190 



BELL SYSTEM TECHNICAL JOURNAL 



Circuit Reliability Curve 



The corrected form of the noise-to-signal distribution curve rep- 

 resented by the line a-c-d-b in Fig. 5 may by a simple translation be 

 put in terms of percentage lost circuit time versus transmission im- 

 provement in decibels where noise rather than quality degradation or 



-20 -15 -10 -5 5 10 15 20 25 



NOISE TO SIGNAL RATIO IN DECIBELS (ARBITRARY REFERENCE) 



Fig. 5— Correction of assumed 6-A noise distribution curve where it is influenced by 

 terminal equipment effects. 



equipment failures interrupts continuity of service. To start this 

 translation, take, for example, the point at which 50 per cent of the 

 noise-to-signal values are greater and 50 per cent are less than a value 

 given on the horizontal scale. This is db and the value in itself has 



