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BELL SYSTEM TECHNICAL JOURNAL 



magnetrons, coded the 4J21-30, in the band 1220-1350 mc/s. A satis- 

 factory resonator system giving proper operating voltage, tt mode frequency, 

 and mode frequency separation was designed prior to and incorporated in 

 the first operating model. Similarly, a satisfactory output circuit for proper 

 loading over the broad band of frequencies and the design of mechanical 

 features involved in the cathode, cathode mount, cooling facilities, output 

 circuit, straps, and resonator system were provided. 



Fig. 50 — An external view of the 4J28 magnetron (one of the 4J21-30 series,. 600 kw., 

 '^1280 mc/s). Note the cooling fins attached to the magnetron body. 



The new interaction space and resonator system were scaled from a com- 

 promise between the 728A-J and the 5J23 designs. Shielded, double ring 

 straps like those of the 728A-J were adopted. Two anode structures 

 differing somewhat in resonator dimensions and size of interaction space 

 were used, one for the short wavelength half of the band (4J21-25), the other 

 for the long wavelength half of the band (4J26-30). The dififerent frequen- 

 cies within each of these groups were attained by the use of straps of different 

 widths. 



A single design of output circuit for the entire frequency range necessitated 

 making the transformer properties as independent of frequency, or as broad 

 band, as possible. The output circuit has three parts. At the outside of the 



