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BELL SYSTEM TECHNICAL JOURNAL 



difference frequency (See Equations 10 and 11) of the carrier of ampli- 



A 

 tude AB and each side band of amplitude — and is therefore propor- 

 tional to 2 .— . AB. The second term of the detected current rep- 



resents the difference frequency — between the two side bands them- 



A 2 

 selves and, as is to be expected, its amplitude is proportional to — . 



In case one of the side bands is suppressed before detection, this term 

 of double frequency is entirely absent in the detected current. Fur- 

 thermore, the amplitude of the detected current of frequency £- 



is independent of the relative amplitudes of the carrier wave and the 



A 

 side bands. In general, AB is large compared to — with the result 



that the term of double frequency in the detecting current is negligible. 

 It follows, therefore, as in the case of modulation that the detecting 

 current is practically free from distortion. 



Grid Potential 



Plate Current 



Audio Current 

 in Telephone 



Fig. 44 



The detecting action resulting from the curved plate characteristic is 

 shown in Fig. 44. 



Equation 13 leads to the result that the output voltage of a detector 

 tube, when working as above, is a maximum when r = i r p . In using 

 these relations note that r represents the value of the output resistance 



