Synchronization system for voice privacy unit

Claim 1

In combination, an apparatus for synchronizing the initiation of enciphering/deciphering of communication signals between two or more communication stations, comprising: a transmitter portion, which includes: means for generating a first signal of known frequency; means for generating a Barker word digital signal; means for modulating said first signal with said Barker word digital signal, thereby producing a first modulated signal; means operative at the conclusion of said Barker word digital signal for initiating the enciphering of communication signals generated at one communication station to produce enciphered communication signals; means for combining said first signal with said enciphered communication signals for as long as the communication signals are enciphered, thereby providing a continuous indication of enciphered communication, said first signal combined with said enciphered communication signals defining a first combined signal; means for transmitting said first modulated signal and said first combined signal in sequence, such that said first modulated signal is transmitted to another communication station substantially immediately prior to transmission of said combined signal to said another communication station; a receiver portion, which includes: means for receiving said first modulated signal and said combined signal from said one communication station; means for detecting the first signal, said first signal providing a continuous indication of enciphered communication between communication stations; means for recovering said Barker word digital signal from said first modulated signal; means for correlating bit-by-bit said recovered Barker word digital signal with a replica of said Barker word digital signal; means responsive to said correlator means for generating a summation signal which is proportional in magnitude to the number of correct correlations between said detected Barker word digital signal and said replica; means for generating a reference signal having a first predetermined magnitude; means for comparing said reference signal with said summation signal; and, means for initiating deciphering of the enciphered communication signals at the conclusion of correlation if the magnitude of said summation signal is greater than said first predetermined magnitude.