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[RFI] Interference computer to AM radio reception

To: <rfi@contesting.com>
Subject: [RFI] Interference computer to AM radio reception
From: dgsvetan@collins.rockwell.com (dgsvetan@collins.rockwell.com)
Date: Mon, 14 May 2001 08:51:48 -0500


The radio probably has an internal loopstick or ferrite rod antenna for AM
reception, so that is likely why the bead on power cord did not help.  The
option with best chance of success would be to separate the computer and
radio as far as possible (as at opposite ends of the dwelling).  There are
some quick experiments you could run before moving the computer to another
part of the house.

You could first try detaching the cable modem to see if that is what is
radiating the signal.  If it is the culprit, using that ferrite bead AT THE
COMPUTER end of the cable might help.  (Be aware, though, that most of the
beads are optimized for performance at 25 MHz and higher - useless for AM
bc.)  If you still get interference with the modem cable detached, try
disconnecting the printer cable, then the monitor cable.  Either (or both)
of those could be the radiating means.  If you find that one or more of the
computer interconnect cables is the radiating culprit, you will need to get
some LARGE ferrite rods or toroids so that sufficient common mode impedance
is added to make for effective signal reduction.)  If you still have a
problem, then you'll likely need to relocate the whole system as far away
as you can from the radio.

Not that this necessarily means much, but does the computer system have
BOTH an Australian approval and a European Union CE Mark?  Many computer
makers simply make ALL of their equipment CE compliant as a means to not
worry about what inventory ships where.  Even though the CE Mark may mean
nothing in your area, the fact remains that equipment so marked is supposed
to withstand 3V/m RF levels for susceptibility.  That buys you a little bit
of insurance against your rig disturbing the computer and generally gets
you a a somewhat improved system for lower emissions.  Assuming that your
machine has at least your local Authority Approval Identifier, you may wish
to contact the vendor and see if they will offer any remedy.   Best luck.

73, Dale

"R Kennedy" <ronkennedy@optushome.com.au>@contesting.com on 05/13/2001
10:53:15 PM

Please respond to "R Kennedy" <ronkennedy@optushome.com.au>

Sent by:  owner-rfi@contesting.com

To:   <rfi@contesting.com>

Subject:  [RFI] Interference computer to AM radio reception

Hello all
I have just installed a computer in my home.?  My mother listens to a local
AM Talk Back Radio Program every night.? When  I turn on the computer there
is a whirring noise over the top of the radio  reception.? This whirrs to a
level where it is basically blocking out the  transmission and levels out.
The radio is a Sanyo clock radio and is never  moved off the radio
frequency - when the computer is turned off the noise  stops.? I have
purchased a Ferromagnetic Beads clip and attached it to the  power
extension lead to no avail.? The modem is attached full time to cable
internet.? To me it sounds like the hard drive on the computer is spinning
up to speed and then levels out.
I would appreciate any comments or suggestions as  to how I can alleviate
this problem - moving my mother or her radio out is not  an option.

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