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BELL SYSTEM TECHNICAL JOURNAL 



frequently decisive in the selection of these materials instead of the 

 technically superior materials noted above. Air-gaps are often found 

 necessary to reduce the superposed field strength in the magnetic core. 



Fig. 8 — Relative sizes of compressed powder cores for loading coils; 

 A. Iron, B. 80-permalloy, C. 2-81 Mo-permalloy. 



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wmm^^W^mm^^ 



PERMALLOY 

 LOADING- MATERIAL- 



Fig. 9 — Permalloy loaded telegraph cable; A. Armored deep sea type, B. Gutta 

 percha insulated core, C. Enlarged cross sectional view. 



This serves to retain a fairly large reversible permeability in the core, 

 and, if the air gaps are not too large, it yields a larger net effective 

 permeability than could be obtained without air-gaps. 



