[Al Skierkiewicz]

Phil,
Since you had power line related noise when on battery, using a power conditioner is not going to improve anything. The distortion on the power line is an indication of a transformer failure. It can be caused by a variety of things including too much of a load for the transformer size. It can also be caused by the transformer arcing internally. The arcing coincidently can cause generated noise. Remember spark gap transmitters? Everything points to something locally generated. Where is the power line transformer in relation to your house? Have you tried taking your experimenter board to a friend's house a couple of blocks away? The display on the scope indicates a rather strong field.

Just to be sure, many appliances still maintain a power supply even when turned off. I came across a rather nasty TV power supply when I was trying to setup a ham station in a hotel room a few years ago. The only way to cure some things is to unplug them from the wall.