INDUCTIVE LOADING FOR TELEPHONE FACILITIES 



181 



reduced to side circuit coil size, for cost-reduction reasons. The resultant 

 economies were large relative to the value of the small attenuation impair- 

 ments which resulted from this change. 



(8) New Telegraph Systems for Loaded Cables 



At several points in this review references have been made to the transient 

 telephone transmission impairments which resulted from the operation of 

 separate, superposed, grounded telegraph circuits over the individual line- 

 wires of the loaded telephone circuits. ^''^ These ''composite" telegraph sys- 

 tems had originally been developed for use on non-loaded open-wire lines 



Fig 8— Reduction of cable ohantom coil size to that of associated side circmt cods. 

 Large No. 581 Phantom Coil (106 m.h.) at left. Small No. 587 Phantom Coil (63 m.h.) 

 at right. N.B. These phantom coils had compressed unannealed iron-powder cores. 



and consequently required the utilization of telegraph currents of very 

 large amplitude relative to the telephone currents. 



The great extensions in the lengths of 19-gauge repeatered loaded cable 

 that were to be expected from the use of the improved loadmg and repeaters, 

 previously considered, put great emphasis upon a much better control of 

 the telegraph-flutter interference, and led to the development of improved 

 cable telegraph systems, along with the improved telephone transmission 

 systems. 



In one of these, known as the ''Metallic Polar Duplex Telegraph 

 System,"i9 ^^e superposed telegraph current was of the same general order 



(«») Reference (10) gives a comprehensive discussion of telegraph-flutter phenomena. 



