THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



40 



20 



!3 



UJ 



ffl 

 o 



ai 



o -20 



z 



^ -40 



-80 

 200 



100 



^ 



D.001 2 5 0.01 2 5 0.1 2 5 i.o 2 5 iq 2 i 



FREQUENCY IN CYCLES PER SECOND 



Fig. 21 — Loop gain characteristic for office regulators. 



100 



available pilot signal of about 0.002 volts in 25,000 ohms. In order to 

 solve drift and stability problems in the dc circuits the pilot is converted 

 to a dc voltage of 60 volts. This requires an amplifier-rectifier of 90 

 db voltage gain, stable with time and temperature. 

 As indicated on Fig. 23, the amplifier consists of three stages using 



ai 



m 2 

 o 



xio' 



-2 



4 



-6 

 -8 



2 3 4 5 6 8 10 20 30 40 60 100 200 400 600 



FREQUENCY IN CYCLES PER SECOND 



Fig. 22 — Feedback characteristic for office regulators showing the gain en- 

 hancement eflfect. 



