394 BELL SYSTEM TECHNICAL JOURNAL 



2-81 molybdenum-permalloy insulated to several permeabilities. 

 The low loss coefficients of the new material as compared with the best 

 previous materials are of importance from two standpoints. First, 

 core permeabilities as much as 50 per cent greater can be now utilized 

 in coils without increasing the total core loss resistance. Second, by 

 utilizing the same permeabilities, core loss resistances about 60 per cent 

 smaller can be obtained. 



In many coil design problems, harmonic generation or modulation 

 assume controlling importance. The modulation factor m which 

 denotes the ratio of the generated third harmonic to the applied voltage 

 may be expressed as follows ^^ 



m = E3IE1 = 3ij,aB„J10Tr. 



The low values of a obtained with the new material yield values of m 

 that are about 6 db and 20 db lower than possible with powdered 

 permalloy and electrolytic iron cores, respectively. 



The wide range of core permeability available with this new material 

 permits a ready choice of the proper values of permeability and core 

 size to suit any particular needs. In the usual design problem the 

 following main requirements must be considered, in addition to pro- 

 viding the desired inductance. 



1. D-C. Resistance, Re. 



2. Coil quality factor, Q = wL/(i?, + RJ. 



3. Modulation Factor, m. 



4. Coil size (which depends directly on core size). 



These requirements can not be satisfied independently however, as 

 fixing any two of them automatically fixes the values of the others. 

 In each case, a particular value of core permeability is required for the 

 proper fulfillment of the conditions. Appendix I lists the formulae es- 

 sential to the determination of these factors. Although these formulae 

 imply an entire freedom of choice of core permeability and size, it 

 becomes necessary for practical purposes to standardize on a limited 

 number of values of permeability and a limited number of sizes of core. 

 It is possible by the proper choice from these types to approach rather 

 closely to an ideal solution for each problem. 



Improved Designs of Loading Coils 



A study of alternate ways of utilizing the advantages ofTered by the 

 new material in coils for voice frequency loaded cables showed that the 

 greatest immediate benefit to the telephone plant would accrue from 

 making the new coils substantially duplicate performance character- 

 istics of previous designs. The new designs chosen are in fact better 



