REFLEX OSCILLA TORS 



549 



loop and is symmetrical about the G axis as shown in Fig. 57. Suppose the 

 — Ye curve lies directly on the G axis. The admittance contours for increas- 

 ing values of a will look somewhat as shown. Suppose build-up starts on 

 Curve 2. When Curve 1 with the cusp is reached, the build-up can con- 

 tinue along either half as the loop is formed and expands, resulting either of 

 the two possible frequencies of Curve 0. l^resumably in this symmetrical 



1 



CONDUCTANCE, G *- 



Fig. 57. — Circuit admittance vs circuit conductance in arbitrar}- units for different 

 rates of build-up at turn-on. When the build-up is rapid {a = 2) the admittance curve 

 has no loop. As the rate of build-up decreases the curve sharpens until it has a cusp a = 1. 

 As the rate of build-up further decreases the curve develops a loop {a = 0). There may 

 be uncertainty as to which of the final intersections with the a = Q line will represent 

 oscillation. 



case, nonsynchronous fluctuations would result in build-up to each frequency 

 for half of the turn-ons. If one frequency were favored by a slight dis- 

 symmetry, the favored frequency would appear on the greater fraction of 

 turn-ons. For a great dissymetry, build-up may always be in one mode, 

 although from the impedance diagram steady oscillation in another mode 

 appears to be j)ossible. 



