All the World's a (TV) Stage

Prospects of worldwide television transmission are looking up. At last week's "scatter propagation" conference at George Washington University, electronics engineers were enthusiastic about the recently declassified techniques for transmitting "line-of-sight" waves much farther than the horizon.

Long radio waves can be used to send code and voice across the oceans because they are deflected downward by ionized layers in the atmosphere, and therefore follow the curve of the earth. They cannot be used for television chiefly because they do not offer a wide enough band of frequencies. The shorter waves, including those that are used for TV, pass through the ionized layer and are lost in space. So

TV signals tend to fade out a few miles beyond the horizon.

Recent discoveries showed that on certain frequencies not all of the energy in the line-of-sight signal makes its escape into space. A small part of it is "scattered" downward. Electronics men compare this effect to the scattering of light from a searchlight beam. Not much light is scattered, but often the beam can be seen from a great distance when the searchlight itself is invisible.

Two bands of waves, VHF (Very High Frequency, 30 to 60 megacycles) and UHF (Ultra High Frequency, 300 to 3.000 megacycles), have been found to scatter. No one seems to know precisely what it is that makes them do it. Meteor trails are suspected in the case of VHF. Small "blobs" of irregularity in the electrical properties of the atmosphere up to 25,000 ft. are supposed to be the scattering agent for UHF. Whatever the cause, the waves do scatter, and special apparatus has been developed for the armed services to take advantage of the scattering. Some of the equipment is spectacular (see cut). Extra-powerful transmitters must be used, and two large receiving antennas placed well apart give better results than one. With the proper setup VHF has been transmitted dependably more than 1,000 miles. UHF, the wave band suitable for TV, is good for 300 miles.

The range is not long enough to carry TV programs across the Atlantic in one hop, but relay stations using Greenland and Iceland as stepping stones can do the trick. Other continents could be reached in the same way without too much difficulty. TV Pioneer Allen B. Du Mont stated at the conference that there is now no electronic reason why nearly all the world should not watch the same TV program at the same time.

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