PUBLIC ADDRESS SYSTEM AND LONG LINES 



147 



over high grade telephone circuits can be secured from Fig. 1, which 

 shows the transmission efficiency at different frequencies for the New 

 York-San Francisco circuit. This circuit is a non-loaded No. 8 B. 

 W. G. open wire line equipped with twelve telephone repeaters and is 

 3400 miles long. Its frequency characteristic meets very well .the 

 requirements for easy understanding of voice transmission although 

 it causes some loss of naturalness. 



The frequency range which can be transmitted with approximately 

 constant efficiency is limited at the lower end by the fact that com- 

 posite sets are employed in order to make it possible to superpose 

 direct current telegraph circuits. The elimination of these composite 

 sets would make it possible to improve the transmission of low fre- 

 quencies and thus improve the operation of the circuit in connection 

 with loud speakers. The resulting improvement, however, would not 



u 10 



Att enua tion E qualizer 

 Line 



X 



}< 



2000 3000 

 Frequency — Cycles 



4000 



5000 



Fig. 2 — Transmission Characteristic of No. 19 Gage Non-Loaded Cable Circuit. 



A — Without Attenuation Equalizer. 

 B — With Attenuation Equalizer. 



be of importance for commercial telephone service and would render 

 it more difficult to avoid noise on circuits exposed to induction from 

 paralleling power or telegraph circuits. 



At high frequencies the range is limited because these same wires 

 are equipped with apparatus to permit super-position of multiplex 

 carrier telegraph circuits above the voice range. This limitation also 



