OP EN -WIRE CROSSTALK 233 



circuit h due to the presence of charges in circuit c is, therefore, pro- 

 portional to Uc. 

 By definition : 



Vac + Uc= Vc or Uc= Vc- Vac. 



Since the crosstalk current in circuit c approaches zero as dx ap- 

 proaches zero, Vc must also approach zero and Uc approaches — Vac- 

 The shunt e.m.f. in circuit h due to charges on circuit a was computed 

 as: 



Ve = VaTa^%' 



To allow for the electric field of circuit c, Ve must be augmented by: 



Cc Cc Cc 



V e ^ U c-i cb '7^1 ^^ VacJ- c&~7^ ^ Va-I- aci cb yr~f ' 



Cc »-c Cc 



Since the part of the direct near-end crosstalk coefficient resulting 



Ca 



from Ve was found to be iV^ = - jirZaTabCb^O^ ^n . by proportion 



Ca 



the indirect near-end coefficient resulting from VJ will be: 



(5) Ni = jirZaTacTcbCblO' ^ = ^^^^m'^^' ^PP''^^- 



Since the far-end crosstalk current resulting from a shunt voltage in 

 circuit b is opposite in sign to the near-end current, the indirect far-end 

 coefficient will be: 



(6) Fi= - Ni. 



Total Crosstalk Coefficients 

 The total near-end and far-end crosstalk coefficients used in com- 

 puting transverse crosstalk coupling will be the sum of the direct and 

 indirect coefficients or: 



(7) N = Na + Ni. 



(8) F = Fd + Fi = Fd- Ni. 



The expressions for Fi and Ni are about independent of frequency 

 in the carrier-frequency range because Za does not depend much on 

 frequency above a few thousand cycles, Cb is about independent of 

 frequency and TacTcb depends only on the cross-sectional dimensions 

 of the wire configuration. 



Since, as indicated by Fig. 2>2>, Nd is usually about independent of 



