CROSSTALK IN COAXIAL CABLES 



353 



The near-end near-end interaction crosstalk NN^ is given by 



NN, 





■"'dx 



(67a) 



X 



X 



4Z(1 - vm)(Ki-{-vi'K2) 



+ 



Kiiji + 7) K2{y2 + 7) 

 X^Zu 



2(1 - 77i7/2)(i^l + r?i2i^2) 

 '?1 , V2 



ViKi r)2Ki 



Ki(yi -f 7) K^iji + 7) 



^ 7i + 7 72 + 7 



r]iK2 , V2K1 



7i + 7 72 + 7 



(67b) 



(67c) 



Near-End Crosstalk with One Tertiary Short-Circuited 

 Although the derivation of the formula for near-end crosstalk N^ 

 with one tertiary short-circuited is too long to be included here, it 

 seems advisable to give this formula without derivation. Under the 

 above mentioned restriction that e"^'' and e'^^' are large compared with 

 e'^\ 



Ns = Nt-\r NN - NNs, (68) 



where 



Nt = near-end crosstalk, tertiaries terminated, 

 NN = near-end near-end interaction crosstalk between two 



adjoining lengths, tertiaries with no discontinuity, 

 NNs = near-end near-end interaction crosstalk between two 

 adjoining lengths with tertiary 1 short-circuited at the 

 junction. 



The first two terms (Nt and NN) may, with the types of cable studied 

 so far, be determined with satisfactory accuracy from the single- 

 tertiary analysis. In such a case, the formulas given herein are suffi- 

 cient for computing the near-end crosstalk with one tertiary short- 

 circuited. 



Ill — Comparison of Computed Crosstalk 

 WITH Measured Values 



With 72-ft. and 145-ft. samples of the twin coaxial cable described in 

 the companion paper by Messrs. Booth and Odarenko, crosstalk and 

 impedance measurements were made in the laboratory, at frequencies 

 from 50 kc to 300 kc, the sheath and quads in parallel being considered 

 as providing a single tertiary, that is, as being connected together at 

 short intervals. 



