84 



BELL SYSTEM TECHNICAL JOURNAL 



rather critical portion of its reactance characteristic. In order to avoid 

 this, the introduction of a fairly small condenser at d is advantageous. 

 Thus, if d were made somewhat smaller than Cz, then the value of Ci 

 required by (19) is roughly: 



Ci 



U 



ic, + a] - G 



which gives an appreciably smaller value of Ci and results in stabiliza- 

 tion with a much less critical adjustment than is the case when the 

 stopping condenser is absent. 



In all of the above analyses, the requirement of a capacity or an 

 inductance is indicated by the fact that the signs come out right in the 

 final equations. If the wrong type of reactive element were used, it 

 would result, for example, that a negative inductance apparently would 

 be required, which of course would indicate the requirements of a 

 capacitance. 



Another Type of Stabilization 



A third general type of stabilization may be illustrated by consid- 

 ering a hypothetical oscillator having its plate circuit coupled back to 

 its grid circuit by means of a transformer coil with a coefihcient of 

 coupling equal to unity. Methods of obtaining the equivalent effect 



Z5 



:Z3 



ixi 



.1X2 



ix. 



iXm = i'VX| X2 

 Fig. 15 — Equivalent circuit of oscillator with unity coupling. 



of such a coil under practical operating conditions will be described 

 later, so that for the present it will be assumed that a unity coupled 

 coil is on hand. The equivalent circuit diagram of the oscillator is 

 shown in Fig. 15, where the primary and secondary windings of the 

 coil are indicated at Xi and X-2, respectively. 



From the properties of unity coupled coils it follows that, no matter 

 what impedances are hung across the coil, or connected between wind- 



