DESIGN OF SYSTEM — NORTH ATLANTIC LINK 65 



temperature. The change in frequency due to crystal aging in 11 months 

 under the sea is considered to He in the range to —0.4 cycle. 



Although the crystals were not designed as sea-bottom temperature 

 indicators and are within a repeater housing, it seems likely that with 

 precise techniques and, after some further stabilization, some uniquely 

 accurate information on change of sea-bottom temperature will be ob- 

 tainable. 



In accordance with previous oceanographic knowledge of sea-bottom 

 temperature, the frequency changes have been larger in the crystals 

 near shore. The greatest change has been in the repeater nearest Oban. 

 This is about 17 miles from shore and in water only about 50 fathoms 

 deep. Its freciuency change, and that of a typical deep-sea repeater, are 

 shown in Fig. 17. 



FUTURE CONSIDERATIONS 



Spare Equipment for Cable Stations 



In a system as far-flung geographically as this one, and as important, 

 much thought must be given not only to the supplies needed for routine 

 replacement of expendable items, but also to major replacements neces- 

 sitated by fire or other causes. Accordingly, a schedule of spare equip- 

 ment has been established, divided into two groups — "shelf" and 

 "casualty". 



Shelf spares are carried in the station itself, and include items such as 

 dial lights, electron tubes and dry cell batteries, which have limited life 

 in normal service. These are maintained in the cable station in quantity 

 estimated as adequate for two years of operation. 



Casualty spares embrace those major, essential frames and equip- 

 ments without which the system cannot be operated. There are two sub- 

 divisions: those which are in common use in the telephone plant and are, 

 therefore, available by "cannibalization", and those which are special 

 to the project, like the cable current supplies and the cable terminating 

 bays. The common-use items are not stocked as casualty spares. Spares 

 of the special items have been built and are stored in locations remote 

 from the cable stations. In event of catastrophe, these can be drawn out 

 and flown as near the point of need as possible, for onward-shipment by 

 available means. 



Spare Equipment for the Undersea Link 



Although every effort has been made to produce a trouble-free system, 

 the underwater link is still subject to the hazards of trawlers, icebergs. 



