88 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1956 



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INPUT LEVEL IN DECIBELS ABOVE SLICING LEVEL 



Fig 19 — Gain characteristics of u repeater providing partial regeneration. 



point F' of Fig. 18. On Fig. 19 all other levels are shown in reference to 

 this unity-gain value. 



From Fig. 19 it is obvious that a pulse which starts out in the loop 

 with a peak amplitude exactly equal to the reference, or slicing level, 

 will continue to circulate without change of amplitude since for this 

 level there is unity gain around the loop. A pulse with amplitude greater 

 than the slicing level will have its amplitude increased by each passage 

 through a regenerator until it eventually reaches a value of +6 db. It 

 will continue to circulate at this amplitude, for here also the gain around 

 the loop isVmity.* Any pulse with peak amplitude less than the reference 

 level will have its amplitude decreased by successive trips through the 

 regenerator and eventually go to zero. We also see that the greater the 

 departure of the amplitude of a pulse from the slicing level the more 

 effect the regenerator has upon it. This means that the device acts much 

 more powerfully on low level noise than on noise with pulse peaks near 

 the slicing level. As examples consider first the case of noise peaks only 

 1 db below slicing level at the input (peak S/N = 7 db). At this level 

 there is a 1 db loss through the repeater so that at the output the noise 

 peaks will be 2 db below reference to give a *S/A^ ratio of 8 db. Next 



* Note that llic ^-fi-dl) level is at a point of stable equilibrium whereas at the 

 slicing level C(iuilil)rium is unstable. 



