1326 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



100.0 



99.8 



99.7 



1050 1000 950 900 850 800 750 700 650 

 EXTERNAL FEEDBACK RESISTANCE IN OHMS 



Fig. 10 — Effect of feedback on frequency. 



600 550 



the leakage reactance of the input winding. As the time rate of change 

 in current is increased by increased feedback these factors become in- 

 creasingly greater although never very large. Fewer turns are required 

 on the coils used for operation at the higher frequencies hence these 

 effects are reduced. 



The output level of the oscillator will vary almost directly with the 

 variations in the dc voltage since the amplitude of ac voltage across 

 collector to base is almost equal to the dc voltage applied. Hence, a varia- 

 tion of approximately 0.9 db will be obtained in the output when the 

 central office battery is reduced from 50 volts to 45 volts due to power 

 failure conditions. 



The over-all output variation from all causes is shown in Fig. 11. This 

 is based on data obtained using the transistors having the distruibtion 

 in characteristics shown in Fig. 7. 



Decreases in the value of Rl with temperature is normally compen- 

 sated by a corresponding increase in a. However small positive or nega- 

 tive voltage changes that alter the level of output do occur in the cut-off 

 voltage. This is minimized by keeping the dc voltage as high as permissi- 

 ble and still meet the 200 milliwatt dissipation limit for the 2N25 

 transistor. 



-2 DBM LEVEL 



MAX VARIATIONS 

 DUE TO TEMP 

 40°F TO 135°F 

 ±0.25 DB 



MARGIN TO 



TAKE CARE OF 



POWER FAILURE 



CONDITIONS 



0.9 DB 



ACCEPTABLE 



LIMITS 



AT TRUNK 



-4 DBM LEVEL 



Fig. 11 — Output level with effect of various factors that may alter the level 

 indicated. 



