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[RFI] Audio isolation transformer and RFI

To: <rfi@contesting.com>
Subject: [RFI] Audio isolation transformer and RFI
From: w8rhs@wvinter.net (Elbert E. Flanagan)
Date: Fri, 21 Jun 2002 16:45:46 -0400
Pete:  You need some ferrite cores or computer stereo cables for the
sound card which are available from All Electronics (no minimum billing
and low shipping rates) telephone 1-800 826 5432.  I have found the
ferrite cores and ferrite protected computer cables for the sound card
to be very effective in reducing RFI.  Also all types of Ferrite cores
type 43 or 73 available from Palomar Engineers   along with information 
on the internet.  Look under Google Search Engine.  Good luck -- Elbert 

Pete Smith wrote:
> I have cobbled together a patch panel to bring the sound-card connections
> of my two shack computers to a more reachable place at the back of my desk
> (the computers are under the desk.
> Unfortunately, in doing so I seem to have created some RFI problems that
> weren't present before.  Specifically, when I try to record off the air
> using audio patched from the 1000MP's external AF jack to the sound card's
> line-in jack through the patch panel, RF causes RecAll to crash.  I know
> it's RF because it doesn't happen unless I actually transmit.  Running a
> stereo cable straight from the MP to the line-in jack cures the problem,
> even when transmitting at full power.
> I'm presuming that the extra length of cabling is responsible for the
> pickup, and have tried all the usual toroid tricks without achieving
> sufficient improvement.  It's been suggested that even though I have no hum
> problems in the audio line, I could try using audio isolation transformers
> as a way of breaking both the shield and signal conductor circuits to the
> sound card.  That's fine with me, but I'm wondering whether the RF won't
> simply couple across the audio transformers.
> Can anyone advise me before I go through all this?
> 73, Pete N4ZR
> Check out the World HF
> Contest Station Database at
> www.pvrc.org
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