REFLEX OSCILLATORS 



479 



that the load conductance is independent of the mode, since we have ex- 

 pressed all our conductances in terms of je , the small signal conductance, 

 and this of course depends on the mode. What it does say is that, regard- 

 less of the mode, if the generator is coupled to the load conductance for 

 maximum output, then, if that conductance is slightly more than doubled 

 oscillation will stop. It is this fact which should be borne in mind by the 

 circuit designer. If greater margin of safety against "pull out" is desired 

 it can be obtained only at the sacrifice of eflficiency. 



ye 



O.b 

 Gr 



ye 



Fig. 11. — The ratio of total circuit conductance for optimum power to small signal 

 electronic admittance, vs the ratio of resonator loss conductance to small signal electronic 

 admittance. 



An equivalent plot for the data of Fig. 10, which will be of later use, is 

 shown in Fig. 11. This gives the value of — for best output for various 



values of — . 



ye 



IV. Effect of Approximations 



The analysis presented in Section II is misleading in some respects. For 

 instance, for a lossless resonator and N = \ cycles, the predicted efficiency 

 is 53%. However, our simple theory tells us that to get this efficiency, the 

 radio-frequency gap voltage V multiplied by the modulation coefficient /3 

 (that is, the energy change an electron suffers in passing the gap) is I.OI8V0 • 

 This means that (a) some electrons would be stopped and would not pass the 

 gap (b) many other electrons would not be able to pass the gap against a 

 retarding field after returning from drift region (c) some electrons would 



