QRZ! Ham Radio 1/QRZ Ham Radio Callsign Database - December 1993.iso/arrl/emitochl.mps

Text File | 1993-11-21 | 5.2 KB | 110 lines

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ARRL RF Touch Lamps 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 tranmissions. In my case, 40-meter operation
gave the most rouble, 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
lam did not eliminate the problem.)

A 1-kohm 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-kohm
resistor was not a complete cure in my case.

A 3.3kohm resistor in series with the signal input on the lamp
helped on all bands except 80 m (an additional 1.8kohm 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 interering signal was considerably
attenuated by the chokd, 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 1.8kohm
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 transeiver.
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 lam 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 lam 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 with out success.

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 soem 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 month. -- 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.

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

"73" from ARRL HQ