GB287673A - Improved method of and apparatus for securing secrecy in telephonic communications - Google Patents

Abstract

287,673. Carr, W. B. H. Jan. 28, 1927. Systems with telephonic receiving arrangements secret signalling by recording and re-transmitting signals with variation of order or speed.-A signalling system comprises means for breaking up a message into sections and means for reversing the order of the signal modulations or elements in each section during a recording or a collecting process. A microphone is connected to an electromagnet C which records the signals on a tape B which is wound from a drum H<1> to a second drum H<2>. Collecting electromagnets D - - D<3> are rotated at twice the speed of the tape so that the sections into which the message is broken by the collecting- magnets are transmitted in reverse direction. At the receiving end the recording electromagnet is connected to the aerial or transmission line, and, when the collecting electromagnets are synchronized, the signal is restored to its proper form. Alternatively a plurality of revolving recording electromagnets is employed and a single fixed collecting electromagnet. According to a modification (Figs. 2 - - 5, not shown) an endless tape passes round two pulleys, and, for example, in the sending apparatus two collecting electromagnets move at three times the speed of the tape and at the receiving end four collecting electromagnets move at one and a half times the speed of the tape. Alternatively a fixed record mav be used with rotating, reciprocating or helically moving collecting and recording electromagnets. Synchronizing signals are sent during the intervals between the transmission of successive portions of the record. For duplex working a sending and receiving apparatus is used at each station, or one set of apparatus with electric and mechanical arrangements for conversion is employed. According to another modification (Figs. 6 - - 9, not shown), tapes are embedded longitudinally in pistons working in open-ended cylinders and connected in the manner of a multicylinder engine to a common crank shaft. An electromagnet mounted in the wall of each cylinder operates alternately as a recording and collecting electromagnet, the connections being effected by distributors mounted on, or driven by the crank shaft. A six-cylinder apparatus is used when frequent synchronizing signals are not required, and eight cylinders when such signals are required. A mechanical record, such as a gramophone, or an electro-optical record may be employed. To obtain additional secrecy the speed of transmission of the modulations or the lengths of the successive sections may be varied.