GB878192A - Improvements in or relating to radar display apparatus - Google Patents

Abstract

878,192. Radar. DECCA RECORD CO. Ltd. Dec. 4, 1959 [Sept. 5, 1958], No. 28662/58. Class 40(7) In a pulse radar adjustable-position electronic interscan markers are produced on a first rangeangle or range-height C.R.T. display, e.g. a P.P.I. display 14, and the echo signals are also applied to a second similar display 40, e.g. P.P.I. or type B, through gate circuits controlled by gating pulses corresponding to the marker signals so that the second display 40 displays only echoes from small regions corresponding to small areas on the first display identified by the markers. As shown the first display 14 comprises a resolved P.P.I. with X and Y scan generators 18, 19 each having separate rate and shift inputs 20, 21 as disclosed in Specification 818,477. During the range scan periods the shift and rate inputs are connected respectively by means of a switch 31 to an off-centering signal generator 23 and a sine-cosine bearing generator 22 driven synchronously with the rotating aerial 10 to produce an off-centred P.P.I. display. During the interscan periods the rate inputs 20 are connected to a marker scan control generator 32 and the shift inputs 21 are connected to both the off-centring signal generator 23 and a marker position signal generator 30 to produce an electronic marker as described in Specification 744,640 whose position relative to the origin of the P.P.I. display is controlled by adjusting the generator 30. The marker may be a circle, a square or a straight line whose direction and length is controlled by the marker scan control generator 32 as disclosed in Specification 837,201. As shown the position generator 30 is adjusted manually but alternatively the marker may be tracked (1) automatically, Fig. 2 (not shown), as disclosed in Specification 867,361 or (2) by rate aiding means as disclosed in Specification 837,201. In order to generate a gating pulse which corresponds in time with a marker signal, additional scan generators 50 and 51 are provided which are similar to the scan generators 18 and 19 but which have no shift inputs. The sawtooth outputs from these additional generators 50, 51 are combined with the outputs from the marker position signal generator 30 in a double coincidence comparator 49 to give the gating pulse which is applied to the gate 52 to select the echoes received within the duration of the gating pulse. As shown the second display 40 comprises a resolved P.P.I. similar to the first display 14, the rate and shift inputs 46, 47 of the corresponding scan generators 44, 45 being connected respectively to the bearing generator 22 and to a corresponding off-centering signal generator 48 so that the second display 40 can be off-centred independently of the first display 14. The scan generators 18, 19, 44, 45, 50, 51 and the transmitter 11 are all synchronized by a trigger generator 55. If required a marker may be displayed on the second display 40 which corresponds to the marker on the first display 14 or which is independent thereof. In the former case, during the interscan periods of the second display 40, the rate inputs of its scan generators 44 and 45 are connected to the marker scan control generator 32 and the shift inputs are connected to both the marker position signal generator 30 and the off-centering signal generator 48. Other information such as track numbers may be displayed adjacent the selected echo signals by means of further interscan signals generated by a monoscope. Specification 837,203 also is referred to.