EVOLUTION OF INDUCTIVE LOADING 1237 



indicated by the previously discussed production and circuit-mileage sta- 

 tistics. 



In short-haul, non-repeatered, toll cable circuits, loaded 19 ga. conductors 

 are generally used for service which would have required 16 or 13 gauge 

 conductors without loading. The plant-cost savings in cable, copper, and 

 lead are much greater per unit length than the average savings realized in 

 the loaded exchange area cables. The aggregate mileage in this type of toll 

 plant, however, is but a small fraction of that in the loaded exchange area 

 plant. 



Until the commercial exploitations of lower-cost carrier telephone systems 

 started during the late 1930's, the loaded repeatered voice-frequency cable 

 facilities satisfactorily met the quantitative and qualitative needs for the 

 rapidly expanding long-distance telephone services along dense traffic routes 

 where the use or the extension and expansion of the open-wire plant would 

 have been unduly expensive, even on a carrier basis. In such backbone 

 routes, and also along slow-growing tributary routes, and for short-haul 

 toll facilities, the repeatered and non-repeatered loaded toll cables have 

 provided more economical service than could have been obtained in an 

 open-wire plant, and with increased dependability. Also, as previously 

 indicated, larger circuit groups have been economically feasible, with valu- 

 able results as regards the speed of service. 



In concluding this part of the review, it is noteworthy that the phantom- 

 group loading ahnost universally used on voice-frequency repeatered and 

 non-repeatered toll cable facilities is a major factor in the plant economies 

 that have resulted from the commercial exploitation of the phantom working 

 principle. These particular plant-cost savings constitute an important con- 

 tribution to the aggregate economies achieved by toll cable loading. 



PART VIII: SUMMARY AND CONCLUSION 



General 



The story of coil loading told in the present review is one of continuing 

 evolution whereby its inherent capabilities have been substantially realized 

 in its adaptation to the growing and changing needs of exchange area 

 facilities and of interurban and long-distance communications by wires, 

 throughout the Bell Telephone System. Also, full advantage has been 

 taken of the opportunities offered by the development of better core- 

 materials and new manufacturing techniques and tools to improve the 

 loading apparatus and reduce its cost. 



It was inevitable that by far the most important uses of coil loading 

 would be for voice-frequency telephony over cable circuits. The very low 



