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[RFI] Line filter

To: <rfi@contesting.com>
Subject: [RFI] Line filter
From: EDWARDS, EDDIE J" <eedwards@oppd.com (EDWARDS, EDDIE J)
Date: Fri, 29 Sep 2000 09:09:52 -0500
> -----Original Message-----
> From: kmarch [SMTP:kmarch@ix.netcom.com]
> I am trying to quite down the slowly intrusive noise environment in my
> rural
> neighborhood.  Some of my neighbors have purchased lamps which generate
> lots
> of RF (Cheep, COSTO, Taiwan...).  Initially I am trying to work with these
> people, rather than filing a complaint.
        Filing a complaint won't do any good since the FCC probably will not
enforce Part 15 which is where these Non-intentional radiators are regulated
or at least supposed to be.  You might find someone at the FCC who is
willing to send a letter, but that's as far as they'll go.  Of course,
things may've changed now that the new FCC Chairman is an "enforcement" guy,
but in these types of cases I doubt it.

> There are some items of info I need
> to be armed with a solution when, and if, I am allowed to enter their
> house.
> (a)  I need to get a good line filter to prevent RF from radiating back up
> the line. It may be a common mode or not, but I need to find out by
> substituting various types of filters and determining if preventing the
> radiation into the power lines (a there is lots, can be heard for a mile
> in
> the car radio) reduces the noise to below band noise.  The noise is mostly
> affecting the 160 band, but also is bad on 80, and still can be heard up
> to
> 10 meters. 
        An AC brute force filter will help if the noise is only thru
conduction and none from direct radiation.  The FCC's Interference Handbook,
which is free, has some listed by ICE,  TCE Labs & Radio Shack.  A copy of
this handbook can be found in the back of the ARRL's RFI Book.  You can call
the FCC at 888-CALL-FCC and ask for a couple of copies of their handbook,
and they'll send them out.  Get one for the neighbors and highlight the
applicable regs if they're hesitant to being accomadating.

> (b) I need to know how to modify a light dimmer switch to reduce
> the RF emission. Any circuit diagrams that anyone has, or can describe, I
> would appreciate.  How does one quite a noisy SCR? There are three primary
> noise sources which I have located with DF.
        Light dimmers & speed controllers as well as touch lamps both
benefit from the use of brute force AC-line filters and ferrites added to
the lines.  But they don't always work.  Sometimes you need to replace the
devices with quieter one that has built in RFI suppression.  The ARRL book
recommends the AC filter and ferrite approach, using an FT-240 or FT-140
sized core with about 15 turns on it.  I think 43 mix material for HF/VHF
noise and #75 or 'J' mtrl for lower HF noise should be used.  It may take
two cores to get the noise down low enough, but then you run out of AC line
so an electrician may be needed to install additional wiring.  Also on
dimmers you may need  cores on the input and output.

        In the case of touch lamps, especially ones radiating, a 1-4 Kohn
resistor and a 10 microHenry choke on the sense line may help as well.
Again, do these mods at your own risk or have an electrician do it to reduce
your liability.

        I've also found that plugging these lamps into different outlets
makes the noise less resonant on some freqs and more on others.  If your
lucky, it'll move to a non-ham freq!

        You might want to check the archives at contesting.com for more

> Next phase is to "meet the neighbors".
>    Don't worry I will have a technician do the work to remove
> liability...if work is required.  Right now I'm trying to fill my bag of
> tricks so I can fix things with a minimum of intrusiveness to the
> neighbors.
>     In the old days hams interfered with neighbors. Now it's the reverse.
> Thanks.
        Below is the ARRL's info on touch lamps from their Info Server.  I
also have some good stories on touch lamps I'll forward to you as well.  If
anyone else wants to see them they're on the contesting.com archives.
Search under K0iL as author.

        I highly recommend getting the ARRL's RFI Handbook.  It has tons of
good info covering the whole spectrum of EMI/RFI problems.

        Also, always report all problems to the manufacturer.  If we don't
do this they'll think everythings hunky-doory with their product and never
change it.  An angry letter from the customer always gets their attention.

        de ed -K0iL

Updated: November 17, 1995

ARRL RF Touch Lamps and Dimmers Information Package


     RF Touch lamps are RF-operated devices that often cause, or are 
susceptible to, EMI problems.  They have a free running oscillator 
that is very broad and rich in harmonic energy.  This oscillator is 
hooked up to a touch plate that changes the frequency of the oscillator 
when a hand is placed near the plate.  Unfortunately, this plate also 
acts as an antenna, radiating some of the energy of the oscillator, or 
picking up nearby radio signals.  When the former happens, it can interfere 
with other services.  When the latter happens, the circuitry inside the 
lamp reacts the same way that it would when the plate is touched -- the 
lamp changes states from "off" to "on".

     Although cases of moderate interference can sometimes be cured by 
using a "brute-force" type AC-line filter and/or a common-mode choke (see 
the ARRL Book,  Radio Frequency Interference -- How to Find It and Fix It 
for more information about AC-line filters and common-mode chokes) most 
cases will require internal modification to the lamp.  For a number of 
different reasons (you may be blamed if anything EVER goes wrong with 
the lamp or house wiring) you do not want to perform this modification 
on equipment that is not your own.  Remember -- house AC power is dangerous.

