Technique for secure communications on FM radio channels

Details Technique for secure communications on FM radio channels Technique for secure communications on FM radio channels

1983-08-22

1986-02-25

Cangialosi, Salvatore

Telecommunications

Transmitter and receiver at separate stations

455 42, 179 15M, 375 22, H04K 102

Patent

active

045732051

ABSTRACT:
This present invention relates to a system for providing secure communications without bandwidth expansion using an encryption method called masking whereby a masking signal is generated at the transmitter using a secret key which includes a predetermined threshold signal-to-noise ratio level that when added to a frequency modulated (FM) signal produces an unintelligible signal. Any type of masking signal as, for example, a sine wave, an FM signal, or bandlimited Gaussian noise, may be used. At the receiver, the corresponding masking signal used by the transmitter is regenerated and subtracted from the FM signal before demodulation. Because of the FM threshold effect, perfect removal of the masking signal is not required. It is only necessary to subtract enough of the masking signal such that the resulting signal-to-noise ratio (SNR) is above the required threshold for reliable demodulation of the original signal.

REFERENCES:
patent: 2758202 (1956-08-01), Wilmotte
patent: 3133991 (1964-05-01), Guanella
patent: 3638121 (1972-01-01), Spilker, Jr.
patent: 3651268 (1972-03-01), Rivkin
patent: 3723878 (1973-03-01), Miller
patent: 4126761 (1978-11-01), Graupe et al.
patent: 4179658 (1979-12-01), Bitzer
patent: 4361729 (1982-11-01), Barnes, Jr. et al.
Proc. of the IEEE, vol. 52, #4, 4/64, "Frequency or Phase Modulation with a Noise Carrier" by Harrison E. Rowe.
1979 Carnahan Conference on Crime Countermeasures, University of Kentucky, Lexington, Kentucky, May 16-18, 1979, "Achieving and Measuring High Security in Analog Speech Communications Security Devices" by Arnold M. McCalmont, pp. 89-93.

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