576 



BELL SYSTEM TECHNICAL JOURNAL 



tive decreasing values of n. Our best determination for the value of n 

 for each mode is given. The base lines are displaced vertically on a uniform 

 wavelength scale, so that the variation of repeller voltage with wavelength 

 is indicated. The power output increases with decreasing values of n 

 but the half power electronic tuning for each repeller mode has a contrary- 

 variation. The repeller mode chosen as providing the best compromise be- 

 tween power output and half power electronic tuning is the 7f cycle mode. 

 The design of the coupling unit and all the primary characteristics of the 

 tube are based on the use of this mode. It will be observed that repeller 



§4 

 O 



UJ 2 

 > 



I- 



LU 



cr 4 



20 40 60 eo 100 120 140 160 180 200 220 240 260 280 300 320 

 NEGATIVE REPELLER VOLTAGE 



Fig. 73. — Operation of the 2K25 in various repeller modes and at various frequencies 

 when connected to characteristic admittance of a 1" x ^" guide by the coupling of Fig. 70. 



modes having n values less than 6 do not appear in Fig. 73. For values of 

 w = to 0, 1, 2 and possibly 3, this is because the conductance representing 

 the resonator losses is in excess of the electronic conductance. For the 

 values of w = 4 and 5 the coupled load conductance plus the resonator loss 

 conductance in the specified transducer are in excess of the electronic con- 

 ductance. Conversely for modes having n values in excess of 7 the coupling 

 is weaker than desired. 



Fig. 74 illustrates the broad band characteristics for a typical W.E. 2K25 

 tube operating in the coupling of Fig. 70 into a matched load. In Fig. 74 



