GB1220892A - Improvements in or relating to radar display apparatus - Google Patents

Abstract

1,220,892. Pulse radar. DECCA Ltd. 15 July, 1969 [25 July, 1968], No. 35617/68. Heading H4D. In a radar P.P.I. display system, means superimpose at least one marker line adjustable in position and direction and having a series of equally spaced marks along the line, means controlling the spacing of the marks is calibrated in terms of speed such that a craft would take a time t to travel between the positions represented by two adjacent marks and delay means gradually shifts the marks along the line such that each mark moves a distance equal to the spacing between marks in the time t. In the embodiment sawtooth generators 12, 13 each having a rate control input produce a marker line on a true-motion P.P.I., and each such input is fed with respective D.C. sine and cosine voltages from an adjustable potentiometer 15 energized by an adjustable potentiometer 16. The sawtooth voltages are fed via respective current generators to fixed orthogonal deflection coils 20, 21. The timebase produced is triggered to begin during an interscan period from a unit 23. To adjust the starting point of the trace D.C. voltages are produced in potentiometers 26, 27 which may be controlled by a rolling ball. The marker trace (which may be invisible) is modulated by brightening pulses from a fixed frequency oscillator 28 and a gate 29 provides for only a predetermined number of marker pulses each time the oscillator is operative; the gate is delayed relative to the start of the marker line by an adjustable pulse width delay circuit 30 (e.g. controlled by clockwork 31) to move the markers in the required manner. Switches 32, 33 enable a marker line to be displayed only when required; a circular marker is provided, controlled in position by potentiometers 26, 27 so that its position corresponds to the end of a line, when switches 32, 33 are closed. Several marker lines may be provided for. Fig. 2 shows the position of the radar-equipped craft at O, the position of a target at P, and respective marker dots such as 41, 42. If the new position, i.e. at a later time, of the target is at P<SP>1</SP>, and not coinciding with Q, the position to which the first marker dot has moved in the interval, potentiometer 15 is adjusted to bring the marker line through P<SP>1</SP> and potentiometer 16 is varied to bring Q and P<SP>1</SP> into coincidence; the direction of the true target track may then be read from a calibrated scale on potentiometer 15. Potentiometer 16 may carry a speed scale. After making similar settings corresponding to the markers for the radar-equipped craft, the display indicates future craft and target positions and the collision risk. Prediction of future position cannot be made if a craft is changing course, but the latter can be detected.