CABLE CROSSTALK 



189 



5 



Z 0.008 



1 2 3 4 5 10 20 30 50 100 200 300 500 1000 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 4— Mutual Inductance between pairs of parallel wires. 



for two arrangements of pairs in a horizontal plane. In both cases the 

 axial separation of the two wires of a pair was about 0.075 inch, but in 

 Fig. 3 the axial separation between the nearest wires of the two pairs 

 was 0.075 inch and in Fig. 4 it was 0.312 inch. The wires were No. 

 20 A.W.G. cotton-covered and were pulled taut to maintain accurate 

 spacing. Two plots are shown for ilf^, one actual and the other after 

 multiplying by — 10 to show the values more clearly. 



The above data are replotted in Fig. 5 to show the frequency varia- 

 tion of Ma and Mh in terms of the values of Ma at one kilocycle. The 

 fact that the frequency characteristics for the two cases are so nearly 

 alike despite the difference in the magnitude of the coupling indicates 

 that the effect depends primarily on the spacing between the wires 

 of a pair and not so much on the relative positions of the pairs. 



The proximity effect may be reduced by separating the wires of each 

 pair as shown in Fig. 6. In this case the frequency characteristic of 

 Ma is nearly flat and M^ is so small that it could not be plotted on the 

 same scale as Ma ; the curves shown are Ma and lOOikf^. A comparison 



