Broadcasting (Jan - Dec 1935)

I lectrons on the circular end of the I be were figuratively "painting" m 3 lines of electrie-to-light imrilses at a rate to produce 30 picires per second, "interlaced" so I actually to frame 60 pictures i|r second. More lines and faster iaming can be achieved, but the jA experimenters think this is iough for good illumination and :;tisfactory clarity. It is ! The pictures were smaller ;an the 240-line visual images at frames per second which Baird 2levision Ltd. demonstrated to me London and which is one of the stems the British will bring out ct spring. Baird screened a x 9 inch picture, which was clear t not quite as sharply delineated the RCA picture. Baird also eened an 8 x 6 inch picture with e same numher of lines and ames, but it was again not as arp as the RCA picture of apoximately equal size. This is not say that the Baird images were oor — far from it. Thev were exllent, but the RCA's are better. It might be pointed out here that e second system which England ill bring out next spring, requir|g the set manufacturers to build |ro circuits in each receiver so at both systems can be "tuned is that of Electrical and Music 'tdustries Ltd., of which until a weeks ago when it sold its lares, RCA was a big stockholder. MI, as it is known, will offer nages of the approximate size of CA's, built up at the rate of 50 _L-amings of 405-line pictures per . , cond. Because RCA has a technical interchange with EMI, which ;es practically the same appaitus, that system is virtually the 4rme as the one demonstrated at pmden — and the acceptance of it the British public next spring .vith receivers costing about $400 »ch) may provide some clue to jmerican observers of the eventual zi Marketability of television receivg apparatus. This Is Television! it" C THE darkened "television the:er", where a young engineer ned in the received images on a al that brought in the synchroned sound at the same time that it -'amed the pictures, we were town a two-foot closeup of a stuo shot consisting of a hefty ^,oung man lighting and smoking ";'. \ cigarette and telling us what was ; ippening at the transmitting stujjSo. He was distinctly recognizee, the smoke of his cigarette ."'.as discernible and even the gleam his glasses could be seen. The elevision camera", of which more rter, was then moved back to ten ."r et and we saw the young man in ut three-quarters length, again clearly as in a photograph. V.Then the camera was pointed out raj window of the studio and we ^€re treated with a street scene. "e first saw a billboard whose advertising, as we were later to obj rve on the spot, was in colors so ■ at the letters and words were of n-ying shades in the reproducpn. But we could read the billiard and we could see the street 'ilow and the houses nearby. More nazing, we saw in the same scene portion of the Camden-Philadelnia bridge, could make out the ructural features, and saw7 above ie concrete bridge rail the tops of my automobiles speeding across ie picture. It was every bit as ear as a motion picture, though (Continued on page 60) THE "EYE" OF TELEVISION— Above is the television camera discussed in this article, showing the insides and mounting of the camera box itself and the mounting within it of the Zworykin "Iconoscope". The lower picture is a closeup of the Iconoscope tube itself, which is to television what the microphone is to sound broadcasting. The deflection of the electron beam for scanning the mosaic is accomplished by a magnetic field, the deflection coils being arranged in a yoke which slips over the neck of the Iconoscope. The assembled deflecting unit is shown at the right of the lower photograph beside the tube. The "Iconoscope" is a large vacuum tube with a long neck, containing a photo-sensitive mosaic plate which is scanned by an electron beam. It is the mechanical duplicate of the human eye, the sensitive plate corresponding to the retina and the electron beam to the nervous system which carries the image from the retina to the brain. The rectangular mosaic plate in the bulb of the tube consists of several millions of light-sensitive cells which are sprayed by electron beams from an electron "gun" located in the tube's long neck. In the same manner that a machine gun sprays bullets, the electron "gun" directs the stream of electrons across the plate from left to right. The beam traverses the plate in a series of parallel lines covering the entire surface of the mosaic in one-thirtieth of a second, and then repeats the entire process. It takes 343 of these lines to make one complete image, corresponding to one frame of a motion picture film. When the image is focussed on the mosaic plate, every photo-sensitive element of the mosaic emits electrons in proportion to the intensity of the particular point of the image being scanned. This leaves the mosaic positively charged, thus creating a sort of electrical image on the surface of the mosaic. When the scanning electron beam touches a point of the mosaic, it neutralizes this positive charge, creating an electric impulse which represents electrically the information about that point of the image. These impulses are transmitted by radio waves just as impulses representing sound are transmitted in sound broadcasting. To eliminate nicker, the scanning is done by alternate lines; that is, all the odd lines (1,3,5, etc.) are traced by the electron beam from top to bottom of the plate, then the electron spray starts again at the top and fills in the even lines. This process takes place 30 times each second, producing 10,290 lines per second. The whole system is entirely electrical without a single mechanical moving part. The transmitted impulses are received by a radio receiver similar to the receiver of broadcast sound waves, only in this case these impulses, after being amplified, are not applied to a loudspeaker but to another cathode ray tube called the "Kinescope". This tube is similar to the "Iconoscope" except that instead of having a photo-sensitive mosaic, it has a fluorescent screen whose purpose is to transform the electrical impulses back again into light, thus reproducing the picture. Television Viewed As Engineering Aid Commercial Operation is Five Years Away, Says Mr. Cruse WITH television and its prospects occupying more and more attention of broadcasters and broadcast engineers, Andrew W. Cruse, chief of the Department of Commerce electrical equipment division, speaking Dec. 12 before the combined engineering societies of Schenectady, N. Y., described television as an "engineering catalyzator" because he said he feels that it is "a development which by its presence is capable of inducing changes in other branches of engineering even while remaining unchanged itself." Mr. Cruse has seen practically all of the major television experiments in laboratory or field operation, having visited the various American laboratories and having been dispatched by Secretary of Commerce Roper last summer to Europe to observe the British and German systems. A report of his observations, as given before the NAB convention at Colorado Springs last summer, was published in detail in the July 15 issue of Broadcasting. While also forseeing many economic obstacles to the public introduction of television in this country, Mr. Cruse is generally optimistic about the ultimate future. May Require Five Years "I HAVE every confidence," he asserted at Schenectady, "of the ability of our own engineers Xo keep this country fully abreast of other countries in this field." It will be "some time", however, he added, before we can hope to parallel our present broadcasting networks with a similar network of visual transmitters, although the FCC has already licensed about 27 experimental television transmitters. "Television on a commercial scale, serving millions of people in all or most of our population centers," he said, "will not, I am sure, materialize within five years. In this connection I think that within the very near future this new television industry of ours — which will probably become known as the Sixth Estate — will have to do something with regard to a program of standardization in order that the pioneer observers will be given some assurance that their receiving sets will not become obsolete before they get out of the packing cases in which they are delivered." Mr. Cruse predicted that television will "make the motion picture industry a bigger and better industry than it has ever in its wildest dreams hoped to be," chiefly because of the increased demand it will create for film subjects. He was certain, he said, that it will not keep people away from the theater any more than sound broadcasting and home movies have done. He predicted a vast new field for research, operation and employment for all branches of engineering having to do with acoustics. "HI-FI" is the nickname for high fidelty broadcasting, now coming into greater vogue, that has been coined in England. December 15, 1935 • BROADCASTING Page 9