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BELL SYSTEM TECHNICAL JOURNAL 



marking the intersections are seen to be displaced from the intersection 

 with the cur\^e for one span by approximately 3, 6 and 10 db. If the phase of 

 the repeaters is as linear as it must be in pulse systems, this single frequency 

 characteristic can be applied for the entire signal band as if it resulted from 

 a single source of third-order distortion. The effect of this distortion is 



20 



16 



14 



12 10 8 6 4 



INPUT IN DECIBELS DOWN 



Fig. 25 — Overload characteristics of multi-repeater systems. 



serious in multiband PCM repeaters, as illustrated by the measurements 

 on Fig. 24, but is, generally speaking, less important in single band pulse 

 repeaters. For instance^* PPM-AM pulses and binary PCM-AM pulses 

 might operate on the flat part of curve 10 (Fig. 25). With PCM of higher 



''' On the grounds that pulse slicers themselves include the compression function to a 

 high degree, one might not see the harm of compression in repeaters. If all of the com- 

 pression occurred after the noise had been acquired there would be no fundamental com- 

 pression penalty in slicing pulse systems. The penalty comes about because as the pulses 

 progress from span to span they shrink and become more vulnerable to noise. 



