Patent GB-644433-A (GB)
Title: Improvements in or relating to echo sounding apparatus
IPC: G01S15/10
Filed: 1947-09-05
Abstract: 644,433. Depth-sounding and distancemeasuring apparatus. INTERNATIONAL PROJECTOR CORPORATION. Sept. 5, 1947, No. 24559. Convention date, March 10, 1945. [Class 118 (ii)] A pulsed echo sounding system comprises a gas-filled grid-controlled valve which fires when each pulse is transmitted and an output circuit thereof which suppresses the receiver during transmission periods. Power is supplied by a vibrator 42 operated by a battery 18 and a blocking oscillator 34 applies pulses to the control grids of a strobotron 74 and a thyratron 76. At each pulse the former conducts and discharges a condenser 82 through a tuned transmitter T. At the same time the thyratron 76 conducts via a screen grid resistor 88 of the first stage 86 of the receiving amplifier 86, 110, 114 to reduce receiver-gain during transmission of a pulse and so avoid cross-talk. The output pulses from the strobotron 74 are also applied to the control grid of a valve 120 which ceases to conduct. The other valve 118 of an Eccles- Jordan trigger pair 118, 120 therefor conducts and its anode current flows through a depth meter 20. When the echo is received on the tuned receiver R it is amplified and applied to the control-grid of trigger valve 118, which ceases to conduct. Its anode current therefore flows through the depth meter 20 only during the time between a transmitted pulse and its echo. The meter is arranged to indicate average current and is calibrated in feet. The low, steady reading of the depth meter 20 due to any cross-talk between the transmitter T and the receiver R is eliminated by suitable adjustment of a gain-control potentiometer 116 of the first amplifying valve 86. The final amplifier stage 114 is biassed beyond cut-off so that weak noise signals will not be sufficient to operate this valve, and the anode potential is the same as that of the control grid of trigger tube 118 so that as soon as the echo is received and the trigger tube 118 ceases to conduct, the amplifier 114 also ceases to conduct and prevents the reception of noise or secondary echoes. The impulse rate is determined by a keying rate potentiometer 26 and the rate is indicated on a meter 22 comprising five tuned reeds. At the correct impulse rate the centre reed resonates, while one of the others does so for fast or slow impulsing. A three-way switch 24 in its upper position allows depth to be indicated as described and in its middle position connects the battery 18 to the depth indicator 20 in order that its charge may be checked. In the lower position the control grid of amplifier valve 114 is earthed, and this conducts, causing trigger tube 118 to conduct over a path which includes the depth meter 20. A cathode-bias calibration potentiometer 30 is then adjusted until the pointer of the depth indicator reaches a set mark. The transmitter T and receiver R comprise magneto-strictive packs of annular nickel laminations and are each housed in a conical reflector filled with castor-oil and closed with a diaphragm. Both receiver and transmitter are mounted in a device P which is towed beneath the surface alongside the ship. Specification 644,456 is referred to.