Systems of Radiovision

Radio Record, Volume II, Issue 31, 15 February 1929, Page 4

Systems of Radiovision

Entirely New Angle Conceived ee Tus difficulties which still hamper the achievement of true radivvision. or the transmission of moving scenes by wireless, do not arise if it is possible to connect the trausmitter: to. the receiving station by one or more line wires. Most of the successful demonstrations of "moving-picture" effects claimed by various experimenters have, in fact, been carried out over connecting Wires. Such. a limitation is, of course, fatal to the popular conception of a movingpicture service: in which signals wiil be broadcast through the ether and picked up on an ordinary garden nerial. If it is uevessary to provide a connecting wire between the central distributing station and each individual receiver, the initial cost of instalation will be so high as to restrict the service to a compiratively small circle of wealthy subscribers.

A Fatal Limitation. HERE are two main reasons why a connecting wire is necessary in the present state of television development. in the first place, owing to the number of separate modulation frequencies required to transmit a clear picture, there is no "elbow room" ayail able for them in the ether. A radio service of moving pictures must there: fore either be coufined to inconvenient hours outside the ordinary broadcasting times, or else give rise to wholesale interference with existing broadcast programmes. In the second place, the energ) picked up by an aerial from a radiated signal wave is so small.that an expensive outfit is necessary to amplify the received currents up, to the point where they are capable of operating the Neon receiving lamp. Quite apart from the expense of a multistage amplifier, it is well known that beyond a certain point the effect. of atmospherics and internal "tube noise’ becomes so great as almost, if not wholly, to mask the effect of the’ original signals,

Telephone Vision. ASSUMING that the use of connecting wires is necessary, the existing service appears to offer the best medium for operating television apparatus in its present state of development The Bell Telephone Laboratories have, in fact, now developed a combined telephone and television system in which it is possible for a speaker at one end of the line to see the distant person with whom he is conversing. and also to have his own features simultaneously televised and_ transmitted to the far end of the line: How the System Works. HIS achieves the ideal of telephonic conversation. Not only does the user hear, but: he. also sees the pérson with whom he is conversing. It is a definite step forward in the ‘annihilation of space. As the speaker talks into the microphone he faces a mereury-vapoyr lamp, bent into the form of a circle, so that the whole 6f his featiires are illum-

inated. Leyond the lamp,is a scien containing two apertures. In the Wcond of these appears the image of the distant speaker. . The reflected rays from the head and shoylders of the local speaker pass through the second aperture, and, after being analysed by a rotating disc fitted with spirally-arranged holes, fall on to a photo-electric cell. This converts the light-and-shade effects into corresponding electric currents, which are then fed to the line wire and re-. appear as a visible image before the distant speaker. . . Meanwhile the picture signals from the distant station cause the intensity of a local Neon lamp to, fluctuate. These light variations arg built up into an image by a second series of spiral holes: formed in the same rotating disc, and are then’ thrown on to the first aperture in th screen referred to above.