SYSTEM DESIGN — NEWFOUNDLAND-NOVA SCOTIA LINK 233 



Temperature Effects and their Compensation 



The effect of temperature changes is hkely to be somewhat complex. 

 The land-and-sea cable sections are expected to behave in different ways 

 in this respect, but data on the manner of variation are not very precise. 

 The submarine cable crosses Cabot Strait, where melting icebergs drift- 

 ing down from Labrador as late as June can be expected to keep the sea- 

 bottom temperature low until well into the summer; temperatures just 

 below 0° C were, in fact, recorded when the cable was laid in May. On 

 land, the cable is buried 3 feet deep in bog and rock, and traverses many 

 ponds; some data on temperatures under similar conditions in other parts 

 of the world were available. 



For planning purposes it was clear that the assumptions made would 

 have to be somewhat pessimistic, and the assumed ranges of tempera- 

 ture, with the corresponding changes of attenuation at 552 kc, were: 

 Sea section . . . . 2.3 ± 3° C; ±4 db 

 Land section . . . . 7.5 ± 10° C; ±3 db 



A possible method of circuit adjustment for temperature changes is 

 to increase the gains equally at the sending and receiving terminals 

 as the temperature rises and to reduce them ecjually as it falls. Under 

 such conditions the effect of temperature variations on resistance noise 

 is not \e\y important; the levels at repeaters near the center of the 

 route remain substantially constant, and the increase in noise from the 

 repeaters whose operating levels are reduced is partly compensated by 

 the reduction in noise from those whose levels are increased. The effect 

 of the level changes on repeater loading is, however, more important as 

 it is undesirable that any repeater in the link should overload, and ad- 

 ditional measures which can be readily adopted to avoid serious changes 

 in repeater levels are clearty desirable. 



The estimated change of attenuation of the land sections is seen to be 

 roughly ecjual to that of the submarine section, so that, from the point 

 of view of temperature changes, Terrenceville is near the electrical 

 center of the link. It was thus both desirable and convenient to provide 

 adjustment at this point: Fig. 10 illustrates the advantage of seasonal 

 changes in equalizer setting at Terrenceville, showing the way the output 

 levels of repeaters are likelj^ to vary along the route. The system of tem- 

 perature compensation adopted therefore involves adjustable networks 

 at both ends of the system and at Terrenceville. All the networks are 

 cable simulators; hence the process of temperature compensation con- 

 sists, effectively^ in adding 'cable' when the temperature falls and re- 

 moving it when the temperature rises. 



