INDUCTIVE LOADING FOR TELEPHONE FACILITIES 159 



velopment of: (1) large-size, very low resistance coils for open-wire lines 

 and for 10 ga. and 13 ga. long-distance toll cables, (2) smaller-size, higher- 

 resistance coils for smaller-gauge toll cables, and (3) still smaller size of 

 coils having still higher resistances for fine-wire exchange cables. Over the 

 years, the progressive use of superior core-materials has made possible 

 several successive, substantial size-reductions in the cable coils, with some- 

 what larger-ratio size-reductions in exchange area loading coils than in the 

 toll cable coils, because of their less complex service-requirements and 

 also in conformity with cost-equilibrium criteria. These progressive size- 

 reductions are well illustrated in the headpiece. 



Improved magnetic materials have been very important factors in the 

 loading coil development work. The different magnetic materials which 

 have been used in standard loading coils are listed in Table III with ap- 

 proximate dates, in terms of the beginning and end of manufacture, and 

 other pertinent data. 



PART II: LOADING FOR LONG-DISTANCE CIRCUITS 



The early applications of standard open-wire loading made loaded 104- 

 mil circuits about as good from the attenuation standpoint as non-loaded 

 165-mil circuits of equal length. When this loading was later applied to 

 165-mil circuits, the first New York-Denver loaded 165-niil line (1911) was 

 approximately equivalent in transmission performance to the original non- 

 loaded New York-Chicago 165-mil line (1892). 



Large economies also resulted from the application of the first standard 

 cable loading to suburban trunk cables and toll connecting trunks in ex- 

 change areas, and to interurban toll cables. Notable examples of the latter 

 were the Boston-Worcester (1904), New York-Philadelphia (1906), and 

 New York-New Haven (1906) cables. The toll cables used heavy loading. 

 Considerable medium loading was used in long exchange cables. 



(1) Phantom Group Loading 



This was the first major new loading development to follow the pioneer- 

 ing standardization work. Beginning late in 1907, it culminated in com- 

 mercial applications on open-wire lines and on new quadded cables during 

 1910. ^f) 



Entirely new types of coils were developed for loading the phantom 

 circuits. Each of its four line-windings comprised a tandem connection of 

 an inner-section winding located on one core-quadrant and an outer-section 

 winding located on the opposite core-quadrant, the two line windings 

 associated with the same side circuit being distributed over the same pair 



(« A much more comprehensive story of the phantom loading development and its 

 relation to the development of quadded cable and to phantom working on open-wire hnes 

 is given in BibUography items (8) and (9). 



