MAGNETRON AS GENERATOR OF CENTIMETER WAVES 



323 



to within 1 mc/s wliich corresponds to a displacement of tlie pins of 0.0001 

 in. and to 0.1 turn of the worm wheel drive. The tuning mechanism is 

 provided with a positive stop at each end of the tuning range. The fre- 

 quency band is covered in five revolutions of the main drive screw and gear. 

 A fle.xible vacuum envelope is provided by means of sylphon bellows. De- 

 tails of the design may be seen in the sectioned model shown in Fig. 71. 



JTe 



n 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 72 — Smoothed characteristics of the 2J51 tunable magnetron {55 k\v., 8500 to 

 9600 mc/s) throughout its frequenc}- band. Shown is the dependence upon frequency 

 of the unloaded Q, Qo] of the external Q, Qexi] of the circuit efficienc}-, t/c; of the electronic 

 efficiency, jj^; of the over-all efficiency, rj; and of the pulling figure , PF. Also shown is 

 the dependence of the operating frequency upon position of the tuning pins, D, measured 

 from the position of maximum intrusion. The dashed lines on either side of the exper- 

 imental curves indicate the range of possible variation of the data. The curves for r]c and 

 rit have been determined from the experimental results by the use of equation (25) of 

 PART I and the relation v = Ve Vc- 



The elimination of radial cathode support leads and the use of the mag- 

 netic pole pieces as the end covers of the magnetron body made possible a 

 large reduction in the magnet gap and magnetomotive force required to 

 produce the necessary magnetic field. Because of the requirement of inter- 

 changeability with the 725 A magnetron, a very awkward V'-shape magnet 

 design in which the leakage flux was tremendous could not be avoided. 



