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BELL SYSTEM TECHNICAL JOURNAL 



the operated mileage of program circuits for the period 1926 to 1940. 

 Of the more than 110,000 miles of circuits shown for 1940, about 45,000 

 miles have been provided for the short-period services and as stand-by 

 facilities for protection. In addition to these, there are still other circuits, 

 normally assigned to other services, which are arranged to be readily adapt- 

 able to program service to supplem.ent the reserve facilities maintained on a 

 full-time basis. 



The time interval necessarily accompanying any extensive construction 

 project makes it necessary to engineer plant considerably in advance of 

 actual service requirem.ents to m.eet, not only the expected growth, but also 

 the changes in network routing. Figure 3 shows for two typical sections 



BEGINNING OF YEAR 

 Fig. 2 — Growth in mileage of major network circuits 



along major routes the variations in requirem.ents for fuU-tim-e network 

 circuits resulting from growth and rearrangements required by the broad- 

 casters. While, in planning to meet these rapid variations in circuit 

 requirements, advantage can be tal en of son e latitude which exists in the 

 choice of routes for occasional services and protection facilities, the task of 

 balancing the provision of circuits against requirer/ents is an entertaining 

 and at tim.es difficult one for the circuit engineer. 



Operating Requirements 



Considering for a moment the variety of programs originating at many 

 different points that can be heard on any hom.e radio set in the course of an 



