478 



BELL SYSTmr TkCSNlCAL JOURNAL 



From the curves of Fig. 9 it can be seen that the maximum efficiency is 

 obtained when the external conductance is made equal to approximately 

 half the available small signal conductance; i.e. ^{je — Gr). This can 

 be seen more clearly in the i)l()t of Fig. 10. Equation (3.8) gives the condi- 

 tion for maximum efficiency as 



Gn 



- /o(X). 



Gl 



ye 



— ^-y^ 



0.4 



0.5 0.6 



ye 



Fig. 10. — The abscissa measures the fractional excess of electronic negative conductance 

 over resonator loss conductance. The ordinate is the load conductance as a fraction of 

 electronic negative conductance. The tube will go out of oscillation for a load conductance 

 such that the ordinate is equal to the abscissa. The load conductance for optimum power 

 output is given by the solid line. The dashed line represents a load conductance half as 

 great as that required to stop oscillation. 



If we assume various values for — these define values of Xo which when 

 substituted in 



^ 



Je 



Gc 



ye 



Gr 



ye 



2/i(Zo) 



Xn 



- /o(Xo) 



(3.12) 



give the value of the external load for ojitimum power. We plot these data 

 against the available conductance 



1 - 



Gr 



= 1 



MX) 



(3.13; 



as shown in Fig. 10. 



In Fig. 10 there is also shown a line through the origin of slope 1/2. 

 It can thus be seen that the optimum load conductance is slightly less than 

 half the available small signal or starting conductance. This relation is 

 independent of the repeller mode, i.e. of the value FN. This does not mean 



