152 



BELL SYSTEM TECHNICAL JOURNAL 



Two condenser-charging circuits are provided, one for space-to-mark 

 transitions and the other for mark-to-space transitions as is indicated 

 in Fig. 5. Graph A of this figure shows an undistorted teletypewriter 



UNDISTORTED 

 SIGNAL 



VOLT -TIME CURVE 

 CONDENSER CI 



VOLT-TIME CURVE 

 CONDENSER C2 



SCHEMATIC 

 CIRCUIT 



HE> 



I 



^AA/ * ^ 



RELAY 

 D 



NOTE 



IN (B38.CC) THE HEAVY 

 SLANTING PARTS OF THE 

 CURVES INDICATE CHARG- 

 ING INTERVALS USED IN 

 MEASUREMENTS. 



LEGEND 



TD- TOTAL DISTORTION METER (PEAK- 

 B - BIAS METER INDICATING) 



CI - M-S MEASURING 



CONDENSER 



C2 - S-M MEASURING 



CONDENSER 



TO TELEG LOOP 



Fig. 5 — Simplified diagram of start-stop telegraph 

 transmission-measuring circuit. 



character having a stop pulse, start pulse, and five selecting pulses. 

 The segments of the distributor, laid out to show their relation to the 

 received signal, are indicated at the top of the schematic circuit {D). 

 It will be noted that there are seven short grounded segments, one 

 for each of the pulses of the character, for initiating the condenser- 

 charging intervals referred to above. 



Assume the distributor brush to be at rest during the stop interval 

 as show^n. The measuring condenser CI is now charged to the refer- 

 ence voltage. As the brush leaves the stop position due to the mecha- 



