Great suggestion, Tony! A good way to tell if your RFI is being picked up by
leaky coax in the shack or by your beam is to rotate the beam. If the noise
changes amplitude during rotation, then at least some of it is being picked up
by your antenna, and the only solution is to eliminate the noise at its
source. This was the case in my situation, where my 6M stacked yagis are
fairly close to the shack (about 35 ft), but far enough to one side that the
directivity of the array had an effect.
Bill W5WVO
N2TK wrote:
I have had good luck replacing RF noisy PC power supplies with PC
Power & Cooling Supplies. They seem to be well filtered.
http://www.pcpower.com/index.html
By the way, something I did in my shack that significantly reduced
noise pickup:
- Any coax line that has to do with receiving I use 100% shielded RG6
with a compression type F-connector. Where I didn't change to an F-
female jack, I use an F-adapter to PL-259 or 1/4" phono.
- Any coax line that has to do with transmitting I use 100% shielded
Buryflex.
It was amazing how much noise pickup dropped by getting rid of
RG-213, RG-8X and RG-58 in the shack.
N2TK, Tony
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Bill W5WVO
Sent: Friday, January 11, 2008 11:58 AM
To: [email protected]
Subject: Re: [Elecraft] Computer Noise ruining 20 & 30m
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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