REFLEX OSQLLATORS 



541 



Actually, of course, the parameters of the curve were chosen so that it 

 corresponds fairly well to the experimental points. The upper value of W 

 at which the tube goes out of oscillation is most strongly influenced by the 

 value of di chosen. We see from Fig. 51 that as TI' is made greater than 

 unity WD increases rapidly and hence, from Fig. 52, /3^ decreases rapidly, 

 increasing Gnlye . On the other hand, as IF is made smaller than unity, 

 jS- approaches unity but the grid loss term W'/D"^ increases rapidly, and 

 this term is most effective in adjusting the lower value of IF at which oscilla- 

 tion will cease. Finally, the resonator loss term, varying as IF~\ does not 

 change rapidly and can be used to adjust the total loss and hence the opti- 

 mum value of Gu/ye and the optimum efficiency. 



It is clear that the power goes down at low frequencies chiefly because in 

 moving the grids very close together to tune to low frequencies with a fixed 

 nductance the resonator losses and especially the grid losses are increased. 



50 



45 



40 



[135 

 < 



I 30 



2 25 



?20 



UJ 



% '5 



o 



'^ 10 



y . \i 



/ • \ 



%.-A_ X- 



0.76 0.80 0.84 



0.88 Q92 0.96 1.00 1.04 



RELATIVE FREQUENCY, W 



Fig. 54. — Computed curve of variation of power in milliwatts with relative frequency W 

 for the parameters used in Fig. 53. The circles are experimental points. The curve has 

 been fitted to the points by the choice of parameters. 



In going to high frequencies the power decreases chiefly because moving the 

 grids far apart to tune to high frequencies decreases /3-. Both of these 

 effects are avoided if a fixed grid spacing is used and the tuning is accom- 

 plished by changing the inductance as in the case of the 707A. In such 

 tubes there will be an upper frequency limit either because even with a 

 fixed grid spacing ^- decreases as frequency increases, or else there will be a 

 limit at the resonant frequency of the smallest allowable external resonator, 

 and there will be a lower frequency limit at which the repeller voltage for a 

 given mode approaches zero; however, the total tuning range may be 3 to 1 

 instead of around 30% between extinction points, as for the 2K25. 



