WORLD- WIDE TELEPHON Y 



499 



Long Submarine Cables Without Intermediate Repeaters 



To design long submarine cables without repeaters requires providing 

 the mechanical characteristics necessary for deep sea cables and 

 meeting rather definite limits of overall attenuation. There is a limit 



5 10 15 20 25 30 35 40 45 50 55 60 



TIME IN SECONDS 



Fig. 9 — The upper curve indicates the short period stability of the long waves. 

 The lower cur\-e indicates the rapid variations which are frequently experienced 

 with short-wave transmission. 



to the power which can be imposed on the sending end of the cable 

 to avoid excessive voltage stress on the cable insulation. Even 

 though the cable be adequately shielded from extraneous noises, 

 there is a minimum amount of received power with which satisfactory 

 transmission can be obtained because of the thermal agitation in the 

 conductor itself. These two limits result in a maximum attenuation 

 of about 160 db for satisfactory operation over such a cable. 



The actual design of intercontinental telephone cables has been 

 largely directed toward the North Atlantic route between the United 

 States and Europe, including a direct section from Newfoundland to 

 Ireland, a distance of about 2100 miles (3400 kilometers). By the 

 use of a new insulating material, paragutta, with dielectric losses about 

 one-thirtieth those of guttapercha, but with similar mechanical char- 

 acteristics, and by the use of perminvar, a new magnetic material for 

 loading the cable, it has been possible to design a cable for this section 



