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BELL SYSTEM TECHNICAL JOURNAL 



for a 500-mile system, result in a frequency characteristic which is flat 

 to within less than 2 db over the range from 12 to 60 kilocycles. For 

 a longer circuit further corrective measures will be provided. 



15 20 25 30 35 40 45 50 



FREQUENCY IN KILOCYCLES PER SECOND 



55 



Fig. 12 — Characteristics of amplifier deviation equalizer. 



Regulation for Temperature Effects. 



The method adopted for controlling the repeater gain to compensate 

 for temperature changes is similar to that which has been found satis- 

 factory for voice-frequency cable circuits. This is the pilot wire 

 method in which a pair of cable conductors extending over the section 



GALVANOMETER 



POTENTIOMETER AND DIAL GEARED 

 ■ TO MASTER TRANSMITTER MOTOR 



REBALANCING MECHANISM 

 TRANSLATES GALVANOMETER 

 DEFLECTION INTO ROTATION OF 

 MASTER TRANSMITTER MOTOR 



MASTER TRANSMITTER MOTOR 

 SETS POSITION OF SYNCHRO- 

 NOUS RECEIVER MOTORS 



Fig. 13 — Flat gain master controller. 



to be regulated forms one arm of a Wheatstone bridge. This bridge 

 is designed for automatic self-balancing and the mechanical motion 

 required for establishing the balance has been made to adjust the 

 gain of the amplifiers. The d-c. resistance of the pilot wire gives an 



