GB980141A - Improvements in or relating to secrecy systems - Google Patents

Abstract

980,141. Secret transmissions. TELEPHONE MANUFACTURING CO. Ltd. May 23, 1963 [June 18, 1962; July 4, 1962], Nos. 23432/62 and 25622/62. Heading H4R. In a speech secrecy transmission system the speech is transmitted alternately clear and inverted the switching between the two conditions being controlled by beating together the outputs of two oscillators which are provided at one station and the outputs of which are fed over the line to the other station, the switching occurring about 10 times per second. The drawing of the first Provisional Specification shows a system in which speech is passed either direct to line or through an inverting modulator MO to the line depending on the condition of switches S1 and S2, the operation of the switch being controlled from two oscillators 01 and 02, at 2,500 and 2,540 c.p.s. respectively, the outputs of which are beaten together to extract the 40 c.p.s. difference signal which is passed through a divider D1 to produce a 10 c.p.s. signal which is used to operate the switches S1 and S2. The outputs of oscillators 01 and 02 are also applied to the line so that they may be utilized at the receiver, by modulating one signal with the other, to control the switching of the receiving apparatus. In an alternative form, the second Provisional drawing (not shown), the inverter unit is switched at each station from the transmit line into the receive line so that it is constantly in use. The Specification also describes a system in which the switching is controlled by dividers fed from a single oscillator provided at one station and feeding the other station over the line.