90 BELL SYSTEM TECHNICAL JOURNAL 



Besides the general circuit of Fig. 17, where stabilization is accom- 

 plished by imposing a critical value on Co, there is the alternative 

 shown in Fig. 16, where the stabilizing element is Ci, a condenser 

 located in series with Li, and of such a size as to cancel the leakage 

 reactance between Li and Lo. The formula giving this size in terms 

 of the other circuit constants is shown in the figure, and the condition 

 that the harmonic content should be small for circuits of the general 

 type of Fig. 16 is that {ii/k)^L2/Li should exceed unity by as little as 

 is consistent with reliable oscillation. 



From Fig. 16 the circuits of various types of oscillators may be de- 

 ri\'ed in the manner which was described in connection with Fig. 17. 

 Of these circuits, the reversed feed-back and the Hartley were not 

 described in connection with Figs. 11 and 12. 



A combination of the features of Figs. 16 and 17 may be employed 

 in the manner shown in Fig. 18 where condensers C] and C^ are placed 

 in series both with L] and Lo, respectively. In this case, the formula 

 for the required size of Ci and C2 becomes quite cumbersome when 

 expressed in terms of the other circuit elements, onl}'. Since, how- 

 ever, the frequency is usually known approximately, we may use the 

 relation 



XJ = X1X2 



for finding Ci and C2 in terms of a; and get: 



\ coCi / \ WL2 / 



As in the case of Figs. 16 and 17, so also may the circuit of Fig. 18 

 be modified to correspond to the reversed feed-back, the feed-back and 

 the Hartley types of oscillators where stabilization is accomplished 

 both on the plate and on the grid sides. 



Experiment 



Of course. Figs. 1 to 18 are intended to represent only the funda- 

 mentals of the corresponding circuits. For practical operation these 

 circuits would have to include the usual stopping condensers, leak 

 resistances, sources, choke coils, and accessories. These circuit ele- 

 ments should be so valued and introduced into the oscillator circuit 

 as a whole as not to interfere with the relations required by the anal- 

 yses, in order to maintain the stabilizing eft'ects of the stabilizing im- 

 pedances. As to the choke coils, this means merely that they must 

 be what the name implies, that is, a substantially infinite impedance. 

 In the case of a Hartley-type oscillator, where the reactance is chosen 



