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# Bandwith calculation

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#### VTI_16V

##### Member level 1
Hello everybody. Please don't get me wrong, I am not asking to do my homework, 99% i found out and learned, but I have some questions where I got stuck. I have some exam, and a lot of the questions are radio communication based, which I never learned of wasn't really interested it. I found most answers on the internet, but I have few of theese questions that I just can't find over google, all that I can find are some complicated formulas which I can't relate to any of theese questions. Maybe my translation is also bad.
The questions are:
1) If we frequency modulate carrier with information signal which has bandwidth of 5kHz. Frequency deviation is 10 kHz. What would be the bandwith of new signal?
-30, 60, 100, 300 kHz?

2) We module the carrier with signal which banwidth is 10kHz. What is the bandwith of resulting DSB signal?
-100, 40, 20, 10 kHz?

3)We modulate the carrier with signal which bandwidth is 10kHz. What is the bandwidth of resulting AM signal?
-100, 40, 20, 10kHz? I think i found something somewhere where it says that formula should be 2X modulated signal, so 20kHz?
Quick elaboration would be also nice so I could understand something from all this... Thanks

Search bandwidth AM signal and Bandwidth FM signal there are plenty of good explanations with diagrams to help you understand.

Google was my friend for 200 pages of questions that I didn't have answer to, but some answers I can not find like this as I wrote in my post. I am not student, and my time is limited, and I am not able to read 500 pages thoroughly for "maybe" finding answers to theese specific questions, I already lost whole day for this and didn't get anywhere. Someone who is good at RF probbably knows this from the sleeve. That is why I asked on this forum, not because I am lazy. Thanks anyway

noori.re

### noori.re

Points: 2
Useful.
Before trying to roast someone maybe you can change your perspective of view. My job has nothing to do with those areas and I am working 10-12 hours a day after which I need to come home and learn things that I don't need so I can continue to run my business which again has nothing to do with this kind of knowledge. But those were only 3 questions out of more then 500 which I learned (belive it or not I invested maximum of time I had in it), and they don't matter anymore because I passed. Maybe it is wrong to ask for this kind of help, if it is I apologise for posting. This is great forum and I don't want to argue, it just goes on my nerves when people behave like they know everything about specific situation where someone is at. Thanks for the link, and thanks for your time to read post. Stay well

I don't think this forum forbids helping people with exam questions, and plenty of time has passed since the question, so I'm probably Not violating any rules here:

1) frequency modulation signal's spectrum translates to the final signals bandwidth. I don't know why you also have a deviation specified. Do you actually mean deviation or did you mean frequency drift?
If information signal BW=5kHz, and carrier drift=10kHz, then BW_total of FM-signal = 15kHz

2) Double side band signal replicates/mirrors the information on each side of the carrier. so if BW-information=10kHz, BW_dss= 20kHz
[10kHz] || [10kHz]
^carrier

3) AM modulation produces Double Side Band signal. Thus the answer is same as above.

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