I 



The Loaded Submarine Telegraph Cable' 



By OLIVER E. BUCKLEY 



Synopsis: With an iiu-rcase of trartir carrying capacity of MW ', over 

 that of corrcs|X)n<lin){ cahlcs of the previous art, the New York-Azores 

 ()eruialloy-liMile<l calile marks a revohilioii in siiliinarine cal>lc practice. 

 This cjlile represents the first practical application of iiiihictive loading 

 to transiK'eanic cables. The copper conductor of the cable is surrounded by 

 a thin l.iyer of the new magnetic material, (lermalloy, which serves to increase 

 its inductance and conseipiently its ability to transmit a rapi<l succession 

 of telegraph signals. 



This (xi(H-r explains the part played by loading in the oix-'ration of a cable 

 of the new ty(H- and disciis.ses some of the problems which were involved in 

 the develr>i>ment leading up to the first commercial installation. Particular 

 attention is given to those features of the transmission problent wherein 

 a practical cable differs from the ideal cable of previous theoretical dis- 

 cussions. 



Brief mention is made of means of operating loaded cables and the |h)S- 

 sible trenil of future development. 



I'KR.M.M.LOV Lo.\I)IN(. 



Till-; .iiiiioiiiufnu-iil on Se()loml)er 21, 1921, that an oprr.itiii^; 

 speed of over l,iOO letters per minute had been oljtained with 

 the new 2,;i00 mile New \'ork-A/ores permalloy-loaded cable of the 

 Western I'nion Telegraph Company, brought to the attention of the 

 public a development which promises to revolutionize the art of sub- 

 n:arine cable telegraphy. This announcement was based on the 

 result of the first test of the operation of the new cable. A few weeks 

 later, with an improved adjustment of the terminal a[)[)aratiis, a 

 speed of over 1,900 letters per minute was obtained. Since this 

 speed represents about four times the traffic capacity of an ordinary 

 cable of the same size and length, it is clear that the permallo\-loaded 

 cable marks a new era in transoceanic communication. 



The \ew York-Azores cable represents the first practical attempi 

 to secure increased speed of a long submarine telegraph cable by 

 inductive loading and it is the large distributed inductance of this 

 cable which is principally responsible for its remarkable performance. 

 This inductance is secured b>' surrotinding the conductor of the cable 

 with a thin layer of permalloy. Fig. 1 shows the cf)nstruction of 

 the deep sea section of the cable. In appearance it differs from the 

 ordinary ty|K- t>f cable principally in ha\'ing a permalloy tape 0.00 > 

 inch thick and 0.125 inch wide, wrapped in a close helix around the 

 stranded cop[H-r conductor. 



Permalloy, which has been described by Arnold and Mlmen,' is an 

 allf)y consisting principally of nickel and iron, characterized b\' very 



' Presented iH-fore the A. I. E. E., June 26, 1Q25. 



'- Jour. Franklin Inst.. \ol. 195, pp. 621-6.?2, May 192.5; B. S. T. J., \ol. II, N'o. 3, 

 p. 101. 



355 



