Patent GB-907890-A (GB)
Title: Improvements relating to plan position indicating radar apparatus
Inventor: CALVERT EDWARD SPENCE
IPC: G01S7/24
Filed: 1959-08-05
Abstract: 907,890. Radar. NATIONAL RESEARCH DEVELOPMENT CORPORATION. July 29, 1960 [Aug. 5, 1959], No. 26701/59. Class 40 (7). A radar P.P.I. display carried by a moving craft is stabilized as to azimuth and also in respect of translational movement. Additionally, the display provides an indication of the craft on which it is mounted which is displaced only in accordance with departure of the latter from its initial course. The display thus indicates the range and bearing of the latter craft and of other craft in the service area (echo signals) with respect to a fixed-heading constanttranslational velocity reference framework. The invention may be carried into effect by known means controlled by signals derived from navigational apparatus and one suitable arrangement is shown in Fig. 5. In this Figure the switches, initially, are in the dotted line positions and the display cathode-ray tube D functions as a conventional P.P.I. display with the addition of an indication (displaced from the centre) representative of the craft on which the apparatus is mounted. With the switches in the initial position two constant-drive units CDR and CD#, the former supplied with range signals from a resolver RR fed from mileage and compass units M and C, respectively, and the latter supplied directly from the compass unit C, provide output signals of opposite polarity to the input signals representative, respectively, of the distance of the craft from an initial position and of the initial bearing of the craft. The units CDR and CD# are such that, when the input signals thereto are disconnected, they continue to supply a constant output signal equal to that at the instant of interruption of the input signals. This condition is brought about when it is desired to operate the invention by putting all switches into the positions shown by full lines. The continuous constant outputs of CDR and CD# are then combined in difference computors DCR and DC# with signals derived directly from RR and C, respectively, to provide outputs representative of the changing (if any) position and bearing of the craft with respect to the position and bearing at the instant of operation of the switches. The output from DCR is then fed to a delay unit DU to control the time of translation thereby of pulses RP from the radar transmitter (to provide the craft indication) and the delay imparted to such pulses is added to the received target (echo delayed) pulses ED in a delay adder DA from which the signals for the display tube D are derived. This operation controls the operation of the display in respect of range " R " translation. To control the bearing " # " translation and to stabilize the heading the output of unit DC# is combined in a differential device DL with a signal from the compass C, the output of device DL being then combined in a synchro device S of the differential type with the rotational scan signals to provide the rotational scan of display tube D. Diagrams showing craft positions reached after equal intervals of time by turning at constant speed and constant radius through different angles to corresponding new straight courses are described with reference to Fig. 4 (not shown), as they would appear on a chart or map and with reference to Fig. 4b (not shown) as they would appear on a display according to the present invention.