752 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1953 



half the primary one, (see Figs. 7 and 11, respectively) it was decided to 

 establish the same conditions in the experimental tube and to compare 

 the results thus obtained with those predicted by theory. 

 Prerequisites for the execution of these experiments were: 



(a) Knowledge of the primary Q. 



(b) Complete calibration of the secondary cavity with respect to 

 both the variation of Q, with penetration of resistance vane and varia- 

 tion of coupling coefficient with size of coupling iris. 



(c) ICnowledge of the location of the load lines with respect to the 

 small signal electronic admittance plot in the complex admittance 

 plane. 



4.3.1 Determination of Primary Q. The above parameter is under- 

 stood to denote the "operating" or loaded Q of the tube with the output 

 iris adjusted to its final and permanent size and the secondary cavity 

 completely decoupled. For the case of an inductively tuned (fixed gap) 

 reflex klystron, it may be determined experimentally using the expres- 

 sion/ 



Q = tt/S 



dVn 



df_ 



dVn 



- ^{N + f), (4.1) 



/r=J\r+3/4 



where t denotes the repeller space transit time. Both dr/dVR and df/dVR 

 are to be evaluated at the center of the mode. 



The functional relationship between r and Vr was obtained by placing 

 the 6BL6 in the tunable primary cavity of Fig. 15 and determining the 

 repeller voltage for maximum power output over the mechanical tuning 

 range of the cavity. Since the same repeller mode was used throughout 

 this test, r must also have been the same at each of these frequencies, 

 namely equal to {N -f %)// seconds. The experimentally determined 

 plot of repeller voltage vs. frequency is given in Fig. 17. It is seen to be 

 a straight line described by the equation, 



/ = (13.5F« + 2495) mc (4.2) 



and since, for the 3 + %-repeller mode, 



r = yi^ 10-« sec, (4.3) 



J(mc) 



the desired relation between r and Vr is obtained from the above two 



equation.- ;is 



T = (3.r)F« -f 665)"' sec, (4.4) 



