OP EN -WIRE CROSSTALK 



227 



greater than C„' the value for a single pair line (without capacitance 

 at the insulators). For a single pair having like wires in a horizontal 



O TD o 



IMAGE WIRES 

 Fig. 32 — Distances used in computing potential coefficients. 



plane, CJ is readily calculated as follows: 



1 



where pn in c.g.s. elst. units is: 



2{pii — pn) ' 



2 log 



Sn 

 >n 



The distances ^u and rn are indicated on Fig. 32. 

 The expression for Vc may be written: 



Cn . C„ 



Ve = VaC„pab = VaCa paby^f — VuT ab J^ ' 



The coefficient Tab is called the "voltage transfer coefficient." It 

 is readily computed since it is a function of potential coefficients and 

 it is independent of the system of units used in computation. Since 

 Ca is about equal to Ca, Tab is about equal to the ratio of Ve to Va. 



The shunt voltage Ve drives a current through the shunt admittance 

 of circuit b in the infinitesimal length dx of Fig. 31. This shunt 

 admittance is (Gb + jcoCb)dx which is very nearly equal to juiCbdx 

 where Cb is the transmission capacitance per mile of circuit h and 



