Resonant ground?

[KC1BAQ]

Steve,

I would suggest that you first install snap-on ferrite beads on each end of your USB to serial cable.

I too operate from a second floor station and have problems getting a good ground. I use an artificial ground like this one which tunes the ground so that it conducts rather than resonates (basically like an antenna tuner, except you are detuning instead...Ha!):
http://www.mfjenterprises.com/Product.ph...id=MFJ-931

Keep us posted.

73,
Joe
KC1BAQ