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BELL SYSTEM TECHNICAL JOURNAL 







Fig. 25 — Telegraph service-monitoring set, test design. 



and special investigations. Among these devices are start-stop and 

 synchronous distortion indicators employing flashes of Hght to indicate 

 the position of the transitions of teletypewriter signals and a photo- 

 graphic recorder of teletypewriter signal transition points. A syn- 

 chronous flashing indicator in combination with a distributor arranged 

 to supply teletypewriter signals with adjustable bias is in use in shop 

 tests of teletypewriters and in the laboratory. 



Acknowledgment 



In the development of the practical telegraph transmission meas- 

 uring devices, which have been described, many members of the Bell 

 System have contributed valuable ideas and eff"ort. The authors 

 wish to express their appreciation of the cooperation they have 

 received. 



APPENDIX 



General 



This appendix considers characteristic distortion of telegraph signals 

 from the standpoint of the development of simple and convenient 

 testing technique for application primarily to circuits transmitting 

 start-stop teletypewriter signals. 



