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Analog modulation

By Ashik

Modulating signal and carrier Wave

 

Modulated wave



 
Frequency spectrum of AM wave

 
If the equation of modulating signal is




And the carrier wave equation is




Then the modulated wave is the superposition of the above two waves.




 












 
Amplitude of the modulated wave is


 
Instantaneous voltage of the Amplitude modulated wave is


 
Expand the above equation using trigonometrically relation

 
The first term represent the nu-modulated carrier.
Second and third terms represent the additional sidebands.





Representation of AM wave




  















 
Modulation index





Power relation in the AM wave



 
Total power in the modulated wave  


Carrier power


 
Similarly 




 
We have from above relations



 
Maximum power in AM wave
 
For m=1
 means 100% modulation


 
Current Calculation:
 
It is the modulated current and Ic is the nu-modulated current and R is the radiation resistance of the antenna. 






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