I sent this yesterday to both W0UN and the list, but I don't think it made
it to the list for some reason... so trying again. Sorry if it's a dupe.
Listen up...John wrote:
>Many of the new computers are omitting the RFI filter in the
>power supply that keeps the garbage from the switching mode supply
>from entering the AC mains. I have had excellent results (as have others
>who have taken my suggestion) in virtually eliminating the interference
>by replacing the AC connector on the back of the power supply with an
>integrated AC connector and RFI filter such as the Corcom 6EF1. The
>mounting hole for the connector must be widened a few millimeters
>on each side--something that can be done with a file in a minute or two.
>Just make sure there is enough room behind the connector position
>to clear the somewhat longer RFI filter. In one case that I made the
>modification I needed to bend a capacitor out of the way.
K6NA adds:
All the other suggestions offered may be helpful here and there, but until
you follow John's advice above, you are wasting your time chasing this kind
of noise around the shack. He offered this advice on here about a year ago.
I've built three computers since then, and EVERY TIME his fix was the answer!
In San Diego we can buy mini-cases for as cheap as $25.00. But the switching
PS is a noisy dog, and there is no filtering. Replacement of the a.c. input
connector with a filtered type is an easy one-hour job, start to finish and
it will probably get rid of 95% of your problem. For the remainder you
might want to play with snap-on chokes, but after I ran coax braid from the
computer chassis to the station ground buss to get everything at the same
potential, I needed only one or two chokes to finish the job.
I also noted reduction of video noise when I powered the monitor from the
accessory a.c. socket on the back of the computer p.s., instead of just a
random socket in the station. When inside the p.s. box I also had added some
ferrites to the leads going to this output socket, as a precaution. I
recommend powering your monitor the same way.
It would be a HUGE JOB to successfully shield a monitor completely, for
example, and may not be necessary at all if you take care of business in the
computer p.s. first.
Thank you John!
73, Glenn K6NA
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