335,935
PATENT SPECIFICATION
Application Date: Jul. 3, 1929. No. 20,386/29
Complete Accepted: Oct. 10, 1930.
Simultaneous telegraphy and telephony., Standard Telephones & Cables, Ltd., and Blumlein, A. D.,
Columbia House, Aldwych, London.
July 3, 1929, No. 20386 [Class 40 (iv).]
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PROVISIONAL SPECIFICATION

Complete Signalling System

In a composite system in which the circuit is alternatively arranged for speech transmission in one or another direction only, the telegraph facilities operate only in the same direction as the telephone transmission, i.e. East-West telegraphy proceeds only during East-West periods of conversation. All frequencies below the speech band may be used for telegraph transmission and arrangements can be made to re-transmit the last part of the message cut off in transmission when the transmission conditions are again set up. For those telegraph systems in which the receiver must be running a preliminary series of impulses may be sent to start the receiver. The figure gives a schematic representation of the apparatus at one end of a cable, that at the other end being similar. The apparatus is set for receiving signals, telephone signals passing through filter VF and amplifier RA and telegraph signals through filter TF and TR. Detector RD enables PR to pull up when signals are being received to short MSR. When speech currents are to be transmitted they pass through amplifier TA to delay network DN and also to detector TD allowing MSR to pull up connecting the cable to DN and also connecting the telegraph transmitter TT to cable. The devices TS and RS stop and step back the telegraph transmitter and receiver respectively when the relay MSR pulls up and releases.