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BELL SYSTEM TECHNICAL JOURNAL 



and capacitance C< with the assumptions of no grid current, low plate 

 circuit resistance, and ju ^ 1. 



From (12.49) it is seen that in order for g to be negative, B must be positive 

 and greater than A , since A is normally positive. That is, the plate circuit 

 reactance must be positive and less than the grid-plate reactance when the 

 latter is a capacitance. Under these conditions b/K and hence the input 

 reactance will be negative according to (12.50). 



Curves of b/K are shown in Fig. 12.23 with B as independent variable 

 and A as parameter. These curves indicate frequency change. On the 



|J=20 



h = o 



Fig. 12.23 — Variations in the input impedance functions of an oscillator circuit for 

 changes in plate circuit tuning 



same figure is plotted b/g called (i>g . This may be considered the sensitivity 

 of the oscillator or, for a given value of uLjRc of the crystal, it represents 

 the activity. The similarity between these curves and the actual change in 

 frequency and activity normally experienced is apparent. 



It should be pointed out here that the presence of harmonics is effective 

 in changing the input impedance of the vacuum tube and hence the fre- 

 quency and activity of the oscillator. The presence of harmonics results 

 from the non-linear characteristics of the vacuum tube. Llewellyn 

 explains that a non-linear resistance may be represented by a linear re- 

 sistance plus a linear reactance. From what has been said concerning the 



