Cryptography – Communication system using cryptography – Frequency shift or inversion
Patent
1992-09-02
1995-03-21
Gregory, Bernarr E.
Cryptography
Communication system using cryptography
Frequency shift or inversion
380 9, 380 33, H04K 104
Patent
active
054004047
ABSTRACT:
The present invention provides a modulation/ demodulation circuit and a communication system utilizing the modulation/demodulation circuit. The modulation/ demodulation circuit can be operated in either of a modulation/demodulation mode wherein an input signal is frequency inverted and scrambled or descrambled and a through mode wherein the input signal is directly outputted therefrom without being subject to any processing. In a private communication system, two such modulation/ demodulation circuits are used as a scrambler in the transmission-side and as a descrambler in the reception-side. In order to prevent the low band characteristic of the reception-side output in the through mode from being different from that of the modulation/demodulation mode, the modulation/demodulation circuit may include a high pass filter. The high pass filter a low band cut-off characteristic reciprocal to a low pass filter for removing the upper side band from the output of a double balanced mixer.
REFERENCES:
patent: 2530579 (1950-11-01), Koros
patent: 4195202 (1980-03-01), McCalmont
patent: 5140635 (1992-08-01), Houghton et al.
patent: 5168522 (1992-12-01), Simanis et al.
Gregory Bernarr E.
Rohm & Co., Ltd.
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