MEASUREMENT OF TELEGRAPH TRANSMISSION 171 



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Fig. 20 — Telegraph signal-biasing set. 



F. Measuring with Teletypewriters 



As is well known, the start-stop teletypewriter, when properly 

 adjusted for this purpose, may be used as a transmission-measuring 

 device. The usual procedure in field testing is to compare the range 

 over which the orientation range finder may be shifted with sub- 

 stantially perfect signals to that obtained with signals from the line 

 under test. The orientation range finder is shifted above and below 

 the usual setting until perfect copy is no longer obtained, these limiting 

 positions determining the margins. 



At the time of the previous paper, ^ the orientation range test was 

 the only test available to the field forces in the Bell System which 

 utilized the start-stop principle. At that time the teletypewriter was 

 not convenient to use and generally the results were not as accurate 

 as desired. However, the machines have been much improved and 

 better methods of use have been developed so that now orientation 

 margin tests furnish a better indication of the grade of transmission. 

 At the same time, the more convenient measuring sets described 

 above have become available and this has, of course, reduced the field 

 of use of the teletypewriter as a measuring device. 



One of the improvements in the machines from the standpoint of 



