[RFI] Computer Speaker RFI

[Jim Brown]

On Sun, 1 Mar 2009 10:19:09 -0500, k2qmf at juno.com wrote:

>Can anyone recommend or suggest
>a good cure for RF getting into
>computer external speakers??

Turn them off. :)  

But seriously -- I assume you're talking about speakers with 
built-in power amplifiers, either battery-operated or AC powered. 
The electronics built into powered loudspeakers are notoriously 
bad for RFI. It's a combination of bad/non-existent shielding, 
bad/non-extistent filtering on input wiring, and pin 1 problems. 

Pin 1 problems can be fixed with a suitable toroid choke, and a 
filter can be added. BUT -- after you've done all that, you're 
stuck with the shielding problem, which is NOT practical to fix, 
and which is usually dominant. 

I work in pro audio, and often have my ham talkie with me when I 
tour the exhibit floor at trade shows. I routinely use the talkie 
to probe each active loudspeaker I see that's hooked up and 
running. So far, I've found ONE product that's immune to RFI. It's 
made in EU by Genelec, and it costs about $3K. 

For more detailed advice, see 

http://audiosystemsgroup.com/RFI-Ham.pdf

There's at least one model of computer speaker advertised in QST 
that claims to be RFI immune. I haven't tested it. 

73,

Jim Brown K9YC