INDUCTIVE LOADING FOR TELEPHONE FACILITIES 173 



tially as good in their efifective resistance-frequency characteristics. The 

 above summarized advantageous electrical and magnetic properties resulted 

 during 1918 in the standardization of the new compressed, annealed, pow- 

 dered-iron core loading coils for general toll cable use in place of the 65- 

 permeability wire-core coils and soft-iron dust-core coils. The availability 

 of the improved loading coils quickly stopped the previously mentioned 

 temporary, compromise practice of using soft-iron dust side circuit loading 

 coils in combination with 65-permeability wire-core phantom loading coils. 

 After the hard-iron dust-core loading coils became commercially available, 

 the remaining development work on improved toll cable loading systems 

 described in the following pages was in terms of these coils. 



(7) New Loading Systems for Repeatered 19 and 16 Ga. Toll 



Cables 

 7.1 General 



The basic problems of learning how to use telephone repeaters most 

 advantageously on long cable circuits began to receive serious attention 

 soon after the completion of the open-wire transcontinental telephony proj- 

 ect, along with the repeater development work that ultimately resulted in 

 the obsolescence of open-wire loading, as previously mentioned. During 

 the decade or more of intensive, continuous development activity on the 

 repeatered toll cable problem that followed, it was found highly advan- 

 tageous to work loading and repeaters together as equal partners in a team, 

 each making its contribution according to its own nature. The important 

 contributions of loading were the substantial reductions of attenuation 

 and of frequency distortion at a cost (for voice-frequency transmission) much 

 lower than the cost of the additional repeaters and the distortion corrective- 

 networks which would have been required on non-loaded cables. Incidentally, 

 the use of loading substantially simplified the solution of the important 

 equalization and regulation problems. 



The attainment of the good working partnership between loading and 

 repeaters involved the development of new loading systems having sub- 

 stantially improved transmission characteristics, and the development of 

 improved repeaters and improvements in repeatered circuits, including 

 equalizing networks and arrangements for controlling the cable transmission- 

 performance changes that result from seasonal and daily changes in tem- 

 perature. A classic report on these related developments is given in a paper^"' 

 by A. B. Clark, entitled, 'Telephone Transmission over Long Cable Cir- 

 cuits." ^^^ The present discussion is primarily concerned with the features 

 of the improved loading that were essential to satisfactory transmission- 

 performance in long repeatered cable circuits. 



<^> Reference (15) is also of interest with respect to engineering aspects. 



