Patent GB-997567-A (GB)
Title: Apparatus for simulating a radar display
IPC: F16K5/04
Filed: 1961-06-30
Abstract: 997,567. Radar simulators; television. GENERAL PRECISION Inc. June 30, 1961 [July 8, 1960], No. 23802/61. Headings H4D and H4F. [Also in Division G4] Relates to means for simulating the radar display of the ground as produced by an airborne radar in which the different contours of the ground are represented on a photographic film strip of corresponding shades of grey and the film is scanned by a flying spot CRT scanner to produce an output signal from a photomultiplier which is applied to a synchronously scanned display CRT, relative movement being produced between the film and the scanner in accordance with the simulated movement of the aircraft, e.g. the film strip may be displaced longitudinally by motor driven sprocket wheels and the scanner may be displaced transversely to the film, Fig. 2 (not shown). According to the present invention means are provided for automatically compensating for (1) variations in the intensity of the scanning flying spot, (2) drift in the photo-multiplier and (3) any undesired variation in the greyness characteristic along the film strip due to variations in the photographic processing. As shown in Fig. 1, an image of the scanning spot on the screen of the scanner CRT 13 is projected by means of a beam splitter 21 (1) through the film strip 11 on to a photomultiplier 16 and (2) directly on to another photo multiplier 20, the output from the multiplier 16 being divided by the output from the photo-multiplier 20 in a circuit 25 so that the resultant output from the divider 25, which is applied through a film calibration amplifier 79 to the display CRT 18 and a clearance plane computer and simulated radio altimeter 80, is independent of variations in the intensity of the light from the scanner tube 13. The divider 25 preferably converts both inputs into logarithmic form, performs an analogue subtraction and then converts the output to the antilogarithm. Sync. pulses for the deflection circuits 35<SP>1</SP> for the scanner and display CRT's 13 and 18 are produced by an elongated light source 27 surrounded by (1) a rotating cylinder 28 having a longitudinal slot 30 and (2) a fixed outer cylinder 34 having an aperture coupled by a light guide to a photomultiplier timing circuit 35. The electron beams of the scanning and display CRT's 13 and 18 are blanked out during the retrace periods and during such periods light from the source 27 is coupled to the photo-multipliers 16 and 20 via light guides 32 and 33, the corresponding output from the photo-multiplier 16 being applied through a gate 36 opened by the timing circuit 35 and a feed-back circuit comprising a memory circuit 37, e.g. a resistorcapacitor integration circuit, and D.C. amplifier 38 to a dynode of the photo-multiplier 16 to establish a desired output level which may be set by gain control 43, the resultant dynode control voltage being held constant during the next line sweep period by the memory circuit 37; the photo-multiplier 20 is stabilized by a corresponding feedback circuit 40, 41, 42. As shown in Fig. 5, the map portion of the film is formed in an area 67 and it may be prepared by photographing a contoured map on to a negative, stripping the area of highest elevation from the negative and exposing the film strip through the negative. The areas o f next highest elevation are then stripped from the negative, the film being again exposed through the negative and this process is repeated until the negative is completely stripped so that when the film is finally developed after the last exposure, areas of high elevation will be darker than areas of lower elevation. Simultaneously with the production of the map portion 67 a grey scale band of standard contours is produced along a strip area 68 by the same photographic process and when the film is completed it is examined and any variation in the greyness characteristic along the length of the film is marked along an area 70 as a four-bit digital code of opaque dots 71 which may also include the pick-up response characteristics of the photo-multiplier 16 and the output response characteristic of the display CRT 18. Since the grey scale 68 is not required when the coding 71 has been established, the scale could be positioned on the extreme edges of the film, the sprocket holes being then cut after the coding 71 had been established. As shown in Fig. 1, the coding 71 is read photo-electrically by means 73, 78 to give corresponding voltages which control relays, Fig. 3 (not shown), to select the magnitudes of the input and feedback resistances and hence the gain characteristic of the film calibration amplifier 79, Fig. 1, to compensate for the variations in the greyness characteristic, the input and feedback resistance networks including diodes to produce suitable non-linear characteristics, Fig. 4 (not shown). Specification 997,568 is referred to.