Patent GB-882905-A (GB)
Title: Improvements in or relating to display systems for radar data presentation
IPC: G01S7/24
Filed: 1957-11-18
Abstract: 882,905. Radar. ATLAS-WERKE A.G. Nov. 18, 1957 [Nov. 26, 1956], No. 35864/57. Class 40(7). Relates to a ship-borne pulse radar with an aerial rotating in azimuth in which the track of the ship and the tracks of other moving objects in 'its vicinity are displayed on a C.R.T. According to the present invention the video echo signals are applied alternately to two storage C.R.T.'s and the signals stored on any one storage tube are read out to the display tube and to the other storage tube. The video storage scans of each storage tube are synchronized with the aerial rotation, the scan frame period being equal to an integral number, e.g. one, of aerial rotation periods, and the scan origin which corresponds to the instantaneous position of the ship is displaced in accordance with movement of the ship and is restored to a datum position, e.g. the centre of the storage screen, at the commencement of each storage period. The read-out scans of the storage tubes are synchronized with the display tube scan which may be controlled so that (1) the image on the display screen corresponding to the instantaneous position of the ship remains at a fixed position, e.g. the centre of the screen, or moves in accordance with movement of the ship and (2) a reference direction on the display screen corresponds either to the ships heading to give a "course oriented" display or to a predetermined compass direction, e.g. north, to give a "compass oriented" display. In one embodiment, Fig. 2 each storage tube 19 and 20 comprises a single beam tube, Fig. 1 (not shown), which is selectively controlled to effect storage or read-out, the readout automatically causing erasure, and in another embodiment, Fig. 7, each storage tube 64 and 65 comprises a double-ended tube, Fig. 6 (not shown), with separate storage and read-out beams so that storage and read-out can be effected simultaneously and independently; in this case the read-out does not cause erasure. The screen of the display tube should have a persistance equal to the display scan period. In the Fig. 2 embodiment a P.P.I. type scan is applied continuously to the display tube 21 and to the storage tubes 19, 20, the storage. tube scans being compass oriented. Video echo signals from the radar 18 are applied continuously to the display tube 21 and during a first aerial rotation with the switches 22-25 in the positions shown they are also applied to the storage tube 20. On completion of the first aerial rotation the switches 22-25 are changed over and during the second aerial rotation the video signals from the radar 18 are applied to the storage tube 19 and the signals stored in storage tube 20 are read out to the display tube 21 and to the storage tube 19. This process is repeated and in addition the origin of the scan in the storage tube 20 is displaced continuously during the first and second aerial rotations in accordance with movement of the ship, returned to the centre of the screen at the end of the second rotation, displaced during the third and fourth rotations and so on whereas the origin of the scan in the storage tube 19 is displaced during the second and third, fourth and fifth rotations &c. and is returned to the centre of the screen at the end of the first, third, fifth &c. rotations. The displacements of the origins of the scans for storage tubes 19 and 20 corresponding to an assumed curved track 30, Fig. 3, of the ship are shown in Figs. 4 and 5 respectively in which the points 1T, 2T &c. correspond to the times of completing the first, second &c. aerial rotations, the full lines show the segments of the track recorded during the storage periods and the dashed lines correspond to the read-out periods. In a modification (not shown) two display tubes 21 are provided which are operated alternately at intervals of time greater than the afterglow period, the screens being viewed selectively by means of a hinged mirror. In order to estimate the speed of the objects displayed, time markers may be produced by periodically suppressing the video signals from the radar. Simplified methods of displacing the scan origin by means of a single rotatable deflection coil are described and the initial position of the scan origin may be displaced from the centre of the screen by half the total expected displacement. In the Fig. 7 embodiment the display tube 49 and the read-out beam of each doubleended storage tube 64, 65, Fig. 6 (not shown), are scanned synchronously with a rectangular television-type raster by a scan generator 67 and the recording beam of each storage tube 64, 65 is scanned (1) with a P.P.I. type scan by a generator 66 synchronized with the aerial of the radar 46 when the corresponding multisection switch 69 or 70 is in the upper position as shown and (2) with a rectangular raster by the generator 67 when the corresponding switch 69 or 70 is in its lower position. The video output from the radar 46 is applied selectively to the storage tubes 64, 65 by the lower section of a two-section switch 68 and the read-out signal from the storage tube to which the radar video signal is being applied is applied to the display tube 49 by the upper section of the switch 68; when the switch 69 or 70 is in its lower position, the read-out signal from the corresponding storage tube is also applied to the recording input of the other storage tube. Shift voltages from potentiometers 58, 59 which vary in accordance with the movement of the ship are applied (1) directly to the display tube 49 to displace the scan raster in a direction opposite to that of the ships movement and (2) through the bottom sections of switches 69 and 70 to the storage tubes 64, 65 such that when the switches 69 and 70 are in their upper position the resultant displacement of the recording raster is in the same direction as the ships movement and when the switches 69 and 70 are in their lower position the scan displacement is opposite to the ships movement. In operation during a first recording period with switch 68 in position I as shown and switches 69 and 70 in their upper positions as shown, the radar video signal is applied to the storage tube 64 and the stored pattern is read out to the display tube 49 so that due to the opposing directions of the recording and display scan displacements the point on the display corresponding to the instantaneous position of the ship remains at the centre of the display screen. Near the end of the first recording period the switch 70 is changed to its lower position thereby transferring the charge pattern from the tube 64 to the tube 65 but due to the opposing directions of the displacements of the P.P.I. recording scan of tube 64 and the rectangular recording scan of the tube 65, the point on the charge pattern produced on the screen of tube 65 corresponding to the instantaneous position of the ship will be at the centre of the screen. When the transfer of the charge pattern has been effected the switch 70 is returned to its upper position, the shift potentiometers 58, 59 are returned to their initial positions and the switch 68 is changed over to position II thereby erasing the charge pattern on tube 64 and applying the radar video signal to the tube 65 which then operates in a similar manner to tube 64 in the ensuing recording period. Specification 849,499 is referred to.