Abstract: A privacy communication system digitizes a voice signal and divides the signal into different frequency bands or time segments and shifts the bands or segments in frequency and/or time under control of a continually changing pseudo-random key word to develop an encrypted transmitted signal having the same time/bandwidth product as the voice signal.

Abstract: Method and apparatus for secure transmission of analog signals, particularly facsimile signals. The analog signal is first converted to a frequency-modulated signal, if not already one, and is then converted to a sequence of digital words representing the instantaneous frequency thereof, by sampling at a fixed rate. Next the digital words representing the sample values are written in sequence into a buffer memory, at the constant sampling rate. The digital words are then read out of the memory at a different, pseudo-randomly variable rate and converted back to an analog FM signal for transmission. The transmitted signal is, thus, a time-delay-modulated version of the original FM signal. Optionally, the digital word values may be transformed before being converted back to analog frequency form, so that the modulation content of the transmitted signal is scrambled, as well. Further security may be obtained by reading out from the memory in a pattern which differs from the write-in address pattern.

Abstract: A signal scrambling system of the type in which the frequencies of the information signal band are inverted by heterodyning the information signal with a varying beat frequency. In accordance with the invention the beat frequency varies in a sequence of small increments which, in their totality, provide large overall frequency excursions and which, individually, are sufficiently small to avoid the generation of unduly strong spurious signals within the information signal band.