Patent GB-578708-A (GB)
Title: Improvements in electrical communication apparatus
IPC: H04B1/48
Filed: 1944-04-05
Abstract: 578,708. Wireless receiving systems. GENERAL ELECTRIC CO., Ltd., and CHUBB, A. A. April 5, 1944, No. 6351. [Class 40 (v)] In a communication system a remote radio transmitter and receiver are alternatively brought into operation from a control station by means of D.C. control currents passed over one or both of the wires of a balanced transmission line which serves to carry the two-way audio signal currents. The control paths may be completed via earth connections, and switching means are provided for operating at the remote station in case of failure of the line. Closing of the mains-supply switch 13 at the control station energizes the audio amplifier LSA, the microphone amplifier MA and the power-supply S1 whose D.C. output energizes the relay A, and via the line RB the relay F at the remote station. The control current returns via earth connections, and is blocked from the second line RA by means of condensers 20. Energizing the relay A causes contacts A1 to close, which bring into circuit the indicating lamp LO connected to the transformer winding T4. Energizing the relay F causes the switch F1 to close, thus energizing from the mains supply the leads 14 to the heater supply circuits of both the transmitter and the receiver and also to the receiver H.T. supply circuit (not shown). The power-supply S2 is also energized, thus energizing the relay R and causing the contact R1 to connect the aerial to the receiver. Audio signals from the receiver appear on the line 15 and pass via the resistance R2, the transformer T2, the line RA, RB, the transformer T1 and relay contacts N4, N5 to the input of the amplifier LSA which operates the loudspeaker LS. To transmit, the switch 16 is closed, energizing the relay N from the powersupply S1. The relay contacts N1 then shortcircuit the loudspeaker LS, the contacts N2 energize the relay B and the line RA, the contacts N3 open to remove the H.T. supply to the amplifier LSA, the contacts N4, 5 reverse, connecting the microphone amplifier MA to the transformer T1, and the contacts N6 energize the relay H from the powersupply of the amplifier LSA, thus closing the contacts H1 and putting an additional shortcircuit across the loudspeaker LS. Energizing the relay B causes contacts B1 to close, thus illuminating the lamp LT, while energizing the line RA causes the relay M at the remote station to be energized. The contacts M1 open, removing the H.T. supply to the receiver on the line 17, and the contacts M2 open, thus removing the energizing current 'from the relay R and causing the contact R1 to connect the aerial to the transmitter. The contacts M3 in the H.T. supply line 18 of the transmitter close, and the contacts M4 by closing cause the slow-acting relay P to be energized from the power-supply S2, the contacts P1 in the line 17 thereby being opened, and the contacts P2 closed, thus completing the H.T. supply through the line 18 to the transmitter. Audio signals from the microphone MA now pass via the reversed switch contacts N4, 5, the transformer T1, the lines RA, RB, and the transformer T2 to the input leads 19 .of the transmitter modulator stage. To recommence reception, the switch 16 is opened, removing the energizing current of the relay N. The contacts N1, 2, 3, 4, 5, 6, B1, M1, 2, 3, 4 and R1 again reverse, the slow-acting relay P finally causing contacts P1 to close and the receiver to be re-energized, while the slow-acting relay H releases contacts H1 at the same time and renders the loudspeaker operative. For operation at the remote station, the line is disconnected from the terminals 11 and replaced by a microphone, and the switches LA, LB closed. For reception, the switch 12 is thrown into the upper position, whereby the short-circuit on the local loudspeaker is removed, while for transmission the switch 12 is thrown to the lower position T, thus energizing the appropriate relays M, R and P.