Faint Reflections

High-frequency TV waves have long been considered undependable at more than line-of-sight distances, i.e., from transmitter to horizon. They punch through the ionosphere (ionized layers in the atmosphere which reflect lower-frequency radio waves), and so are lost in space instead of curving conveniently around the bulge of the earth. Once in a while a TV picture is received strongly at a great distance, but such events are freaks which cannot be counted upon.

Last week the National Bureau of Standards was proclaiming that high-frequency waves do reflect from the ionosphere and can get around the earth's curve. The bureau got the Collins Radio Co. of Cedar Rapids, Iowa to slant a powerful beam of 49.8 megacycle waves into the air in the direction of its own Radio Laboratory at Sterling, Va. The distance between transmitter and receiver is about 800 miles, so the signal might be expected to come through only in freakish bursts.

Something different happened. Bureaumen Ross Bateman and G. Franklin Montgomery had little trouble picking up the Cedar Rapids signal. Slanting down from above, it was faint but continuous.

The bureaumen now believe that the ionosphere is not entirely transparent to high-frequency waves (above 30 megacycles). They think its ionized layers are stirred into turbulence, perhaps by meteors, and that patches of its gas are always in a condition to reflect small amounts of high-frequency energy.

The most obvious use for this discovery is in beaming television pictures beyond the line of sight. A few relay stations might carry TV programs all the way to Europe. This would be difficult, however, for the reflected waves are extremely weak.

The bureaumen refuse to conjecture what other duties these waves may perform, but their tight-lipped secrecy and intense interest suggest a military function. Best guess is that they may be used to steer guided missiles.

At present, radio-guided missiles go blind when they pass beyond line-of-sight distance from a friendly transmitter. Low-frequency waves, which curve around the earth, are not much good for them. Only high-frequency waves can be beamed with sufficient accuracy to do an adequate steering job. Now that it has been proved they stay on earth, they may be used to guide missiles for 1,000 miles or so.

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