ADVANCES IN CARRIER TELEGRAPH TRANSMISSION 



199 



signals having a rate of 11 d.p.s. The reason for providing 11 -cycle 

 reversals is that experience has shown that these more nearly simulate 

 miscellaneous teletypewriter signals, both with respect to bias and 

 drift, than the higher speed reversals used in the past. An end scale 



BIAS SIGNAL 

 POLAR , p p — P-P^ 

 RELAY 4 J I JV 



POLAR I 

 NEUTRAL I 



1 



X 



TO INTERLOCKING JACKS 

 CONNECTED TO RECEIVE 

 SIGNALS FROM NORMAL 

 AND REVERSED 130-VOLT 

 LOOPS AND 48- VOLT 

 "HUB" CIRCUITS 



Fig. 23 — Carrier-telegraph test set. Bias measuring circuit. 



adjustment EA permits correction for battery variations, while a 

 second adjustment RA allows for correcting any residual bias which 

 may be present in the 215 type relay or in the dot signals used for 

 the tests. 



DISTRIBUTOR 



o">-T — -I- -1 r~ 



M 



DRIFT METER 

 (5 MILS) 



CIRCUIT TO BE OBSERVED 



Fig. 24 — Carrier-telegraph test set. 



DRIFT MEASURING CIRCUIT 



Drift measuring circuit. 



In order to observe and correct for the drift effect discussed previ- 

 ously, a special circuit is provided which is illustrated in Fig. 24. The 

 skeletonized diagram of the carrier-terminal circuit to which it is 

 applied, shown to the left in dotted lines, will help to understand the 



