Bandwidth of AM - some explanation please

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mehboob_iiui

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Bandwidth of AM

In bandwidth we change the amplitude of a carrrier with respect to a signal, the frequency of the carrier remains constant but its spectrum covers a range of frequencies, why is it so?
 

Bandwidth of AM

In AM we have 3 frequency.
Carrier frequency
Upper side band
lower side band
in the other word we have: Fc, Fc+Fm, Fc-Fm
(Fc=Carrier freq, Fm=message freq.)
 

Bandwidth of AM

I'm Agree with Davood Amerion, but remember that the signal to transmit is baseband and frequency limited, that is from 0 to 4kHz for voice, or 0 to 20kHz for music, etc.

So you can calculate AM DSB from Fc-4kHz to Fc+4kHz for voice.

Fc-20kHz to Fc+20kHz for music.

You can consult the modulation theorem in any book of Fourier.
 

Re: Bandwidth of AM

in AM

we get the components of final modulated signal at fc+fm and fc-fm, so it is seen the carrier frequency actually changes but as

fc >>fm (fc much greater than fm)

we assumes that carrier frequency fc does not change.
 

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