148 



BELL SYSTEM TECHNICAL JOURNAL 



TIME 

 BIAS- 7o 



-61.7 



-34 7 



-7 8 



-H9.2 

 + 46.1 



f730 

 -73 





 



note; (I) TIME BIAS = 



MARKING TIME -SPACING TIME 

 MARKING TIME-H SPACING TIME 



Fig. 1 — Signals used in measuring systematic distortion. The first six signals and 

 the eighth signal are teletypewriter characters. 



desirable to extend the test to include biased test signals, as described 

 below. 



As an example, curves are given in Fig. 2 showing the results of 

 tests with the six characters on a d-c. metallic telegraph ^ circuit 

 operating on 112 miles (180 km.) of composited 19-gauge cable pair. 

 Curves 1 and 2 show the results before and after equalization respec- 

 tively; it will be noted that considerable improvement was effected. 

 On the basis of both experiment and theory, the slope of Curve 1 is 

 known to indicate that the received direct current is larger than it 



Fig. 2 — Equalization test result for a 112-mile section of metallic telegraph; signalling 

 speed 23 d.p.s. Curve 1, before equalization; curve 2, after equalization. 



