Radio Broadcast (May 1928-Apr 1929)

Some Useful Standards TRANSMITTING AMATEUR TELEVISION By BOYD PHELPS A victim posing in front of Phelps' televisor A GREAT deal of credit for the development of short waves has been given to the amateurs but only a handful of their large numbers did any degree of pioneering, as Mr. Kruse has pointed out in previous articles in this magazine. Jenkins, Maxim, the Secretary of the Navy, and a host of others are looking to the amateurs for the development of television. Television, however, has been with us for some time but somehow the amateurs, like proverbial mules, have been backward about coming forward in the field. A few experimenters have set up receiving apparatus to satisfy their curiosity, but transmitting seems to be considered out of the question. Knowing that amateurs like particularly hard problems, the Federal Radio Commission took the recommendations verbatim of a group of amateurs interested primarily in two-way telegraphic-code communication and assigned the worst and least usable of amateur channels to amateurs for television purposes. The 5.00 to 5.35 meter (60 to 56 megacycle) band is highly experimental with only spasmodic distant reception and the lone twoway contact of the writer and former 2nz to its credit. It is suspected of being a daylight wave for very long distances under certain conditions, or rather a whole flock of conditions, but little is known of this band for telegraphy, let alone television. The remaining legal amateur television band, which is from 150 to 175 meters (2,0001715 kc), is practically deserted because most amateurs wish to take advantage of the much better carrying power of the shorter waves over great distances on low power. The inability to erect a large enough antenna in the average back yard to permit efficient sub-fundamental operation constitutes a serious disadvantage to some. Also, the band is largely occupied by illegal but never-the-less present harmonics of practically every broadcasting station from one to a thousand miles distant. Other conditions such as static and distance to power ratios are not unlike the so-called "graveyard" broadcast waves around 200 meters. In other words, amateur television must not be expected to cover every continent with a few watts of power for it will take considerable power and good conditions to cover a few hundred miles. Before any of us drift too far apart we ought to think of some standardization of the many optional methods of producing and reproducing the images so that we may all use the same type of receiver for many transmitting stations. As receiving does not require learning the code and taking a license examination it is quite probable that the non-transmitting experimenters "looking-in" will outnumber the television transmitters many times over, and it is for these that standardization should be especially helpful, so that it will not be necessary to use different discs, different speeds, different arrangement of holes, and The pictures below show three induction motors which have been converted for synchronous operation different directions of scanning to receive each transmitter. Rules of Standardization rY^O START things along the same path, let J us adopt some simple rules of standardization, based on how the resultant signals must be "unscrambled" at the receiver. The first rule I propose is to make all transmitters such that the receiving disc holes will scan the image from left to right and the spiral more slowly progress from top to bottom, exactly as we read a printed page. Random design of a trans • february. 1929 page 247 •