INDUCTIVE LOADING FOR TELEPHONE FACILITIES 183 



known as telegraph crossfire, is mainly due to capacitance coupling between 

 the cable conductors and in the central office equipment. In long circuits, 

 the inductive coupling between the two line windings of each side circuit 

 coil, and among the four line windings of each phantom loading coil, are 

 important factors in the over-all crossfire between the telegraph circuits that 

 are associated with the same cable quad. 



(9) Compressed Permalloy-Powder Core Loading Coils 



Since the transmission characteristics of the compressed, unannealed, 

 powdered-iron core coils, which became available for general use in toll 

 cables during 1918, were as satisfactory as was expected for the rapidly 

 expanding repeatered toll-cable plant, greater emphasis was placed on cost 

 reduction than on transmission improvement, in the continuing studies of 

 new loading coil design-possibilities. 



9.1 Core-Material Development 



It was inevitable that permalloy^ should be considered. This remarkable 

 new nickel-iron alloy, invented by Mr. G. E. Elman of Western Electric 

 research department, had important early applications in thin-tape form for 

 continuous loading of deep-sea telegraph cables. 



Some early studies and experiments indicated interesting possibilities of 

 using it in thin sheets in non-toroidal type loading coil cores, but the pros- 

 pects were much more intriguing if permalloy could be made available in 

 compressed-powder toroidal cores. However, the initial experimental results 

 with powdered-permalloy were disappointing. When the processes used in 

 making compressed powdered-iron cores were employed, the permeability 

 was unsatisfactorily low in consequence of the magnetic changes caused by 

 the severe mechanical treatment involved in the embrittlement processes. 

 The development moved forward rapidly after experiments with a physically 

 sturdy type of ceramic-powder insulation for the permalloy particles proved 

 that an annealing treatment after the core rings were pressed could erase 

 the objectionable magnetic effects of the powderizing process and raise the 

 permeability to desirable, high values. A complete account of this very im- 

 portant development is given in an A.I.E.E. paper^ by W. J. Shackelton 

 and I. G. Barber, "Compressed Powdered Permalloy, Manufacture and 

 Magnetic Properties." 



In the form developed for voice-frequency loading coil cores, the effective 

 volume-permeability of the improved core-material was 75, more than twice 

 that of the standard compressed, unannealed, powdered-iron core-material, 

 and the intrinsic permalloy characteristic of very low hysteresis was retained. 

 The combination of magnetic and electrical properties was such that large 

 size-reductions could be made in the loading coils without degrading the 



