Patent GB-1102504-A (GB)
Title: Improvements in or relating to radar display apparatus
Inventor: MICHELL RICHARD BURGESS
IPC: G01S7/22
Filed: 1966-01-11
Abstract: 1,102,504. Pulse radar. DECCA Ltd. 2 Jan., 1967 [11 Jan., 1966], No. 1304/66. Heading H4D. Relates to a P.P.I, radar display of the kind where the craft carrying the radar is at a fixed position on the display which is compassstabilized. According to the invention a position marker is generated to mark a selected target on the display and the position marker is displaced across the display in accordance with but in the opposite sense to the motion of the craft. The display may be off-centred. A line joining the position marker to the new position of a target on the display represents the true track of the target. Several independently adjustable position markers may be provided each being displayed in the inter-scan periods. A position marker may be converted into a line trace extending towards the craft to facilitate estimation of risk of collision. In the embodiment the persistence of the screen of cathode-ray tube (C.R.T.) 14, Fig. 4, is long enough to leave an afterglow trail behind a moving response and three markers are provided for, each arising from a D.C. generator 20 having two adjustable controls; these may be for range and bearing respectively or for Cartesian co-ordinates directly. Calibrated scales for the controls are added. Modulated D.C. signals from the generators are selectable by a switch 24 and are fed to orthogonal deflection coils 27 via a gate 25 controlled from the pulse radar timing so as to be effective in the inter-scan periods. Switch 24 may be driven quickly and automatically so that all marker traces appear to be simultaneous. Phase-quadrature modulation of the deflection currents in generators 26 afford circular position markers. A generator 32 controlled by compass 19 and log 33 provides for " reverse true motion " of the position markers. Closure of switch 28 applies modulation to generators 20 to give a line marker. A suitable apparatus comprises a D.C. source 40, Fig. 5, with its centre point earthed and pairs of potentiometers for marker positioning and a modulation source 23. A circuit 36, Fig. 4, includes a halfwave rectifier to suppress the C.R.T. beam for one half of each modulation cycle, outward movement of the marker thereby being blanked. The marker line will shorten the nearer it is to the display position of the radar-equipped craft. To reduce confusion on the display when displaying a marker line signals from generator 32 are interrupted when switch 28 is closed. To assess the effect of avoiding action against one target on avoidance of other targets marker traces may be displaced to a parallel position the D.C. output of a motor-driven potentiometer wiper 51 being applied to a sine-cosine potentiometer 53 having an earthed centre-tap and set to an angle corresponding to the vector difference between the " trial " course and speed and the actual course and speed; resistor 55 is set to the speed of that vector difference. After a short interval switch 56 is closed and the marker lines are displaced, Fig. 3; if a target is on the corresponding displaced marker line it is on a collision course with the trial course of the radar-equipped craft. The optimum trial course may thus be found by adjusting potentiometer 53 and resistor 55. To avoid confusion, repetitive interruption of the marker lines may be arranged when switch 56 is closed. The above arrangement in Fig. 4 may be modified by adding a second sinecosine potentiometer and bridging resistor for vector subtraction and controlled automatically from the compass and log, Fig. 6 (not shown). A line marker extending from a position marker and rotatable in direction may be provided by inserting the two stator coils of a magslip in the output lines from generator 20, the rotor being fed with A.C.