360 



BELL SYSTEM TECHNICAL JOURNAL 



An illustration of how the equalizers introduce the necessary attenua- 

 tion correction is given on Fig. 9. The lower curve on this figure shows 

 the loss of a 300-mile section of 165-mil circuit. The losses introduced 

 by the particular sections of low and high-frequency equalizers that 



500 1000 



FREQUENCY IN CYCLES PER SECOND 



10,000 



Fig. 9 — Loss of 300-mile line section and associated equalizers. 



would be required for this length of line are indicated by the cross- 

 hatched areas, and the total line and equalizer loss is shown by the 

 top horizontal line. Sufficient gain is introduced by the line amplifier 

 to annul this loss. 



Amplifiers 



Two types of amplifiers are provided, one of which is used as a 

 line or monitoring amplifier and the other which is used as a means 

 for transforming one circuit into several circuits so as to feed various 

 branches at points required. 



For certain combinations of program circuits as many as 50 ampli- 

 fiers may be connected in tandem. This necessarily imposes severe 

 requirements on the transmission performances of the amplifiers par- 

 ticularly with reference to flatness of gain-frequency characteristics 

 and phase distortion. By designing the coils used in the amplifiers 



