NOISE FIGURE 



431 



Accordingly, the magnitude of the noise convection current at the cathode 

 does not matter. If we assume that the gun is a short-circuited diode as far 

 as r-f goes 



V,- Va = 



Then from (10.6), (10.10) and (10.11) we obtain 



/ = 



Va 



(10.11) 

 (10.12) 



Fig. 10.2 — Some expressions useful in noise calculations, showing how they approach 

 unity at large transit angles. 



Accordingly, from (10.7) and (10.8) we obtain 



^^= 1 



^'5 = 1 - 



G*C* 



F*Va 



I*Va 



(10.13) 



(10.14) 



In Fig. 10.2, I 1 - D*C*/F*A* j and | 1 - G*C*/I*A* \ are plotted 

 vs d, the transit angle. We see that for transit angles greater than about 

 iiT these quantities differ negligibly from unity, and we may write 



More specifically, we find 



qb 



Qb = F*Va 

 Vb = I*Va 



Vg h jQi e~^' 



Ub 



Vb — —Vae 



(10.15) 

 (10.16) 



(10.17) 

 (10.18) 



