Trying to work up a Hantek DSO2250 into a useful tool, I notice that the frequency compensation changes abnormally, as it is changed from AC to DC coupling. By abnormally, I mean that AC coupling introduces what looks like HF roll-off. Calibrated in the AC-coupled mode, a 10:1 probe overshoots when switched to DC coupling. (Using a 1KHz square wave.)
I'm thinking that this can't be done by hardware, that it's got to be some kind of signal processing bodge - even though you hear a mechanical relay moving to physically short out the coupling capacitor, as the mode change occurs.
How can things be screwed up in this manner, if not in software? Relay shunt capacity in the wrong place?
It seems to have unequal effects on the seperate channels and even on the rising or falling edge, if I'm not fooling myself.
The self-calibration feature doesn't seem to involve an AC signal. Compensated probes can't be swapped from one channel to the other, without re-adjustment
I'll have to run a frequency sweep to see what it looks like, though I'm not sure if the display can be believed. Will I get differing frequency response, depending on simple horizontal display settings, for example....
RL