This is the spectrum of the signal:
And this is the signal:
On the FFT spectrum you can notice the high amplitude peaks and I think these frequencies are the main ones in the signal:
I think that the "low" harmonic must be clean, but I have the problem that low amplitude components are placed in every frequency interval. The main problem is that I haven't got any model of the signal for a hypothesis about noise, and as result, I must detect noise components. After this step, I must design a filter or use another method of filtering for denoising the signal. Which methods can I apply for (1) detecting noise and (2) filtering?