GB812638A - Improvements in or relating to echo sounders - Google Patents

Abstract

812,638. Echo sounders. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. Feb. 22, 1957 [May 30,1956], No. 16762/56. Class 118 (2). In a fish-finding echo sounder the echoes from the sea bottom are substantially suppressed before recording takes place; another, displaced, recording of the normal type is added on the same record chart. In Fig. 4 the recorded representation provided by the invention of a shoal of fish near to the sea bottom appears as shown in the upper part of the Figure, the normal recorded representation being as depicted in the lower part. In Fig. 5 the receiving transducer 5 feeds amplifiers 6, 7 having variable gain controls 8, 9 respectively the latter being so adjusted that sea bottom echoes only appear at terminal B and this amplifier output controls gating circuit 10 (see below) so that no sea bottom echoes appear at terminal F. A short pulse corresponding to the beginning of a sea bottom echo appears at terminal BI and may be used to record a fine line indicating the sea bottom contour. The normal display output appears at terminal FB and this is delayed (see Fig. 7) by a lumped capacitance/inductance delay line and is thereafter mixed (see also Fig. 8, not shown) with the output from terminal F, the mixer output being fed to recorder RD; the delay line may be replaced by a known acoustic delay device or a known recording- playback system using a magnetic drum, and the delay is conveniently made equivalent to a depth of ten fathoms. To counter any delay arising in the operation of gating circuit 10 (see Fig. 5) an electrical or acoustic delay line may be inserted at the point X; and to preserve correct relative timing between the outputs at terminals F and BI a delay device may be inserted at the point X1. Gating circuit.-The gating circuit (see Fig. 6) includes a known " flip-flop " circuit triggered by the positive-going front edge of a pulse derived by differentiating the positive-going pulses corresponding to sea bottom echoes only, applied at terminal B. Resistor 16 is so adjusted that the suppressor grid of valve 18 is normally at zero, or a slightly negative, voltage and bias to its control grid from point 22 is applied so that it is normally near cut-off. At terminal F there appears a signal representing only the fish and the leading edge of the sea bottom. The positive pulse 24 is differentiated by capacitor 25 and resistor 25A to give the short pulse at terminal BI.