[Antennas] Re: [RFI] Computer speaker RFI

Dan Richardson [email protected]
Mon, 01 Sep 2003 11:29:08 -0700 

Rob,

You didn't mention what type of ground system you're using for you station. 
On the surface it sounds to me that you could be having a problem with 
common mode radiation from your transmission line. Are you using any 
choke/baluns on the transmission line(s)? What type of ground system are 
you using?

Danny, K6MHE



At 10:14 AM 9/1/2003 -0500, you wrote:
>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
>K5UJ
>[email protected]
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