GB706530A - Indicating device - Google Patents

Abstract

706,530. Optical apparatus. RAYTHEON MANUFACTURING CO. March 13, 1952 [Aug. 23, 1951], No. 6605/52. Class 97(1) [Also in Group XL(c)] An indicator arrangement for use in conjunction with a P.P.I. display in a radar system comprises a transparent plotting screen mounted above and substantially parallel to the screen of the display cathode-ray tube with a half-silvered mirror disposed substantially midway between the two screens, means being provided for compensating for the curvature of the cathode-ray-tube screen to reduce parallax between this screen and the image of the plotting screen in the half-silvered mirror. The plotting screen is edge-illuminated so that marks made with a crayon on the plotting screen are illuminated and appear as reflections in the mirror superimposed upon the display on the cathode-ray-tube. In the arrangement illustrated compensation is achieved by giving the plotting screen 20 an equal and opposite curvature to that of the screen 18 of the cathode-ray-tube. A mirror 23 is arranged with its upper half-silvered surface midway between the upper surface of the screen 20 and the inner fluorescent surface of the screen 18. Edge-illumination of the screen 20 is achieved by tamps 22 arranged in a housing around the edge of the screen. In a modification, Fig. 3 (not shown), the plotting screen is flat, compensation being achieved by constructing the mirror with a similar curvature to that of the cathode-ray-tube screen but with twice the radius of curvature. In a further arrangement, Figs. 4 and 5 (not shown), a divergent lens is arranged betweeen the mirror and the cathode-ray-tube, both the plotting screen and the mirror being flat.