公开(公告)号：US3803542A

公开(公告)日：1974-04-09

申请号：US67073367

申请日：1967-09-26

Applicant: BENDIX CORP

Inventor： LONGERICH E ,  RUDY E

IPC: G01S15/52 ,  G01S9/66

CPC classification number: G01S15/52 ,  Y10S367/901

Abstract: A sonar receiving system is described including a receiver and a detector for supplying a brightness signal to a cathode ray tube, the system including a circuit for preventing the display of received signals whose carrier frequencies have less than a minimum doppler shift. The system includes a frequency measuring system system having a monostable multivibrator, a time constant circuit and a bistable multivibrator having a differential output for producing output signals varying with the difference between the transmitted carrier frequency and the instantaneous received signal frequency, an amplifier for amplifying said output signals, a feedback loop connecting part of the amplified signals to said time constant circuit, a threshold gate for passing only those signals representative of velocities of reflecting objects below a threshold value. A special low pass filter is supplied including a capacitor which tends to receive a charge in proportion to the output of the video detector and a transistor which is connected to said capacitor and which responds to signals from the threshold gate to discharge said capacitor to prevent a brightness signal from reaching the cathode ray tube, such that only signals representing velocities above said threshold are displayed.