EVOLUTION OF INDUCTIVE LOADING 1223 



and was part of the system of copper tapes previously mentioned which 

 served as a return conductor. 



The effective permeability of the iron-wire loading material was about 

 115. The distributed inductance of about 4.35 millihenrys per nautical mile 

 resulted in a low nominal impedance of about 115 ohms. The energy losses 

 in the loading material were the principal factors in limiting the top of the 

 working frequency band to about 4000 cycles. At KXX) cycles per second, 

 the bare line equivalent was of the order of about 22 db (for the mean value 

 of the longest and shortest cable). At 4000 cycles it was about 2.2 times as 

 great. 



Space limitations prevent a more complete description and discussion 

 here. Comprehensive information regarding all features of the project is 

 given in a 1922 A. I.E. E. Paper'^^ prepared by Messrs. W. H. Martin, G. A. 

 Anderegg and B. W. Kendall. Engineers of the A. T. &. T. Co. and W. E. 

 Co. were responsible for the electrical design of the cables, method of opera- 

 tion, and arrangement of the repeaters and other terminal apparatus. The 

 cables were manufactured late in 1920 and installed early in 1921 by The 

 Telegraph Construction and Maintenance Co. Ltd. of London, for the Cu- 

 ban-American Telephone and Telegraph Company. The latter organization 

 is jointly owned by the A. T. &. T. Co. and the Cuban Telephone Co. (a 

 subsidiary of the International T. &. T. Co.) 



1930 Non-Loaded Cable: Since the 1921 cables were not suitable for carrier 

 telephone operation (largely because of excessive losses and non-linear 

 distortion at high frequencies), it became necessary during 1930 to install a 

 fourth cable between Key West and Havana in order to meet the demand 

 for additional facilities. Advantage was taken of advances in the communica- 

 tion art, notably an improved cable insulation (paragutta), improved re- 

 peaters and carrier telephone systems, to design a non-loaded cable system 

 which would be suitable for carrier operation. The initial carrier set-up 

 provided three carrier telephone circuits, using a type C4 system which had 

 originally been developed for open-wire lines. Early in 1942, a seven-channel 

 system was substituted. Comprehensive information regarding the 1930 

 cable and its use of the 3-channel carrier telephone system is given in a 1932 

 A.I. E. E. paper by Messrs. Affel, Gorton and Chesnut.'*^ 



High Speed Transoceanic Loaded Telegraph Cables 



During the First World War when the need for increasing the message- 

 carrying capacity of existing non-loaded transoceanic telegraph cables be- 

 came urgent, the Bell System engineers who worked on this problem finally 

 came to the conclusion that to obtain a great advance in the existing art it 

 would be necessary to have much better cables. 



