Patent GB-655148-A (GB)
Title: Improvements in and relating to radar apparatus
IPC: G01S7/22
Filed: 1948-10-07
Abstract: 655,148. Radiolocation. COSSOR, Ltd., A. C., and WILLIAMS, B. C. FLEMING-. Oct. 7, 1948, No. 26219. [Class 40 (vii)] [Also in Group XL (b)] Means for producing electronically a movable identification symbol on a twodimensional radar cathoderay tube display, e.g. a P.P.I. 25, comprises an unmodulated auxiliary cathode-ray tube 12 with a short-persistence screen which is scanned synchronously with the display cathode-ray tube 10 and an optical system 13- 16 for directing light from a small zone on the screen of the auxiliary tube to scan a representation 23 of the symbol, e.g. the numeral "1," the light transmitted through the representation being collected by a photo-electric cell 17 whose voltage output is applied to intensity modulate the display tube 10, means being provided for adjusting the position of said zone. The symbol may comprise a numeral, letter or design and the representation may comprise a transparent symbol on an opaque background or vice versa. As shown, the optical system comprises two plane mirrors 13, 14 and two lenses 15, 16, mirror 13 being mounted obliquely on a supporting shaft and mirror 14 being mounted on a shaft parallel to its plane, the two shafts being orthogonally disposed in a plane parallel to the screen of the tube 12 so that the position of the zone may be adjusted by energizing D.C. motors 18 and 19 coupled to the shafts. In operation the mirrors 13 and 14 are adjusted so that the symbol 27 is adjacent the response 26 on the screen 25 which it is desired to identify and if the response is moving in a rectilinear path the voltages controlling the motors may be set by potentiometers so that the symbol and response remain adjacent; if the response movement is irregular, the adjacency may be maintained automatically by known methods. A plurality of similar optical systems, e.g. 13<SP>1</SP>-16<SP>1</SP>, cooperating with the photo-cell 17 may be disposed around the axis of the auxiliary tube to provide further identification symbols, e.g. 28, 30 and 32. The control voltages applied to the motors 18 and 19 are proportional to the X and Y velocity components of the zone on the auxiliary tube and hence to the corresponding velocity components of the symbol on the display tube and the symbol may be modified, Fig. 4 (b), to indicate the resultant direction of motion by mounting the symbol representation on a disc carrying an arrow and a magnetic needle which aligns itself with the resultant magnetic field produced by two orthogonal coils energized respectively by the motor control voltages, Fig. 3 (not shown); alternatively the arrow may be displayed adjacent the corresponding symbol, Fig. 4 (a), by means of a separate optical system. The known method of video-mapping as disclosed in Specification 614,595, may be employed to display fixed objects 37, a transparent map 34 With opaque markings being mounted over the screen of tube 12 and the light transmitted through the map being collected by a photocell 35 whose voltage output is applied to intensity modulate the tube 10. A lightproof hood 38 encloses the screen of tube 12 and the optical systems, and screens 39 and 40 prevent undesired light from reaching photo-cell 17.