CONSTANT FREQUENCY OSCILLATORS 



81 



impedances to cause the frequency to be independent of changes in 

 battery voltages. In Fig. 11 the stabilizing impedance is placed be- 

 tween the plate and the tuned circuit; in Fig. 12 between the grid and 

 coupling coil; and in Fig. 13 stabilization is accomplished by imped- 

 ances placed in both positions. Again, the mathematical analysis gives 

 the values of the stabilizing impedances as shown on the figures and 

 indicates that oscillation is possible when these values are used. 



Other Types of Oscillator Circuits 



As an instance of the stabilizing of another general class of oscillator 

 circuits which has wide application in a number of special cases, atten- 

 tion is drawn to the tuned-plate, tuned-grid circuit of Fig. 14. The 



Fig. 14 — Tuned-plate, tuned-grid oscillator with no magnetic coupling. 

 L-,r ^ . {l+n)C,C, 



Ci 



--rl'^'^ 



C, + (1 +n)Cs 



]-a. 



input and output circuits are shown in the drawing as consisting of 

 condenser and inductance combinations connected in parallel. At any 

 specified frequency, however, the parallel combination may be replaced 



C3 



r-ih-, 



Fig. 14-a. 



by a series circuit, or, in fact, by any form of network which has the 

 same impedance, and none of the currents or voltages in the remainder 

 of the circuit will be altered. In particular, the inductance and capac- 

 ity shown on the input side in Fig. 14 may be replaced by a piezo- 

 electric crystal, as shown in Fig. 14-a, having the same impedance at 



