PLANNING AND OVER-ALL PERFORMANCE 17 



Since the transatlantic circuits were to connect two extensive net- 

 works, the broad objective was to add as Httle loss and other forms of 

 impairment as practical. To this end, they were to be designed essentially 

 to the standards of international circuits as defined by the C.C.I.F.* 

 and of circuits connecting main switching points in national networks, 

 as for example, "Regional Centers" in the Bell System network and 

 "Zone Centers" in the Post Office network. 



The possibility of increasing the circuit capacity of the system by 

 using channel spacings less than 4 kc was obvious. It was decided, how- 

 ever, to adopt, initially at least, the 4-kc spacing commonly used by 

 long distance systems on both sides of the Atlantic. This would make 

 possible the use of standard multiplexing arrangements, and it was 

 believed that the number of circuits provided would be adequate for 

 the first few years of operation. It would undoubtedly be desirable to 

 increase the number of circuits in later years, but a decision on the 

 method to be used was left until completion of exploratory work on 

 several methods which promised capacity increases with less degradation 

 than narrow-band operation. 



The decision to use standard terminal equipment led naturally to 

 acceptance of the principle that the 36 circuits across the Atlantic would 

 be assembled as three 12-channel groups in the range 60-108 kc and the 

 60 circuits between Newfoundland and Nova Scotia as five 12-channel 

 groups and thence as a supergroup in the range 312-552 kc. These are 

 standard modulation stages in the multiplexing arrangements for broad- 

 band carrier system on both sides of the Atlantic. Two of the 12-channel 

 transatlantic groups would be connected to New York and the third 

 would be split to provide 6| circuits to Montreal and 5| to New York in 

 accordance with the Agreement. 



To provide for program circuits, three eastbound and three west- 

 bound channels in each of the three transatlantic groups would be made 

 available when required; equipment would be pro\-ided to replace either 

 two or three 4-kc message telephone channels by a music channel. In 

 order to avoid the agreed group pilot frequencies and to provide service 

 to Montreal, it was agreed to utilize the frequency bands 68-76 kc and 

 64-76 kc in the 12-channel groups for this purpose. Terminals of British 

 Post Office design would be used at all points for translation between 

 program and carrier frequencies. The normal Bell System terminals 

 could not be used since they occupy the frequency ranges 80-88 kc and 



* The International Consultative Committee on Telephony (C.C.I.F.) bases 

 its recommendations on a circuit 2,500 km (1,600 miles) in length, with implied 

 pro rata increases for noise impairment. 



