GB1232176A - - Google Patents

Abstract

1,232,176. Pulse thresholding; pulse radar. INTERNATIONAL BUSINESS MACHINES CORP. 26 Nov., 1969 [20 Dec., 1968], No. 57760/69. Headings H3T and H4D. A circuit A2 for thresholding pulses received at E, more particularly in a radar receiver, derives the thresholding voltage Vs from a circuit comprising two capacitors C1 and C2 connected to respective charging circuits G2 and G<SP>11</SP>2 operative in response to the pulses and respective discharging circuits G1 and G<SP>11</SP>1, the latter circuit being controlled by the voltage across C1. In the circuit described, the threshold tends towards a value such that the total number of noise and signal pulses during a radar cycle is constant. The pulse output from the threshold circuit A2 is applied via a gate 12 which is opened during the period desired reflections are expected. These pulses operate a monostable circuit C2 which allows G2 and G<SP>11</SP>2 to pass a fixed charge to C1 and C2. The rate of charge and discharge is much greater for C1 than C2 and the fluctuations across C2 are very small so that a substantially steady threshold level is passed through buffer A1 to the thresholder A2. If the number of pulses above the threshold decreases, the threshold slowly decreases and vice versa. Leakage of charge from C2 is compensated by controlling the discharge rate through G<SP>11</SP>1 by the voltage across C2, the larger the voltage the slower the discharge. In the absence of any pulses during the expected periods (t2) an integrating circuit eventually operates a further charging path G<SP>1</SP>2 which prevents the output level of A2 falling below the threshold of A3. The useable period of MC may be varied to vary the threshold level and the effect of repeated pulses due to a high level of noise can be reduced by reducing the highfrequency response of amplifier A1.