GB1397412A - Communication systems and apparatus for use in such systems - Google Patents

Abstract

1397412 Secret transmission; television GENERAL ELECTRIC CO Ltd 26 May 1972 [28 May 1971] 18053/71 Headings H4R and H4F Successive portions of an input signal are jumbled by giving each portion a time delay corresponding to a number of portions where the number for each portion varies in a pseudorandom sequence and the signal is then transmitted to provide secret communication to a receiving terminal where the portions are given a complementary time delay so that they can be re-assembled into their original order. In the system shown, the time delay of stores 10-16, 46-60 determines the unit length of signal that can be considered as a portion. The filling and emptying of the stores occurs in the same pseudo-random order in both the transmitter, Fig. 1, and receiver, Fig. 2, under the control of the switches shown. In the transmitter, Fig. 1, the pairs of switches associated with each store 18, 30 operate together so that the incoming signal is divided into four portions which are stored in the respective stores where they recirculate until the output switch is next closed in the pseudo-random order to transmit the portions in a jumbled order. The corresponding receiver has eight stores which are operated in groups of four with the group 46-52 storing the first received four portions of the transmitted signal and the second group of four portions received are stored at 54-60. Switches 62-68 and 70-76 operate on the same pseudorandom sequence as the transmitter switches to provide this storage. The output switches are controlled by a pseudo-random sequence which is the same as the transmitter one but delayed by eight time delays and commences with switch group 88-94 followed by switches 80-86. This operation of the receiver switches provides an output signal on line 78 which is substantially identical with the input signal. In a modification the transmitter has six stores arranged in series with the interconnecting junctions connected to an output line through individual switches which are operated in a pseudo-random manner, Fig. 3 (not shown). The corresponding receiver can have its series connected stores junctions connected to the input line through switches, Fig. 3 (not shown), or can have changeover switches used to normally make the series connection but when operated to make connection to the input line, Fig. 4 (not shown). A video system where both the camera and receiver have their vertical scan provided on a pseudo-random basis is disclosed, Figs. 7 and 8 (not shown).