I had to learn that my wood table significantly contributed to my noise floor, with different equipment on it (like Lab style PSU, Laptop). Don't ask me how this is supposed to work but hey - you learn something new every day I guess. I had different breadboards on it but could not get anywhere near the values I expected - noise wise. then I added a single layer of AL foil insulated with some thin plastic foil so that I don't short stuff accidently and attached that to ground and voila, suddenly I had much more realistic noise measurements. now if you test inside your shielded enclosure this is something else of course.
reducing the radiated noise from laptops and the like helped a lot also....
- Michael
