A NEW KEY WEST— HAVANA CARRIER TELEPHONE CABLE 199 



of representative submarine cable insulations. It is evident from 

 these figures that the use of paragutta effects a considerable reduction 

 in the size of a cable for a given attenuation, not only for telephone 

 cables but also for telegraph cables. This decrease in size is due both 

 to the smaller dielectric constant and to the smaller leakance.f The 

 smaller dielectric constant is equally effective in reducing the size of 

 both loaded and non-loaded cables. The smaller leakance is especially 



TABLE I 



Comparative Electric.\l Properties of Gutta Percha and Paragutta 



Insulations of Submarine Cables at 22 Kilocycles per 



Second under Sea Bottom Conditions 



Dielectric Ratio of Leakance 

 Constant to Capacitance 



Gutta Percha (telegraph cable) 3.3 4040 



Gutta Percha as used in 1921 Key West-Havana Cables. 3.1 — 



Gutta Percha as used in Tenerife-Gran Canaria and 



Algeciras-Ceuta Telephone Cables * 2.92 3815 



Paragutta (Key West-Havana 1930 Cable) 2.67 229 



* Electrical Communication, Vol. 9, p. 217, 1931. 



important in the case of loaded cables. The decrease in size due to 

 the use of paragutta varies, of course, with the size of the cable. Some 

 idea of its amount may be obtained from the fact that a cable insulated 

 with gutta percha of the sort used in the 1921 cables would weigh 

 45 per cent more and cost about 65 per cent more than the new cable, 

 The use of this new material in the manufacture of a cable gave rise 

 to numerous problems, one of which deserves particular mention, 

 namely that of jointing the paragutta. A new technique of jointing 

 was developed which not only produces good joints in paragutta- 

 insulated cable but also produces better joints in gutta percha-insulated 

 cable than can be made by the conventional process which has been 

 in general use since gutta percha cables were first manufactured. 



Cable Design 



The 1930 cable is similar in type to the 1921 cables except that it is 



not loaded. It is provided with copper return tapes ^ and also with 



a thin copper tape under the return tapes for protection against 



marine organisms. The principle of the electrical design of the cable 



was to strike an economic balance between all of the factors affecting 



the attenuation and thus to secure a cable of the desired attenuation 



at the lowest possible cost. The result of this procedure is a core 



structure having a much greater thickness ® of insulation compared 



t The term leakance, as used here, includes all energy losses in the dielectric. 

 ^ "Transmission Characteristics of the Submarine Cable," Carson and Gilbert, 

 Jourtial of the Frmiklm histitule, Vol. 192, p. 705, 1921. 



• British Patent No. 343093, May 7, 1931. 



