464 THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



standards of transmission-service performance. On the other hand, the pen- 

 alty ratings for trunks using the old standard types of loading having lower 

 cut-off frequencies range from nearly 1 db to 4 db or more, depending pri- 

 marily upon the theoretical cut-off frequency. 



From the foregoing, it can be understood that the distortion penalty in 

 old cables having old types of low cut-off loading may be a substantial frac- 

 tion of the total allowable effective transmission loss in the trunk. 



(21) Compressed Molybdenum-Permalloy Powder Core Exchange 



Area Loading Coils 



21.1 The Improved Core MateriaP^ 



A brief general description of the new compressed molybdenum-permalloy 

 powder core-material is given under this heading in Section 11.1. 



The low-inductance exchange area loading coils described below were 

 given priority in the commercial exploitation of the improved core-material 

 in message circuit loading. 



21.2 622 (88 mh), 628 (44 mh), and 629 (22 mh) Loading Coils 



The preliminary development-activity was in terms of 88 mh loading, 

 on account of the added importance of this loading which resulted from the 

 adoption of the higher cut-off loading-standards, described in the preceding 

 pages. 



The transmission engineering studies and the cost-equilibrium design 

 studies resulted in a decision to reduce the coil size as much as possible, 

 without degrading transmission performance. 



A size reduction of about 60%, relative to the 612 permalloy-core coil, 

 proved to be feasible. The new coil. Code 622, was closely equivalent to the 

 612 coil. Actually it had somewhat better frequency-resistance character- 

 istics, because of the superior eddy-current loss characteristics of the im- 

 proved core-material. On the other hand it was not quite so good as the 

 612 coil with respect to susceptibiHty to magnetization by superposed d-c 

 signaling currents. Coil H in the headpiece is a 622 coil (Coil G being its 

 standard predecessor, the 612). 



The ability to make so small a molybdenum-permalloy core coil as the 

 622 coil, without degrading transmission, was principally due to the in- 

 genuity of the factory engineers in devising an entirely new, high-speed, 

 winding machine capable of winding a small toroidal core to a finished 

 inside diameter of 0.5" — an achievement which seemed impossible a decade 

 earlier when the 612 coil was developed. The use of an enamel-film insula- 

 tion on the core ring, in place of the overlapping fabric-tape employed on 

 larger and older designs, was a favorable factor in the more efficient utiliza- 



