GB631601A - Improvements in or relating to subaqueous signalling systems - Google Patents

Abstract

631,601. Subaqueous signalling systems. GENERAL ELECTRIC CO., Ltd., FARREN, L. I., and GRIFFITH, G. W. S. Dec. 20, 1946, No. 37503. [Class 118 (ii)] A subaqueous signalling system comprises means for transmitting pressure wave signals at one or more frequencies, means for receiving the signals adapted to operate one or more relays on receipt of said signals and adapted to discriminate against extraneous noise of the type which contains approximately equal energy throughout the frequency band to which said receiving means is responsive. It is stated that random noise such as is produced by a ship's propeller has a continuous frequency spectrum. The transducer 1 at the receiving end may comprise resonant quartz-steel elements energized through a rubber sheet and feeding an amplifier 2 and limiter 3. The output from the limiter, which is substantially constant for all wanted signals, is fed to a discriminator circuit comprising two resonant circuits 5, 7, and 6, 8, in parallel, tuned to different frequencies f, and f 2 . Rectifier networks comprising elements 9, 10, 11, and 12, 13, 14 are connected respectively across units 5 and 8 and the voltages developed across the resistors and capacitors in response to applied signals are applied to opposite ends of resistor 15, and also to the control grids of valves 20 and 21, whose cathodes are connected together and to the centre tap of resistor 15. In the absence of signals, relays 24 and 25 in the anode circuits of the two valves are unoperated as the permanent bias applied to the valve grids cut off each valve. For noise having equal energy levels at the frequencies of the two tuned circuits f 1 and f 2 , equal voltages are generated across the rectifier circuits and there is no voltage drop across resistor 15. Thus the circuit is not operated by such noise but may however be operated by signals of frequency f 1 or f 2 which cause positive bias to be applied to one or the other of the valves which then passes current causing the corresponding relay to operate. In " mark " and " space " signalling, signals may be sent at frequencies f 1 and f 2 , or the system may be used to control lights fitted to moored floats or buoys. To indicate that the light is actually on, a small transmitter utilizing the receiver transducer may be switched on by relay means in the lamp circuit.