Patent GB-546202-A (GB)
Title: Subaqueous sound transmission system
IPC: H04B11/00
Filed: 1939-12-06
Abstract: 546,202. Sounds locating &c. ROST, H. F., and CLAESSON, P. H. E. Dec. 6, 1939. [Class 118 (ii)] [Also in Group XXXIX] In a system for observing the direction and distance of an object in a liquid medium, supersonic pressure-waves of cyclically varying frequency are transmitted by a rotary transmitter and an adjacent rotary receiver responds in accordance with the beat frequency due to the direct and reflected waves, the output of the receiver being used to determine the extent of deflection of a cathode beam, the direction of deflection being determined by synchronous control of the deflection system of the cathode ray tube with the rotary movement of the receiver. When the object has been located, telephonic communication may be effected by frequency or amplitude modulation of the pressure waves. In the arrangement shown in Fig. 2, the transmitter 7 is mounted on a rotary shaft 9 which also controls a variable condenser or potentiometer for varying the frequency of a valve oscillator 53 the output of which is amplified at 54 and used to excite the transmitter. The receiver 8 is mounted on rotary shaft 10 and its beat output detected at 58, amplified at 59 and after rectification at 60 is applied to the trap plate 69 of cathode ray tube to direct the beam along the tube. The output of amplifier 59 is applied to a device 61 providing an output proportional to frequency which after rectification at 62 is applied to potentiometers 64, 65. The potentiometers are driven from the receiver shaft 10 so that the potentials applied and the deflection system of the tube cause the beam to vary in angular position synchronously with the receiver, the extent of the deflection being dependent on the intensity of the output from 61. Fig. 1 (not shown), in which the indicator is diagrammatically represented by measuring instruments, comprises detailed arrangements for controlling the rotation of shafts 9, 10 and for varying the frequency of the oscillator. The oscillator comprises a back-coupled valve in which the coupling comprises windings on iron cores the permeability of which is varied cyclically by the potentiometer 56 on the transmitter shaft 10 to vary the frequency. Alternatively condenser 55 on shafts 10 may be used to vary the tuning of the circuits. The shafts 9, 10 are normally geared so that the receiver shaft performs a number of revolutions for each rotation of the transmitter shaft, but when there is an output in the receiver due to the reception of beats, the driving motor is stopped by a relay and the gears are changed so that the shafts may be rotated synchronously with the transmitter and receiver pointing in the same direction. Thereafter the shafts are rotated under manual control of the motor until maximum output is obtained. Several objects may be detected one after the other by this method. Fig. 3 shows curves 74 of the transmitter frequency which varies from #f1 (say 6,500 ~) to -#f1 (say 55,000) and curves 76 showing reflected waves, and it will be observed that the change from 55,000 to 65,000 occurs rapidly. This results in a reflected wave arriving between time t1 and t2 having an incorrect transmitted wave to beat with. This is obviated by the use of two oscillators 81, 82. Fig. 4, providing frequencies down to 50,000. To receive reflected waves from long distances up to 50,000 metres, the cycle of frequency change may extend over 9 revolutions of the transmitter shaft. The connections of the oscillators are controlled by cams 85, 86. As shown, oscillator 81 is connected to the transmitter 77 or 78 and receiver 95, each transmitter being arranged only for forward scanning through 180 degrees under control of contact 79. At time t1, cam 85 operates relay 91 to change the transmission from 81 (55,000~) to 82 (65,000 ~ ) and to connect 82 to the receiver 95 to which 81 remains connected to provide frequencies below 55,000 with which reflected waves may beat. After time t2, cam 86 operaates relay 92 to disconnect oscillator 81 from the receiver. Networks 93, 94 are connected to the oscillators when disconnected from the transmitter. By using alternative shafts carrying frequency changing condensers or potentiometers and running at different speeds the apparatus may be made suitable for different ranges, e.g. in depth sounding. An arrangement described with reference to Fig. 11 (not shown) enables the control and indicating arrangements to be located at a point remote from the pressure wave transmitter and receiver. Synchronous step-by-step motors are provided at the control point and at the transmitting receiving position. Separate motors drive the transmitter and receiver different speeds and separate motors at the control point drive the cathode tube control potentiometers and the potentiometer or condenser of the variable oscillator. Supersonic transmitters and receivers, construction of. The transmitter 1 and receiver 2, Fig. 2, preferably of magmeto-strictive type, are mounted in streamlined shells 7, 8 carried by the rotating shafts 9, 10, and provided with "diaphragms" and parabolic reflectors 3, 4 which may be oil filled. The "diaphragms" may be plane or in the form of lenses 5<SP>1</SP>, 6<SP>1</SP>, constructed of synthetic resin, e.g. polystyrol, or a polymerized acrylic acid ester, and their diameter large compared with the wave length. The thickness of a diaphragm may be a multiple of a half wavelength. In the modification shown in Fig. 6, the instrument comprises a threelimbed magneto-scrictive core 115 one limb being associated with a parabolic reflector mounted within a shell comprising two parabolic reflecting portions 120, 121 associated with the other two limbs. The instruments may be carried by a member arranged at the bow of a ship to be lowered into the water by suitable gearing.