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To: doc@kd4e.com
From: "Dennis Vernacchia" <n6ki73@gmail.com>
Date: Thu, 20 Dec 2007 19:31:52 -0800
List-post: <mailto:rfi@contesting.com>





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". 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 signal generated by the lamp's circuitry signal
is present at all times, regardless of whether the lamp is on or off.
Although cases of moderate interference can sometimes be cured by using a
"brute-force" type AC-line filter and/or a common-mode choke, most cases
will require internal modification to the lamp.

The easiest route here is simply to get rid of these pesky things, and
return them to the store, if possible.

A simple cure for those touch-controlled lamps that turn themselves on and
off during nearby radio transmissions on 40 and 80 meter operation. A 1k ohm
resistor in series with the signal input lead (from the lamp base) to the
encapsulated circuit that operates the lamp may cured the problem for me. If
this isn't sufficient, add an RF choke (100 uH, 139 mA) in series with the
resistor. The choke alone may be enough to clear up the problem in some
cases. If these cures don't work, it may be possible to shield the
electronic switch module, but this must be done safely!

Hope those help

73, Dennis N6KI

On Dec 20, 2007 6:40 PM, kd4e <doc@kd4e.com> wrote:

> Touch-control lamps have long been on the short-list
> of RFI-vulnerable and RFI-generating devices.
> I have copied this to the two RFI-related Ham lists.
> > I have an RFI issue in the house here... I was wondering if
> > anyone else has seen this...
> >
> > I have a tall torchiere in another part of the house, and it
> > is the type that you can turn on by TOUCHING the vertical
> > bar. If you touch it repeatedly the britghtness changes too.
> >
> > The only problem is that my rig turns it on too! In fact, with
> > every DIT oir DAH of CW it either changes the brightness
> > or turns it on/off.
> >
> > I am getting this on 40m, 30m and 20m CW. The antenna is an
> > end fed random wire with an L-network tuner, upstairs on
> > the second floor. My "ground" is a wire to the screw on the
> > wall plate. Not great I know.
> >
> > I haven't tried other bands yet!
> >
> > Any suggestions?
> >
> > Thanks & 73 - Bry, AF4K
> --
> Thanks! & 73, doc, KD4E
> Personal: http://bibleseven.com/kd4e.html
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