It’s actually AC with a DC offset.
It’s a bitch to check such mixed signals with scope. You either get DC coupling and then the offset can get the small signal out of the screen, or you get AC coupling and can make it more sensitive but then you don’t see the DC component.
What I did for rapid examination of such signals is a splitter that connects one probe to both scope channels, then set one channel to DC and the full DC range, and the other one to AC and higher sensitivity. So you then can see 100 mV signal riding on 3 V DC bias, and simultaneously see both components.
…of course then you get half the input impedance of the scope, which will screw up with the signal magnitude so the scope shows smaller voltage than what is on the probe. You have to multiply it with a factor manually. Or disconnect for a moment one of the channels.
…we need an opensource Rigol scope firmware that’d allow such functionality…
