There isn't an easy solution as far as I know, because consumer electronics
for PCs is pretty bad garbage as far as rfi is concerned--ditto for DSL
modems. The solutions offered will help, but not using amplified speakers
is a bust because the pc sound cards I'm aware of do not put out enough
audio power to drive speakers directly. you can try removing the little
solid state 10 w. amp in the speaker cabinet but in my experience they are
made in a way that makes removal difficult and you may wind up destroying
the card or cabinet.
you may have luck with a separate audio amp inside the pc cabinet (assuming
it's a metal box) connected to the sound card and audio cables going out to
non-powered speakers.
What I ran into was diode rectification of rf in the s.s. audio amp inside
the unshielded plastic speaker enclosure. I went so far as to consider
using a vacuum tube amp, thinking that elimination of semiconductors would
eliminate the rectification problem. Another possibility might be to place
the powered speakers inside metal boxes with wire mesh screens to let the
sound out. All in conjunction with the other suggestions such as ferrite
cores, shielded audio cable with the shield unconnected at one end, or
balanced audio cables.
by the way, it is interesting that the problems are on 40 and 15. My worst
audio rfi is on 75 m., followed by 160 m. and 40 m. Probably a matter of
field patterns, and prox. to antennas more than frequency.
I will post a question about this to the broadcast email list and see what
is done about pc speakers (if anything) at medium wave bc tx sites.
rob / k5uj
From: dgsvetan@rockwellcollins.com
To: k3lr@k3lr.com
CC: rfi@contesting.com
Subject: Re: [RFI] RFI Proof Computer speakers needed!!!
Date: Wed, 1 Nov 2006 09:34:42 -0600
Tim,
I read the excellent reply from Jim Brown, K9YC, and have only one other
comment to add.
As I understand it, most, if not all, sound cards in computers have the
capability to drive speakers directly (ie: they have a built-in audio
power amp that can deliver a watt or two per channel to external speakers).
For some reason, most of the supplied speakers that come with system
packages are self-amplified, and these are the types that have most of the
problems as decribed by Jim. It might help if your neighbor could switch
to non-amplified speakers, which is what I used for many years in my first
computer set-up. Since the sound card is integral to the computer, it gets
a fair degree of shielding from the computer case and chassis, plus the
power source is internal. The only "antennas" for the computer audio are
then the speaker leads themselves. You will probably still need to treat
those with ferrites and by-passes per Jim's instructions, but it might be a
much less painful and time-consuming solution. Of course, those ferrites
and by-pass caps would go as close to the speaker plug (where it conmencts
to the sound card) as possible. Non-amplified speakers are just that, and
should have no non-linear devices within to become RF detectors. Good
luck.
73, Dale
WA9ENA
Tim Duffy K3LR
<k3lr@k3lr.com>
Sent by: To
rfi-bounces@conte rfi@contesting.com
sting.com cc
Subject
10/31/2006 11:17 [RFI] RFI Proof Computer speakers
PM needed!!!
Please respond to
k3lr@k3lr.com
I really need to find a solution for 40 and 15 meter RFI (caused by my near
field RF) that gets into my neighbors computer speakers. I have asked this
before, but I need to find a good set that is close to RF proof. I need to
get
them fixed once and for all and a new set of RFI proof speakers is the way
to
go.
I have good ferrite rods (#43) on all leads (audio and power) now and it
helps,
but they still squawk.
Do you have any ideas?
73,
Tim K3LR
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