400 BELL SYSTEM TECHNICAL JOURNAL 



the inductance-current and resistance-current characteristics of the 

 loaded conductor, as determined in the factory, the attenuation 

 measurements also afford a check on these characteristics. 



Conclusions 



Measurements of attenuation, time of propagation and dielectric 

 capacity of the laid cable at various frequencies, supplemented by 

 measurements of eddy current resistance in the factory and by informa- 

 tion regarding the manner in which sea return resistance and dielectric 

 leakance vary with frequency are sufficient for determining the values 

 of the four parameters of a loaded cable and for dividing the resistance 

 into its component parts. A quantitative comparison of the results so 

 obtained with the values of parameters that would be predicted from 

 factory measurements alone would require a detailed discussion of the 

 methods involved in such measurements, and is outside the scope of 

 the present paper. A general conclusion that can be drawn from the 

 results of measurements made on three cables of somewhat different 

 characteristics is that the method of estimating the characteristics of 

 laid cables from measurements made on short lengths of core during 

 process of manufacture is capable of considerable accuracy. The 

 values of inductance and dielectric leakance obtained from factory 

 measurements are close enough to the actual values in the laid cable 

 to give a value of attenuation constant within a few per cent of the 

 actual value. The value of resistance obtained from the cable 

 measurements appears to be about three to five per cent higher than 

 the estimated value. This may in part be due to latent errors in 

 measurement or in the method of allowing for the effect of reflections 

 along the cable. 



The greater part of the discrepancy between the estimated and 

 measured values of resistance is perhaps due to erroneous assumptions 

 involved in computing the value of sea return resistance employing 

 the method described in the paper by Carson and Gilbert. In this 

 work it was assumed that the cable is surrounded by a homogeneous 

 medium, the sea water. For values of frequency higher than the 

 telegraphic range this assumption appears to be sufficiently close to 

 the truth, since only a comparatively small region around the cable 

 plays any part in the phenomena. In the telegraph range, however, 

 the return current is distributed through a comparatively large cross- 

 section and more exact specification of the electrical characteristics 

 of this region is required. To determine by rigorous methods the sea 

 return impedance in the case where the cable lies in a plane separating 



