Patent GB-442342-A (GB)
Title: Improvements in or relating to electric signalling systems
IPC: H04W88/02
Filed: 1935-05-16
Abstract: 442,342. Wireless signalling; valve relaying-circuits. STANDARD TELEPHONES & CABLES, Ltd., 63, Aldwych, London.-(Assignees of Wadsworth, P. W. ; 176, Austin Street, Lindenhurst, and Taylor, C. C. ; 3917, 215th Place, Bayside, both in New York, U.S.A.) May 16, 1935, No. 14407. Convention date, May 26, 1934. [Class 40 (v)] In an electric signalling system, particularly intended for note-frequency calling in radio telephony, the detected received signal is passed through a limiting-amplifier to two circuits, one tuned to the calling note and the other to a different note, the circuits being connected respectively to rectifiers feeding opposed windings on a relay, which is thus operated by the calling note but not by speech or noise containing both notes. The limiting-amplifier gives a high gain for the intermittent calling-note, but a much lower gain for sustained speech or noise. A sequence of pulses of the calling note controls a selector switch, providing the pulses are of the requisite frequency. As shown in the Figure, a carrier wave is received on the aerial 10 and the audio-output from the receiver 11 is fed to the input transformer 27 of the valve 17, which is resistance-coupled to a further amplifier 18. The output circuit includes two circuits 28, 29 tuned respectively to the calling-note and to another audible tone. Each of these is connected to a bridge or other rectifier 32, 33 feeding respectively an operative winding 34 and a reversed winding 36 of a relay 35. Reception of the pure calling- note operates the relay, whilst speech or noise is ineffective. Speech or noise currents are reduced by the provision of a resistanceshunted condenser 26 in the grid circuit of the valve 17, which biases the grid negatively, and so reduces the output when sustained strong signals are received, but permits high amplification of the short pulses of calling- current. On receipt of a calling pulse, relay 35 closes and energizes a relay 38 which operates to reverse the connections of a battery 22 to the selector relay 39. Relay 38 also closes a hold-on circuit through relay 37, so that when the calling-pulse ceases relay 38 remains energized. The next calling-pulse however short-circuits the relay 38 through contacts 47, 54, lower contact of relay 35, and contact 53, with the result that the connections of the battery 22 to the selector 39 are reversed. The selector is of the kind described in Specification 117,170, [Class 40 (v)], in which an arm is progressively advanced by pulses of current alternating in sign. The circuit of relay 39 includes a condenser 46 and a resistance 45 which are designed to permit operation of the selector only by current pulses of the correct frequency. On receipt of the correct sequence of pulses the selector arm closes the circuit of a bell 49 ; and when the telephone 12 is removed from its hook 50, a relay 51 operates to disconnect the selector relay 39 from the reversing-switch, and to discharge the condenser 46 through that relay. This advances the selector arm one step, acting as a release signal and returning it to normal. Alternatively the hook switch 50 may be across the contacts of the relay 35.