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[RFI] RFI Troubles

To: <rfi@contesting.com>
Subject: [RFI] RFI Troubles
From: Hare,Ed, W1RFI" <w1rfi@arrl.org (Hare,Ed, W1RFI)
Date: Fri, 22 Dec 2000 18:48:23 -0500
Hello, Gerry,

> and my neighbor there has been complaing about RFI
> from my HF rig. His main complaint is that I'm coming > through the
speakers on his computer.

One first good step for you and your neibhbor to take is for you to both
understand the differences between RFI caused by rules violations at your
station and that caused by the inability of some (most?) consumer equipment
to function properly in the presence of strong radio signals.  The FCC
requires you to correct interference to other radio services caused by rules
violations at your station, but the FCC rules do not address "fundamental
overload" of non-radio equipment. The latter is really a local problem.  In
most cases, a ham may want to help out, but this becomes a matter of your
helping your neighbor find a solution.

In the case of interference to non-radio devices, the FCC RFI material is
pretty clear -- the device is improperly functioning as a radio receiver.
This suggests that the cure in that case would be to apply the necessary
filtering and/or shielding to the affected equipment.

ARRL publishes a pamphlet jointly with the Consumer Electronics Association.
It is available at:

The FCC information about RFI is also valuable. See:


I also recommend ARRL's general info about RFI at:


Start by reading the info to give yourself a good understanding of the
problem, then print a copy of the pamphlet and the FCC material and give it
to your neighbor. RFI problems sometimes get rather "heated," and this will
give things a chance to calm down. You should also correct any RFI problems
to your own equipment.  It will really help your neighbor understand that if
your own computer works well, the problem must be on his end.  Once you have
done so, it is time to talk things over with your neighbor.

Start this conversation by explaining that interference to other radio
services can be caused by problems at your station and that the FCC requires
you to operate your station legally.  Your neighbor will be listening at
this point because you are telling him or her what YOU need to do.  You can
then explain that you have put the necessary filters on your transmitter
(get a filter for your transmitter and install it, whether you need it or
not.  You can then point to it with pride.) 

Next, you can show him your station (clean it up first!) and the filters you
have put onto your own equipment.  This helps him understand that the
problem is on his end and that the cures you suggest will do no harm.

Then, explain that you have checked your station throroughly.  Point out
that the FCC's material identifies that for interference to non-radio
devices (their material specifically names computers), the cure must be
applied to the computer.  At this point, I suggest that you let your
neighbor know that even if the interference is not caused directly by your
station, you would like to be a good neighbor and help him find a cure.
This usually keeps him talking.

Interference to computer speakers is generally an audio problem.  For
completeness, see:


The cure will usually involve common-mode chokes.  For computers, obtain
about a half dozen F-140-43 ferrite cores.  For larger wires, you may need
the F-240-43 size.  For HF, you need some inductance to make a good
common-mode choke, so don't substitute those handy clamp-on ferrite beads.
You will need about 10 turns of wire on the choke.  Some computer speakers
are amplified.  This generally requires that you put a ferrite on the end of
each of the speaker wires connected to the computer and at the speaker end,
as well.  Most of the computer speakers "daisy chain" from one speaker to
another.  The speaker may have an ac "wall cube" power supply. In that case,
might be worth trying a core on the power supply lead, right at the speaker.

These cores are available from Palomar and other distributors. See
http://www.arrl.org/tis/tisfind.html to look up addresses, phone numbers and
web sites.

This quick email is an overview.  Go through the more detailed ARRL and FCC
material.  I also recommend the ARRL RFI Book
(http://www.arrl.org/catalog/6834) for more info yet.

Good luck.

Ed Hare, W1RFI

Ed Hare, W1RFI
ARRL Laboratory Supervisor
225 Main St
Newington, CT 06111
Tel: 860-594-0318
FAX: 860-594-0259
Internet: w1rfi@arrl.org
ARRL Web: http://www.arrl.org
ARRL Technical Information Service: http://www.arrl.org/tis/

-----Original Message-----
From: gm@netsync.net [mailto:gm@netsync.net]
Sent: Friday, December 22, 2000 5:27 PM
To: rfi@contesting.com
Subject: [RFI] RFI Troubles


I wonder if I could get some advice on an RFI problem. I live in an
apartment that is part of a large house. There is one other apartment
here too, and my neighbor there has been complaing about RFI from my HF
rig. His main complaint is that I'm coming through the speakers on his
computer. My main antenna is a Butternut HF5B 2 el mini-yagi that is
mounted up on the roof. The bottom of the antenna is roughly 15 to 20
feet above his computer, and 5 feet away horizontally.

My first question is: In the eyes of the FCC, is my antenna too close to
his apartment? I have heard some people say that the FCC expects a ham's
antenna to be at least 50 feet away from any neighbors, otherwise the
ham can be blamed for interference. Is there any truth to this? I
normally run 100 watts output, and I know that my neighbor's apartment
is within the FCC's RF saftey limits. I occasionally run 500 watts for
DX pile-ups, which is also within limits, but I only do it when the
neighbor is out. It's very possible that the FCC will be coming here to
look at the problem, so I need to know if my antenna is too close (at
100w), and if I could be held responsible for the RFI problem.

I also have dipole for 30 and 40 meters, but I only use it when the guy
is out. That antenna is roughly parellel to his 2nd floor apartment, and
about 20 feet away from it. There isn't enough room here to put up
anything better.

As for cleaning up the RFI, I have not been able to do much since my
neighbor is not very cooperative. The problem is from HF fundamental
frequencies. I'm coming through the speakers on his computer, which he
insists on leaving on 24 hours a day. He won't turn off his amplified
speakers - not even before going to bed at night. He uses rabbit ears
for a TV antenna, and we are in a fringe reception area. His TV is at
least 30 feet from my antenna, and I clobber every channel. He also says
I come in through the phone line. 

Since his main complaint is with the computer speakers, that is where I
have been trying to help him so far. I don't seem to cause any
interference at all on his monitor. I tried using ferrite beads on
various speaker cables and mananged to reduce the interfence by maybe
50%, but it is still very noticeable. I only had 2 beads, so I couldn't
do as much as I wanted, but I doubt that beads alone would have done the
job. He has a total of 5 speakers, with 2 separate ampifiers. At one
point I grabbed a hand-full of the speaker wires and the interferece
dropped WAY down. I'm thinking I might be able to wrap several turns of
wire around these cables, then ground the wire to simulate the same
thing. Does that make any sense? His computer is grounded btw. I
grounded it because the AC wiring in this place is not grounded. 

For the phone line, I will try a bead or a torroid core. For the TV,
I'll try a high-pass filter, but I have doubts that it will help much. 

It's been hard to do much of anything because the neighbor isn't very
cooperative. We agreed yesterday to work on the problem at noon today,
before he would go to work at 2 pm. He wouldn't answer his door or his
phone when I tried to reach him several times between 12 and 1:30.
Finally, just before he had to leave for work, he anwered his door. He
said he "must have been sleeping" earlier. This is typical for this this
guy, - it's happened before. So, I'm about ready to just go ahead and
operate and let him make complaints to the FCC. It's easier than dealing
with his lousy attitude. I need to know first though if my antenna is
too close to him. I'll probably be able to get in his place one last
time to try a few things though, so any advice on solving the RFI
problems is also appeciated. I've never had problems with RFI before, so
all of this is new to me. 

Gerry KA2MGE

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