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[RFI] Audio isolation transformer and RFI

To: <rfi@contesting.com>
Subject: [RFI] Audio isolation transformer and RFI
From: n4zr@contesting.com (Pete Smith)
Date: Fri, 21 Jun 2002 15:57:49 -0400
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

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