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In its simplest terms, a radar set shoots radio energy at a target, catches the reflected echo, times the round trip, divides by two, and. since the speed of the radio wave is known, translates all the information into a "blip" of light on a fluorescent (television) screen showing the target's distance and position.
In practice radar is not that simple. A conventional transmitter, sending continuous radar waves, would not do, for the same reason that a man roaring incessantly at a cliff would get back only a confusing noise. To get a clear, time-able echo, he must utter a short, sharp shout. That is exactly what radar does. It sends staccato "pulses" of electric energy, each less than a millionth of a second in length, at a rate of about 1,000 a second. Each pulse has time to make a round trip (about a thousandth of a second for a target 100 miles away), and record its message without interference from the next.
The big problem in radar is to generate enough power to get a detectable echo from a distant point. Of the total energy sent out in a radar beam scanning the skies, only a tiny fraction hits the target (e.g., a plane), and a much tinier echo gets back to the receiver. Engineers estimate that if the outgoing energy were represented by the sands of a beach, the returning echo would be just one grain of sand.
Little Waves from Overseas. To produce a compact instrument, small enough to be carried in a plane, that would handle the enormous power nee:'ed (surpassing that of the most powerful radio station), required a revolution in radio.
One fine autumn day in 1940, a. British engineer, carrying a small black bag, debarked from a ship in Manhattan. He was met by a Bell Telephone engineer. They meandered into a movie before driving out to the Bell man's suburban house. Next day, satisfied that they had shaken off any possible spies, they turned up at the Bell Laboratories with the supersecret device that broke the radar bottleneck. The Briton, a member of a radar mission to the U.S., brought designs anda model of an electronic tube called the "magnetron."
The magnetron, by whirling electrons at high speed inside a magnetized cylinder, produced extremely short radio waves and great power. Its principle was not new. But the British had developed a high-powered version of it, and U.S. engineers perfected its radar adaptation.
With the magnetron's help, the M.I.T.
Radiation Laboratory and Bell Laboratories proceeded to develop an uncharted part of the radio spectrum—microwaves. For radar, the relatively long radio waves (one and a half meters) used early in the war had serious shortcomings: 1) they gave only a crude, distorted echo; 2) they had some blind spots, especially close to the ground; 3) they required huge "bedspring" antennae. Microwaves solved all these problems at one stroke. These tiny waves, which are measured in centimeters, can be formed into a beam precise enough to detect the periscope of a submerged submarine.
Four-Part Reporter. The major working parts of a typical radar set are:
¶A bowl-shaped antenna which beams the outgoing radio pulses, catches the echo.
¶A high-powered transmitter using a magnetron.