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[RFI] Computer speaker RFI

To: <rfi@contesting.com>
Subject: [RFI] Computer speaker RFI
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
Date: Mon, 1 Sep 2003 10:14:05 -0500
List-post: <mailto:rfi@contesting.com>
Hi everyone:

I'm battling a problem with RF getting into the speakers on my PC here in the 
shack.  I had a similar
 problem with rf getting into my packet tnc when I transmitted on 75 meters and 
I was able to fix that by putting ferrite beads on the leads going into the 
TNC.  the speakers are a tougher problem.  There
 are two of them each in its own plastic cabinet.  Inside of one, there is a 10 
watt AF solid state amplifier that boosts the soundcard audio enough to drive 
the speakers.  my problem is with that amp. 
 It is rectifying the rf big-time.  I was able to make some progress by pulling 
the amp pc board out of the speaker cabinet it was in and placing it inside the 
metal computer cabinet and putting chokes on
 all the leads going into and out of the amp.  I was giving myself a pat on the 
back--peace at last on 75 meters without having to kill the speakers before 
transmitting--then the other night I got on 40 and
 experienced the same old loud growling I used to hear on 75.

Since all the shielding and chokes are just a bandaid fix for the real 
problem--transistors acting like
diodes--I got a crazy idea yesterday that I thought just might be bizarre 
enough to work:  feeding
 the soundcard audio into a small simple outboard vacuum tube AF amp.  other 
than matching the low Z soundcard impedence with the hi Z amp input, does 
anyone see any other problems with this idea?  I'm thinking No transistors; no 
solid state rfi problems.

tnx & 73,

Rob Atkinson
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