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[RFI] Audio isolation transformer and RFI

To: <rfi@contesting.com>
Subject: [RFI] Audio isolation transformer and RFI
From: dgsvetan@rockwellcollins.com (dgsvetan@rockwellcollins.com)
Date: Fri, 21 Jun 2002 15:29:22 -0500

Yes, the RF could couple across the transformers via the internal stray

The extra length MIGHT be an issue, but are you affected on all HF bands?
I would expect you to have a problem on perhaps 1 or 2 bands, but not all.
If all HF are affected, then you might want to confirm the following:

1.  Cable shield is intact and solidly terminated at each end connector.

2.  Use of metal housings (not plastic) at the cable end connectors.

3.  Does the patch panel maintain a fully shielded environment for the
patching jacks?

4.  Is the patch panel grounded with a low-Z path to the RF grounds?

Just a few thoughts.  Good luck.

73, Dale

Pete Smith <n4zr@contesting.com>@contesting.com on 06/21/2002 02:57:49 PM

Sent by:    rfi-admin@contesting.com

To:    rfi@contesting.com

Subject:    [RFI] Audio isolation transformer and RFI

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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