Long-Jump Beam

The highly serviceable microwave, used for faithful transmission of television or multi-channel telephone service, has always had one shortcoming: in long distance use it cannot follow the curve of the earth, must be relayed in short jumps from stations placed about 30 miles apart. This week the Bell Telephone Laboratories and M.I.T. disclosed that their scientists, working together, have devised a new system to overcome this distance limitation of microwave beams.

Instead of transmitting on direct line-of-sight, the Bell-M.I.T. method shoots a beam into the sky like a giant searchlight. A searchlight beam passing through the air is visible many miles away although the light itself may be behind a hill. A microwave beam can be "seen" in much the same way. If it is very powerful, an

Across water and wilderness.

appreciable amount of its energy is reflected downward and can be picked up by sensitive apparatus as much as 200 miles away from the transmitter.

Long-jump microwave beams are not likely to replace the short-jump relay systems: the power must be enormously greater (10,000 watts instead of half a watt), and the antennae must be great parabolic "dishes" 60 ft. in diameter. But long-jump has uses that are vitally important in military communication, where construction of short-range relay stations is impossible or impractical. For example the long-jump method could be used across the water gaps and wilderness stretches of arctic Canada, where it would make sense to relay to a rear headquarters the pictures picked up by the far-flung radar outposts. There have been hints that a part of this system is already installed.

Another use is for controlling guided missiles. If a missile depends on microwaves for guidance, it loses touch with its control station as soon as it passes out of "sight" beyond the curve of the earth. It is possible that the new system can keep the missile firmly on a microwave leash over a far greater distance than the line-of-sight method permitted.

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