Patent GB-1046761-A (GB)
Title: Improvements in and relating to pulse-responsive apparatus
Inventor: HALLIDAY WILLIAM
IPC: G01S15/42
Filed: 1961-07-31
Abstract: 1,046,761. Echo-sounding. SMITHS INDUSTRIES Ltd. Oct. 26, 1962 [July 31, 1961], No. 27733/61. Heading H4D. In an echo-sounding system, particularly for fish detection, a display of echoes from fish and from the sea-bed is produced which, for a given and predetermined direction with respect to the sea-bed below the vessel carrying the equipment, is independent of rolling or pitching of the vessel. One embodiment utilizes a broad-beam transmitting transducer, so that the nearest point on the sea-bed is reached irrespective of the-motion of the vessel, and a plurality of receiving transducers in a linear array extending (in the case of " rolling " correction) athwartships the array being horizontal when the vessel is horizontal. (For " pitching " correction a similar array extending fore-aft is utilized.) Fig. 2 shows the equipment associated with each receiving transducer together with some equipment common to the whole array and Figs. 3a and 3b show the various waveforms a1 to g at the points indicated in Fig. 2. As shown, echoes from fish and from the sea-bed received by transducers 12 are delayed for 10 m.s. in 26 and supplied via switch 27 (in the " write " position) to a storage cathode-ray tube 17, the time base 29 of which is triggered by pulses b1 derived from the sea-bed echo. Since the " writing " scan C 1  . . . C n  of each storage tube 17 is controlled by the seabed echo received by its associated receiving transducer and since all echoes are delayed by the same amount (i.e. 10 m.sec.), echoes due to objects (e.g. fish) on or near the vertical line from the vessel to the sea-bed are stored in similar positions on the electrodes 19 of all storage tubes irrespective of whether or not the array of receiving transducers has departed from the horizontal due to rolling (or pitching) of the vessel, whereas, echoes from other directions which are received in succession by the elements of the array are stored in different positions on the storage electrodes of the different tubes. Thus, when the latter are simultaneously scanned by respective " reading " beams the former echoes reinforce each other so that when displayed they produce a stronger display than the latter echoes. For control of the " reading " scan of all of the tubes 17 the waveform b 1  derived from the first received sea-bed echo is selected by device 30 which produces a corresponding spike e 1  for triggering a mono-stable multivibrator 31 the triggered conditions (waveform f) of which is delayed by a fixed amount in 32 (sufficient to allow storage in all of the tubes 17 to be completed) to produce a 10 m.sec. pulse (waveform g) which is supplied via individual isolators 33, to initiate the reading scan of each of the tubes 19, to trip switch 27 to the "read" position (producing a " bright-up " pulse for each tube) and to initiate the scan of a display cathode-ray tube 21 the " Y " deflection of which comprises the combined outputs of the various tubes 19. The " predetermined direction " of such display is along the vertical to the sea-bed below the vessel. Other directions, however, may be employed by progressively varying the delays of the delay devices 26. Fig. 4 shows a second arrangement which may be employed alternatively, or in addition to, the embodiment of Fig. 2. In this arrangement the positively-going step of pulses b 1  . . . b n  are utilized to gate respective circuits 39 which commence charging at a constant rate as shown by waveforms j 1  . . . j n  (Fig. 3b) until the occurrence of the pulses g (all of which occur simultaneously). The circuits 39 then discharge at the same rate of change of charge and when the latter reach zero a gate 40 applies a trigger signal to an oscillator 41 which applies a pulse of ultrasonic oscillations to transducer 12 which in this embodiment acts as a receiving and transmitting transducer. Since the instant at which the discharge is initiated is the same for all the circuits 39 the transducer 12 which is the last to receive the sea-bed echo transmits pulse of ultrasonic oscillations first and vice versa so that, irrespective of the roll (or pitch) of the vessel, the " predetermined direction " is along the vertical below the latter. The latter direction may be retained for transmission whilst employing a wide angle for reception by utilizing a separate receiving transducer or a selected one or a group of the transducers 12 connected to a display device or pen-recorder or both. If desired, the sea-bed echo signals derived by an auxiliary echo-sounder operating on a different frequency from that of the main echo-sounder may be utilized to control storage and reproduction of echo signals and/or transmission of pulses by the main echo-sounder. The invention is stated to be applicable to secondary radar systems.