Patent GB-601016-A (GB)
Title: Improved arrangements for producing marks on a screen indicating elapsed time particularly for use in radar devices
IPC: G01S1/02
Filed: 1944-08-09
Abstract: 601,016. Cathode-ray oscillographs. WESTERN ELECTRIC CO., Inc. Aug. 9, 1944, No. 15193. Convention date, Aug. 12, 1943. [Class 37] [Also in Group XL (c)] In a system for reducing equally spaced time markers for an oscillograph, a freely oscillatable means is provided which is shock excited by each of a series of pulses from a pulse generator to produce a wave of frequency independent of the recurrence frequency of the pulses, the timing markers then being derived from the wave so obtained. The invention is described as applied to a pulse radar system with a type A cathode ray tube display. In the timing circuit, Fig. 2, tube valve VI is normally conductive and is cut off by the negative pulse 150, Fig. 4a, from the pulse generator in the transmitter, producing a damped train of 1 mc/s. oscillations, Fig. 4b, in the tuned circuit T which dies away before the arrival of the next synchronising pulse 151. This damped train is fed to V2 which is heavily biassed by the potentiometer 67, 69 and the output consisting of a train of negative half-cycles, Fig. 4c, is differentiated by the circuit 41 ,40 to give a series of alternate negative and positive pulses, Fig. 4d, which trigger the valve V3 of the flip-flap V3, V4. V3 is an unbiassed and V4 is heavily biassed by the potentiometer 42, 94 so that in the absence of a trigger pulse V3 is conductive and V4 is cut off. The negative trigger pulses reverse this condition for a short period determined by the circuit constants but the positive pulses have no effect so that a series of negative square pulses of equal amplitude, Fig. 4e, is produced in the output of V4 and these are applied to the Y plates of the cathode-ray tube as time markers. Alternatively the timing pulses may be applied to the grid of the cathode-ray tube to brighten or blackout the trace. In a modification, Fig. 5 (not shown), the train of negative half cycles, Fig. 4c, shock excites a circuit tuned to a higher frequency, e.g. 5 mc/s., which is in the grid circuit of a valve V9 so that all oscillations after the first negative half-cycle are damped by grid current. The train of position half-cycles in the output of V9 are applied through a cathode follower to the cathode-ray tube as time markers. Time-base and black-out circuit, Fig. 3. A positive synchronizing pulse from the amplifier 100 triggers the valve V5 of the flip-flop V5, V6 producing a positive square wave 220, Fig. 4, in the output of V6 the duration of which is determined by the circuit constants and is made more precise by biassing the grid of V6 positively. V7 is normally cut off by the cathode bias derived from the potentiometer 125, 127 but on receipt of the positive square wave it becomes conductive and discharges the selected time base condenser C1, C2 or C3 to give a saw-tooth wave, Fig. 4g, which is applied through the sweep amplifier 140 to the X plates of the cathode-ray tube. The selector switch 130, 132 gives a choice of three sweep periods of 3, 15, and 35 Á secs. The negative square wave, Fig. 4h, from the output of V5 is applied to the grid of the cathode ray tube through the amplifier 141 to give a positive unbalancing square wave, Fig. 4i, which brightens the trace for the duration of the sweep. The synchronising pulse may be applied to the time-base circuit directly or through a delay circuit. Alternatively the delay circuit may be placed in the received signal path or between the pulse generator and the transmitter modulator if it is desired to start the time-base before the ground pulse arrives. Specifications 477,875, [Group XXXV], 582,494, [Group XL], 592,580 and 594,888 are referred to.