DESIGN OF SYSTEM — NORTH ATLANTIC LINK 33 



Proven Integrity 



Assurance of reliability dictated use of elements whose integrity had 

 actually been proved by successful prior experience in the laboratory 

 or in the Bell System. This resulted in adoption of a coaxial cable struc- 

 ture explored by the Laboratories soon after the war, field tested in the 

 Bahamas area in 1948 and applied commercially on the USAF Missile 

 Test Range project^^ in 1953. It also resulted in specification of a basic 

 flexible repeater design which had been imder test in the Laboratories 

 since before the war and had been in use on the Key West-Havana 

 submarine cable telephone system'* since 1950. 



Cable 



The cable adopted was the largest which had actually been success- 

 fully laid in deep water, and its size afforded an important benefit in 

 the form of reduced unit attenuation. The structure and characteristics 

 of this cable are covered in detail in a companion paper.' Suffice it to 

 point out here that by its adoption for the North Atlantic link, there 

 were specified for the system designers (a) the attenuation characteris- 

 tic of the transmission medium, (b) the influence on this of the pressure 

 and temperature environments, (c) the unit contribution of the cable 

 to the resistance of the power loop, and (d) the impedances faced by the 

 repeaters. 



Re'peater 



The adaptation of the basic Key West-Havana repeater design to 

 the present project hkewise presented the system designers with cer- 

 tain restrictions. Most important, the space and form of the long, tubu- 

 lar structure limited the size of the high voltage capacitors in the power 

 separation filters, and thus their voltage rating, to the extent that this 

 determined the maximum permissible number of repeaters. Likewise 

 the performance of the repeater circuit was at least partially defined 

 because of several factors. One was the effect of the physical shape on 

 parasitic capacitances in the circuit, which in turn reacted on the feed- 

 back and hence on modulation performance, gain-bandwidth and the 

 aging characteristic. Use of the Key West-Havana electron tube in- 

 fluenced the above factors and also tended to fix the input noise figure 

 and load capacity. 



System Design 



In similar respects, the principle of proven integrity reacted into the 

 broad consideration of system design. For instance, in a long system 



