23-i THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



At Terrenceville, the networks permit adjustments equivalent to 

 ±1 nautical mile of cable (3 db at 552 kc), but at Clarenville and Syd- 

 ney Mines adjustments equivalent to 0.5 db at 552 kc are provided. It 

 should therefore always be possible to maintain the overall loss of the 

 system within ±0.25 db, and the level at any repeater should never 

 change by more than ±2 db. 



System Pilots 



The use of pilot tones applied at constant level at the input of a 

 system with indicating or alarm meters at the receiving end is standard 

 on land systems on both sides of the Atlantic, although the philosophies 

 underlying the methods of use differ. On the submarine cables round the 

 British Isles, with or without submerged repeaters, pilot tones are used 



SYDNEY MINES 



TERRENCEVILLE 



CLARENVILLE 



AT MINIMUM TEMPERATURE 



Fig. 10 — Deviation from mean of transmission levels with optimum adjust- 

 ments of equalizers at Sj'dney Mines, Terrenceville and Clarenville. 



^ W-E at 260 kc. 



■ E-W at 552 kc. 



jVIaximum deviation in the two directions occurs at the above frequencies. 



