66 THE BELL SYSTEM TECHNICAL JOUKNAL, JANUARY 1957 



anchors and submarine earthquakes or land slides. There must be con- 

 sidered, too, the possibility of fault from human failure. 



So it is necessary to contemplate the replacement of a length of cable, 

 or a repeater or equalizer. For such contingency, spare cable of the vari- 

 ous armor types has been stored on both sides of the Atlantic. Spare 

 repeaters and equalizers are also available. 



In addition, a spare called a "repair repeater" has been stocked. Need 

 for this arises from the fact that except in very shallow water, a repair 

 cannot be effected without the addition of cable over and above the 

 length which was in the circuit initially. The amount of cable which 

 must be added is a function of water depth, condition of the sea at the 

 time of the repair, and the amount of cable slack available in the im- 

 mediate vicinity of the point in question. 



When excess cable is introduced in amount sufficient to significantly 

 reduce the system operating margins, its loss must be compensated. 

 Hence, the repair repeater. 



A repair repeater is a two-tube device, essentially like a regular re- 

 peater although its impedances are designed to match the cable im- 

 pedances at input and output ends. However, its gain is sufficient to 

 offset only about 5.3 miles of cable. A second type of repair repeater is 

 under consideration, to compensate for about 15 miles of cable. 



Long-Term Aging 

 General 



In a system with some 3,200-db gross loss at its top frequency between 

 points which are accessible for adjustment, a long-term change in loss 

 of only one per cent would have a profound effect on system performance. 



For this reason, the repeater design included careful consideration of 

 net gain change over the years.^ The degree of control over aging is such 

 that in a period of at least 20 years, and perhaps much longer, the esti- 

 mated change in 51 repeaters might total 8 db added gain at the top 

 frequency. The gain variation with frequency would be proportional 

 to either curve of Fig. 15, and the rate of aging would be slower in earlier 

 than in later years. 



Estimates of cable aging are discussed in the section on "Net Loss 

 Tests." 



Means of Combatting Aging 



The effects of aging would become important on the top channels first. 

 Remedial measures to improve signal-to-noise, especiall}^ in the top 



