GB578322A - Improvements in or relating to electrical signalling systems - Google Patents

Abstract

578,322. Electric selective signalling. WRIGHT, G. M., and WRIGHT, C. S. March 28, 1944, No. 5739. [Class 40 (i)] An electrical signalling system comprises a signal generator controlled through a commutator arm which sweeps continuously over a series of contacts each connected to a separate key of a typewriter keyboard or like device so as to effect transmission of a repetitive signal when a key is actuated, and one or more receiving stations each provided with a cathode ray tube indicator having a circular scan synchronised with the movement of the commutator arm and marked to correspond with the series of contacts and associated keys whereby the position of the scanning spot on the cathode ray tube registers an indication of each transmitted signal. At the transmitter, Fig. 1, an arm 1 is driven at about 10 revs. per sec. by a constant speed motor over a circle of contacts corresponding to letters or other signals to be transmitted. Each contact is connected to the corresponding key of a typewriter so that on depression of a key, a potential is applied through connecting bar 2 and arm 1 to the grid of a keying valve 3 to transmit a signal each time arm 1 passes over the corresponding contact. The signals are received at 4, Fig. 2, and after detection are passed to a pair of deflecting coils 7, 8 which are rotated in synchronism with the transmitting arm 1 about the axis of a cathode ray tube 5. The screen of tube 5 is marked corresponding to the transmitter contacts and the luminous spot rests on the corresponding signal marking as long as the key of the transmitter keyboard is depressed. Instead of using rotating deflection coils 7, 8, the receiver cathode ray tube may have a circular scan provided by a synchronised time base, and the received signals are then fed to a modulating grid of the tube. Secrecy may be provided by transposition of signal elements at the transmitter, a special mask being used at the receiver for decoding.