1,024,511. Echo sounders. RAYTHEON CO. Jan. 13, 1964 [Jan. 23, 1963], No. 1461/64. Heading H4D. An echo sounder is provided with means whereby an alarm is actuated when the depth of water below the sounder reduces to below a predetermined limit. In the embodiment described a depth sounder produces a pulse, which is fed to a transducer 14, for conversion to an acoustic pulse and transmission towards the sea bed, and to a rectifier 16 and filter 18 which produce the envelope of the pulse signal. The envelope is then inverted and differentiated, and the resulting positive, trailing edge spike chosen by clipper means 24. The positive spike is then fed to a one shot multivibrator 26 to start a positive pulse, having a duration representing the predetermined depth limit and determined by the setting of a resistor 46, adjusted by a shaft, coupled to a depth indicating scale and pointer 49. The positive pulse is fed as a gating pulse to one electrode of a gate pentode 103, such that the pentode passes signals applied to its control grid 105 within the period of occurrence of the gating pulse. Echo signals are passed from the transducer to the sounder 12, and to a two-stage amplifier 69, comprising a triode 61A with a rapid time varying amplification due to the charging up of biasing capacitor 58, and a triode 61B with a slow time varying amplification due to the charging up of capacitor 88 by a pulse from the one-shot multivibrator 26. The time varying amplification is provided so that weaker echoes arising from deeper bodies will receive more amplification. The amplified echo pulse is then passed to the control grid of gating pentode 103, and is passed therethrough if it should occur within the period of the gating pulse. The gated echo pulse is passed through bandpass filter 110, tuned to the frequency of the transmitted pulses, and is rectified by diode 114 to charge up a capacitor 116. If the gated echo pulse is random and not due to the sea bed, the capacitor will discharge through resistor 118, faster than the gated echo pulses can charge it. Successive echo pulses, however, charge the capacitor 116 up until the voltage across it fires a thyratron 121. The current through the thyratron operates a relay 147 such that contacts 148 and 150 switch over and internal and external alarms 152 and 154 are energized. The circuit may be returned to normal by operation of push switch 136, such that capacitor 116 is discharged and the thyratron ceases to fire. The gated echopulse is also applied to a neon lamp 164. The gating pulse from the one-shot multivibrator 27 is also differentiated by capacitor 170 to produce positive and negative leading and trailing edge spikes, which spikes are passed to a tuned circuit 172 to produce bursts of oscillations at the transmitter frequency. With switch 176 connected to a positive bias supply amplifier 174 is activated whereby a test circuit is produced wherein the amplified bursts from circuit 172 are applied to the depth sounder 12, to produce, on the recording instrument included therein, an indication of the predetermined depth limit, enabling a check of indicator 49 to be made. The invention may be used to set off an alarm when an extensive shoal of fish is detected above the predetermined depth limit.
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