1.03 IN. (O.D.) 

 0.06 LB 



Headpiece. — A panorama of loading coils 1904-1948. 



The Evolution of Inductive Loading for Bell System 

 Telephone Facilities 



By THOMAS SHAW 



{Continued from January 1951 issue) 

 PART III. LOADING FOR EXCHANGE AREA CABLES 



THIS portion of the present review is primarily concerned with non- 

 phantom t3^e of loading on non-repeatered non-quadded cables, since 

 the evolution of exchange area loading has been ahnost entirely in terms of 

 these facilities. 



Phantom working has not been extensively practiced because in general 

 it is not economical on exchange cables. In the occasional long cables where 

 phantoming is economical, the phantom group loading makes use of loading 

 apparatus developed for short-haul, two-wire type toll cable faciUties. 



The very wide range of impedance characteristics of the many different 

 types of exchange cables (with and without loading, and as influenced by 

 the terminal impedances provided by the many different kinds of subscriber 

 loops and station sets) is such that telephone repeaters are necessarily Hm- 

 ited to low gains when used at exchange area switching points. Moreover, 

 it has not been generally feasible to use intermediate repeaters in the lines. 

 Furthermore, the conventional two-wire type of telephone repeater used 



447 



