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Date: Sun, 11 Nov 2001 22:19:55 -0500
From: "ZOOM" <kandrparker at sympatico.ca>
To: <wb2vuo at juno.com>,
        "Low Power Amateur Radio Discussion" <qrp-l at Lehigh.EDU>
Subject: [111305] Re: A Quiet ATX Computer Supply?
Message-ID: <007b01c16b28$e7204480$3294fea9 at robertpa>
MIME-Version: 1.0
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        charset="iso-8859-1"
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I had the same problem with my ATX power supply.  S9 of noise on all rigs in
the shack.  I went and purchased another powersupply for $40 and no more
proble.  Allot of the generic computers skimp on filtering on powersupplies
and this is what you get is an RF dog's breakfast.

Get a bigger supply that can handle at least 300W and you should be ok.

Cheers,
Robert
VE3RPF

----- Original Message -----
From: <wb2vuo at juno.com>
To: Low Power Amateur Radio Discussion <qrp-l at Lehigh.EDU>
Sent: Sunday, November 11, 2001 9:09 PM
Subject: A Quiet ATX Computer Supply?


> Hi.  Keith here in the Depths of the Great Bergen Swamp
>
> I have graduated from the AT to the ATX-form in the shack
> computer, and have discovered that the ATX-type supply is
> a great RF generator, not a desirable thing in the ham shack!
>
> Have any of you on the List found an ATX supply/case that
> is RF-quiet?  I asked around in the local amateur community
> and found no one that was happy with the level of RF noise
> out of their ATX-based computers.
>
> I am using the same drives/cards/monitor here and with the
> K6-233 on an AT-form motherboard and PS the old comp
> was quiet, RF-wise...
>
> Before one suggests, I already checked Google.com, looked
> for reviews of cases on CNET and ZDNet and the like.
>
> I may have to go back a step to the old comp!
>
> 72/73, Wm. Keith Hibbert, WB2VUO, TC/ARRL WNY Section
> 100% QRP from the Depths of the Great Bergen Swamp
> "My night light runs more power than my Rig!"
> mailto:wb2vuo at arrl.net


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Date: Mon, 24 Mar 2003 11:01:52 -0800
From: Vic Rosenthal <vic at rakefet.com>
To: Bozidar Benc <benc at benc.hr>
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Computer noise problem

Bozidar Benc wrote:

> My antenna was 20m long wire with 10:1 transformer at the end, which is
> connected to my K1 with 20 m of RG58 cable.
> 
> Now the interesting part.
> After I added a 10 m long counterpoise to the antenna, the noise from my PC
> almost completely vanished!

Before you added the counterpoise, the shield on the RG58 was acting as 
part of the antenna.  Since the coax ran close to the PC, it picked up 
noise.  After you added the counterpoise, the coax shield was decoupled 
from the antenna (the counterpoise was an odd multiple of 1/4 wavelength 
on 40 meters, so it effectively 'grounds' the coax shield).

Good demonstration of a useful principle!

Vic K2VCO

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From: "Guy Olinger, K2AV" <olinger at bellsouth.net>
To: "Bozidar Benc" <benc at benc.hr>, elecraft at mailman.qth.net
Subject: RE: [Elecraft] Computer noise problem
Date: Mon, 24 Mar 2003 14:31:10 -0500

The K1 cannot directly hear what is travelling along the OUTSIDE of the coax shield where it
attaches to the K1. It can only hear what is coming to it on the inside.

The PC is inducing noise voltage on the OUTSIDE of the coax INSIDE the shack. The noise travels
away from the K1 and out to the end of the coax, where the outside of the coax is attached to the
inside. Then the noise travels back to the K1 on the inside of the shield. 

The 10 to one transformer would have blocked the shield current from getting to the antenna wire.
IF the coax shield was somewhat near a multiple of a half wave, then the coax turns out near the
antenna would not have stopped the voltage. The noise voltage would have been impressed against
the inside of the shield, with the center conductor at relative zero, hence a noise voltage
difference. Hence you hear the PC.

If you add the counterpoise, the noise voltage going out has another 1/4 wave of wire to go to a
hard end, the coax turns are at a CURRENT point, and become effective. The amount of voltage
transferred from the outside of the shield to the inside of the shield is greatly reduced.

This kind of noise transmission issue is well known to those trying to get the last few DB of
quiet from beverage listening antennas and the like. Common mode current on the outside of a
shield out to the antenna, coupling in somehow, and coming back mixed in with the desired signal
is a classic beverage killer.

73, Guy.

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