Jetrader - January/February 2012 - 21

The 360-foot transmitting radar towers and smaller receiver towers.

The WAAF operators saw ﬂickering images to interpret as range, number of enemy and altitude.

quite late in the Battle of Britain when they attacked them and ﬁghter airﬁelds. The damaged radar towers were back in operation in less than three days. Not only could they initially pick up Luftwaffe aircraft at a range exceeding 100 miles (160 kilometers), but in 1944, it could also detect V2 rockets being launched against London. On 7 December 1941, in the hut housing a primitive radar unit receiver overlooking Pearl Harbor, the operator noticed an echo he believed could be a large group of aircraft heading toward the island. His superiors told him the ﬂickering CRT blip was possibly a heavy rainstorm, as no aircraft was expected from the mainland. A short time later, the rainstorm arrived with bombs and shallow-water torpedoes to change the course of history. In 1920 at General Electric’s Research Laboratories in Schenectady, N.Y., Albert Hull developed a simple, two-pole magnetron for the magnetic control of vacuum tubes. Two physicists in 1924, one Czeck, the other German, independently discovered that the magnetron could generate very high electrical frequencies in the range of 100 MHz to one GHz; the result not only meant that dinner could be cooked in a microwave oven in a couple of minutes, but the night ﬁghter was converted in to a deadly weapon against the night bomber. First, the magnetron’s technical problems had to be overcome, and ready to solve these issues were two scientists at Birmingham University in the UK. In 1935, Hans Hollmann in Berlin patented the multi-cavity resonant magnetron and in the same year, Romanian physicist Theodor V. Ionescu came up with the same idea. They gave the very

high power frequencies needed, but their drift was too unstable for the receivers to use them, so the German military decided to use the stable, low-powered Klystron (50 kW at 545 MHz) on their night ﬁghters; this put them at a disadvantage over the much longer range three to 30 GHz centimetric band magnetron based radar in British Mosquito night ﬁghters escorting the RAF bombers. From then on, it was tit-for-tat in counter-measures between the two systems. When one German ﬂyer accidently landed in Scotland, the British discovered his ﬁghter’s radar was limited to three frequencies, which made it vulnerable to jamming with aluminized paper strips cut to one-half of the known German units’ wavelengths. The Mosquito radar unit was installed in a streamlined thimble nose with a parabolic scanner that rotated at 200 rpm

and simultaneously tilted up and down and left to right to trace a spiral over a 45-degrees ﬁeld. Some 5,000 units were produced during the war. John Randall and Harry Boot, the two British scientists developing their cavity magnetron, used liquid cooling and increased the unit’s power a hundred fold. They managed to synchronize the receiver to the generated frequency by coupling alternate cavities within the magnetron and eliminating instability. In September 1940, Winston Churchill sent Sir Henry Tizard to lead what became known as the Tizard Mission to the United States, which introduced to the U.S., amongst others, the newly invented resonant-cavity magnetron and other British radar developments, the Whittle gas turbine, and the British Tube Alloys (nuclear weapons) project.

A sample magnetron valve. John Randall and Harry Boot, the two British scientists developed their cavity magnetron using liquid cooling.

Jetrader 21

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Jetrader - January/February 2012

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