The Bell System Technical Journal 



Vol. XIX July, 1940 No. 3 



Crosstalk in Coaxial Cables — Analysis Based 

 on Short-Circuited and Open Tertiaries 



By K. E. GOULD 



The problem considered herein is that of estimating, from meas- 

 urements on short lengths of coaxial cable, the crosstalk to be 

 expected in long lengths of the same cable. The method devel- 

 oped, which is particularly applicable to cases in which the effect 

 of tertiary circuits on the crosstalk is large, is based on measure- 

 ments of crosstalk in a short length, with the tertiaries first short- 

 circuited and then open. The application of this method to the 

 cable described in the companion paper by Messrs. Booth and 

 Odarenko gave crosstalk values in good agreement with their 

 experimental results. 



Introduction 



X70R a number of years the problem of crosstalk summation in long 

 -^ open-wire lines or cables has been studied by measuring crosstalk, 

 in phase and magnitude, in short lengths. The crosstalk within a 

 short length, between two circuits terminated in their chai acteristic 

 impedances, would be measured with all important tertiary circuits 

 also approximately terminated. Then the crosstalk between two 

 circuits in adjoining short lengths would be measured with the ter- 

 tiary circuits terminated. From these coefificient measurements the 

 crosstalk in a long length could be estimated by a process of integration. 

 The application of tlis general method to crosstalk in the usual 

 types of coaxial cable would require great accuracy in the coefficient 

 measurements, because in 'onger lengths the desired crosstalk value 

 depends on the diffe.-ence be (ween two nearly equal quantities involv- 

 ing the coefficients. Tn the following analysis the computation of the 

 crosstalk for long len_th^ of co.ixial cable is based on crosstalk measure- 

 ments, in phase and magnitude, between two coaxial circuits in a 

 single short length with the tertii^ry circuits first open and then short- 

 circuited, no crosstalk measurements with terminated tertiary circuits 

 being involved. 



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