Patent GB-581175-A (GB)
Title: Improvements in or relating to apparatus for detecting and locating enemy vessels
IPC: G01S1/72
Filed: 1943-01-09
Abstract: 581,175. Photo-electric direction indicators. FERREL, C. B. Jan. 9, 1943, No. 468. Convention date, Dec. 22, 1941. [Classes 40 (iii) and 40 (v)] [Also in Group XXXVIII] .An apparatus for detecting the presence and direction of enemy vessels comprises a buoy containing a device for detecting sound waves, and also a radio transmitter for broadcasting the sound and the direction from which it emanates. The buoy A, Fig. 2, is arranged to float on or near the surface of the water and is provided with an aerial B, the lower end of which is coated with or enclosed in insulating material 2 to prevent it being short circuited by sea water. A sound-detector 6 is supported below the buoy and is secured to a shaft 3 which is rotated by an electric motor 4 within the buoy. The detector consists of a conical casing with a narrow slot 7 in its base and behind which is a cone 8. The large end of the cone is closed by a diaphragm 10, while the small end is closed by a microphone which is connected through a switch 15 and an amplifier C with the radio transmitter D. Normally, all circuits are open and the motor is at rest, but the circuits are closed when a surface ship or submarine comes within predetermined range. This is effected -by an annular diaphragm 18 which actuates a microphone 19 connected through an amplifier E to a relay 24, a band-pass filter 22 being included in the amplifier to prevent operation of the relay except by selected vibrations, such as those emitted by the propellor of a submarine. The relay 24 operates a multiple switch that connects a battery with the radio transmitter D, the motor 4, amplifiers C and F, and an electric lamp 38. The direction from which sound emanates is determined by a compass needle or magnetised bar 34 which carries a band or ring 35 of light material perforated with wide and narrow slots 36 arranged in code formation to indicate different points of the compass. The ring 35 is straddled by an arm 37 which is secured to the shaft 3 and carries the lamp 38, a lens 39, and a photo-electric cell 40. This cell is connected through slip rings 42, 48 and switches 44, 50 with the battery and with a thermionic valve 52 that forms the input section of the amplifier F and modulates the main control section which is connected to the transmitter D. A signal to identify the buoy is also broadcast, and this is effected by a code wheel 60 which is rotated by the shaft 3 and operates a switch 54 in a series of dots and dashes. Periodically the circuit of the switch is connected to the amplifier F by means of a rotating cam 70 that connects the switches 44, 50 to the circuit of the switch 54 at the same time interrupting the circuit of the photo-cell 40. In use, the approach of a vessel vibrates the diaphragm 18 and causes the various circuits to be closed and the motors 4 to be started. As the shaft 3 revolves, the photo-electric cell 40 passes around the compass card or band 35 and the directions indicated by the successive groups of slits 36 are broadcast in code. Simultaneously the sound picked up by the detector 6 is also broadcast, and this rises to a maximum as the detector faces the direction from which the sound emanates. Periodically this broadcast is replaced by the signal identifying the buoy.