GB624442A - Improvements in or relating to echo sounders - Google Patents

Abstract

624,442. Echo sounding and distancemeasuring apparatus. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., TWATT, J., and GRAY T. Aug. 27, 1946, No. 25674. [Class 118 (ii)] A subaqueous echo sounding or like receiving system comprises means for differentiating between received pulses of more than a pre-determined duration with relation to received pulses of shorter duration so as to favour response to the former. The incoming signals are received on a normal high-frequency amplifier (not shown), the last stage V1 of which is transformer-coupled to a full-wave rectifier A, which develops an output potential across a resistor R1 shunted by a smoothing condenser C1. This potential is applied via resistor R2, transformer T2 and an integrating circuit R3, C2, to the grid of a valve V3, noise pulses of an excessive amplitude being byepassed to earth by a diode V2. The output of V3 is then applied to a discharge trigger tube V4, or other indicating or recording means. With a damped magneto-strictive projector having a resonant frequency of 14 kc/sec. and a decay rate of 40 dbs/sec., the integrating circuit R3, C2 is given a time constant of 1.5 ms. Noise pulses will in general give rise to a 14 kc/sec. vibration in the receiver which decays by 40 dbs. in 1 ms. and therefore will not last long enough to raise the potential of condenser C2, and hence of the grid of V3, sufficiently to cause V4 to strike. It is shown that received echo pulses, because of the divergence of the transmitted beam, will in general have a sufficient duration to cause the tube V4 to strike (e.g. 2 ms. at 200 fathoms, or 5 ms. at 500 fathoms). The time constant of the integrating circuit may be adjustable and a plurality of such circuits may be provided in cascade.