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BELL SYSTEM TECHNICAL JOURNAL 



bridge-like arrangement between the carrier source and the sending 

 filter, which is balanced at all times with respect to the d-c. pulses so 

 that these do not tend to be propagated into the line or towards the 

 generator. When x is positive relative to y, rectifier elements ai and 02 



TO 

 GENERATOR 



■^ 



92 



ib, 



(A) 



LOOP-BALANCING 



SOUND- 

 ER 



RESISTANCE 4-| 



'■" ^^^^ -I 



TO 

 GENERATOR 



TO SENDING 

 FILTER 



TO 

 GENERATOR 



SUPPRESSOR 

 CIRCUIT 



■+^ 



TO SENDING 

 FILTER 



W^ 



(c) 



Fig. 9 — Varistor sending-circuits. A. Series-parallel arrangement. 

 B. Phase inverter. C. Non-polar arrangement. 



are conducting while hi and 62 are non-conducting. This allows a free 

 path for the carrier between transformers Ti and Ti and thus from the 

 generator to the sending filter. If, however, point x is negative rela- 

 tive to 3^, ai and a^ acquire a high resistance, thereby greatly impeding 

 the passage of current between T\ and T2, while hi and &2 become 

 conducting and efifectively shunt the primary of Ti. 



