Patent GB-398509-A (GB)
Title: Improvements in or relating to two-way signalling systems and echo suppressing arrangements for use therein
IPC: H04B3/20
Filed: 1932-03-11
Abstract: 398,509. Two - way transmission. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London, KEMP, C. G. and KEMP, L. G., 92, Cedar Road, Southampton. March 11, 1932, No. 7370. [Class 40 (iv).] In a repeater comprising a normally operative receiving amplifier and a normally inoperative transmitting amplifier, the receiving echo suppressor comprises a diode valve which applies a potential to a rectifying valve in the transmitting echo suppressor which in the absence of speech is just sufficient to prevent operation of the transmitting echo suppressor by received noise currents passing round the hybrid coil through imperfect balance but in the case of speech definitely disables the transmitting echo suppressor so that it cannot be actuated by the local subscriber. First system, Fig. 1 (Prov.). In the absence of speech, the transmitting amplifier 8 is paralyzed by the battery 27. Noise incoming over circuit 33 passes via amplifiers 15<1>, 46 to the quick-acting diode rectifier 55, which over lead 58 applies a voltage to the rectifier 20 in the transmitting echo suppressor which owing to the effect of the networks 15<1>, 16<1> which discriminate against noise and to the form of the diode characteristic in conjunction with the setting of the potentiometer 43<1> is just sufficient to prevent its operation by the noise currents passing through the hybrid coil through imperfect balance. Received speech on the other hand produces a much larger voltage on lead 58 and prevents the actuation of the transmitting echo-suppressor even if the local subscriber on line 1 talks. Received speech also, with the aid of rectifier 47, which biasses a triode valve 48, controls a relay 49 to short circuit the transmitting path. Speech from the local subscriber on line 1 passes via amplifiers 12, 13, 14 with means for discriminating against noise to the rectifier 20 which by reducing the current through valve 22 and therefore the voltage drop in resistance 24 increases the current through valve 23 and the voltage drop in resistance 26 and so brings the transmitting amplifiers 8 into operative condition. At the same time valve 29 causes relay 30 to short circuit the receiving path. Second system, Fig. 1 (Comp.). Diode rectifier 151 in the receiving echo suppressor controls the rectifier 20 in the transmitting echo-suppressor as in the first system. Rectifier 20 however disables the receiving amplifier 38 by controlling the application of a paralyzing bias to the lead 40. On the arrival of signals from the local line 1, the current through valve 22 and consequently the voltage drop in resistances 25, 26 are reduced to bring the transmitting amplifier into operative condition. At the same time the current through valve 29 is increased and that through valve 30 is reduced, the resulting change in the voltage drop in resistances 32, 33 disabling the receiving amplifier 38. Further systems. In another arrangement, Fig. 2 (not shown), which is otherwise the same as the second system, the rectifier 20 is replaced by a pair of valves in push-pull, the valve 22 is omitted and the control leads 9, 40 for the respective amplifiers are transposed. In a further modification, Fig. 3, the valve 20 has its plate and grid connected together and controls the valve 22 through the resistance 152, 153 in the circuit of the diode rectifier 151 in the receiving echo-suppressor.