Patent GB-602789-A (GB)
Title: Improvements in or relating to voice or like signal operated switching circuit arrangements
IPC: H04B1/54
Filed: 1945-12-18
Abstract: 602,789. Valve relay circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., COOPER, C. P., and NOBLE, G. E. WILLIAMSON-. Dec. 18, 1945, No. 34333. [Class 40 (vi)] In a voice or like signal-operated switching circuit, the voice signals are applied to a phasesplitting circuit, the outputs of which are applied to a pulse generating circuit which is connected to a controlling valve, the anode current of which controls a relay, so that each half-wave of input signal above a certain minimum produces a predetermined change in the controlling valve current to control the relay. The Figure shows a circuit arrangement suitable for use in a duplex radio telephone system, in which an audio-frequency input above a certain minimum level effects the switching on of a transmitter and the disconnection of a receiver within two milliseconds, and the reduction of the input below the minimum level restores the original connections after an adjustable time delay. The audio input is applied through transformer T1 and potentiometer P1 to valve V1. Valves V3 and V4 are reciprocally coupled and resemble a cathode-coupled multivibrator circuit with one stable position. Under no input conditions, valve 4 passes grid current and a large anode current, and valve V3 passes a small anode current. The output from the cathode of valve V1 is applied to the suppressor grid of valve V3. When this is driven positive, the current through valve V3 increases, which tends to reduce the potential of the grid of valve V4, but the effect on the grid potential and anode current of valve V4 is not appreciable until grid current ceases. When this occurs, multivibrator action takes place, and the anode current of valve V4 is rapidly cut off, and the anode current of valve V3 is increased at the expense of its screen current. When the potential of the suppressor grid of valve V3 falls to a certain level, the process is reversed, valves V3 and V4 reverting to their normal state. Thus, a sine wave input to the suppressor grid of valve V3 produces a train of rectangular pulses of constant amplitude at the cathode of valve V4, so long as the input is sufficient to drive valve V4 from grid current conditions. Valves V2 and V4 constitute a similar circuit to that of valves V3 and V4, but the input to valve V2 from valve V1 I is arranged 'to be in opposite phase to that of valve V3, so that a positive or negative input half-cycle to valve V1 results in the production of the rectangular pulse output. The pulse output from the cathode of valve V4 is applied to the cathode of pentode valve V5, which acts as a diode. The grid and anode of valve V5 are connected to the grid of valve V6 in association with a resistance-condenser network C6, R16, R17, R18. Valve V6, the anode current of which operates the switching relay 51, is normally conducting. When a negative pulse is applied to valve V5, condenser C6 rapidly discharges, thereby reducing the anode current of valve V6 and releasing relay S1. Condenser C7 assists this reduction in anode current while not appreciably affecting the operate time. At the end of the pulse, valve V5 ceases to conduct, and condenser C6 recharges through resistances R16 and R17 to the voltage developed across resistance R18. After a certain interval, controlled by the adjustment of resistance R17, the anode current of valve V6 is sufficient to operate the relay S1. Owing to the cathode follower action of this valve, the voltage across resistances R16 and R17 is maintained substantially constant, so that condenser C6 may be of relatively small value to provide any given operate time. The operate delay period is longer than the normal period between pulses, so that relay S1 is not operated during the normal pulse train resulting from an input to valve VI. Some time after the anode current of valve V6 is sufficient to operate the relay, valve V5 starts to conduct, preventing any further rise in the potential of the grid of valve V6. The contacts M and S of relay S1 control the operation of the radio transmitter and receiver respectively, by connecting some appropriate point to earth.