GB668400A - Improvements in or relating to radar p.p.i. systems - Google Patents

Abstract

668,400. Radiolocation; saw-tooth generating circuits. DECCA RECORD CO., Ltd., and LAWSON, W. June 1, 1950 [June 1, 1949], No. 14745/49. Classes 40 (vi and 40 (vii). A plan-position-indicator display in a pulse radar system comprises means for producing alternating-voltage control signals at the pulse repetition frequency having amplitudes proportional to the sine and cosine of the angular position of the aerial, a cathode-ray tube having a pair of perpendicularly-arranged fixed deflecting means, and scanning generators, associated respectively with the deflecting means, to which gated portions of the two alternating-voltage control signals are applied whereby they generate sweep voltages which cause deflections of the cathode-ray beam in perpendicular directions at ratio proportional to the instantaneous values of the respective control signals, thus producing a radial scan on the screen of the cathode-ray tube in a direction corresponding to the angular position of the aerial. The alternating-voltage control signals are generated in circuit 24 comprising four equally angularly spaced stator coils and a rotor coupled mechanically with the aerial and fed with an alternating voltage of the pulse repetition frequency. The outputs therefrom, comprising two signals of opposite phase haying amplitudes proportional to the sine of the angular position of the aerial and two signals of opposite phase having amplitudes proportional to the cosine of the same angle, are applied as shown to the grids of pentode valves 14, 15, 16 and 17, acting as Miller saw-tooth generators. These valves are normally biased to cut-off by signals applied through diodes 30, 31, 32, 33; however, a gate pulse is periodically applied to the diodes to prevent their conducting so that the signals applied to the valves 14, 15, 16, 17 from generator 24 control the rate at which anode current flow increases therein. The anode circuits include deflecting coils 10, 11, 12, 13. The gate pulses are timed to be applied when the alternating voltage is in the region of its peak value so that the values of the signals applied to the pentodes vary little during the gating interval and the linearity of the sweep is substantially unaffected. The alternating voltage has considerably greater amplitude than the grid base of the valves; thus during any one scanning interval only two of the four pentodes is conducting, and the cathode-ray sweep is effected by the corresponding two deflecting coils. The outputs from the generator 24 are applied to the pentodes through resistors the values of which may be selected by a switch 29 go that the scanning speed may be controlled. Diodes 34, 35, 36, 37 are provided to prevent the control grids of any of the pentodes from going positive.