292 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



the trench above the cable. The two repeaters in the land section will 

 be identical with those in the sea and, according to the terrain de- 

 termined in the final survey, will be laid in ponds, buried in the ground, 

 or located in small manholes. 



TANK-TYPE REPEATERS 



The mechanical design of the tank-type repeaters which will be used 

 in the Clarenville-Sydney Mines section is shown in figure 7. The 

 electrical equipment is mounted in an inner sealed cylinder 4 feet 2 

 inches long and 7% inches in diameter, filled with dry nitrogen. This 

 is mounted between brazed-in bulkheads in the pressure-resisting outer 

 housing which is 9 feet long with a maximum diameter of lOi/^ inches. 

 The gaskets or glands are suitably molded polythene. The cable- 

 armoring wires are fastened under clamps which transfer the laying 

 tension to the housing ; the design of these clamps is adequate to permit 

 the laying of the repeaters at ocean depths although, of course, such 

 strength will be unnecessary for cable-laying operations between New- 

 foundland and Nova Scotia. 



The 16 repeaters in this section will be located approximately 20 

 nautical miles apart. There are two 3 -stage vacuum-tube amplifier 

 units in parallel in the repeater and the circuit is so designed that the 

 failure of a vacuum tube or any other faulty component in one ampli- 

 fier will not affect seriously the functioning of the over-all circuit. 



In this respect tlie repeaters have some margin over the repeaters 

 used in the main deep-sea portion of the circuit since, because of space 

 limitations, the latter have only a single amplifier. To some extent, 

 this is offset by the fact that the vacuum tubes employed in the deep- 

 sea section are of a design which has been subject to a longer period of 

 test and experience. 



The space afforded by the rigid housing not only allows more compli- 

 cated circuitry, such as required to achieve two-way operation through 

 a single amplifier, but it also makes it possible to design some of the 

 components on more generous lines than can be fitted into the American 

 flexible housing. All components are manufactured and tested to 

 extremely high standards. 



TESTING ARRANGEMENTS 



It is an advantage of a two-Avay cable that, provided some form of 

 frequency translation is possible in each repeater, signals transmitted 

 from one terminal can be returned from the repeaters to the same 

 terminal. In this case, the frequency translation at the repeater is 

 effected by a so-called frequency-doubler associated with filters in the 

 range of 260 to 264 kilocycles. Signals at twice these frequencies are 

 returned to the sending terminal and enable an accurate measurement 



