18 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1957 



76-88 kc which are not compatible with the spht group arrangement or 

 with the 84.08 kc end-to-end pilot. 



Net Loss 



The nominal 1,000-cycle net loss objective between London and New 

 York for calls switched to other long distance trunks at each end (i.e., 

 the via net loss) was set at 0.5 db. For calls terminating at either New 

 York or London, the loss would be increased by switching a 3.5-db pad 

 in London, as recommended by the C.C.LF., and a 2-db pad at New 

 York as standard in the Bell System. Thus a New York to London call 

 would have a net loss of 6 db. 



Variations from these nominal net losses owing to temperature effects, 

 lack of perfect equalization and regulation, etc., are to be expected and 

 a standard deviation of 1.5 db was set as the objective for such variations 

 in the absence of trouble. The allocation of this variation to the various 

 links is shown in Table L 



It is interesting to note that a smaller variation was allocated to the 

 submarine links than to the over-land links. It was believed that the 

 more stable environment on the ocean floor would make it possible to 

 meet the rather small variation assigned to these links. 



While these loss variations are consistent with normal long distance 

 trunk objectives, they would not be satisfactory if compandors were 

 found necessary to meet the noise objectives, and it was agreed that any 

 of the links lying between such compandors would have to meet ob- 

 jectives half as large as those in Table I. 



Frequency Characteristics 



For telephone message circuits, the frequency characteristic recom- 

 mended by the C.C.I.F., Fig. 3, was adopted with the expectation that 

 it could be bettered by a factor of two, since channel equipments would 

 be included at the circuit terminals only, as described later. 



Table I — Standard Deviations of Net Loss Objective 



