162 



BELL SYSTEM TECHNICAL JOURNAL 



10 20 30 40 50 60 70 80 90 100 110 120 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 7 — Near-end crosstalk on a triple coaxial system of conductors at Phoenixville, 

 Pa. Outer to inner circuits. Length .088 mi. 



continuous contact. The curves in Fig. 7 show a comparison between 

 measured and computed values of near-end crosstalk for a system of 

 three coaxial conductors .88 mile long as installed at Phoenixville, 

 Pennsylvania. 



Also, as was already stated above, full agreement between theory and 

 experiments was established as to validity of equation (49). 



Crosstalk in Long Lines Employing Coaxial Conductors 



In a system consisting of two coaxial pairs, where two outer con- 

 ductors are in contact, essentially only one kind of crosstalk is present 

 depending on the direction of transmission on both pairs. It is near- 

 end crosstalk when transmitting in opposite directions and far-end 

 crosstalk for transmission in the same direction. Where more than 

 two coaxial conductors are grouped together and transmission is in 

 both directions both types of crosstalk are present. 



Although for a sufficiently short length of crosstalk exposure near-end 

 and far-end crosstalk are identical, in a sufficiently long system the 

 transmission characteristics of the line and associated repeaters will 

 make a marked difference between them. It has been a common 

 experience that in a long system using unshielded balanced structures 

 near-end crosstalk imposes more severe requirements on balance 

 between crosstalking circuits than far-end crosstalk. 



We shall now consider a coaxial pair. Here, the magnitude of the 

 far-end crosstalk was found to be given by expres.sion (19). The 



