Radio age research, manufacturing, communications, broadcasting, television (1941)

NEW TUBE HAS "MEMORY" Graphcchou, Developed at R( A Laboratories as a Teleran Adjunct, Can Store Visual Information for More Than a Minute. RADAR sig-nals or oscilloscope traces, which occur in less than a millionth of a second and which remain in view only a few seconds on fluorescent screens, can now be "stored" for more than a minute by a new electron tube that has "visual memory". The tube, called the Graphechon, is based upon the discovery that certain materials may be used both as insulators and conductors of electricity. It was described by Louis Pensak, research physicist of RCA Laboratories, Princeton, N. J. at the March convention of the Institute of Radio Engineers in New York. The first major use of the tube will be in Teleran, the television-radar air navigation sys- tem under development by RCA. The Graphechon is a "booster" device which is employed between the stage where a radar beam is re- ceived and where it is reproduced on a television kinescope. It retains for more than a minute images that have a life of less than one- millionth of a second. With the Graphechon the radar signal is kept in the form of an electrical charge, which is "written" on the tube target by the radar beam and "read" from it by an icono- scope-type beam, similar to that used in telecasting. The signal is then amplified and applied to the kinescope, the television viewing screen. Here it can be observed, or monitored, and picked up from the kinescope, by the television camera, retaining the brightness and good contrast of the screen image. The Graphechon makes it possible to observe a radar pattern on a Ijright-screen kinescope, instead of the dim radar scope, in a normally lighted room and without any spe- cial preparation. Electrons "Write" and "Read" The heart of the Graphechon is a metal target, 3 inches square, coated on one side with a layer of pure quartz, 20 millionths of an inch thick. In the original model, two beams in the legs of a V shaped tube are aimed at this target. One is the radar beam, which "writes" on the quartz surface: the other is the iconoscope-type beam — such as is used in a television camera — which "reads" from it. Unlike a fluorescent screen, the target is not light sensitive, but is sensitive to electrical charges. The beam of electrons from the "reading" gun strikes the target and every electron knocks off sec- ondary electrons, which fly to the conducting coating that lines the tube. Removal of negative electrons builds an increasing positive charge i;n the target surface, until a maxi- mum point of equilibrium is reach- ed. When this occurs the excess of secondary electrons, over the beam current, returns to the target, main- taining the electrical status quo. The quartz coating is now acting as an insulator and permits the charging of the surface to a higher voltage than the metal sheet. At this point the iconoscope beam has prepared the target for the radar beam, which will "write" on it. When the radar receiver picks up a reflection — of a plane, some point of the terrain, etc. — the signal turns on the radar beam of electrons which crashes through thi quartz layer, makes it conducting' at that point, and there discharges the voltage. In short, the action of the icono- scope type beam is to put a uniform positive charge over the entire sur- face of the insulating film. The action of the radar beam is to make the insulator conducting at the points of impact, and so dis- charge the film in some pattern. The iconoscope type beam then pro- ceeds to charge up the film once more. The iconoscope scanning beam then knocks secondary electrons (Continued on page 27) LOUIS PENZAK OF RCA LABORATORIES HOLDS ORIGINAL MODEL OF GRArHECHON TUBE WHICH HAS A "VISUAL MEMORY." READINO GUN CROSS-SECTION OF V-TYPE GRAPHECHON Tl BE SHOWINc; RELATFVE POSITIONS OF "READING" AND "WRITING" ELECTRON GUNS. [20 RADIO AGE