1256 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1953 



ville-Zeeland cable was 1.54, obtained by expanding the conductor in- 

 sulation to the point that 35 per cent of the volume was gas. 



The curves on Fig. 7 represent the attenuation over the N carrier- 

 frequency range for a paper-insulated cable and three polyethylene- 

 insulated cables all designed to have a capacitance of 0.066 microfarads 

 per mile and a voice frequency attenuation of 1.1 db per mile. The lower 

 carrier-frequency attenuation of the polyethylene cables is evident. The 

 size of the polyethylene cables varies with the degree of expansion as 

 illustrated in Fig. 8. 



Since the dielectric strength decreases as the degree of expansion in- 

 creases, the saving in first cost must be balanced against the value of the 

 reduction in reliability. As mentioned before, the Grand ville-Zeeland 

 project was the first trial installation of expanded polyethylene cable. 

 A very moderate degree of expansion was chosen for this project. How- 

 ever, as more experience with expanded polyethylene is gained, it should 

 be possible, for a given application, to determine the degree of ex- 

 pansion which strikes the optimum balance between dielectric strength 

 and dielectric constant, giving proper weight to the mechanical proper- 

 ties and to cost factors. 



REFERENCES 



1. Modern Plastics Encyclopedia. 



2. Maupin, J. T., Measurements in Multipair Cables. Bell Sys. Tech. JL, 30, pp. 



652-667, July, 1951. 



3. Horn, F. W., and H. B. Ramsey, Bell System Sheath Problems and Designs. 



A.I.E.E., Trans., 70, Part I, pp. 1811-1816, 1951. 



4. Shockleton, W. J., General Characteristics of Polyethylene. A.I.E.E., Trans., 



64, pp. 912-916, Dec, 1945. 



5. Schelkunoflf, S. A., Electromagnetic Theory of Coaxial Transmission Lines 



and Cylindrical Shields. Bell Sys. Tech. Jl., 13, p. 532, Oct., 1934. 



6. Boettcher, C. J. F., Recueil des Traveaux Chimiques des Pays Bas, 64, p. 47, 



1945. 



