586 



BELL SYSTEM TECHNICAL JOURNAL 



well. Here the frequency varied not more than one part in one hun- 

 dred million for a voltage range from 120 to 240 volts. Curve h was 

 taken with the two tuning capacitances C\ and Ci decreased 5 per cent 

 from their optimum settings, and curve c with both capacitances 

 increased 5 per cent. These detunings introduced phase shifts of 

 about ± 40° (± 0.70 radian), decreased \)x\ by 0.8 dh and changed 

 the frequency, as shown in Fig. 6, approximately ± 2 parts in ten 

 million. Although the analysis should not be expected to apply 



0.1 



O - 0.2 



7 8. 9 10 11 



FILAMENT BATTERY POTENTIAL IN VOLTS 



Fig. 7 — Oscillator frequency vs. filament battery potential. 

 a — Ci and d tuned for maximum amplifier gain. 

 b — Ci and d decreased 5 %. 

 c — Ci and Ci increased 5%. 



accurately for such large phase shifts, calculation of the frequency 

 deviations by means of (18) gives ±1.4 parts in ten million — in fair 

 agreement with the experimental results. As might be expected, 

 curves h and c show somewhat less stability with battery voltage 

 changes than does curve a. 



Figure 7 presents a similar set of curves for variations of filament 

 voltage. Here, for the "maximum-gain" tuning adjustment, a drop 

 from 10 volts, the normal value, to 8 volts caused less than one part in 

 one hundred million change of frequency, as shown in curve a. 



