Find spectrum of part of the signal

Hello everyone, I would like to ask a question. The thing is I have a signal like this.

And it's spectrum is like this:

And I know that this signal is made up from elements such as theese:

Basically 4-5 (in my case 4) different sine waves and noise signal mashed into one. And I get my signal, now I found a way to get the sine wave frequencies, but now I need to find the starting and ending points of each sine wave. How would I do that ? I would aprecciate the simplest answer I can get since I am complety new to this, I found the frequencies of the sine waves, by going trough cycle and searching for sudden change in value, that is seperated by some space. So if someone could show me a way to find the frequency, without any fancy formulas that would be nice. My lecturer suggested taking part of the signal like for example 100 values and calculating the spectrum of thoose, and if the frequency I want show's up then that means I can get the start time, but I am really struggling with that.

Answer 1

[Amrtanshu Raj]

Hi,

You can consider dividing your signal into small parts of 100 samples as you mentioned and then doing an FFT analysis on each of those to get the frequencies in that segment of Signal. That will help you get an estimate of the start and end points of various signals.

Hope this helps !!

[Justas Kvederis]

Well, it's irrelevant now, but still thanks for the answer. But for the future reference, how would I approach it, since when I was trying to split the signal into 100 or so samples, my spectrum got all messed up, or didn't show all the required frequencies.