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

it will prove to be of great value. One cannot say now whether the post-war relay system will use the tubes developed for it before the war or whether, instead, some of the great wartime developments will be used. In any case, the suc- cess of the radio relay depends on the new tubes which are made available in the ultra-high fre- quency or microwave region of the spectrum. What has been said of the inti- mate relationship between tube de- velopments and the application of microwaves to the relay system applies to almost all other applica- tions of microwaves. For new- ap- plications, new tubes are required. Outstanding RCA Record In the field of television, the rec- ord of RCA Laboratories physicists and engineers is outstanding. Tele- vision became an electronic art— and a practical possibility— through their development of the Iconoscope and the Kinescope. The Iconoscope receives the optical image of the scene to be transmit- ted, stores it, analyzes it into its elements, and converts it into elec- trical impulses for transmission. The Kinescope converts the elec- trical impulses at the receiver back into an image for viewing. Remarkable as was the perform- ance of the Iconoscope and the Kinescope, further progress was demanded. The Iconoscope required too much light for the transmission of a satisfactory picture. In the studio, the performers comiilaincd of the glare and the heat. Outdoors, the last quarter of a football game on a rainy November afternoon, when viewed on a television re- ceiver, might become lost in the "snowstorm" of background dis- turbances, similar to "noise" or static in the case of sound broad- cast programs when the signal is weak. An increase of tenfold in sensitivity of the Iconoscope was demanded. To the Iconoscope ex- perts, this was an almost impossible demand—but only almost. The first step for a research man in solving a problem is to analyze it. The Iconoscope stores electrical charges produced by photoemission and then converts these charges into signal current. For many years, research has been conducted on photoemission by hundreds of scientists for many purposes. It appeared that the Iconoscope al- ready had been given a photoemis- sive surface nearly as sensitive as could be expected. Research direct- ed toward further improvement could pay only small dividends. Looking at the next step in the process, the research men knew that only about 10 per cent of the stored electrical charge was finally converted into a useful signal. If this conversion efficiency could be increased to 100 per cent, the de- sired tenfold increase in sensitivity would be achieved. It was w-ell knowTi that the 90 per cent loss of stored charge was caused by the scattering of the "secondary" elec- trons knocked out of the target by the high-speed electrons of the scanning beam. There seemed no satisfactoi-y way to control these secondary electrons so it was de- cided to eliminate them completely. To do so would require that the target be scanned by a beam of very low-speed electrons. No one had ever found a way to focus and con- trol such a beam so the solution of DR. H. B. DE VORE M.^KES A PRELIMI- NARY ADJUSTMENT ON THIS HIGH- VOLTAGE TEST CAGE, IN WHICH THE TUBE IS FI.NALLY CHECKED IN A COM- PLETE CIRCUIT. the problem required invention of a high order. The story of the development of the more sensitive Icono.scope—now called the Orthicon—is a highly technical one which can hardly be told here. The necessary inventions were made and the ideas were de- veloped to practical form through much painstaking research with the result that the Orthicon met the "almost impossible" reciuirements which had been specified to the tube research men. This development made it possible to transmit by tele- vision scenes which previously had been too dim. One of the most in- teresting aspects of the develop- ment is that a new path was opened, the following of which promises further large increases in sensi- tivity. The day may come w'hen any scene which is illuminated brightly enough so that one can see it di- rectly can be transmitted by tele- vision. Projection Kinescope The Kinescope, too, was found short of perfection. The television image in the receiver was repro- duced on the end of a glass bulb where it was viewed directly. Nat- urally, the picture could be no larger than the end of the bulb. The high cost of large glass bulbs lim- ited the size of the picture to per- haps twelve inches on the diagonal as a maximum. This was large enough for a few people to enjoy the picture, but it would obviously be very much better if the picture could be considerably larger. There was even a demand for a picture large and bright enough for a theatre. The solution of this problem was by no means easy. Several different approaches were tried. One of the more obvious was also one of the least hopeful: the projection Kine- scope. The idea was simply that the picture would be projected on a screen from the end of a small Kinescope by the use of a projection lens, much as in a magic lantern. The great weakness with this pro- posal was that not enough light could be produced on the end of the necessarily small Kinescope to pro- vide a satisfactorily bright picture of useful size, even using the best [RADIO AGE II]