One thing to be aware of -- and I too have had quite a bit of undesired
experience in this area -- hash from switching power supplies in computers is
typically common mode noise, not differential noise. Consequently, a
differential line filter often won't knock it down very much, if at all. What
you need is ferrite toroids -- big ones -- around and through which you wind
the power cord. In my case, the computer power supply is a 470W job in an ATX
form factor, and because of the high power components, there wasn't any room
in the PS case for filtering! So the RF noise from this PS was horrendous. It
took TWO large ferrite donuts in series, with the ENTIRE power cord wound
around them, to suppress the noise on 6M. I had bought a rather expensive
differential noise filter for the line, and it did absolutely nothing.
Brute-force common-mode filtering using ferrite toroids will usually cure the
problem, but you may need a lot more saturability than you think.
Bill W5WVO
G4ILO wrote:
Alan D. Wilcox wrote:
Hello,
I gave away the feeble old PC I had by my radio equipment and
replaced it with a newer one ...
Now I have S9+ noise wiping out 20 and 30 meters.
Using same keyboard, mouse, monitor; just the PC in a new case.
Evidently it has a
noisy switcher supply in it. Tried 110V in-line filter, also
different 110V house circuit,
but still have noise. Grounds don't help. Don't happen to have a box
of toroids for chokes.
It's very likely to be the power supply, especially if it is a home
build or a local PC store build rather than a branded model. Most of
the PC cases and power supplies that home builders and small
assemblers use are made in China, and the manufacturers often leave
out all the components they can get away with, like anything to do
with interference suppression. I remember someone a few years ago
took apart a noisy power supply and could see all the holes in the PC
board where the suppression components should have been. It was quite
an eye opener.
Replace it with a power supply from a decent manufacturer and all
should be OK.
-----
Julian, G4ILO K2 s/n: 392 K3 s/n: ???
G4ILO's Shack: www.g4ilo.com
Zerobeat Ham Forums: www.zerobeat.net/smf
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