70 



BELL SYSTEM TECHNICAL JOURNAL 



we have from (22) 



2ma^^ 12roA 



e9p^ 



r 



(29) 



In addition to the graphs in Figs. 1 and 2 showing the real and 

 imaginary components of impedance and velocity, the graphs shown 

 in Figs. 3 and 4 give their respective magnitudes and phase angles. 



■0.40 

 • 0.60 

 •0.80 

 - 1.00 



F"ig. 1 — Plate impedance of diodes or of negative grid triodes as a 

 function of electron transit angle. 



The impedance charts show a negative resistance for diodes in the 

 neighborhood of a transit angle, ^, of 7 radians. The possibility of 

 securing oscillations in this region has been discussed by Benham, so 

 that only a few additional remarks will be made here. 



The magnitude of the ratio of reactance to resistance is about 15 

 when the transit angle is 7 radians. This means that oscillation con- 

 ditions require an external circuit having a larger ratio of reactance to 

 resistance. On account of the high value of reactance required, a 

 tuned circuit or Lecher- wire system is needed, which would have to 

 operate near an antiresonance point in order to supply the high reac- 

 tance value. But the resistance component of the external circuit 

 impedance is large at frequencies in the neighborhood of the tuning 

 point, so that the ratio of reactance to resistance is small. Calcula- 



