CROSSTALK BETWEEN COAXIAL TRANSMISSION LINES 145 



between radio transmitting or receiving apparatus and antennae, as 

 well as a wide frequency band transmitting medium for long distance 

 multiplex telephony or television. It has been a subject of discussion 

 in several articles published in this country and abroad.* 



The purpose of this paper is to dwell at some length on the shielding 

 characteristics of a structure exposed to interference from a similar 

 structure placed in close proximity. Such interference is usually 

 referred to as crosstalk between two adjacent circuits, so that the 

 purpose of this paper is a study of crosstalk between two coaxial 

 circuits. In what follows we shall give an account of the theory of 

 crosstalk, the results of experimental studies, and application of these 

 to long lines employing coaxial conductors. 



General Considerations 



Let us consider a simple case of two transmission lines (Fig. 1) and 

 let us assume that both lines are terminated in their characteristic 



Fig. 1 — Direct crosstalk between coaxial pairs. 



impedances Zi and Z2, and that their propagation constants per unit 

 length are 71 and 72 respectively. If the disturbing voltage E is 

 applied to the left end of line (1) and the induced voltage F„ is measured 

 at the corresponding end of line (2), the ratio F„/£ is called the near- 

 end crosstalk ratio from circuit (1) into circuit (2). Similarly, if Vf is 

 the induced voltage as measured at the right end of line (2), when the 

 disturbing voltage E is applied to the left end of circuit (1), we define 

 the ratio VflEe~'^^^ as the far-end crosstalk ratio from circuit (1) into 

 circuit (2). For convenience, we shall speak of the near-end crosstalk 

 and the far-end crosstalk whenever the voltage crosstalk ratios are 

 actually involved. Thus, the magnitude of crosstalk will be given by 

 the absolute value of the corresponding crosstalk ratio. It might be 

 expressed either in decibels as is done in this paper or it might be given 



* For references see end of paper. 



