[RFI] Computer RFI problem

[James C. Hall, MD]

Here is an interesting problem:

I put up an old Cushcraft R-7000 on the roof as a secondary antenna. My
primary antennae are on a tower 150 feet from the shack and perform very
well without RFI difficulties. When receiving with the vertical on 20
meters, I hear S9 computer generated interference. Changing antennas to
either the beam or an inverted V yields no such interference. This only
occurs on 20 meters - at least very audibly - and only with the vertical.  I
used to have trouble with the lower frequency bands ie. 75/80 meters until I
switched out the computer power supply with a better filtered and shielded
one. Now no problem on those bands.

I'm thinking about adding some length to the coax off the vertical to see if
that would help ... but I doubt it.

Any ideas ?

Thanks,

Jamie
WB4YDL