N-1 CARRIER TELEPHONE SYSTEM 



421 



Adjustable magnetic cores are used with these latter inductors to facilitate 

 precise tuning with associated capacitors. The mutual inductance inherent 

 between inductors wound in this manner is desired in the case of the channel 

 band filters. In the high and low pass carrier frequency filters, where the 

 effect of mutual inductance is detrimental to filter performance, a small 

 inexpensive inductor is added to annul this mutual. This inductor comprises 



Fig. 2 — Various types of inductors used in the N-1 carrier telephone system. 



a parallel pair duo-lateral winding on a solenoidal iron dust core. Figure 2 

 illustrates some of the inductors used in the system. 



Transformers 



In the transformer designs used in the system both miniaturization and 

 low cost are attained through the use of few parts and common parts wher- 

 ever possible, improved manufacturing techniques allowing the use of much 

 finer wire than heretofore practical, and multiple-winding methods for all 

 designs. For the voice and signaling circuit transformers, where there is no 

 superimposed direct current flowing through the windings, the core struc- 

 ture consists of interleaved "E" and "I" permalloy laminations. For the 



