280 BELL SYSTEM TECHNICAL JOURNAL 



a semiportable radar pack set and a searchlight control radar involved the 

 desgn of a new magnetron in the frequency range 1050 to 1110 mc/s to 

 operate at a maximum pulse voltage input of 25 kv. with power output 

 of at least 200 kw. Since these requirements, except for frequency, were 

 essentially those of the 7 28 A- J magnetrons already under development, 

 the new work closely paralleled that already in progress. 



Because of the maximum current limitation being encountered in the 

 development of longer wavelength magnetrons, a relatively longer anode was 

 designed for the new magnetron, coded the 5J23, thus insuring satisfactory 

 operation at higher current and input power. The resonator system was 

 "heavily" strapped with echelon wire straps [see Fig. 24(c) in PART I]. 

 Coarse frequency variation was accomplished by the use of straps at different 

 heights above the surface of the anode block. Finer frequency adjustments 

 were made in "pretuning" the structure, before seaUng, by small displace- 

 ments of the wire straps already in position. 



Output circuit work on the 5J23 was done together with that on the 728 

 A-J magnetrons and went through the same series of developments. The 

 output circuit used in the manufacturing design is identical with that of the 

 728A-J except for the dimensions critical to wavelength. 



For operational reasons, only one magnetron, the 5J23, in the frequency 

 range 1074 to 1086 mc/s, was coded. Fig. 49 shows a cut-away view of its 

 internal structure. Performance characteristics and other data are to be 

 found in Table I. Note that the 5J23, by virtue of its greater anode length 

 and higher frequency, has a higher critical current, L , above which tt mode 

 operation fails, than^do the 700A-D or 728A-J magnetrons. 



13.4 The 4J21-30 Magnetrons: When development work on the 5J23 

 had just been completed, an international agreement on frequency alloca- 

 tion made the frequency range of the 5J23 unavailable for radar purposes 

 at some future date. Consequently the work was to be redone for opera- 

 tion in the band 1220 to 1350 mc/s. The 5J23 and the equipment in 

 which it was used were to continue in manufacture and be used in the 

 period necessary for the development of the new equipment and magne- 

 trons. In addition to the frequency change, power output demands on 

 the magnetron were raised considerably, it being required that the new 

 magnetrons produce at least 500 kw. output power. Although the maximum 

 current limitation had seriously affected maximum output power capabilities 

 of the magnetrons in this wavelength range, it appeared that the new high 

 power demands were within reach by virtue of the higher frequency at which 

 the new magnetrons were to operate. 



The new assignment came just upon completion of the 5J23 and made it 

 necessary to build or acquire new laboratory equipment, C\V oscillators, 



