Hi everybody, this is my experience for anybody, who's making decision as I did few days ago:
I chose Siglent and sent it back after few days. Now I'm waiting for Rigol (DS2202 in my case).
I'm not sure, if Siglent I got was broken or not, but my piece had big vertical offset below 10mV scale on both channels and self calibration didn't fix it. In additions, it changed every time I switched a device on, independently I had quick calibration in menu set to on or off.
Secondly, device acted as transmitter - I'm working on RF stuff primarily and when I switched Siglent on, all receiver band was disturbed. It went even worse, when I connected a probe - even layed on table only.
FFT mode - as a one of reasons I choose this mark - had some problem too. There was permanent peak on low frequencies even I had input shorted.
And there was more small things that made me disappointed.
I have old second hand Rigol oscilloscope for many years and there's no problems like this. I hope, that new Rigol will be at least same quality - not like this Siglent toy.
That is a bit of funny story....
If any scope has "toy" implementation of FFT that is older Rigols. They are good entry level scopes but FFT is not well made on those.
What Siglent scope? What model?
What was the offset, in numbers? At which V/div?
Those are important pieces of information...
FFT peak on low frequencies..... That is you, not understanding how FFT works. Sorry.
Frequency of 0 Hz in FFT is representing any DC component (DC offset) in signal. Including DC offset from signal not being fully symmetrical and scope offset. And if you plot FFT in vertical log scale (dBV, dBuV, dBm) it will be visible.
For instance if you feed the scope squarewave that is not symmetrical (say 10% duty cycle) that one will have large DC component. You will see that
So please let us know which exact model of Siglent that was, and also if it was new. If it was new and offset was really bad, you should have sent it back for replacement. If it was used it might have been damaged.
If offset was really bad, you could have seen that in FFT too...
Also, I hope you didn't buy old Rigol DS2202 but current model Rigol DS2202A. That is a decent scope.
FFT will still be much worse Than Siglent has.