Patent GB-1118251-A (GB)
Title: Improvements in or relating to radar display apparatus
Inventor: EASY MAURICE HENRY
IPC: G01S7/24
Filed: 1965-01-28
Abstract: 1,118,251. True motion radar display. DECCA Ltd. 28 April, 1966 [28 Jan., 1965], No. 3886/65. Heading H4D. The invention relates to a method of simultaneously presenting a relative motion and a true motion display on the same display screen. Fig. 4 shows a relative motion display of the radar carrying craft (0) and a target craft (T0<SP>1</SP>-T9<SP>1</SP>) together with successive true motion indications (0-0<SP>1</SP>) and (T1<SP>1</SP>-T2), (T2<SP>1</SP>-T3), . . . &c. Fig. 8 shows a true motion display of the radar carrying craft (R0-R9) and a target craft (T0-T9) together with successive relative motion indications (T1-T2<SP>1</SP>), (T2-T3<SP>1</SP>) . . . &c. The apparatus for producing the display of Fig. 4 is shown in Fig. 1, wherein a pulse-producing ship's log 19, a mono-stable circuit 20 and a smoothing circuit 21 produces a D.C. voltage indicative of the craft's speed v. Positive and negative versions of this voltage are produced by converter 22 and applied to either end of a sine/cosine potentiometer 25, having tappings 27 and 28 varied in position by a compass repeater, to yield voltages representing v sin α and # cos a respectively, where α is the craft's heading. These signals are used to supply respective currents for application to orthogonal deflection coils 16, 16a of the PPI display 15 to produce a true motion displacement of the display. Only the use of the v sin a signal will be explained in detail, the use of the v cos α signal being similar. The v sin a signal which represents the E-W component of the craft's velocity is integrated in Miller integrator 29, 30, 31 to produce a corresponding E-W displacement signal which is applied to one contact of a time sharing switch 41. The other contact of the switch is eventually connected to a starting point potentiometer 34 which defines the relative motion position of the craft and target, and normally gives zero deflection in true motion coil 16. The moving contact of switch 41 is fed via current amplifier 35 to coil 16 and is moving from one contact to the other in synchronism with successive scans, such that on one scan a relative motion display is produced and on the next scan a true motion display is produced. In this way there is produced in the interval t 1  to t 2 , the relative motion of the craft (0-0) (i.e. fixed) the true motion of the craft (0-0<SP>1</SP>), the relative motion of the target (T1<SP>1</SP>-T2<SP>1</SP>) and the true motion of the target (T1<SP>1</SP>-T2). At time t 2  a cam 133 under the control of motor 233 momentarily closes switch 33 such that the output of the integrator falls to zero, and then starts to build up again so that a new relative and true motion display section (T2<SP>1</SP>-T3<SP>1</SP>) and (T2<SP>1</SP>-T3) is displayed. The display of the craft again moves from (0-0<SP>1</SP>). If the result of a change of bearing and/or speed on the craft's port is required, a sine/cosine potentiometer &c. may be added to produce artificial v<SP>1</SP> sin #, v<SP>1</SP> cos # signals (Figs. 5 and 6). Fig. 7 shows the modification of the circuit of Fig. 5 necessary to produce the displace of Figs. 8 and 9. The display tube may be a colour tube with the relative and true motion displays in different colours. The relative motion display and the true motion display may be produced in separate storage tubes and each storage tube may be read out alternately.