402 BELL SYSTEM TECHNICAL JOURNAL 



been made tolerably small by suitable choice of insulating materials, 

 stranding of conductor and configuration of winding. 



Conclusion 



Compressed powdered cores of 2-81 molybdenum-permalloy have 

 properties which are superior to those of earlier powdered cores in 

 respect to permeability range, hysteresis loss and eddy current loss. 

 Because of the lower losses and greater permeability range, inductance 

 coils are now possible which have greatly increased Q values for a given 

 volume. Because of the low hysteresis losses and attendant lowering 



Fig. 14 — Comparative size of non-magnetic core and molybdenum 

 permalloy core filter coils. 



of modulation effects to tolerable levels, magnetic core inductance 

 coils can now be employed where non-magnetic core coils have pre- 

 viously been necessary, with a very great increase in Q values for a 

 given volume. Temperature coefficients can now be obtained which 

 are equal to the temperature coefificients of other high grade electrical 

 elements such as mica condensers and quartz crystals. Moreover, the 

 ability to make the temperature coefficient of coils negative or positive 

 at will permits the attainment of remarkable stability in resonant 

 combinations of coils and condensers. Two important applications 

 have been made in the field of communication apparatus. For voice- 

 frequency circuits, new loading coils of improved quality and reduced 



