LOADING FOR TP.I.EPIIONE CIRCUITS 



24.S 



iiiNolving rcpealered coinposilcd circuits, i^o-pcrmeability cores should 

 be employed. All of the compressed powder core coils intended for re- 

 peatered circuits were adjusted to meet zt 2 per cent, inductance limits. 



The effective resistance-frequency characteristics of 95-permeability 

 and G5-permeability wire core coils and (iO-permeability and 3o- 

 permeability powdered iron core coils having the same inductance 

 (0.174 henry) and the same over-all sizes are gixen in Fig. 7. The 

 large impro\ement as to freedom from residual magnetization effects 

 afforded by the 35-permeability powdered iron core, compared with 

 the 65-permeability wire core is evident from the curves of Fig. 8. 

 The effective resistance and inductance variation with current strength 

 are shown in Fig. 9 for a 35-permeability powdered iron core coil. 

 The remarkable property of these cores of maintaining constancy of 

 permeability is shown by the change of only 1 per cent, in permeability 

 as the current strength varies 400 per cent, from, say 0.001 to 0.005 

 ampere. 



It is interesting to note that after the process had been fully worked 

 out and production was running on a commercial scale, the cost of 

 the improved cores w-as comparable with that of the wire cores which 

 they replaced. 



TABLE IX 

 Typical Compressed Powdered Iron Core Loading Coils 



Note. Resistance values apply to side circuits and phantom circuits of complete 



phantom groups. Effective resistance corresponds to 0.002-ampere line current. 

 These coils are used in the loading systems listed in Tables V and X. 



