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Origins of the Magnetron
Hi All,
Just a bit of RF history obtained from "Forty Years of Radio Research," by George C. Southworth while I was doing some research for a correspondent: "As early as 1921, Dr. A.W. Hull of the General Electric Company described the characteristics of a device which he called a magnetron. It consisted of an axial filament surrounded by a cylindrical plate between which a constant radial electric field could be impressed. Superimposed on this arrangement and at right angles to the electric field was an axial magnetic field. ... "Later the inductive load was reduced to a tiny Lecher frame. A magnetron with this configuration was placed inside a small waveguide by Dr. Harold S. Howe of the University of Michigan to obtain a top frequency of nearly 50,000 mc. (1938). "A few years earlier, 1934, Dr. Cleeton and Professor Williams also of the University of Michigan had ... discovered a pronounced absorption band for ammonia at about 27,300 mc. This ultimately led to a new time-keeping device of high accuracy. ... "Finally the plate was made from a single block of copper with appropriate segments milled inside its hollow periphery, each representing an individual oscillator. This important step was taken by physicists at the University of Birmingham in the late thirties. They also applied plate power in short pulses and at much higher levels than had been used previously. This was not only more appropriate for good magnetron operation but it provided an almost ideal signal for radar use. ... Details of this device were brought to America first by Sir Robert Watson-Watt and Drs. Cockcroft and Bowen in September, 1940." 73's Richard Clark, KB7QHC |
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