Radio Broadcast (May 1928-Apr 1929)

186 KAJJ1U bKUALXJAbl AUGUST, 1928 Of course, if you can vary the motor speed 100 per cent, through the range of 600 r.p.m to 1260 r.p.m., the substitution of discs will let you receive either station at will. Or, it is possible to have two sets of holes in the same disc. The spirals may be concentric and the speed changed, or a large disc used and the wgy spiral placed only half way round, with two such spirals for each disc, and the wrny spiral all the way round. The disc would then need a speed of about 600 r.p.m. to receive either number of pictures. These matters will be brought out in various constructional articles and are mentioned here only to indicate the details in which one receiver will differ from another. The point is that it is only in the disc that any distinct difference will lie between the various television systems, with the exception of the Baird arrangement— and he will probably come to this sooner or later, just as Jenkins and Alexanderson have. WHO IS DOING THE WORK? THE roll of sponsors for television apparatus at present include Nakken, who is manufacturing; Jenkins, who is negotiating with a view to manufacturing; Baird, who has interested American manufacturers; Alexanderson, whose firm seems at present only interested in broadcasting pictures experimentally at wgy; and a Boston group of experimenters who announce that wlex will be on the air with pictures before long. Nakken will use wrny. While all the other devices use simple neon lamps in the set output instead of (or in series with) the loud speaker, the lamp being viewed through the holes of a rotating Nipkow disc, Baird has been using a lamp, a Nipkow disc, a slotted disc, another disc, a mirror, and a collection of prismatic cells at the receiving end. At present this assorted collection is being sold abroad. It is believed, however, that the American type of the Baird receiver may be simply a Nipkow disc, a slotted disc, and the collection of cells, together with the neon lamp. This was illustrated in the July Radio Broadcast in the article "What Hope for Real Television?" (P 125) So far as reception itself is concerned, any receiver with sufficient amplification and a power output can be used. Actually, the audio amplifier NEON TUBES FOR SALE This window display in New York's Radio Row offers the television fan neon lubes at the modest charge of fifty-five cents, and a glimpse at a distinctly experimental set-up for television reception. The si;e of picture possible may be judged from the opening in the board behind the magnifying glass. Obviously the magnifying glass is a very necessary part of the set-up should preferably be changed to straight resistance coupling until transformers are available which do not have a distinct cut-off of frequencies above 5000 cycles. For the present, however, there is a legal limit of plus and minus 5000 cycles for the width of sidebands and this limit will not be exceeded. While the wgy figures give a possibility of 12,096 impulses per second, basing the modulation of each line as equal to the number of lines, actually the simplicity of the picture and quantity of white space in the background cuts down the line modulation. Likewise, Nakken's intention to send 36 lines and 10 pictures per second would run into 12,960 impulses per second if each line had 36 modulations. Here, too, the simplicity of the figures and the abundance of white background will act to bring the actual picture within the legal 5000 impulses per second. It is not meant to imply that any regulations specifically limiting television have been adopted, so far as known. The fact remains, however, that the legal sideband possible without interfering with the next station is 5000 impulses, and it makes no difference, so far as interference is concerned, whether these impulses arise from sound variations at the studio or light variations which are transformed into electric impulses. It is true that wgy was given almost carte blanche on the occasion of one demonstration to the press. Various editors and writers still tell how much better that demonstration was than anything else they have seen, apparently not realizing that the use of 20,000 or more impulses to the pictures naturally would be infinitely superior in results to any picture, regardless of how it was sent, that uses 5000 impulses or less. The difference would be much greater than that between a newsprint half-tone of poor quality and the fine prints made for framing. The legal limitation must be overcome by some new method of transmission before even the crude possibilities of present television devices can be realized. The contrast of the picture will depend upon the relative light intensities of the neon plate under slight voltage fluctuations or on the extent that those fluctuations are varied. The brilliancy of the image will depend largely on the size of the holes in the disc and the speed of the disc. High speed and small holes will make an image hard to see WHAT WILL THE FAN SEE? THIS brings us, of course, to a consideration of what is to be sent and what you can see through these whirling discs. There is much talk of sending the pictures of performers so that you can see them and hear them, too. There may be an occasional attempt at this. Only the head will be sent, and no groups, such as orchestras, will be included. A single head can be put across, but it will be hardly recognizable except for the outline. You will know it is a head and distinguish between a man or woman. With proper make-up on the face, which art may be developed especially for a televisor, possibly a distinctive type of face and head can be recognized. A sneeze on the part of the artist, and the face will disappear. I am also inclined to believe that any attempt at singing by the artist while before the televisor will result in a blank Actual size and shape ' of image with 2" radius to outer hole ■ Actual size and shape of image with 4" radius to outer hole THE ACTUAL SIZE OF PICTURE POSSIBLE This shows how the si{e of the scanning disc determines the si^e of the received picture. When the si%e of the disc is such that the radius from the center to the outer hole is two inches then the received image has a si\e and shape as indicated in the left hand shaded portion in this diagram. If the disc has a radius of four inches to the outermost hole then the si\e of the picture is as indicated in the shaded portion at the right. In both cases, however, the total number of scanning lines is the same and therefore with the four-inch radius the number of lines per inch is only half as many as with a two-inch radius. Consequently the larger the radius the less apparent detail there is to the picture.