GB206813A - An improved method of and means for signalling by oscillations of audible frequency - Google Patents

Abstract

206,813. Submarine Signal Corporation, (Assignees of Dorsey, H. G.). Nov. 11, 1922, [Convention date]. Thermionic amplifiers.-Sound waves of definite audible frequency, transmitted through water, are received by a detector which converts them into electrical oscillations, the desired frequencies being amplified and undesired frequencies eliminated by means of tuned circuits and reactively-coupled thermionic valves. The valve circuits may be arranged to operate according to the method known in wireless reception as superregeneration,. described in Specification 182,135. The currents arising from reception of sound waves by the detector 10 are transferred to the circuits of a valve B by a coil 12 of few turns placed around or adjacent to the transformer T<1> by which the plate and grid circuits of the valve B are coupled. The circuit of the grid coil 14 is tuned to the signal frequency by a number of fixed condensers 32 - - 34 selected by a switch 35, and by a smaller variable condenser 31. The plate coil 13 is connected between the valve plate and the high-tension battery 20. The second valve C also has a transformer T<2> coupling its grid and plate circuits. The grid coil 36 is tuned to a low frequency, say 10 cycles per second, by a variable condenser 37, and is connected between the grids of the two valves. The plate coil 54 is connected in series with a telephone 55 and the battery 20, a by-pass condenser 56 being provided across the phones and battery. Between the grid and plate of the valve C, a variable inductance 52 and variable condenser 53 are connected in series, this branch being tuned to the signal frequency. Filament current for the valves is adjusted individually by rheostats 19, 51 and jointly by a master rheostat 21. By means of the rheostats, the tube B is adjusted to the verge of self-oscillation at the signal frequency, and the tube C adjusted to oscillate at sub-audible frequency. Incoming sgnals then cause the valve B to commence to oscillate, but continuous oscillation is prevented owing to the effect of the sub-audible currents in the circuit 36, 37 on the grid potential of the valve B. In adjusting the circuits initially, the, valve B may first be made to oscillate, and the filament current of valve C gradually increased until valve B ceases oscillation. Incoming signals will then be selectively amplified, but will be varied or modulated by the sub-audible currents in valve C. If it is desirable to receive the signals without this distortion, as for instance in bell signalling, the filament currents in the valves are increased in steps, first causing valve B to oscillate and then quenching it by increasing the filament current in valve C. At the same time the condenser 53 and inductance 52 are adjusted until the incoming signals are received without distortion and extraneous noises are suppressed.