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BELL SYSTEM TECHNICAL JOURNAL 



illustrated by Fig. 3, the distortion of miscellaneous teletypewriter 

 signals on working circuits. It has the distinct advantage of giving 

 immediate indication of the occasional isolated peaks as well as the 

 average distortion. In using this set, it is unnecessary to have a 

 knowledge of the transmitted text. 



This set employs the condenser-charging principle in the measure- 

 ment of small time intervals corresponding to the distortion of the 



Fig. 3 — Meters and control apparatus at telegraph board. 



signals. The outstanding feature of this device is that the beginnings 

 of the condenser-charging intervals are timed with relation to the start 

 transition by a start-stop distributor which forms an integral part of the 

 set. The charging intervals are terminated by the occurrence of tran- 

 sitions in the characters, at which times the operation of a receiving 

 relay causes the condenser voltages to be compared to a reference volt- 

 age. The circuit is arranged to charge the condenser at a constant 

 rate; hence the voltage attained is determined by the duration of the 

 charging interval. In this way the displacements of the transitions 



