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New Daylight Viewing Screen for Radar Can Hold an Image for Minutes A RADAR viewing screen capable of retaining for several minutes a picture so bright that it can be clearly seen even in brilliant sunlight may result from a new electron picture tube developed by a research team at the David Sarnoff Research Center of RCA at Princeton, N.J. The tube has been designed as a simple electronic tool for the direct daylight viewing of radar in an air- plane cockpit or on the bridge of a ship. Today, airborne or marine radar screens are hooded to prevent daylight from obscuring the relatively dim images that appear. and even under a hood that cuts out all daylight the viewer may have to wait for 2 or 3 minutes before his eyes adapt themselves to the low light level of the radar image. Fine details of test pattern on the new picture tube are examined by H. O. Hook, of the development team. A distant cousin of the television kinescope, the new tube was developed by RCA scientists under a United States Army Signal Corps contract. The development team included Dr. Max Knoll, H. O. Hook and Dr. R. P. Stone, all of the Princeton laboratories staff. Far Brighter than Standard TV Picture The tube is able to present pictures five to ten times brighter than those on a standard television kinescope, or picture tube, and to retain a half-tone image on the screen for some 30 seconds without any deterioration, or up to several minutes in useable form. In radar scan- ning reproduction, the viewing duration needs only to be about ten seconds before a new picture is to be dis- played. In other applications where half-tone reproductions are not required, such as the display on an airplane in- strument panel of continuous visual instructions from a ground station, a single black-and-white image can be held on the tube for an hour or longer. The RCA research team said these characteristics of the tube point to possible use in airborne facsimile systems, oscillo- scopes, and wherever a bright electronic picture of transient data needs to be held over extended periods for viewing or photographing. In appearance and operation, the developmental tube is a small approximation of the standard television pic- ture tube. Like the latter type, it uses controlled streams of electrons to paint a picture on a phosphor-coated screen on the face of the tube. However, to present exceedingly bright pictures and to retain them on the tube face for minutes or longer, a number of different techniques were developed. Three Electron Guns In the neck of the tube are three electron guns, each producing an independent stream of electrons directed toward the tube face. One of these, similar to the elec- tron gun in a standard kinescope, "writes in" the picture. The second gun floods the viewing area with a con- tinuous shower of electrons, producing the picture seen on the phosphor screen. The third "erases" the retained picture when it has served its purpose. In a standard television picture tube, the writing beam directly scans the phosphors on the viewing screen, 26 rad;o age