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[RFI] Interference computer to AM radio reception

To: <rfi@contesting.com>
Subject: [RFI] Interference computer to AM radio reception
From: EDWARDS, EDDIE J" <eedwards@oppd.com (EDWARDS, EDDIE J)
Date: Mon, 14 May 2001 09:58:06 -0500
> -----Original Message-----
> From: R Kennedy 
> 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.
        Hi Ron, 

        Is the ferrite installed in the power extension of the computer or
the radio?  I'm assuming the computer.  Most ferrite beads probably won't
have any effect on AM freqs.  

        Have you also install a good AC powerline filter/surge suppressor on
the computer?  Something with some isolation and filtering like Trip-Lite
makes.  Plug the computer into it and wind up the excess power cabling.
ALSO make sure the AM radio and the computer equipment are on different AC
electrical circuits (and therefore circuit breakers) in the house.  

        An AC line filter on the radio might help as well to keep any noise
out of the radio where the internal antenna might pick it up.

> 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.
        Hopefully the noise is being conducted to the radio or something
near the radio, and not directly radiated to the radio.  How close or far
away are the two devices?  If they're in different parts of the house, then
it's probably being conducted.  

        Start by TOTALLY simplifying the computer system; unplug everything
you can that is not required for the CPU to start up and run:  i.e. The
cable to the modem, the CRT, the printer cabling, any serial cables, any USB
cables, etc...  

        Now turn on the computer and listen for the noise.  If it's still
there, start disconnecting what's left listening for the noise after
disconnecting each item: the keyboard & the mouse is probably all that's
left.  If it wasn't there, start reconnecting stuff one at a time listening
for the noise as you reconnect everything one at a time.  Start with the
CRT, then the printer cable, then any serial & USB cabling, then the cable
to the modem last.  

        Hopefully with this procedure you'll be able to isolate the
component that is generating the noise and also be able to deduce whether it
is directly radiating or being conducted via an electrical cable and which
one.  Once you've pinpointed the equipment involved, contact the
manufacturer about the problem and ask for a suggested fix.  Let us know
what the outcome is.

        Hopefully your mother is listening to AM talk-back radio for the
entertainment value and not actually believing that stuff!  ;^)

        Good Luck,

        Ed -K0iL
-.-. --.-  -.-. --.-  -.. .  -.- ----- .. .-..  .-.-.  -.-
Ed Edwards
--... ...--  . ...  --. .-..  - ---  ..-  --- --  ...-.- . .

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