Patent GB-848507-A (GB)
Title: Improvements in or relating to radar displays
Inventor: PARKER ERIC
IPC: G01S7/22
Filed: 1958-03-28
Abstract: 848,507. Radar. DECCA RECORD CO. Ltd. March 13, 1959 [March 28, 1958], No. 10145/58. Class 40(7). The invention relates to control arrangements for an electronically generated marker presented on the screen of a radar system display tube provided with orthogonal deflector means. The marker itself may be a spot or small circle or it may be in the form of a line trace representing speed and direction of travel by its length and direction. The marker is caused to move by waveform generators associated with the respective deflector means and having shift and rate control inputs. According to the present invention means are provided producing two rate control voltages proportional to the sine and cosine of the angular position of a control member and having adjustable amplitudes which are applied to the rate control inputs of the waveform generators, a fraction of these voltages or of voltages proportional thereto being also combined with the respective generator outputs. The effect of feeding such voltages to the generator outputs is to displace the marker in the direction of its travel. Thus if adjustment is made to position the marker on a radar target and to apply what are thought to be appropriate inputs having regard to its speed and direction of movement it may be found later that marker and target part company due to an incorrect speed assessment. With an arrangement according to the invention a single readjustment of the speed setting input, providing it is made at a predetermined time after the initial setting will correct the marker position at the same time as it corrects the speed of movement. The correction is likewise effective in connection with directional errors. The compensation introduced may be that appropriate.for a time interval of one minute and a warning device may be arranged to operate to indicate the time at which resetting should be effected if necessary. Alternatively the compensation circuits to the generator outputs may include a three position switch giving, no compensation, slight compensation, or greater compensation, selectable at will. The Figure shows an embodiment in which the marker is introduced on to the P.P.I. display of a pulse radar during interscan periods. In this, electronic switches, shown schematically at 19 and 20, disconnect the scanning waveform generators from the aerial bearing information unit and the off-centring potentiometers 22 during interscan periods, earthing the rate control inputs. The shift control inputs are connected to the outputs of waveform generators 40, 41. These generators are fed from position voltage generator 42, by which the initial position of the marker may be fed in, and four-armed sine cosine potentiometer 30 adjustable for direction of marker movement. The input to the potentiometer includes a "speed of movement" control 38 and the generators have capacitive feedback arranged so that the inputs from potentiometer 30 control the slope of the output waveforms. As indicated at 32, 34, the second sine and cosine outputs from the potentiometer 30 are fed respectively through variable resistors 61 and 63 to the generator outputs. It is these connections which enable the marker position to be corrected automatically when the speed and/or direction of travel of the marker is readjusted after the appropriate time interval. Specifications 818,477, 837,201, 837,202, and 848,506 are referred to.