I to everybody, I have to analize the spectrum of a pc power supply. I connected the 3.3V output of the power supply and what I got is the following one:



Sorry for the graph. I wanted to know if it is possible to understood the meaning of each harmonichs, why we have some harmonics in thet particular frequency (for examples i know that 244 Hz harmonic is due to the home power supply), and how the amplitude (mV) is related with my signal, i mean why I have a dc component of 8.5mv with a dc signal of 3.3V, what does it means?another information is that the signal on the oscilloscope had 200mV for division vertically.

 

I think (i am not sure) that i got 8.5mV because i was using the AC coupling in the oscilloscope sittings.

 

you are seeing noise generated by the switching supply and its harmonics.