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BELL SYSTEM TECHNICAL JOURNAL 



a phantom circuit and some other circuit is generally similar to the 

 problem of crosstalk between two pairs. In other words, the discussion 

 of transverse, interaction and reflection crosstalk is applicable. 



Measures of Crosstalk Coupling 



In designing transposition systems, the usual measure of the coupHng 

 effect between two open-wire circuits is the ratio of current at the 

 output terminal of the disturbed circuit to current at the input terminal 

 of the disturbing circuit. For circuits of different characteristic 

 impedances this current ratio must be corrected for the difference in 

 impedance. The corrected current ratio is the square root of the 

 corresponding power ratio. 



The current ratio is ordinarily very small and for convenience is 

 multiplied by 1,000,000 and called the crosstalk coupling or, in brief, 

 the crosstalk. This usage will be followed from this point in this 

 paper. For example, crosstalk of 1000 units means a current ratio 

 of .001. Crosstalk may also be expressed as the transmission loss in 

 db corresponding to the current ratio. A ratio of .001 means a 

 transmission loss of 60 db corresponding to 1000 crosstalk units. 



Ir I 



TO LONG CIRCUITS 



Fig. 5 — Schematic of near-end and far-end crosstalk. 



Figure 5 indicates two paralleling communication circuits a and b 

 with an e.m.f . impressed at one end of circuit a. The crosstalk currents 

 in and if in circuit b are due to the crosstalk coupling in length AB. 

 The near-end crosstalk in the length AB \s the ratio X^HuJIa, while the 

 far-end crosstalk is IOH/JIa- The ratio 10H//Ib has been called the 

 "output-to-output" or "measured" crosstalk. This ratio is a con- 

 venient measure of far-end crosstalk between parts of similar circuits 

 because it is related in a simple way to the far-end crosstalk between 

 the terminals of the complete circuits. The following discussion 

 explains this relation. 



