Radio Broadcast (May 1928-Apr 1929)

HE PLANS TELEVISION FOR WRNY Theodor Nakken is shown here with a television receiver designed to receive the television broadcasts from wrny. The Nipkow disc and its driving motor are set at an angle, and the sloping panel which covers the front of the receiver has a small window through which the images are viewed. What Can We See By Radio? By R. P. Clarkson M 'ORE and more the most enthusiastic radio fans are wondering what all the shooting is about. They realize that true television is not here but it is apparent that something is happening. Just what is being done, how it is being done, and what any fan can do to be "in the swim" is the purpose of this article in Radio Broadcast. First of all. the fan will come to realize that he faces a new handicap. He has been used to twirling the dials and getting one program as easily as another. The set that reproduces any music from wgy will also give any music played at wrny. Nowi he is to find that while he may tune-in on the pictures from either station, the television receiver which works on wgy's experiment won't do a thing on wrny, and vice versa. This, it seems to many of us, is particularly unfortunate at the beginning of the new pastime, particularly as there is no reason for this condition except the whim of the sender or the desire of the manufacturer to be exclusive. The heart of all present television devices is the Nipkow disc, which dates back to 1884. It is a rotating plate with a series of spirally arranged holes; aluminum is the material generally used for the disc. The speed of the disc is always determined by the number of pictures sent per second. This speed is capable of variation, of course, because the disc is driven by an electric motor and the motor speed can always be changed. In the commercial devices I have Author of "The Hysterical Background of Radio'? seen, however, there is no provision made for any considerable speed change. The fan who builds his own device can insert a speed control to advantage. A PICTURE Ij INCHES SQUARE NOW, as to the size of the picture, nobody needs to ask what size is being transmitted. It makes no difference to the receiver so long as the picture is square. Your receiving projector can be arranged to give you any size your heart desires, limited only by the si\e of the illuminated plate in the neon receiving lamp. The Raytheon type of neon lamp with \\" plates will safely cover a picture image lj" square. Probably no manufacturer will go much larger. Commercial receivers now planned are of that size or smaller, although at least one will put a magnifying lens in front of the viewing plate. This will enlarge the image and decrease the quality but make the picture more easily seen by a group. While the plate of the neon tube will absolutely limit the maximum picture size you can get, the spacing of the holes in the spiral disc and the pitch of the spiral will determine what size picture is actually projected at the receiving end. That is, if the holes are spaced one inch apart and the inner hole is one inch nearer the center of the disc than the outer hole, your picture will be one inch square. The spacing of the holes determines the width of the picture. The 185 . pitch of the spiral determines the depth of the picture. The size of the holes themselves is automatically determined by the size of the picture you want and the number of "lines" to the picture. Divide the depth of the picture by the number of lines transmitted and the result will be the diameter of the holes. Preferably, they will be a few thousandths of an inch larger than this calculation gives, so that each line will overlap the preceding one very slightly. These technical details are all that distinguish one apparatus from another. First, the speed of the disc, which must turn each second the same number of times as there are pictures per second transmitted. Second, the number of holes in the spiral, which must be equal to the number of lines per picture transmitted. These two facts must be known, and undoubtedly will be published by each station as it takes up television transmitting. At present, wgy sends 24 lines per picture and 21 pictures per second, wrny will send 36 lines per picture and 10 pictures per second. Hence, the speed for a disc to receive wgy must be 21 revolutions per second or 1260 r.p.m. For the Nakken pictures from wrny there must be a disc speed of 10 revolutions per second or 600 r.p.m. On the other hand the wgy disc will have 24 holes in a spiral while the Nakken disc will have 36 holes. For the same size of picture, therefore, the Nakken disc must be larger, but it goes at half the speed and will give better definition.