362 



BELL SYSTEM TECHNICAL JOURNAL 



around the balanced circuit composed of the two outer conductors. 

 For the present we shall not consider the voltages eijl which are in 

 the same direction in the outer conductors. 



The current in the "balanced" intermediate circuit of characteristic 

 impedance Zz and propagation constant 73 due to the balanced voltage 

 ei in the elementary length dl is iz = ei/lZs. This current flowing 

 along the outer coaxial conductor of the disturbed circuit produces a 

 voltage 62 = isZapdl on the inner surface of this outer conductor and 

 this voltage in turn causes a current iia in the disturbed coaxial circuit 



-dl- 



I'fj.k 



COAXIAL 1 



'* e, = IiZa/2.cll- 



(a) 



TlZi 



■»'3,Z3 



COAXIAL I 



ei 



n's.Za 



3 



i::: 



(b) 



7Y77Z//'/////////////////7? , 



COAXIAL 1 



y3,Z3|(i 



I vot^e, e, V3^ I 



.A ®i - 



2 2_ 



13 



»1^ 



\ I 



COAXIAL 2 

 (C) 



^)/ 



COAXIAL I 



-<sy 



COAXIAL 2 



<sy 



4--- 



Hr) 



(d) 

 Fig. 1. — Coaxial crosstalk schematics. 



equal to eil2Z, where Z is the coaxial characteristic impedance.* In a 

 long line other elementary lengths of the disturbed coaxial are also 

 affected by iz because of its propagation along the intermediate circuit. 

 (This crosstalk by way of a tertiary circuit from one length into another 

 is known as indirect or "interaction crosstalk" and because of its 

 presence the summation of crosstalk with length is not a simple function 

 of length even for systematic coupling such as occurs with coaxials.) 

 This is a crosstalk case for which the general solution is already 



* The subscript "a" in i^a relates this current to the so-called "mode a" current 

 used by Carson and Hoyt in their paper entitled "Propagation of Periodic Currents 

 Over a System of Parallel Wires," Bell Sys. Tech. Jour., July, 1927. 



