198 BELL SYSTEM TECHNICAL JOURNAL 



for more circuits by an adaptation of standard carrier apparatus. The 

 design was made sufficiently liberal so that when still more facilities 

 are required certain further development work should make it possible 

 to obtain them over the same cable. From a transmission standpoint, 

 the feature of most interest is the unusually low receiving levels at 

 which operation is successfully carried on. 



The Cable 

 The new cable, which has been designated the 1930 cable, is the 

 longest deep sea telephone cable in existence and is also unique in 

 being the longest telephone cable circuit without intermediate re- 

 peaters and without inductive loading. It is somewhat longer (3.7 

 nautical miles *) than the longest of the 1921 cables and is operated 

 over a far wider frequency range. The new cable operates at fre- 

 quencies up to about 28,000 cycles per second, and can operate up to 

 a still higher frequency, whereas the old cables are operated only up 

 to 3,800 cycles per second. The longest deep sea carrier frequency 

 cable before the laying of the present cable was that connecting 

 Tenerife with Gran Canaria in the Canary Islands. This cable ^ is 

 non-loaded and is intended to utilize approximately the frequency 

 range now utilized by the new cable but is much shorter, being only 

 39.7 nautical miles in length, 



Paragutta 



The feature of the new cable which has enabled this great improve- 

 ment to be attained is the insulation, which is of paragutta. This 

 material was developed at the Bell Telephone Laboratories and is 

 composed of deproteinized rubber, deresinated balata, and wax. It 

 has been described in detail by A. R. Kemp.^ Heretofore submarine 

 cables having waterproof insulation, with the exception of the Catalina 

 Island cables ^ which are insulated with a special rubber mixture, have 

 almost invariably been insulated with gutta percha, or balata, or a 

 mixture of these substances, Paragutta has better electrical properties 

 than any of these materials. 



Some idea of the improvement represented by paragutta can be 

 had from Table I which lists the significant a-c. electrical properties 



* One nautical mile = 6087 feet (1855 meters). 

 = 1.1528 statute miles. 



^ "Tenerife-Gran Canaria and Algeciras-Ceuta Submarine Cables," K. E. Latimer 

 and J. R. Vezey, Electrical Communication, Vol. 9, p. 226, 1931. 



^ "Paragutta, a New Insulating Material for Submarine Cables," Journal of the 

 Franklin Institute, Vol. 211, p. 37, 1931. 



*" Carrier Current Communication on Submarine Cables," H. W. Hitchcock, 

 A. I. E. E. Transactions, Vol. 45, p. 1169, 1926. 



