Optimizing Bandwidth in AM Modulation

[Faiq]

Homework Statement

The Attempt at a Solution

What should the bandwidth be over here? Confused since there is no mention of carrier frequency.

 

[Faiq]

is this correct?

For sound to be represented/interpreted by the receiver it will receive it as the difference in frequency of the carrier wave. Since the difference in frequency has to 4500 for max frequency of audio to be represented thus bandwidth is also equal to this. (Bandwidth = difference in carrier and audio frequency )

 

[TSny]

is this correct?

For sound to be represented/interpreted by the receiver it will receive it as the difference in frequency of the carrier wave. Since the difference in frequency has to 4500 for max frequency of audio to be represented thus bandwidth is also equal to this. (Bandwidth = difference in carrier and audio frequency )

I don't believe this is quite correct. See if this helps
https://www.electronics-notes.com/a...odulation-am-bandwidth-spectrum-sidebands.php

 

[rude man]

I agree with #3, consider the entire span of frequencies at the worst-case signal frequency.

 

[CWatters]

Confused since there is no mention of carrier frequency.

It mentions a range of carrier frequencies.

 

[rude man]

Right.
At this point I would direct you to post 2 & study the link's contents.

 

[Faiq]

I don't believe this is quite correct. See if this helps
https://www.electronics-notes.com/a...odulation-am-bandwidth-spectrum-sidebands.php

I was taught that bandwidth is Sideband - Carrier frequency. However here it is 2*(Sideband - Carrier frequency). Why is this happening over here? Does this also apply to single tone modulated AM waves? What about FM modulation?

 

[CWatters]

Bandwidth is basically the width of the spectrum used (as per that diagram). So for a typical double side band broadcast it's roughly twice the maximum audio bandwidth.

I was taught that bandwidth is Sideband - Carrier frequency.

That would be the case for a single sideband broadcast.

https://en.wikipedia.org/wiki/Single-sideband_modulation

 

[Faiq]

Okay and in FM modulation, the bandwidth is again twice the Fs-Fc?

 

[CWatters]

With FM there are potentially more sidebands depending on the modulation index.
http://www.radio-electronics.com/in...y-modulation/spectrum-bandwidth-sidebands.php

Although in most cases the modulation index is small and only one pair of sidebands is used.

It's slightly more complicated for real world commercial broadcast FM radio stations because they usually broadcast in stereo and that needs more bandwidth for the Left and Right audio...

Edit: Tried to add a link to an image but it failed. Scroll down here to "Typical spectrum of composite baseband signal"

https://en.wikipedia.org/wiki/FM_broadcasting

 

[Faiq]

Thank you very much.

 

[Faiq]

Thank you very much.