396 



BELL SYSTEM TECHNICAL JOURNAL 



resistance-frequency characteristics for typical coils. Figure 9 shows 

 the improved telegraph flutter ^^ characteristics of a commonly used 

 toll type coil. 



to 70 



2 



^ 40 



> 



ZZ 



liJIO 



UJI 



15 



< LU 



r £L 



iu>- 



zz 



<iu 

 uE 



D_l 



Q -1 



10 15 20 25 



TELEGRAPH CURRENT IN MILLIAMPERES 



30 



35 



Fig. 9 — Flutter characteristics of typical toll loading coil; P — with 

 permalloy core, MP — with molybdenum-permalloy core. 



Figure 10 pictures the reduction in size of cores and coils which are 

 commonly used in toll and exchange area circuits. In the preparation 

 for commercial manufacture of the smallest of the new coils, a difficult 

 problem in the development of winding machinery was involved 

 because of the small dimensions of the hole in the finished coil. This 

 problem has been successfully solved by the Western Electric Company. 



