GB424503A - Improvements in or relating to electric carrier signalling systems - Google Patents

Abstract

424,503. Code telegraphy. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and FARREN, L. I., c /o General Electric Co., Wembley, Middlesex. Sept. 5, 1933, No. 24619. [Classes 40 (iii) and 40 (v)] In a voice-frequency telegraphic receiver in which a relay 13 is operated by applying trains of carrier waves, constituting the signal impulses, to a valve 12 which is preferably a gas-filled triode arranged to come into and out of action for equal values of the grid voltage, as described in Specification 408,961, the grid bias of the triode 12 varies automatically with the mean amplitude of the signals so that the impulses recorded may all be of the correct length, although the impulses may have been distorted in transmission. The envelopes of the carrier impulses are square at the transmitter but are rounded in transmission so that at the receiver the carrier takes time to rise to its maximum amplitude and to fall to zero. They will usually be recorded with the correct length by the relay 13 if the voltage at which they become operative upon the grid 11 is half the maximum voltage, and the grid bias is accordingly made to consist of a variable part, produced by a rectifier 10 and coupling 4 in dependence upon the average value of the signals received through the input valve 2, together with a fixed part determined by battery 14 and potentiometer 9 through resistance 7, the adjustments being such that the operative value of the grid voltage is reached when the amplitude of the carrier has risen or fallen to half its maximum. In a modification the function of the rectifier 10 is performed by a subsidiary anode in the valve 2, Fig. 2, (not shown). Specification 365,907 is referred to.