192 



BELL SYSTEM TECHNICAL JOURNAL 



0.60 



0.55 



y 0.50 



IT 



Z 0.45 



X 



6 0.40 



0.35 



0.30 



Z 0.25 



5 0.05 



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



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 8 — Mutual inductance between pairs of parallel wires. 



Fig. 8 to show the shapes more clearly. A comparison of the fre- 

 quency characteristics of Ma and Mh for the two wire gauges is shown 

 in Figs. 9-A and 9-B in terms of the one-kilocycle value of Ma for each 

 case. In Fig. 9-A the frequency scale is logarithmic and in Fig. 9-B is 

 linear. As would be expected, the use of smaller wires (No. 18 gauge) 

 decreases the effect of proximity on the magnetic coupling and shifts 

 the frequency at which Mh reaches a maximum value. 



The results of tests on the 55-foot length of No. 19 A.W.G. quadded 

 cable are shown on Figs. 10-A and 10-B. The data cover a range of 

 10 to 480 kilocycles. These figures show the variation with frequency 

 of the average values of Ma and Mh in terms of the ten-kilocycle 

 average value of Ma which is taken as unity. In Fig. 10-A the fre- 

 quency scale is logarithmic and in Fig. 10-B it is linear. It will be seen 

 that Mh is negative with respect to Ma as in the case of two pairs in 

 space. As in Figs. 3, 4 and 7, curves are given both for Mh and for 

 — lOikfft, the purpose of the latter curve being to show the shape of 

 Mh more clearly. The value of Ma decreases with frequency, becoming 

 nearly constant above 300 kilocycles at a value 22 per cent less than 

 the value at 10 kilocycles. The component Mh is of negative sign 

 and at 56 kilocycles reaches a maximum value which is 13.4 per cent 

 of Ma at this frequency. 



