DESIGN OF SYSTEM 



NORTH ATLANTIC LINK 



61 



if any net change in the cable temperature averaged over the whole cable 

 length. The greatest possibility of change would be in the shallow-water 

 sections, and crystal measurements indicate that at the end of a year 

 the average temperature of the shallow-water sections returned nearly 

 to its initial value. Hence about 5 db seems chargeable to one year's 

 aging. Extrapolation into the future, however, is uncertain. Theoretical 

 considerations lead to the idea that the rate of cable aging should 

 decrease. 



Information on long-term change in transmission loss of previous 

 cables is very limited. The Havana-Key West cables were accurately 

 measured just after laying, and again five years later. The change in 

 that system due to aging is very small, if indeed there is a change. That 

 cable is generally like the transatlantic, though it is smaller and has a 

 perhaps significant difference in construction of the central conductor. 



The above applies to the net loss of the undersea part of the system 

 only. The group-to-group net loss variation with time of the Clarenville- 

 Oban link has been held within a much smaller range by temperature 

 equalizer adjustments. Practices have been worked out which it is be- 

 lieved will hold the in-service variation with time to a fraction of a db. 



Net Loss versus Carrier Frequency Power Level 



Single-frequency tests of carrier frequency output power versus input 

 power were made, up to a test power a little below the estimated overload 

 of the highest-level repeater. An increase of 0.1 db in system net loss oc- 

 curs at a power 2 to 3 db below the load limit of the transmitting am- 

 plifier. This is about 15 or 16 db above the expected rms value of the 

 in-service system busy hour load. The 0.1 db change is presumably due 

 to the cumulative effect of smaller changes in several of the undersea 

 amplifiers. 



mo ■* 



^5 3 

 LU< 



Dai 2 

 -J 15 



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4 6 8 10 



MONTHS FROM OCTOBER 1,1955 



12 



Fig. 14 — Change in system gain in first eleven months. 



