CONSTANT FREQUENCY OSCILLATORS 77 



CoLPiTTs Oscillator 



This property may be utilized to even greater advantage in connec- 

 tion with the Colpitts type of oscillator, which is illustrated in Figs. 5, 

 6, and 7 and will now be investigated with the aid of (8) in the same 

 manner in which the relations necessary for stabilizing the Hartley 

 oscillator were secured. Thus, for the Colpitts circuit: 



coCi 



X - -J- 



C0C2 



X„. = 0, 



"^ ^Laia + C; 



The values of the stabilizing elements required by (8) are given in 

 Figs. 5, 6, and 7 which show several arrangements for the stabilizing 

 impedance, as applied to the Colpitts-type oscillator. In particular, 

 Fig. 7 shows a choice of either an inductance or a capacity on the 

 grid side. 



In Figs. 5 and 6 and in Fig. 7 when inductance is used on both plate 

 and grid sides it is evident that if the condensers, Ci and C2, are con- 

 nected together in a "gang" mounting so that when they are varied, 

 the ratio of their capacities remains constant, then the frequency of the 

 oscillator may be changed by changing Ci and C2 without disturbing 

 the stabilizing adjustment which causes the frequency to be independ- 

 ent of battery voltages. 



Feed-Back Oscillator 



Figures 8,9, and 10 show conventional drawings of the type of oscil- 

 lator circuit known as a "feed-back" or sometimes as a "tuned input" 

 circuit. In Fig. 8 stabilizing is accomplished on the plate side; in 

 Fig. 9 on the grid side; and in Fig. 10 on both sides. A mathematical 

 analysis analogous to that which was described in detail in connection 

 with Fig. 1 gives the values of stabilizing impedances which are shown 

 in the figures, and also indicates that the conditions for oscillation may 

 be met when these values are employed. 



