. The Bell System technical journal . dricaldiode or 2-electrode tube, with a uniform magnetic field in the directionof the electrode axis. The original type of tube has been largelysuperseded for ultra-high-frequency generation by the so-called split-plate magnetron, first used by Okabe,^^ in which the cylindrical anodeis divided longitudinally into two (or more) segments to the terminalsof which is connected the tuned circuit. Such a tube is shown inFig. 25. In the frequency range from 300 to 600 megacycles the split-platemagnetron compares favorably with the negative grid tube both inoutput
. The Bell System technical journal . dricaldiode or 2-electrode tube, with a uniform magnetic field in the directionof the electrode axis. The original type of tube has been largelysuperseded for ultra-high-frequency generation by the so-called split-plate magnetron, first used by Okabe,^^ in which the cylindrical anodeis divided longitudinally into two (or more) segments to the terminalsof which is connected the tuned circuit. Such a tube is shown inFig. 25. In the frequency range from 300 to 600 megacycles the split-platemagnetron compares favorably with the negative grid tube both inoutput and in anode efficiency. Its use has been limited because ofthe complicating factor of the magnetic field, and the attendingmodulation difficulties. For frequencies higher than 600 megacyclesthe magnetron provides larger outputs than those so far reported byother means. It has been used at frequencies up to 30,000 mega-cycles, a value well above that so far reported for any other type ofvacuum tube. 126 BELL SYSTEM TECHNICAL JOURNAL. Fig. 25—An experimental model of the split-plate magnetron showing a possiblearrangement of the magnetic field. The magnetron depends for its operation upon the curvature of theelectron orbits produced by the magnetic field. As first shown byHull ^^ in 1921, a critical field exists beyond which the anode currentfalls off rapidly to zero. This field is given by the relationship // Vf, (3) where R is the anode radius and V is the potential of the cylindricalanode with respect to an axial filament. Although the originalmagnetron of Hull and Elder made use of variations in the magneticfield in its operation as a generator, it was soon discovered thatoscillators could also be produced with steady fields by two somewhatdifferent mechanisms. The one, first pointed out by Habann,^^ makesuse of a negative resistance effect observable in the static charac-teristics and the other, first described by Zdcek,*^ involves the electrontransit time in a way
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
