Patent GB-1011583-A (GB)
Title: Improvements in or relating to radar display apparatus
Inventor: PARKER ERIC
IPC: G01S7/22
Filed: 1961-11-30
Abstract: 1,011,583. Radar displays. DECCA Ltd. Feb. 28, 1963 [Nov. 30, 1961], No. 42880/61. Heading H4D. In a true motion radar display a marker trace corresponding to the motion of one craft relative to another is provided by means whereby electrical signals representative of the true motions of the two craft are provided and combined to produce a signal vectorally representative of the motion of the one craft relative to the other, and whereby a marker trace is provided on the display screen, under the control of the combined signal, extending from the position on the display screen of the response of the one craft, in a direction corresponding to the said relative motion of the craft. The arrangement may be adapted to provide a true motion trace on a relative motion display. The arrangements may be used for anti-collision purposes and to determine an interception course. The motions of the two craft are set up in, and orthogonally resolved by, two interconnected magslip resolvers 20 and 21, having the feed to the rotatable input windings 22 and 23 controlled by ganged three-position switches 24 and 25. In the third or top position of the switch sinusoidal signals are fed to the two input windings 22 and 23 from source 27, which windings are respectively set at angles corresponding to the heading of the remote craft plus 180 degrees, and to the heading of the radar carrying craft. The potentiometers 26 and 28 are set such that the currents passing through the windings 22 and 23 have amplitudes respectively proportional to the speeds of the remote craft and the radar carrying craft, the former speed being determined from the display or from an automatic radar tracking system. The two signals are resolved into orthogonal components by windings 30 . . . 33 and corresponding components of the two signals are added to each other and the resulting components passed to orthogonal deflection coils 34 and 35. The orthogonal deflection signals are in phase and of such relative amplitudes as to produce a straight line trace in a direction corresponding to the direction of the relative motion between the craft. The trace, however, is only brightened by control means 39 during alternate half-cycles of the deflection signals so that only that half of the possible line trace which points in the direction of the relative motion of the distant craft is displayed. It is required to start the displayed trace (i.e. the centre of the available scan), at the image of the remote craft, and for this purpose start position control means 37 and 38 are provided under the control of joystick means, to introduce D.C. bias currents into the two deflection currents. To set these two control means the switches 24 and 25 are set in their first or lowest position, when small amplitude signals in quadrature are fed from source 41 to the two input windings to produce a marker on the C.R.T., the position of which is made to coincide with that of the image of the remote craft, by varying the control means 37 and 38. The switches are now set to their second on middle position wherein a signal is fed to the input winding 22. This produces a line trace on the C.R.T. starting at the image of the remote craft. The angle of the winding 22 is adjusted until the trace points back along the past position glow trail of the remote craft. The winding 22 is now at an angle corresponding to the heading of the remote craft plus 180 degrees. The switches are now set in their third or top position and the relative motion display produced as described. The length of the relative motion display may be increased for collision investigation purposes by adjusting potentiometer 36 which may be calibrated to determine the time to go to closest approach. The signals from the resolvers and the brightness control signals have to pass through gates 40 which are controlled from the radar transmitter and receiver 11 to only allow the display of the relative motion traces between successive scans of the normal display or during a period when the aerial is scanning through a small arc aft, when the normal display is blanked out. The latter case allows the use of slower scanning rates and simpler construction of the coils 34 and 35. Sawtooth waves having slopes proportional the two crafts' speeds may be used, instead of the sinusoidal signals, Fig. 2 (not shown). The speed co-ordinates produced by windings 30 . . . 33 may alternatively be represented by D.C. signals which are correspondingly subtracted from each other to provide new D.C. signals which control the slope of sawtooth waves produced by integrator means. Parts of the arrangement may be duplicated &c., to enable several traces to be produced.