amplifier, first switching means to alternately connect said broadband mixer to said first broadband amplifier and said modulation generator means, and second switching means to alternately connect said broadband mixer to said detector and said second broadband amplifier.