DESIGN OF SYSTEM — NORTH ATLANTIC LINK 31 



viding for 36 4-kc voice message channels. Below this band are assigned 

 the telephone (speaker) and telegraph (printer) circuits needed for 

 maintenance and administration of the facility. Above the working band, 

 between 167 and 174 kc, are the crystal frequencies, which permit evalu- 

 ation of the performance of each repeater individually from the shore 

 stations. 



The signal complex carried by the cables is derived in the carrier 

 terminals from the signals on the individual voice frequency circuits by 

 conventional frequency division techniques such as are employed in 

 the Bell System types J, K and L broadband carrier systems manu- 

 factured by the Western Electric Company. (See Fig. 2.) These signals 

 are applied to the cable through a transmitting amplifier which provides 

 necessary gain and protects the undersea repeaters against harmful 

 overloads. At the incoming end of each cable, a receiving amplifier pro- 

 vides gain and permits level adjustment. 



Shore equalizers next to the transmitting and receiving amplifiers 

 insert fixed shapes for cable length and level compensation. Adjustable 

 units provide for equalization of the system against seasonal tempera- 

 ture changes on the ocean bed, and some aging. 



The power equipment at each cable station includes (a) regular 

 primary power with Diesel standby, (b) rotary machines for driving 

 the cable current supplies, with battery standby, (c) battery plants for 

 supplying the carrier terminal bays, and (d) last but by no means least 

 in complexity, the cable current supplies themselves. These latter fur- 

 nish regulated direct current to a series loop consisting of the central 

 conductors of the two cables, with their repeaters. A power system 

 ground is provided at the midpoint of the cable current supply at each 

 cable station. 



FACTORS AFFECTING SYSTEM DESIGN 



General 



A repeatered submarine cable system differs from the land-wire type 

 of carrier system in two major respects. First, the cost of repairing a 

 fault, and of the concurrent out-of-service time, is so great as to put 

 an enormous premium on integrity of all the elements in the system and 

 on proper safeguards in the system against shore-end induced faults. 

 Second, once such a system is resting on the sea-bottom it is accessible 

 for adjustment only at its ends. These two restrictions naturally had a 

 profound influence on the design of the North Atlantic link. 



