[RFI] Filtered connectors for video noise

Pete Smith n4zr@contesting.com
Wed, 24 Oct 2001 15:14:45 -0400

I have what's gotta be the noisiest video card in the world, in my wife's
computer.  When it's on, I get severe broadband noise (no birdies here!) in
an HF receiver not only in the room with the computer, but adjacent to the
furnace thermostat, any electrical conductor, and out in the back yard.

I'm pretty well fixed on the source because when I unplug the video cable
from the rear of the computer the noise (on a portable HF radio right next
to the computer) goes away completely.  

The good news seems to be that virtually all the noise is coming from the
video card, rather than the switching PS or direct radiation, judging by
hoiw much good disconnecting does.  The bad news is that there don't seem
to be enough snap-on chokes or cable length to begin to touch the problem.
I estimate I need at least 30 dB of attenuation.

The ARRL RFI Book suggests filtered connectors as an option, and a quick
look at my Mouser catalogue lists male-female adaptor type units for ~$33.
Obviously, I'd like some idea of whether this is likely to work.  They are
listed as coming in 310 pF Pi, 1000 pf PI and 4000 pf Pi configurations --
presumably, the pF rating is the total bypass capacitance in a Pi
configfuration that also includes a ferrite bead.

Has anyone used these successfully?  Is higher capacitance better, or at
some point does it interfere with video performance?

Alternatively, would I be better off to first try changing the video card?
It is a generic S3 PCI video card, and a generic AGP of some sort wouldn't
be much more expensive than the filtering.  On the other hand if the
filtering would work, I'd get one for the shack too.

Advice much appreciated.

73, Pete N4ZR