# Bandwidth in AM modulation

Tags:
1. May 5, 2017

### Faiq

1. The problem statement, all variables and given/known data

3. The attempt at a solution
What should the bandwidth be over here? Confused since there is no mention of carrier frequency.

2. May 5, 2017

### 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 )

3. May 5, 2017

### TSny

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

4. May 5, 2017

### rude man

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

5. May 5, 2017

### CWatters

It mentions a range of carrier frequencies.

6. May 5, 2017

### rude man

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

7. May 6, 2017

8. May 6, 2017

### 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.

That would be the case for a single sideband broadcast.

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

9. May 6, 2017

### Faiq

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

10. May 6, 2017

### CWatters

With FM there are potentially more sidebands depending on the modulation index.

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"

11. May 6, 2017

### Faiq

Thank you very much.

12. May 6, 2017

### Faiq

Thank you very much.