530 BELL SYSTEM TECHNICAL JOURNAL 



force, dotted in the figure, clearly correspond to a somewhat larger ca- 

 pacitance, especially when the length of the cavity is smaller than its 

 diameter; but this larger capacitance is probably still less than the active 

 capacitance Cn- 



In so far as the gain-band product depends on the circuit capacitance 

 degradation factor (Fig. A2-3), the curve is probably fairly accurate up to 

 2000 megacycles and somewhat optimistic for higher frequencies where the 

 coaxial line predictions are evidently too small. 



Above 5000 megacycles the quarter-wave tuning cannot be used for the 

 1553 tube since the glass would interfere with the tuning plunger. A 

 glance at Fig. A2-3 shows that moving the plunger back a half-wave to 

 the next node involves a drastic loss in gain-band product— a factor of 

 four at 6000 megacycles — because of the great increase in circuit passive 

 capacitance. Redesign of the tube for good figure of merit at 6000 mega- 

 cycles would therefore require the use of first-node tuning. A reduction in 

 outer diameter would be necessary, and the use of an internal pre-tuned 

 cavity might also be indicated. 



