1232 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



distance telephone service, and the provision of a tremendous amount of 

 new exchange plant to take care of more than eleven million new Bell 

 System telephone stations, made it necessary to build up the production 

 rates to higher values than those during the war period. An important 

 factor in the new heavy demands was the desire to restore the speed of 

 service to the pre-war standards. 



The post-war demand for exchange area loading has been greatly in 

 excess of that in any previous spurt in demand, reaching its peak value 

 during 1948, and has been very large in relation to the toll cable loading 

 requirements. The post-war rapid build-up of a backbone network of 

 coaxial cables, together with the expanding use of carrier systems in existing 

 and new cables of the conventional types, and the introduction of micro- 

 wave radio relay systems have held down the demand for new toll cible 

 loading to relatively small quantities for use on relatively short circuits. 



Relative Costs y Toll and Exchange Loading 



Production statistics by themselves do not indicate the relative economic 

 importance of exchange area and toll cable loading. Except in the early 

 years when coils of the same size were used for both types of loading, the 

 toll cable loading coils have been considerably more expensive than the 

 exchange area loading coils. During the periods of maximum production 

 and use portrayed in Fig. 35, the average prices per potted toll cable loading 

 coil have ranged up to about twice or three times as large as those per 

 p)otted exchange area coil. Consequently, the total plant investment in 

 toll cable loading is substantially greater than the total investment in 

 exchange area loading, notwithstanding the somewhat greater total use of 

 exchange area loading, as indicated by the production statistics. This is 

 consistent with the fact that more expensive types of cable are used for the 

 toll circuits and the service requirements are more difficult. 



Analysis in Relation to Core Materials 



There now follows a rough breakdown of total production in terms of 

 core materials, in recognition of the importance of the cores in determining 

 the coil performance characteristics and costs: 



In general, the production percentage figures in Table XX do not dis- 

 criminate between types of facilities (toll or exchange area). If separate 

 percentage-of-total figures should be derived for toll facilities and for ex- 

 change area facilities, those for toll facilities would substantially exceed the 

 tabulated figures for total iron-wire, iron-dust, and permalloy-powder core 

 loading coils, especially in the case of the latter, and the percentage-of-total 

 figure for exchange area molybdenum-permalloy core coils would greatly 

 exceed that for toll cable loading. 



