See this image, it's a composite video signal on my scope.
As can be seen the dc offset of the signal is varying with time; it also varies with brightness in the scene.
I am plugging the signal from a composite video signal directly into my scope, however the cable is also spliced and goes to my computer's TV card. Without the TV card attached I do not see this. Now I would like to be able to debug my signal using the TV card, but it seems to be interfering (maybe it's loading the signal too much) - what could be causing this? I have another card I'm going to try but I'm not hopeful. Apart from buffering the signal using expensive video buffer amps, what can I try?