[RFI] RFI Note of Interest
Tim Duffy <firstname.lastname@example.org>
Thu, 08 Jan 1998 15:02:30 -0800
Received: by MOT; Thu, 8 Jan 1998 9:14:00 -0600
Date: Thu, 8 Jan 1998 9:14:00 -0600
From: Ehud Zager-CEZ002 <Ehud_Zager-CEZ002@email.mot.com>
Subject: RFI Note of Interest
To: email@example.com (Receipt Notification Requested)
From ARRL InfoServer:
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
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
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
These modifications must only be performed by qualified service
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
themselves on and off during nearby radio transmissions. In my case,
40-meter operation gave the most trouble, with 75-meter operation a
second. Higher frequencies presented no problem. (I use a
vertical antenna for 80, 40 and 15 meters, and the lamp is
150 feet from the antenna. An AC-line filter at the lamp did not
A 1k ohm resistor (in series with the signal input lead to the
encapsulated circuit that operates the lamp) cured the problem for me.
suppose the required resistor value would vary with the RF-field
-- 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
on and off by my transmissions (100 W to a roof-mounted vertical, with
radials per band). The problem occurred during operation on the 80-
15-m bands, but 10-m operation had no effect. A 1-k ohm resistor was
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
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
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
-- Colin Hall, G4JPZ/W6, Marina Del Rey, CA
When my wife told me she had bought a three-way lamp that switched
and off at the touch of any of its metallic parts, I did not realize
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
to eliminate the interference, I tried a commercial AC filter, coiling
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
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
-- Cal Enix, W8EN, 209 S Kalamazoo St, White Pigeon, MI 49099
If these cures don't work, it may be possible to shield the
switch module, but this must be done safely! You may also want to
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
dimmers will be interested to know that at least one domestic
Lutron - produces light dimmers that incorporate RFI suppression
The Lutron NOVA series uses toroidal chokes that provide a significant
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
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
Admittedly, this is not zero, but installing the N-600 some distance
provided a reduction in RFI that is very gratifying. Indeed, I new
noise sources, heretofore undetectable through the dimmer din.
You're not likely to find these dimmers at your local discount
and they are not inexpensive. Check for the availability of these
at a lighting fixture store and expect to pay about $25 apiece for
-- Richard G. Brunner, AA1P, 10 Brookside Dr., Foxboro, MA 02035
If you come up with a better solution for these problem, please
to the RFI Desk with the solution. It sounds like it would be a good
candidate for Hints and Kinks!
"73" from ARRL HQ
In article <firstname.lastname@example.org>, email@example.com
My XYL bought a pair of touch lamps last week, and they generate an S8
noise level, even when they are turned off. They turn off and on when
Has anyone had any luck eliminating these problems.
Thanks for any help.
Administrative requests: rfi-REQUEST@contesting.com