Patent GB-946839-A (GB)
Title: Improvements in and relating to echo sounding apparatus
Inventor: HASLETT ROY WILLIAM GEORGE
IPC: G01S15/42
Filed: 1961-07-21
Abstract: 946,839. Echo sounding. S. SMITH & SONS (ENGLAND) Ltd. July 13, 1962 [July 21, 1961], No. 26597/61. Heading H4D. Echo sounding apparatus, particularly for the location of fish, comprises a single transmitting transducer and two receiving transducers, the echoes received by the latter being supplied to a display device via a gate circuit which is rendered conducting only when control pulses derived from the initial part of each echo signal overlap in time. With this arrangement, assuming the receiving transducers are mounted in a plane which is horizontal when a vessel carrying transducers is horizontal, echo signals are only displayed which arise from targets (fish) lying near the vertical plane bisecting a line joining the two receiving transducers. The directional properties of such an arrangement depend on the width of the derived control pulses and effective beam widths of 5 degrees may be obtained utilizing transducers of relatively large (30 degrees) beam widths. Also, by varying the instants of occurrence of the control pulses relative to the echo signals from which they are derived the (effectively) narrow receiving beam can be swept for searching purposes. Alternatively, such variation may be employed to stabilize the system to compensate for the effects of departure of the plane containing the transducers from the horizontal (e.g. to compensate for rolling of the vessel). Fig. 1 shows the general arrangement comprising a transmitting transducer T 1  (providing pulses of ultrasonic energy of about 30 kc/s.) symmetrically positioned with respect to two receiving transducers R 1 , R 2  spaced three feet horizontally athwartships each being of standard 3# by 2# construction. Each receiving transducer supplies respective identical channels comprising, referring to channel 1 and to the waveforms shown in Fig. 2 (c) and 2 (b), sections 10. . . 15 (which includes an A.G.C. system 10-12 operating in response to the amplitude of the bottom echo) producing from the received echo a, the waveform b which is limited in 16 at level 24 to provide an accurate trigger pulse on the initial rise of the echo (to discriminate against noise) and after amplification and squaring in 17 employed to trigger a ramp generator 18 the triggering level of which is shown at 25 (waveform f). The ramp waveform gl is supplied to an amplitude gate 19, the gating level 26 of which is determined by the algebraic sum of a fixed D.C. voltage from source 42 and a variable input voltage to be described later. The output of gate 19 is processed in devices 20 . . . 23 to produce the pulse waveform ql which is supplied together with a similarly produced pulse q2 from channel 2, to an adder 29, the output pulse of which is fed to an amplitude gate 30 having a gating level 32 such that an output pulse l is only produced if the sum of ql, q2 exceed the level 32. This condition arises only when q1, q2 occur simultaneously. Pulse l is then utilized to trigger a mono-stable multivibrator 36 which when triggered holds a gate 34 open (conducting) until it returns to its quiescent condition and during this inverval echo signals from an adder 33 supplied with the outputs of the two receiving channel amplifiers 10, 10<SP>2</SP> are passed to the display device 35 which may be a cathode-ray tube or a pen recorder. To compensate for rolling of the vessel the gating level 26 of amplitude gate 19 is partly controlled, as referred to above, by a variable voltage derived from a resolver synchro 38 comprising a Magslip controlled by a pendulum swinging athwartships and providing positive and negative voltages proportional to the angle of roll. These voltages, which change phase (i.e. sign) as # passes through zero are supplied to the gates 19, 19<SP>2</SP> via smoothing networks as shown. By employing two more receiving transducers spaced horizontally along the fore/aft line of the vessel together with additional apparatus as described above, an effective beam width of about 5 degrees in the fore/aft direction may be also obtained.