MAGNETRON AS GENERATOR OF CENTIMETER WAVES 279 



Ten different magnetrons, coded the 728A-J, were put into manufacture. 

 These covered the frequency range from 900 to 970 mc/s, a 7 mc/s range 

 being allotted to each code type. The operating characteristics of the 

 final design together with other pertinent data are tabulated in Table I. 

 An external view of the magnetron is shown in Fig. 48. A maximum current 

 limitation for satisfactory operation in the ir mode was also encountered in 

 this magnetron but at current values above the 20 ampere operating point 



Fig. 48 — An external view of a 728A-J magnetron (275 k\v., ^930 mc^s). The con- 

 centric cylindrical sleeve to be seen inside the output circuit coupling, from which the mag- 

 netron is supported, is a part of the "choke" (see Fig. 47). Note the heavy glass protec- 

 tive housing over the input leads. 



at which the required output power was attained. Because of the shorter 

 wavelength, the current limitation was not as severe as that encountered 

 in the 700 A-D. 



The 728A-J magnetrons were driven by a spark wheel, line type modu- 

 lator. The greater tendency of the driving voltage to overshoot with this 

 modulator, by virtue of the slowness of buildup of RF oscillation, was re- 

 duced by the use of a series resistance and capacitance network coupled 

 across the magnetron input like that used earlier with 720A-E magnetrons 

 at 10 cm. 



13.3 The 5J23 Magnetron: The request for the Laboratories to develop 



