Patent GB-811440-A (GB)
Title: Improvements in or relating to subaqueous echo sounders
Inventor: WATT JAMES
IPC: A61H1/02
Filed: 1955-07-18
Abstract: 811,440. Echo sounding. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. June 12, 1956 [July 18, 1955], No. 20704/55. Class 118 (2). In a marine pulse echo sounder used for locating fish and comprising a deflectionmodulated (type A) cathode-ray tube displaying echoes received from within a depth interval fixed in relation to the bottom of the sea, the time-base is triggered by an echo from the sea bed. In a first embodiment, Fig. 1 and Fig. 4 (not shown), recurrent pulses are transmitted in the normal manner, the bottom echo for triggering the time-base is selected by an amplitude discriminator and all the received echoes are applied to the signal deflector plates through an electrical delay device producing a time-delay d equivalent to the distance of the top of the depth interval from the sea bottom. In a second embodiment, Fig. 2 (not shown), recurrent pulse pairs are transmitted, each pair comprising a first exploring pulse and a later main pulse of different wave frequency, e.g. 28 kc/s. to 20 kc/s. respectively, the time interval between said first and second pulses being equal to said equivalent time delay d; the received reflected exploring and main pulses are separated by frequency selective means, the time-base is triggered by the exploring pulse bottom echo as selected by an amplitude discriminator and all the main pulse echoes are applied to the signal deflector plates. The transmitted exploring and main pulses may be radiated by a single broad-band transducer coupled to a single oscillator whose frequency and active periods are controlled by camoperated switches. In a third embodiment, Fig. 3 (not shown), recurrent single pulses are transmitted, the duration of each pulse being equal to said equivalent time delay d. Each rectified echo pulse is differentiated to give two short pulses of opposite polarity coincident respectively with the leading and trailing edges thereof and the pulses of opposite polarity are separated by oppositely connected diodes, the leading-edge pulse derived from the bottom echo being selected by an amplitude discriminator and applied to trigger the time-base and all the trailing-edge pulses being applied to the signal deflector plates. As shown in the first embodiment, echo wave pulses appearing at terminals 13 are rectified at 14 and applied through a low-pass filter 15 to a phase splitter 16, the negative output pulses from the cathode thereof being applied through a delay line 19 and amplifier 20 to relay an oscillator 21 whose output is applied to the X plates of a cathode-ray tube (not shown). The positive pulses from the anode of the phasesplitter 16 are applied to a gate valve 6 which is blocked for a period of slightly greater duration than the pulse transmission duration by means of a negative pulse generated by a monostable circuit 3, 4 triggered by a switch 2 in synchronism with the pulse transmission. The output pulses from the gate valve 6 are applied through an amplifier 7 to a cathodefollower 8 with an R.C. cathode load 9, 10 having a time constant approximately twice the pulse repetition period such that a bias voltage is developed across the cathode load which blocks all but the strongest echo pulses, i.e. the bottom echoes. The bottom echo pulses thus selected are differentiated and applied to trigger a phantastron 12 providing time-base and bright-up outputs from terminals Y and G respectively. In a modification, Fig. 4 (not shown), the amplitude discriminator 8 and the phasesplitter 16 are omitted, the echo signals being applied to the gate valve 6 and the delay line 19 through separate variable gain amplifiers which are adjusted respectively to select the bottom echo and to suit the signal display requirements. In order to change over to a normal full range display, ganged switches are operated which remove the delay in the signal channel and apply a suitable trigger pulse to the gate valve 6. Reference has been directed by the Comptroller to Specification 785,001.