Patent GB-1097445-A (GB)
Title: Improvements in or relating to methods of and apparatus for echo sounding
IPC: G01S7/527
Filed: 1965-01-25
Abstract: 1,097,445. Echo-sounders. ELECTROACUSTIC G.m.b.H. Jan. 25, 1965 [Jan. 23, 1964], No. 3212/65. Heading H4D. In an echo-sounding system, adjacent objects whose received echoes overlap (e.g. a fish shoal near the sea-bed, a mud-layer overlying the sea-bed, or irregularities in the sea-bed) are distinguished on a cathode-ray tube display or electrochemical recording by applying the composite echo signal to a circuit responsive to the time rate of change of amplitude of the received signal, whereby those sections of the signal having a high rate of change of amplitude are accentuated. In the embodiment of Fig. 11, a composite echo signal from a receiving transducer is applied to amplifier stages 65, 66 having networks 78, 81 for providing automatic gain control. The amplified echo signal is rectified by two voltage doubler circuits 70, 71 and fed through two integrator circuits 34, 35 to the grid and cathode respectively of a valve 48 whose output 46 is fed to the recording electrode of an electrochemical recorder. The time constant of circuit 34 is made smaller than that of circuit 35, so that for low rates of change of echo amplitude the voltages developed across resistors 54 and 55 and appearing at the grid and cathode of valve 48 are substantially the same, whereas for high rates of change the voltage appearing at the grid is greater than that appearing at the cathode. The gridcathode voltage is thus greater for high rates of change of echo amplitude, so that small peaks, due to fish echoes, in the echo amplitude envelope (Figs. 2 and 5, not shown) are accentuated. The resolution of the system may be increased, at the expense of sensitivity, by reducing the difference between the time constants of circuits 34 and 35. To achieve optimum recording conditions, the time constants of one or both of the circuits 34 and 35 may be adjusted between zero and a maximum value by varying resistors 54 and 55 or capacitor 64, the relative levels of the echo signal applied to the two circuits may be varied by a potentiometer 76, and voltage doubling may be effected in only one of the two circuits 70, 71. A potentiometer 61 permits adjustment of the grid bias on valve 48 such that with no echo signal input the voltage on the recording electrode is just insufficient to cause blackening of the recording paper. A modified rectifying arrangement for feeding circuits 34 and 35 is illustrated in Fig. 10 (not shown), and a high-pass filter circuit (84) (Fig. 12) may be provided after the circuits 34 and 35. Swept gain of the receiver amplifier to compensate for reduction of echo amplitude with increasing range of a reflecting object is envisaged. In an alternative embodiment (Fig. 9), the two output voltages from circuits 34 and 35 are applied directly to the horizontal deflection electrodes (25, 26) of one beam of a double-beam cathode-ray tube (24), and are applied in antiphase to the horizontal deflection electrodes (27, 28) of the second beam of the tube (24). A sawtooth waveform is applied to the vertical deflection electrodes of both beams and is triggered through an adjustable delay for displaying echoes within a selected partial range.