GB1382558A - Privacy transmission system - Google Patents

Abstract

1382558 Secret transmission systems MULLARD Ltd 10 April 1973 17045/73 Heading H4R In a secret transmission system, successive signal elements are stored, transmitted at a rate which varies over the period of each element and in a programmed, rearranged order, and the original order reconstituted after transmission. Signals at 17 are pulse-code modulated 18 successive elements fed to shift-register 5-7 (or core stores), via electronic switches 8-10 programmed by a multiplexes, and recirculated, all under clock pulse control CK1. Switches 11-13 are opened in scrambled sequence but in sync. with switches 8-10 to read-out at a variable rate CK2 switched at 14-16. The received signals are similarly read into registers 25-27 at rate CK2, rearranged and read-out at. rate CK1 and demodulated. The rate CK2 may vary pseudo-randomly in programmed manner in successive time periods. A random generator (Fig. 2, not shown), includes a register (41) whose last three stages are fed via resistors (R, 2R, 3R), to an adder feeding 1.p.f. (46) and v.c.o. (47). The generator cycle may be shorter than each element period so that successive elements have a different time axis, or the cycle may be equal to each period with an artificially generated start-point for increased security.