EVOLUTION OF INDUCTIVE LOADING 1235 



Because of the speculative uncertainties involved in making assumptions 

 regarding relative transmission-performance and relative plant-size, with 

 and without loading, and because of the practical difficulties involved in 

 evaluating in monetary terms the differences in transmission performance 

 and in speed of service, no complete appraisal of the economic value of coil 

 loading has ever been attempted for the exchange area plant. These, and 

 additional special complications subsequently discussed, have also prevented 

 accurate appraisals of the economic value of toll cable loading. 



Exchange Area Loading 



During the first two decades or so of the use of exchange area loading, 

 rough estimates of its economic significance were sometimes made by 

 comparing the total costs of the loaded faciUties with the much higher cost 

 of the non-loaded cable plant which otherwise would have been required to 

 meet the same trunk-loss limits at 800 or 1000 cycles. Depending on the 

 period under study, the estimated aggregate plant-cost reduction figures 

 ranged up to and beyond $100,000,000. These estimates included the 

 plant-cost reductions that resulted from the use of less expensive pole fines 

 for aerial cables, and less expensive conduit systems made possible by 

 utilizing a smaller total number of cables, each having a larger number of 

 pairs. If similar studies should be made now, the corresponding hypothetical 

 plant-cost reduction figure would probably be many times as large as the 

 figure previously mentioned. These figures ignore the superior over-all 

 transmission in loaded trunk plant that results from the much more favorable 

 distortion characteristics. Also they assume equal sizes of trunk plant, with 

 and without loading. Because of these qualifications, and because of the 

 magnitude of the cost-reduction estimates, it is difficult to define their real 

 significance. 



A better understanding may perhaps be obtained from consideration of 

 the cable data given in Table XXI, following. This compares some of the 

 most important types of cable on which loading has been used with the 

 types which would probably have been required for transmission reasons, 

 if loading had not been available. 



The large savings which loading permitted in the use of cable copper and 

 in the amount of lead sheath per cable pair, are indirectly indicated by the 

 tabulated data. Moreover, with loading on finer-wire cables a given total 

 number of facilities can be provided with a much smaller total number of 

 cables, thus permitting the use of less expensive conduit systems. This 

 factor is extremely important in some routes of congested sections of large 

 metropoHtan areas such as Manhattan and the loop section in Chicago, 

 where there might well be a question as to the physical practicability, dis- 



