NEIV YORK-CHICAGO CABLE 



79 



the line as nearly as possible at telephone frecjuencies. This balance 

 is essential to proper repeater operation. The circuit arrangement is 

 such that part of the incoming energy is diverted to that part of the 

 circuit containing the input coil directly associated with this three- 

 winding transformer. By the action of the vacuum-tube arrangement 

 amplified energy is transmitted to the line east. That part of the 

 original incoming energy from the line west that goes through the 

 balancing network or the output coil is not, of course, transmitted 

 along into the line east. The operation in the case of currents incom- 

 ing from the line east is similar and it w^ill be noted that the complete 

 repeater circuit is made up of two symmetrical parts. This circuit 

 arrangement constitutes what is known as a two-wire repeater and the 

 apparatus is, of course, all closely associated in the same office. 



FbuR Wire CKCurr 



Equipped with TelepNsne Repeaters end 

 Ai-ranged for Connection to Wn Wire Circyiti ft the Terminil* 



I aSoTi 



Hybr.d Cal 





»«y 



I 1 



I- I rMT 



Hybrid Co.1 



2-Wir* 

 Line 

 Enl 



Fig. 23 — Four-Wire Circuit equipped with telephone repeaters and arranged for 

 connection to two wire-circuits at the terminals 



Several of these repeaters may be inserted in tandem at appropriate 

 points in a circuit, but there is a limit to the length of circuit that can 

 be satisfactorily operated with this arrangement, this length depend- 

 ing upon the type of the facilities used. When longer circuits are 

 required, a four-wire arrangement is used, as shown in Fig. 23. It 

 will be noted that in this arrangement the three-winding transformers 

 are not located in the same office but may be in offices several hundred 

 miles apart. At each of the intermediate stations a vacuum-tube 

 amplifier arranged for amplification in one direction only is connected 

 to each of the two branches of the circuit. Two circuits are, of 

 course, required between the terminals and these may be either 

 physical or phantom circuits. 



An advantage of this arrangement is that balancing networks are 



