Narrowband analog message privacy system

Abstract

A privacy system in which an analog information-bearing signal is linearly combined with a noiselike coding waveform to produce a composite waveform of unrecognizable, scrambled signal for transmission to an authorized system user at a remote receiving terminal. The noiselike waveform is developed from the original information signal, and the original signal reproduced from the composite waveform, to eliminate any need for synchronization between transmitter and receiver. At the transmitting terminal, the composite waveform is infinitely clipped and amplified to produce a digital format which is serially fed through a shift register in accordance with shift pulses derived from the clipped signal transitions. Various outputs of the several stages of the shift register are selectively applied, via a switching matrix, to an encoder which generates the noiselike or pseudo-random signal therefrom. After passage through a narrowband filter, the coding waveform is added in a linear mixer to the original information signal for transmission. An inverse operation is performed at the receiving terminal.

Dependencies are inferred from the claim text.