Radio Broadcast (May 1928-Apr 1929)

12 RADIO BROADCAST NOVEMBER, 1928 pretation of the law may Baird "televise," which in itself constitutes transmission of intelligence, unless he obtains a license. And he has been refused the necessary license! It has been prophesied that Baird will be enjoined by law from transmitting as soon as he commences to do so! Surely this attitude on the part of the authorities can be due to nothing more or less than lack of faith by the British Post Office engineers (under whose scrutiny radio is microscopically preserved) in Baird's present methods. Re« Baird, it must be admitted, has made remarkable strides in the advancement of the art but now, it is felt, he has come to the end of his tether, and is being criticized severely for placing on the market apparatus representing a germ of an idea still in an embryonic stage of undevelopment. It is argued that Marconi had no more to offer the public in those early days when he first fought to establish his ideas about wireless, but then, he appealed to a far more critical public (and then only to highly-trained engineers) than Baird is doing. Moreover, Baird, aided by colorful and exaggerated reports in a general press that knows nothing more about his invention than the fans who will be expected to invest in his televisors, is meeting with considerably less opposition than did Marconi. COLOR TELEVISION /^OLOR TELEVISION, the latest development of Baird, was described in the London daily papers in glowing terms. The writer was given a personal demonstration of this new child of television, by Baird, and was impressed only to the extent that is due to a radical development yet in its cradle days. A man's head, covered alternately with a blue or red cloth, afforded the subject to be transmitted in the demonstration. It was possible to see when the subject opened or closed his mouth, put out his tongue, and possibly when he rolled his eyes, and to see the different colors of the head coverings, but to say that the features were recognizable would highly exaggerate the matter. Monochrome (black and white) television, however, affords several times as much detail as color television. The following explanation of the principles of color television was dictated by Mr. Baird especially for Radio Broadcast. Except for the changes outlined below, the equipment is similar to that used by Baird in his monochrome experiments and already described in this magazine on several occa-Biue sions: T! Triode Oscillators ra — 3 .-1000Per Sec ^--10Per Sec Magnets , FIG. 2 BAIRD S EXPLANATION HE transmitting machine consists of a disc perforated with three sets of holes arranged in spirals and set round the periphery of the disc. See Fig. 1. One spiral is covered with red filters, the second spiral is covered with green filters, and the third spiral with blue filters, so that each spiral lets through only light of one color. As the disc revolves, a spot of red light first traverses the object being transmitted, this red light being thrown back from the object and effecting a photo-electric cell. The red light, having completed this traversal of the object, the green spiral next comes into operation and traverses the object with a spot of green light. This is then followed by the traversal of the object with a spot of blue light from the spiral covered with blue filters. Thus, the object is traversed first by green, then by red, and then by blue illumination and three images are sent out to the receiver, the first image showing only the red parts of the object, the second image showing only the green parts, and the third image showing only the blue parts. At the receiving station a similar disc to that of the transmitter revolves exactly in step with the transmitting disc, and behind this disc in line with the eye of the observer are two glow discharge lamps — a neon lamp, and a lamp filled with helium and mercury vapor. The neon lamp supplies the red constituents of the light and the helium and mercury vapor the blue and green. The eye of the observer sees first a red image, then a blue image, and then a green image, the images being presented so rapidly that persistence of vision causes them to blend and the observer to see a composite image made up of these three colors. Now red, green, and blue constitute the three primary colors from which all other colors are made up: for example, purple is a combination of red and blue, yellow is a combination of green and red, and in the same way all other colors are made up of various proportions of these three primaries, red, green, and blue. The process used in color television is exactly similar to the three-color process used in color cinematography. The application of color television will naturally be considerable, but it is not proposed by the Baird Television Company to put color machines on the market for some time, as this apparatus is still in the experimental stage. The first television machines to be marketed will be simply monochrome, showing one color, and these machines were exhibited at the Radio Exhibition held at Olympia, on September 22nd last, and will be placed on the market at a price of £25. The image appears on a glass screen approximately eight inches in diameter and the televisor includes a loud speaker of the electrodynamic type. A special receiving device has been designed which enables both vision and speech to be received fr@m the same aerial and at the same time. As three separate images must be sent in color television the speed of transmission should be increased three times. In practice, however, it is found that this increase of speed is unnecessary as each of the three images contains in itself quite a large proportion of the visual image received and it is not necessary to transmit at more than twice the speed of normal television to obtain a satisfactory blend of the images and colors. CAMPBELL SWINTON S EXPERIMENTS 'l^HE favorable opinion tendered toward the * suggestion of Oliver Lodge and others who suggest the utilization of electrons as a basis for experiment in the development of television leads one to expect that newer experimenters in the field will turn their attention to such systems as that avocated by Campbell Swinton. His experiments have been carried to a much farther stage than Mr. Clarkson explained in Radio Broadcast recently. It was only shortly after Braun, in 1897, introduced the cathode-ray oscillograph that it occurred to Swinton to work on the cathode-ray principle in an endeavor to make practical some system of television. He found in experiments that the cathode-ray beam could be deflected both magnetically and electrostatically with remarkable precision. With two similar cathoderay beams simultaneously controlled and deflected by electric or magnetic forces due to identical currents Swinton expected to obtain absolute synchronism in the motions of the beams with maximum accuracy, irrespective of the speed. He planned to use one of Braun's oscillographs at the transmitting end and another one at the receiving end, the beams to be synchronously and simultaneously deflected by the varying fields of two electromagnets placed at right angles to each other, and energized by the same two a. c. currents of widely different frequencies. In this manner the moving extremities of the two beams would sweep over the surfaces at the transmitting and receiving ends with remarkable rapidity and synchronism, so rapidly, in fact, as to take advantage of the wellknown phenomenon of persistence of vision. To produce the required picture at the receiving end it was only necessary that the rapidly scanning extremity of the cathode-ray beam be impinged on a sensitive fluorescent screen. The beam, of course, would be caused to vary in intensity by the varying signals from the transmitter, thus producing the necessary graduations of light and shade to produce a picture. Swinton's real difficulty lay in devising a system which would efficiently accomplish the variations in 1000-v Per Sec: 10~ Per Sec: Magnets • Triode Oscillators FIG. 3