Method and means for the prevention of listening in telephonic and telegraphic intercourse by means of electric waves and for multiplex intercourse by means of electromagnetic waves

摘要

212,261. Kramolin, L. L. de. March 3, 1923, [Convention date]. Void [Published under Sect. 91 of the Act]. Secret and selective signalling systems; multiplex systems.-The plate of an electric discharge tube is divided into segments 1 - - 4, Fig. 3, which are traversed in succession by the cathode stream, the path of the stream through the tube being controlled by an external rotating field derived from an harmonic of the signal frequency and maintained in synchrony at the transmitting and receiving stations. Each plate segment is connected to a separate receiving circuit T1 - - T4, whereby four separate signals can be received simultaneously, the interval between successive impacts of the cathode stream on any particular segment being super-audible. At the transmitting end, the discharge tube is provided with four separate grids, each fed by its own microphone under the control of the external rotary field. To ensure secrecy, disturbing noises may be imposed on the circuits not used for signalling; or the plate segments may be arranged asymmetrically. A mercury vapour lamp may be used in place of a discharge tube.