NEGATIVE FEEDBACK 



423 



disturbance levels. Measurements were made in the absence of modu- 

 lation and hence are indicative of the manner in which background 

 noise is modified by feedback. The signal level indicated is that 

 which could be maintained at low noise levels by increasing the modu- 

 lation in proportion to the feedback, and is not significant for observa- 

 tions falling within or close to the shaded area, as will be explained 

 subsequently. 



8 10 12 14 16 



FEEDBACK IN DECIBELS 



20 22 24 



Fig. 10 — Effect of feedback upon receiver distortion. Conditions same as indicated 

 for Fig. 9 up to 15-decibel feedback; modulation held constant thereafter. 



The lowest noise level shown is that generated within the receiver 

 while the higher levels were produced by disturbances introduced from 

 the noise generator. The relative magnitude of the effective carrier 

 and disturbing voltages at the grids of the amplitude detector is indi- 



