INDUCTIVE LOADING FOR TELEPHONE FACILITIES 



165 



pairments, however, were negligible in the repeatered circuits. The 

 headpiece includes a 550 coil (the largest coil, designated A). 



During the decade that followed the beginning of transcontinental tel- 

 ephony, a large enough quantity of Nos. 549 and 550 coils were installed 

 to load approximately 300,000 circuit miles. In the beginning, the improved 

 loading was concentrated on parts of a proposed backbone-network of re- 

 peatered 165-mil lines. Soon it became apparent from: (a) the continuing 



Fig. 4— Typical installation of high stability open-wire loading coils. Note the three 

 phantom loading unit combinations in 3-coil cases supported on the poles; other m- 

 dividually potted side-circuit and phantom coils are supported on the crossarms. 



development work on telephone repeaters, repeater circuits and auxiliary 

 apparatus and transmission networks, and from (b) field experiments sup- 

 plemented by theoretical cost studies, that non-loaded 165-mil liiies with 

 additional repeaters would have much more satisfactory transmission char- 

 acteristics than repeatered loaded Hnes, and would be less expensive. The 

 principal transmission advantages were: (1) the practicability of securing 

 materially lower net losses, in consequence of the effect of the higher velocity 

 of transmission in reducing echo-current disturbances, (2) more uniform 

 attenuation and impedance characteristics under varying weather condi- 



