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BELL SYSTEM TECHNICAL JOURNAL 



the amplitude detectors is 11 decibels greater than that admitted by 

 an amplitude modulation system having the minimum intermediate- 

 frequency band width of 8 kilocycles. 



Aural observation of the character of the output noise showed that, 

 excluding the shaded area in Fig. 13, the normal characteristics of 

 fluctuation noise are preserved as feedback is applied. Upon crossing 



10 12 14 16 

 FEEDBACK IN DB 



Fig. 13 — Effect of feedback upon receiver output noise level for various amounts 

 of high-frequency disturbance. Ratio of root-mean-square values of carrier and 

 disturbance is shown on each curve. Shaded area indicates region of "crackling" 

 in the absence of modulation. 



the boundary of the shaded area the noise becomes punctuated with 

 intermittent clicks which increase in rapidity and violence as the feed- 

 back factor is raised, giving rise to what can be described as "crack- 

 ling." After passing through a region of maximum turbulence the 

 noise gradually assumes the nature of a much higher level of fluctuation 

 noise, 