These modifications must only be performed by qualified service personnel!

Here are some reprints from QST "Hints and Kinks":

RFI and Touch-Controlled Lamps.  
     I have found a simple cure for those touch-controlled lamps that turn 
themselves on and off during nearby radio transmissions.  In my case, 
40-meter operation gave the most trouble, with 75-meter operation a close 
second.  Higher frequencies presented no problem.  (I use a ground-mounted 
vertical antenna for 80, 40 and 15 meters, and the lamp is approximately 
150 feet from the antenna.  An AC-line filter at the lamp did not eliminate 
the problem.)

     A 1k ohm resistor (in series with the signal input lead to the 
encapsulated circuit that operates the lamp) cured the problem for me.  I 
suppose the required resistor value would vary with the RF-field intensity 
and frequency. 
-- John M. Adams, W7OTC, Sun City, CA

More on RFI to Touch-Controlled Lamps.  
     I had the same problems as W7OTC with a touch-controlled lamp switched 
on and off by my transmissions (100 W to a roof-mounted vertical, with two 
radials per band).  The problem occurred during operation on the 80- through

15-m bands, but 10-m operation had no effect.  A 1-k ohm resistor was not a 
complete cure in my case. 

     A 3.3k ohm resistor in series with the signal input on the lamp 
helped on all bands except 80m (an additional 1.8k ohm prevented the lamp 
from functioning).  When the resistor was replaced with an RF choke 
(100 uH, 139 mA), the problem abated on all bands except for  80 m. 
On 80 m, the interfering signal was considerably attenuated by the choke, 
but the lamp still switched.  The choke alone may be enough to clear up 
the problem in some cases.

     The final answer turned out to be both the RF choke and a 1.8k ohm 
resistor in series with the signal-input lead to the touch-control circuit. 
-- Colin Hall, G4JPZ/W6, Marina Del Rey, CA

Touch-Lamp Transceiver.  
     When my wife told me she had bought a three-way lamp that switched on 
and off at the touch of any of its metallic parts, I did not realize she 
had purchased a transceiver.  I found that my transmitted signal would 
cause the lamp to operate exactly as if I had touched its metal parts.  
Later I discovered a raspy, S8 signal at 1875 kHz -- it was coming from 
the lamp, which was located three rooms away on a different AC circuit.  
The lamp signal is present from 40 meters down.  At frequencies from 20 
meters up, my operation is undisturbed. 

     A box inside the lamp contains a circuit board through which AC 
line voltage is routed and which has a wire connected to the metal base 
of the lamp.  When the lamp is plugged in, the lamp signal is present 
at all times, regardless of whether the lamp is on or off.  In my attempts 
to eliminate the interference, I tried a commercial AC filter, coiling the 
lamp cord on some ferrite material and other such approaches without

     To make sure the lamp my wife had was not defective, I borrowed a 
similar lamp from a neighbor to try it.  I found it to perform in exactly 
the same manner except that the frequency of oscillation was somewhat 
different.  There is no manufacturer or distributor name on the lamp or 
packing container.  The lamp was made in Taiwan.

     I am writing so that others who may be experiencing similar 
difficulties may have some idea of the probable source of interference.  
After I described what I discovered to a ham friend, he realized that 
such a unit had been causing interference to his station for more than a
-- Cal Enix, W8EN, 209 S Kalamazoo St, White Pigeon, MI  49099

     If these cures don't work, it may be possible to shield the electronic 
switch module, but this must be done safely!  You may also want to contact 
the manufacturer and send a report of your problem to ARRL Headquarters 
RFI Desk, 225 Main St. Newington CT 06111. 


Light-dimmer Interference Reduction.  
     Radio Amateurs who've have been cursed with RFI from solid-state light 
dimmers will be interested to know that at least one domestic manufacturer -
Lutron - produces light dimmers that incorporate RFI suppression techniques.

The Lutron NOVA series uses toroidal chokes that provide a significant level

of RFI suppression. 

     I bought a Lutron model N-600, which will handle up to 600 watts of 
incandescent lighting.  Temporarily installed in my radio shack, a generic 
light dimmer produced an S9+ reading at 230 kHz (an arbitrary noisy 
frequency).  The N-600 produced a reading of S3, a difference of about 40
Admittedly, this is not zero, but installing the N-600 some distance away 
provided a reduction in RFI that is very gratifying.  Indeed, I new hear new

noise sources, heretofore undetectable through the dimmer din.

     You're not likely to find these dimmers at your local discount store, 
and they are not inexpensive.  Check for the availability of these dimmers 
at a lighting fixture store and expect to pay about $25 apiece for them.  
-- Richard G. Brunner, AA1P, 10 Brookside Dr., Foxboro, MA  02035

Lutron Electronics Co., Inc.
Suter Rd.
Box 205
Coopersburg, PA  18036

     If you come up with a better solution for these problem, please write 
to the RFI Desk with the solution.  It sounds like it would be a good 
candidate for Hints and Kinks!

"73" from ARRL HQ

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