About removing DC from signal....
Let's say you have a 12 volt power supply. But when you use it, you hear hum on speaker. You'd think, there GOT TO BE some noise coming through this power supply.....
So you set it to DC and measure 12 volt. It looks clean. You scratch your head and go get some dinner.
You'd come back and remember the discussion. Switch to AC. You see NOTHING. Then you'd use AUTO button or start to lower the vertical sensitivity. All the sudden 60Hz, or 50Hz, depending on what your country use for mains show up. Aha....
What is happening here is, SMALL (like 100 millivolt) signal was super imposed on 12 volt. So if you are seeing 12 volt DC, you won't really see anything. You may notice your trace is a bit fatter than usual. But that's it. (noise is about 1% of 12 volt!) When you remove your DC components, you get to focus on the noise. Sure, you'd have to increase the sensitivity, but by doing so, you'll see the cause of the problem. Very small, relative to DC, AC noise!
By the way.... I have never seen this kind of rapid response to a newbie question. I think everyone has this tall blond woman with blue eyes in back of their mind....
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