Patent GB-326877-A (GB)
Title: Radio telephone and telegraph system
IPC: H04B1/46
Filed: 1928-12-22
Abstract: 326,877. Standard Telephones & Cables. Ltd., (Western Electric Co., Inc.). Dec. 22, 1928. Supervising interstation signalling; duplex signalling.- In a combined land-wire and iong-distance radio-telephony system, provision is made for allowing full duplex transmission of telegraphic messages in order to enable the necessary terminal connections to be established prior to the transmission of the longdistance wireless message. The main radio telephony system is of the known kind in which, m order to prevent " singing," voice-operated relays TVR, TVR1 and RVR, respectively, prepare the line TL feeding the transmitting aerial T to carry the outgoing signals by removing a short-circuit, and also short-circuit the incoming line RL from the receiving aerial R so long as transmission from the aerial T is in operation. In order to allow the superposition on such a system of duplex telegraphic " supervisory " messages, a different note frequency is used for the outgoing and incoming messages, and a filter circuit RSF is inserted in the incoming line to prevent interference from the local transmitter T. In order to prevent this filter RSF from distorting the normal reception of the incoming long-distance radio telephony, it is inserted in circuit only when outgoing telegraphic signals are being sent. This is effected by diverting a part of the undesired signal energy picked up from the transmitter T at the points x1, y1. The diverted energy after passing through a filter RF is applied to a rectifier valve RD. Normally relays RR1, RR2, and RR3 in the plate circuit of that valve connect the receiver R directly to the line RL. The effect of the undesired frequency currents from RF is to reduce the normal plate current and cause the relays RR1 and RR2 to bring the suppression filter RSF into circuit so as to shut out the interfering notes from the line RL. The relay RR3 simultaneously energizes a lamp 30 to indicate'that the filter RSF is in circuit. The grid leak 50 and condenser 40 of the valve RD are designed to give a sufficient time-lag to prevent false operation of the relays by atmospherics &c. The outgoing telegraphic signals, having a note frequency corresponding to the source G, are sent from a transmitter TP via the jack J1 (the normal short-circuit on the line TL being previously removed through a connection 20), and are impressed on the outgoing carrier. Telegraphic keying is such that only the marking signals are represented by no-tone intervals. Accordingly the filter RSF is maintained in the line RL so long as the telegraphic transmitter TP is in circuit, but is cut out, to restore the line for normal telephonic communication, when the jack J1 is removed. Meanwhile the relay TVR prevents any incoming message via the aerial R from reaching the jack J1. To overcome this inhibition, the incoming telegraphic signals are tapped off across the points x, y and pass through a filter RF1 for selecting the distant note frequency and detector RD1, and then actuate a polar relay RR<1>1 which in turn operates the printer recorder RP. The polar relay RR<1>1 prevents a continuous marking signal from being recorded by the printer RP. In a modified arrangement the switching in and out of circuit of the filter RSF is controlled by a series of polarized relays, and similar means are employed to prevent the receiver RP from printing a continuous signal before the distant telegraphic key is operated.