68 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1951 



lines and, as in land lines, the permissible spacing between repeaters usually 

 diminishes as the desired frequency increases. The great difficulty in the 

 case of submarine cable routes is that there are usually no land sites on which 

 repeaters can be located. Artificial islands consisting of floating platforms or 

 buoys have been proposed as a solution, but ocean currents and storms have 

 disastrous effects on such structures. Interruptions due to such causes would 

 make it difficult to meet the requirement on continuity of service which is 

 necessary in the case of important telephone circuits. Therefore, it appeared 

 that the safest place for a submarine cable repeater is on the ocean bottom. 



Requirements on Repeater 



The decision to place the repeater on the ocean bottom resulted in special 

 requirements on the structure the first of which is that it be capable of re- 

 sisting the considerable hydrostatic pressure that is encountered in deep 

 water. It also seemed desirable that the operation of getting the repeater 

 overboard from the cable ship should not impede the smooth functioning of 

 the laying process. The best way of meeting this requirement appeared to be 

 to make the repeater structure flexible, within practicable limits, and as 

 small as possible in diameter so that it could pass around the drum and 

 sheaves of the laying gear like any length of cable. 



In order to make such a repeater attractive from operating and commercial 

 points of view another requirement was necessary, namely, that the electrical 

 circuit elements of the repeater, including electron tubes, resistances, con- 

 densers and coils be designed for long life under operating conditions, so that 

 there would be assurance of freedom from trouble or need of replacement of 

 parts over a long period, perhaps twenty years or more. Servicing of 

 the repeater would be in the nature of a cable repair, and the repair 

 of a submarine cable is something not to be sought after. The procedure is 

 apt to be expensive and time consuming, due to circumstances beyond con- 

 trol such as bad weather or lack of availability of a repair ship; and the dis- 

 turbance of the cable involved in lifting it to the surface and dropping it 

 again, possibly in something of a heap, is not desirable. It is obvious that 

 the requirement on long life of circuit elements presents a difficult problem, 

 especially in view of the fact that the space available for these elements is 

 minimized in order to keep the repeater diameter small. 



There was still another requirement on circuit elements, that of rugged- 

 ness. The stresses involved in laying cables in deep waters are quite con- 

 siderable. The cable is under a tension of several thousand pounds and 

 ''incidents" might occur which would have no effect on an ordinary cable but 

 which might result in dangerous shocks to the delicate elements of the 

 repeater. 



