Hi all,
Yet again another update to my under cabinet touch lighting situation.
To refresh your memory, on 20m I am having problems with my RF turning the
lights on and stepping them through their various dimmer stages.
The lighting system consists of a dimmer unit which contains the sensing
circuitry and a switching power supply unit which takes the AC voltage
output of the dimmer unit and steps it down to 12 V DC or less.
Here is where I am now. I have successfully eliminated the interference on
all amateur bands from my lighting system when it is uninstalled. This
solution consisted of wrapping the cord going to the AC mains around a large
Amidon torroid (I forget the material number - but it's correct for HF) and
wrapping the cord going between the dimmer unit and the power supply unit
the same way. I've tested on all bands but 160M and I have no interference
to the light.
I did not need any bypass caps or anything like I thought I might.
The current unit I have been messing with gets mounted above a fan hood.
The hood is basically a big stainless steel box (simplest way to describe
it). The lighting circuitry is mounted above it. The sensing line is then
attached to the metal hood. This way whenever the hood is touched, the
lighting system is activated. With the sensing line attached to the hood, I
get my 20m interference problem again. The hood is acting like a big
antenna. The hood is not grounded but isolated from DC ground since
grounding the hood when then ground the sense line and the switching would
not work.
I've tried adding a .01 uF cap (and other values too) from the sensing lead
to ground. So far no matter what value I have tried, adding the cap ends up
loading the oscillator in the dimmer unit to the point that it is no longer
sensitive to touch. I've also tried winding the sensing line around a
torroid. If I get too many wraps, I again destroy the sensitivity of the
sensing line and it no longer does it's job. And anyhow, it still doesn't
stop my RF problem. I've tried resistors in series with the sensing line to
the hood. Above a few 100 Ohms and I lose my sensitivity just like with the
torroid.
So far, I have found no good way to RF bypass the sensing line. What I want
to do is basically shunt all HF energy to ground on that line, but I can't
load down the line otherwise the sensing circuitry won't help.
Does this make sense and does anyone have any ideas?
Thanks es 73,
Jon
NA9D
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