Patent GB-957718-A (GB)
Title: Improvements in or relating to data handling systems
IPC: H03K5/26
Filed: 1960-06-09
Abstract: 957,718. Pulse radar. SOC. NOUVELLE D'ELECTRONIQUE ET DE LA RADIO INDUSTRIE. June 9, 1960 [June 26, 1959; April 7, 1960], No. 20329/60. Heading H4D. Relates to means for discriminating against the effects of random noise in a pulse radar in which an echo pulse is produced by a target in each of a plurality of successive radar pulse recurrence periods, the timing of each echo pulse being quantized with reference to clock pulses i, j, k, Fig. 1, synchronized with and of higher recurrence frequency than the transmitted pulses such that if the timing of a predetermined number of the resultant successive quantized echo pulses is the same then a single output pulse representing the target is produced by a correlation circuit; a time quantum is defined as the time interval between two successive clock pulses. In such a system the correlation condition may not be satisfied if the echo pulse is adjacent a clock pulse since due to fluctuating noise some of the echo pulses may be assigned to the time quantum preceding the clock pulse and others may be assigned to the succeeding time quantum; alternatively if the echo pulse actually coincides with a clock pulse the quantizing circuit may fail to operate. According to the present invention correlation under such conditions is achieved by generating an " object " pulse m of predetermined amplitude in response to each input pulse of amplitude exceeding a predetermined threshold level, deriving from each object pulse a delayed " image " pulse m<SP>1</SP>, the delay time #t being less than the recurrence period of the clock pulses, applying the object and image pulses to the trigger input of a bi-stable trigger circuit and applying the clock pulses to the reset input of the trigger circuit. Thus if the time interval between an object pulse m and the succeeding clock pulse is not less than #t as shown in Figs. la, 1b, 1c the trigger circuit produces a single output pulse in response to each pair of object and image pulses but if the time interval is less than #t as shown in Fig. 1d then the trigger circuit produces two output pulses occupying adjacent time quanta. Furthermore if an object pulse coincides with a clock pulse, a trigger circuit output pulse is produced by the image pulse in the time quantum succeeding said clock pulse. As shown in Fig. 2 the object pulse and the clock pulses are produced respectively by generators 5 and 8 and applied to a comparator circuit 61 which includes a delay line 6, Fig. 4, producing the image pulses and the bi-stable trigger circuit 7. The triggering threshold of the generators 5 is controlled automatically by integrating the output pulses from the generator 5 in an integrator 10 and applying the resultant control signal to a threshold control circuit 15 through a gate 11 and filter 12, the gate 11 being opened during the latter portion of the radar pulse recurrence period by the output from a monostable circuit 14 triggered by the radar sync pulses applied at B through a delay circuit 13. The output from a sawtooth generator 9 synchronized by the radar sync pulses is also applied to the circuit 15 to provide a range dependent threshold control and the output from the filter 12 is also applied to control the gain of the I.F. stages of the radar receiver. In a modification, Fig. 3 (not shown), an output from the amplifier 4 is applied to control the threshold of the generator 5 through a threshold amplifier and an integrator, the output from the integrator being also fed back to control the threshold level of the threshold amplifier. Output signals coded in accordance with the amplitude of the input echo signals may be produced by providing a plurality of generators 5 having different triggering thresholds. Specification 957,719 is referred to.