GB1089085A - Signal amplifier - Google Patents

Abstract

1,089,085. Interference suppression; wave energy position finding. BENDIX CORPORATION. May 31, 1966, No. 24239/66. Headings H4D and H4L. The invention generally relates to the reception of randomly occurring pulses of distinctive frequency in a high noise environment. It particularly describes a position finding system for a ship, wherein, a plurality (e.g. four) transponders are placed in known positions on the sea bed, and reply with pulses of distinctive frequencies to an interrogation pulse from the ship. By timing the replies the distance of the ship to each transponder is determined thereby enabling the determination of the ship's position. The acoustic reply pulses are received at the ship's transducer 10 against a high background of widely spectrumwise distributed noise. After transformation into electrical signals and amplification, the noise and replies are passed through a broadband bandpass filter 14, having a bandpass just sufficient to pass all the replies. The passed noise and the replies are fed to a very highgain saturable amplifier 16, which since it saturates to a constant limit with only low noise at its input, may be considered, as a limiter. The output of " limiter " 16 is constant in amplitude and comprises an always present noise component, made up of frequency components having individual average low amplitudes, and the reply pulses of constant frequency and constant high amplitude. The reply pulses are separated out by respective narrow band filters 20-26, and via detectors and smoothing filters (not essential) cause Schmidt trigger circuits 50-56 to trigger, thus giving the required timing of the replies, the noise frequency components falling within the bands of the filters 20-26 being at too low an amplitude to trigger the circuits 50-56