GB946591A - Improvements in or relating to radar systems - Google Patents

Abstract

946,591. Producing azimuth markers in radar displays. MARCONI INTERNATIONAL MARINE CO. Ltd. Nov. 1, 1961 [March 9, 1961], No. 8662/61. Heading H4D. In a radar system, comprising means for producing azimuth markers on a P.P.I. display tube D.T. (Fig. 1), rotor R of resolver 3, rotating with the aerial 1, induces the deflection waveform shown into a three-phase stator S feeding the display tube deflection coils D1, D2, D3 and the stator winding S<SP>1</SP>1, S<SP>1</SP>2, S<SP>1</SP>3 of a second resolver 4, having a rotor carrying two windings R<SP>1</SP>S and R<SP>1</SP>C in quadrature and forming two oscillatory circuits with capacitors C1 and C2. The flyback edges FB of the induced waveform shock the two oscillatory circuits into a series of damped oscillations with the initial pulses thereof having a sinusoidal envelope, due to the rotation of the rotor R, differing in the two circuits by 90 degrees, Fig. 2. The oscillations from windings R<SP>1</SP>S and R<SP>1</SP>C are detected respectively by valves V1 and V2, diodes D1 and D4 allowing only the negative pulses to pass to the grids, whilst diode D3 is negatively biased so as to allow only those negative pulses from winding R<SP>1</SP>C having a maximum amplitude greater than that of the largest second pulse therein to pass to valve V2, the resulting waveforms applied to the grids of V1 and V2 being as shown shaded in Figs. 2a and 2b respectively. The anodes of V1 and V2 are connected to the two control grids of valve V3, the arrangement being such that V3 only conducts during the overlapping period # (Fig. 2) once in every rotation of the aerial 1. Pulses so produced by V3, trigger flip-flop FF to produce square pulses for differentiation by circuit D.C. and application therethrough to the display tube DT to produce the required azimuth marker which may take the form of a " bright up " single or double trace on a blacked off sector. The angular position of the azimuth marker is controlled by the position of the rotor of resolver 4, which in the case of ship-borne radar may be controlled by the ship's compass to give a " north up " indication. In an alternative embodiment, a three-phase rotor may be used in the second resolver 4 and only two of the windings used to form the oscillatory circuits. An alternating type of coincidence detector is described, Fig. 4 (not shown), comprising two forwardly biased diodes connected with their cathodes each to the anodes of valves V1 and V2, and with their anodes to the cathode of a. reversibly biased output diode.