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[RFI] Computer Speaker RFI

To: <rfi@contesting.com>
Subject: [RFI] Computer Speaker RFI
From: Blackburn <blackburn@qnet.com> (Blackburn)
Date: Fri, 24 Sep 1999 16:10:48 -0700

This is a very common problem.  The first thing to try is common-mode
chokes on the speaker wires.  Wrap a number of turns (whatever will fit
or whatever length of wire is available...more is better, within reaon)
through a ferrite core.  The split ones sold by MFJ & Radio Shack are
fine for applications like this and are easy to use.  You can also add
things like this without have to worry about violating someones

You'll need multiple turns to get enough inductance to have a
significant effect at HF, and you may have to experiment a little to
find the best location. With unamplified speakers I would try putting a
choke on the cable right where it comes out of the computer.

Good luck,

Keith KB6B

MGTGAZ wrote:

> Hello fellow RFI'ers: I'm new to the list and looking for some
> assistance. I'm bleeding through audio to myneighbors amplified
> speakers. My station DR70T to AL80B running 800W SSBGAP Vertical up
> 10' in my backyard about 120ft run from shack in center of houseAll
> shack equipment (rigs, tuners, amps, accessories are all grounded to a
> central bus to gnd)1KW Low-Pass filter.  and Radio Works 4KVLI
> (line-isolator with tie to gnd also) My house is clean with no
> interference in any device (computer or otherwise)400 ft away my
> neighbor is picking up my 15m transmission at 100W and 800W. Only
> differenceis it's louder and stronger at higher power. The pick up is
> through a set of computer speakersconnected to the computer. They are
> an amplified set of speakers, and signal bleeds throughwhether power
> is applied to the amp or not.    Common mode??? Anyway, I'll take
> suggestions on attempted filtering, but also interested in whether
> themagnetically shielded computer speakers I see advertised are much
> less susceptible tothis type of interference. Also if there are any
> brands and models this group of experts has experience with that
> arerecommended, I'd be most interested in that as well. Thanks in
> advance for any help, 73,Mark gustoff@access1.net
> orwo7t@juno.com

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