GB799703A - Improvements in or relating to secrecy systems - Google Patents

Abstract

799,703. Secret transmission. INTERNATIONAL TELEMETER CORPORATION. Jan. 12, 1956 [April 18, 1955], No. 1091/56. Class 40 (4). [Also in Group XL (c)] In a system in which two transmission channels are available for the transmission of two intelligence signals, one of which is intermittent, the transmission circuit provides for the following sequence of operations : (1) transmitting the steady intelligence signal over one channel and the intermittent signal over the other; (2) gradually decreasing the level of the intermittent signal on its channel and replacing it by the other intelligence signal at the same level as on the one channel; and (3) gradually decreasing the steady intelligence signal on one or the, other channels and reintroducing the intermittent signal on the freed channel, which is randomly controlled by mechanical or electronic means. A television audio programme signal at 70 in a transmitter, Fig. 5, and an announcement signal from a pick-up 50 are connected to a system of potentiometer resistors 58, 60, 62, 66 as shown so that the downward movement of slider arm 64 decreases the announcement signal and increases the programme signal on the channel B connected thereto and upward movement of arm 68 has a corresponding effect on channel A. The channels A and B are connected to a frequency modulation transmitter, the former being modulated in unit 14 (Fig. 2, not shown) on a harmonic of the line rate generator 86. The sliders 64, 68 are controlled from a unit 92 which may comprise a variable speed motor 116, Fig. 6, driving a number of cam discs 110, 112, 114 which control slider drive motors 100, 102 and a switching signal generator 94, or an electronic counter randomly excited. In the coil-freed receiver, Fig. 7, the announcement signal which precedes a programme which is to be charged for, indicates the charge, and the insertion of the necessary coins in box 135 connects the switching signals from the transmitter to channel switch 136 so that the television audio circuit 138 follows the programme as it is switched from channel A to channel B and back. The switching signals may be sent in code and may be hidden in continuously transmitted false switching signals. Specification 799,704, [Group XL (c)], is referred to.