Patent GB-983324-A (GB)
Title: Improvements in and relating to recording means for echo signals
Inventor: SOTHCOTT JOHN ERNEST LEON
IPC: G01S7/534
Filed: 1962-07-03
Abstract: 983,324. Echo-sounders. S. SMITH & SONS (ENGLAND) Ltd. June 25, 1963 [July 3, 1962], No. 25545/62. Heading H4D. Pulse echo-sounding apparatus for echosounding in water in which echo signals received from transmitted pulses of acoustic or ultrasonic waves are recorded, replayed a plurality of times and displayed on the screen of a cathode ray tube comprises additional recording means for making a permanent record of the echo signals and means for selecting and feeding to the recorder only the echo signals of a single replay. A receiving transducer 10 receives echoes from each pulse of ultrasonic waves transmitted by a conventional pulse transmitter using the transducer 10 or a separate transducer and in the signal waveform (a) at the output of the receiver, breakthrough of the transmitted pulse into the receiver is indicated by T, the echo signal from the sea bed, for example, by B and an echo from a fishby F, the interval between successive transmitted pulses being 600 ms. The echo signals of the waveform (a) are recorded on a magnetic drum in a recorder 11, as described in Specification 785,001, and are replayed to produce the echo signal waveform (b) which is fed to a cathode ray tube 13. Recording apparatus 11 introduces a time delay of 20 ms. and replays every 20 ms., four replays I-IV being shown. Waveform (b) is rectified at 12 and used to trigger the timebase of the cathode ray tube in fixed time relation to the initial edge E of the bottom (sea bed) echo signal, each such triggering serving for the display of echo signals from the next replay. The rectified waveform (c) is applied through an amplitude limiter 14 to a slope/amplitude diseriminator 15, as described in Specification 878,111. The resulting waveform (d) is fed to an amplitude gate 16 from which the pulses (e) are used to trigger the timebase generator of the cathode ray tube 13 and are also fed to trigger delay device 17, which may be a multivibrator, having to be primed. Priming pulses (f) having a positive leading edge 4 ms. after the leading edge E 0  of pulse B and a negative edge between the next transmitted pulse and the next fish echo F are applied to a gating pulse generator 18, each positive edge triggering generator 18 to initiate a pulse (g). The leading edge of pulse (g) primes trigger delay device 17 which remains primed throughout the duration of the pulse (g). Trigger delay device 17 is triggered by the first pulse of waveform (e) that arrives after its priming by waveform (g) to generate a positive-going edge of waveform (h), recovering automatically after 6 ms. to produce negativegoing edge E 1 . Negative-going edge E 1  triggers a drive -pulse generator 14 to generate a current pulse (m) which is fed to a stylus-drive motor 20 which initiates the sweep of a recording stylus over a moving paper strip, as described in Specification 852,566. Four milliseconds after the stylus has started to move a pulse (j) is generated and fed to a gating waveform generator 21 which generates a waveform (k) which opens a marking gate 22 which then permits signals (c) from the rectifier 12 to reach the stylus of the recorder. When the next pulse (e) reaches the still-primed trigger delay device 17, it generates the leading edge of a pulse P which terminates the pulse (k) in the gating waveform generator 21 and thus closes the marking gate 22 and terminates the priming waveform (g) in the gating pulse generator 18. The pulse P is thus cut short abruptly having a duration of only 100 microseconds. This prevents any further mark being made on the recording paper until further signals are received by transducer 10. The effect is therefore the equivalent of the " white line " produced on the recording paper as described in Specification 865,111. The second replay echo signals II are permanently recorded, the bottom echo signal of the first replay being used to prime and trigger the replay circuits. The current pulse (m) may be generated by means of a thyratron arranged to discharge a capacitor.