TOLL TRANSMLSSION IN TIIK UNITED STATES 



127 



concentrate on ihe surface, so increasing the effective series resistance. 

 Dielectric losses in the insulalion between the conduclors also increase 

 with the frequency, and so increase the effective shunt conductance. 

 Figure 6 shows graphically the increase in attenuation with frequency, 



100 



200 



BOO 



1000 



300 400 500 600 700 



FREQUENCY IN KILOCYCLES PER SECOND 



Vi^. 6- At I ciuiat ion-frequency characteristics of various types of tclcijlione circuits. 



and also shows the relative attenuations of various types of con- 

 struction. 



Until ihe vaciuim tube ami)lifier became available, the only practical 

 method of overcoming high attenuation in a given type oi line con- 



