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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1952 



patch. Obviously echo suppressors must be disabled when a message 

 circuit is used for telegraph. 



When the telegraph circuit contains one or more branches at inter- 

 mediate points, it would be difficult and often impractical to use an 

 ordinary message circuit to replace the telegraph stem in emergencies. 

 The branching location frequently will not be manned and so no one 

 will be available to patch the branch line to the message circuit. In such 

 cases each intermediate branch circuit may be made good over a separate 

 message circuit which is individual to it. Fig. 16 shows this arrangement. 

 A patch trunk is provided between the 43 A 1 channel terminal at the 

 central office and the telephone switchboard. At the switchboard which 

 is nearest to the intermediate branch subscriber, the branch line is 



43A1 



CHANNEL 



TERMINALS 



SWITCHBOARD 



SWITCHBOARD 



Fig. 16 — Emergency circuit for intermediate branch. 



VAr 



DIFFERENTIAL 

 LOOP REPEATER 



Fig. 17-Connection to other telegraph repeaters. 



