OPEN-WIRE CROSSTALK 



33 



Figure 7 shows the crosstalk paths from a to c and back again. 

 In this figure, circuit a is indicated as two separate circuits for com- 

 parison with Fig. 2B. It is assumed that circuit a in Fig. 7 is energized 

 at point A, the currents J a and Ib being the currents which would 

 exist at the input and output of the short length d if there were no 

 tertiary circuits. The near-end crosstalk path indicated by n will 

 cause a small crosstalk current in at point A in circuit a. There will 

 be a crosstalk path similar to n in each thin slice of the parallel between 

 a and c. Each of these paths will transmit a small crosstalk current 

 to point A in circuit a. The sum of all these crosstalk currents will 

 increase the input current Ia and, therefore, the impedance of circuit 



r TO LONG 



CIRCUITS" 



i 



Fig. 7 — Effect of circuit c on propagation in circuit a. 



a is lowered. Thin slices remote from the sending end will contribute 

 little to this effect, since the crosstalk currents from such slices will be 

 attenuated to negligible proportions. A long circuit on a multi-wire 

 line will, therefore, have a definite sending-end impedance slightly 

 lower than that for one circuit alone on the line. 



Figure 7 also indicates a far-end crosstalk path / which produces a 

 crosstalk current if at point B in circuit a. This reduces the trans- 

 mission current Ib at this point and, therefore, increases the attenu- 

 ation constant of the circuit. For calculations of both the circuit 



