CROSSTALK BETWEEN COAXIAL TRANSMISSION LINES 147 



factors depending upon the length of transmission lines and the 

 character of their terminations. 



Direct and Indirect Crosstalk 



Let us now return to the circuits shown in Fig. 1. Because of the 

 mutual impedance between the two circuits a certain amount of the 

 disturbing energy is transferred from line (1) to line (2), producing 

 voltages at both ends. The voltage at the end A determines the near- 

 end crosstalk. The type of crosstalk present in a simple system of two 

 circuits only in consequence of the direct transmission of energy from 

 one circuit into another we shall call the direct crosstalk. Later on we 

 shall discuss the case where three circuits are involved in such a way 

 that the energy transfer takes place via an intermediate circuit, causing 

 the crosstalk which we call the indirect crosstalk. Both direct and 

 indirect types of crosstalk have a close correspondence to the types of 

 crosstalk used in connection with work on the open-wire lines or the 

 balanced pairs as discussed in the paper on open-wire crosstalk.^ The 

 direct crosstalk of the present paper is the direct transverse crosstalk; 

 our indirect crosstalk is the total crosstalk due to the presence of the 

 third circuit and as such is the resultant of the indirect transverse 

 crosstalk and the interaction crosstalk of the above paper. Following 

 the general method outlined in the present paper one can easily 

 subdivide the indirect crosstalk into its components. Since only 

 simple crosstalk systems consisting of two coaxial conductors are 

 considered in our paper, the work has not been carried through. 



Direct Near-End Crosstalk 



We proceed now to develop the formula for the direct near-end 

 crosstalk. The line (1) being terminated in its characteristic impedance 

 Zi the current through the generator is EjZi and therefore the current 

 in the section ab is 



lab = — ^ (1) 



Hence, by definition of the mutual impedance, the electromotive 

 force induced in the section kl is 



£'e~'i'i^ 

 Cki = iabZndx = — ^ — Zndx, (2) 



and the current in the section kl 



