576 



BELL SYSTEM TECHNICAL JOURNAL 



At the regulating repeater stations the arrangement is the same as 

 at the non-regulating stations, except that another stage is added 

 to the amplifiers. This stage includes a potentiometer associated with 

 relays controlled by the master pilot-wire mechanism, the whole being 

 arranged so as to compensate for the changes in transmission loss of 

 the cable pairs caused by temperature changes. 



In the lower part of Fig. 3 is shown a transmission level diagram, 

 from which can be noted the losses and gains introduced by the 

 different parts of the system, for a frequency of 1,000 cycles. 



Cable 

 The transmission paths are provided by means of 16 B. & S. gauge 

 non-phantomed pairs having a capacitance of 0.062 microfarads per 



a. 

 u 

 a 



z 

 o 



1- 

 < 



z 



LJ 



y- 



to 



30 



50 



100 



200 



500 



1,000 2.000 



5,000 8,000 



CYCLES PER SECOND 



Fig. 4 — Attenuation-frequency characteristic for 16-ga. B-22 cable pairs at 55° F, 

 terminated in characteristic impedance. 



mile. These pairs are loaded with 22-milhenry inductance coils spaced 

 3,000 feet apart. Present long distance message telephone circuits in 

 cable have loading coils spaced 6,000 feet apart. The nominal cutoff 

 frequency of the new circuit is about 1 1,000 cycles, permitting effective 

 transmission of a frequency band extending up to about 8,000 cycles. 

 The nominal impedance is about 800 ohms and the attenuation per 

 mile, at 1,000 cycles and average temperature, about .24 db. Fig. 4 



