Cryptography – Communication system using cryptography – Frequency shift or inversion
Patent
1990-10-01
1992-09-01
Buczinski, Stephen C.
Cryptography
Communication system using cryptography
Frequency shift or inversion
380 13, 380 19, H04K 104, H04N 7167
Patent
active
051446669
ABSTRACT:
Decoder for encrypted sound signals which are encrypted by modulating the sound signals on an alternating carrier signal having a frequency which is generally unknown to receiving parties. A modulator receives the encrypted sound signal as well as a second reference electrical signal. The reference signal is provided by an oscillator controlled through a phase locked loop. The phase locked loop includes a phase comparator connected through an exclusive OR logic gate and a sequential circuit to supply a control signal for the oscillator. The sequential circuit provides for a control signal polarity depending on the relative phase between the oscillator signal and input alternating carrier frequency signal. A signal divider is provided on each input of the comparator to require only comparison between phases of signals with frequencies lower than the carrier frequency signal and oscillator frequency signal. The circuit will provide the demodulation of the alternating carrier signal whose frequency has been maintained secret and is not known by unauthorized parties wishing to decode the signal.
REFERENCES:
patent: 4148063 (1979-04-01), Chomet
patent: 4166984 (1979-09-01), Jenkins
patent: 4659875 (1987-04-01), Taurin et al.
Patent Abstracts of Japan, vol. 9, No. 159, Jul. 4, 1985 (E-326) and JP-A-60 37824.
Buczinski Stephen C.
SGS-Thomson Microelectronics S.A.
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