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Q: AM radio interference caused by PC ( No Answer,   2 Comments )
Subject: AM radio interference caused by PC
Category: Computers > Hardware
Asked by: lscott165-ga
List Price: $5.00
Posted: 23 Sep 2002 20:24 PDT
Expires: 23 Oct 2002 20:24 PDT
Question ID: 68290
My computer is causing very bad radio frequency interference with a
low-frequency AM radio station that my landlord listens to.  I have a
custom-built Athlon system with an ATI All-In-Wonder card, normal
speakers, an LCD monitor, trackball, and two hard drives.  Nothing
terribly unusual about the system, but I thought maybe the casing
isn't shielded.  It was quite cheap, so I'm sure the parts are
bargain-basement, and I was wondering if most brand-name computers
cases have a lot of metal shielding to avoid this problem.  I have
tried 6 rf chokes in various configurations around all of the power
and network cords, and an AC Interference Filter that you plug the
computer into.  No luck--the only thing that has had any effect was
unplugging the satellite coaxial cable from the tv tuner card--but the
problem largely remains.  Are there any other possible solutions? 
Would putting sheet metal around the PC work at all?  I'm desperate to
fix this.
There is no answer at this time.

Subject: Re: AM radio interference caused by PC
From: crabcakes-ga on 23 Sep 2002 20:35 PDT

The problem is not your case. I built myself almost the exact system,
and I have a radio, and a TV, and tons of electronic "stuff" around my
computer, with no problems or interference. I in fact keep one side of
my case open at all times, because in spite of a case fan, a CPU fan
and an extra heavy duty card fan, my box still runs HOT.

Your problem is almost certainly the satellite coaxial cable is not
properly grounded, if grounded at all.

There is a grounding lug that goes to the shield of the satellite coax
cable, that needs a ground wire to a ground rod -You can use the
telephone wire ground wire as a ground, or the power ground wire if
it's copper.(Don't use a water pipe for a ground)

If you can't do it, call your satellite company to properly ground the

I had a very similar problem with my cable modem giving me poor
service, very slow service, and constant drops. After over a year, I
found an intelligent tech at my ISP, who, came and in 5 minutes
removed a pico filter from the pedestal. I have had not one problem

Good luck!
Subject: Re: AM radio interference caused by PC
From: booradley23-ga on 24 Sep 2002 06:18 PDT
Hi I agree it could well be that coaxial but have a load of
information anyway

There are two possible ways the radio is suffering interference,
either "conducted" or "radiated," according to Jim Nelson, senior
project engineer at Illinois-based Oneac, a company that makes
products that provide protection against power and data-line

"Conducted" means the interfering radio frequency noise is flowing out
the power cord of the PC and up the power cord of the radio.

"Radiated" means the interfering radio frequency noise is being
emitted directly from the PC or cables connected to it through the
air, just like a radio station.

"It's true that a PC sends a much weaker signal than any radio

"It is infinitely closer, as far as the radio is concerned, so the
noise wins," said Nelson

First, try a battery-operated radio in the same location and tune it
to your regular station. If the interference goes away the problem is
likely conducted, though this is no guarantee. The portable radio may
be better filtered.

If you think the problem is conducted, plug the radio into a different
electrical circuit than the one the computer is on.

Or try using a line filter on the PC and radio. Look for
transformer-based Uninterruptible Power Supplies (UPS) that filter out
noise and protect against surges. (Oneac makes them, said Nelson.)

Look for one that has built-in filters for Radio Frequency
Interference/Electro-Magnetic Interference (RFI/EMI) and that has high
isolation rating (in "db" or decibels).

If the problem seems to be radiated, first try repositioning or
re-orienting both pieces of equipment and their cords.

Some radios use the power cord as the antenna. The cables coming out
of the PC can work as antennas, too. A device at the end of the wire
doesn't need to be in use or even on for the cord to be a problem.

Turn the PC and radio on so you can hear the interference. Start
disconnecting the cords from the back of the PC one at a time to see
if one in particular is causing the problem.

The problem may be caused by several sources. 

So the interference may diminish slightly if one cord is removed. You
can't pull the power cord, but it may be the source, so don't forget
it when you try some of the following suggestions provided by Nelson.

- If there are screws on any of the connectors make sure they are
tight, as some shielded cables require them for good grounding.

- If you suspect some of the cables going to your printer or serial
device are unshielded, go buy replacements that say shielded wire is

- If any cables are longer than they need to be, bundle and tie them

Don't roll them into a coil. Weave them back and forth as tightly as
possible and tie or tape them.

- Ferrite cores or beads in a cable can help at certain frequencies. 

These look like a small cylindrical lump near the connector. Your
monitor's video cable probably has one.

Snap-on versions can be bought at places like Radio Shack. Try them on
the cables that you suspect.

They work best nearest the source (the PC main box), though sometimes
sliding them up and down the cable changes the effect.

If the hole in the bead is large enough, loop the cable more than once
to increase effectiveness.

- Sometimes long slots or breaks in the metal PC cabinet can act as an
antenna. Make sure the PC cover is seated properly and screwed on
tight, if you have ever taken it off.

If there are still long openings in the box try to seal them with
aluminium foil tape sold at heating and air conditioning suppliers.

Don't put the tape near electrical connections or use it where it
could fall on something that has power running through if it came

Also, be sure not to cover openings used for ventilation. The tape
trick is a last resort.

"It's rare that this is the source, but I've seen it work," said

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