Eric:
Thank you for the info on Touchlamp interference---for all their
notoriety, this is the first >detailed< info I have seen on the
characteristics of their emissions! Now I know what to look for.
Eric Gustafson wrote:
>
> 5. If it is a dimmer, the maximum noise amplitude coincides with "device
> off" state. Minimum noise coincides with "maximum brightness" state.
>
However, I partly disagree with you on this point. Although there could
be dimmers out there whose "off" position is not really off but near the
triac conduction threshold, I have usually noted maximum radiation
emission partway between minimum dimming and full brightness. My
understanding of this is as follows.
Most of us know that the dimming control sets a threshold point for the
triac device at the heart of the dimmer, above which, on each
half-cycle, the ac to the lamp load is cut off. Unfortunately, the
triac often oscillates during each transition though its linear region
from one polarity of the ac waveform to the other, which occurs 120
times per second. This generates 120 short RF bursts each second. At
"minimum" threshold, the ac waveform is radically chopped, but is of
very low amplitude, while at "maximum" the ac waveform is unchopped, and
these oscillations do not--or at least should not--occur. So it is
reasonable to expect the worst-case to be somewhere in between, where
the waveform is both substantial in amplitude, and substantially
chopped. Moreover, the chopped ac waveform contains harmonics, and I
presume these are also involved in the modulation process, "enriching"
and widening the radiated interference.
Most consumers are unaware that the cheapest dimmers are partially so
because no suppression devices-presumably ferrite beads--are
incorporated. The "better" dimmers have such devices and are
usually--but not always--marked as "RFI suppressed," "RFI filtered," or
similar. These cost a fraction more; that they look the same as the
cheapest units in the next bin probably causes people to pass them up
and buy for lowest price at the neighborhood hardware stores, Home
Depots, etc. This can be disastrous for us suffering lowbanders,
especially when neighbors decide to jazz up their homes by installing
dimmers in every room. I wish the manufacturers and distributors were
enlightened enough not to sell the unprotected products! Dream on!
Recently, as an experiment, I went to various hardware stores,
department stores and electrical supply houses and bought single pole
600W dimmers, mostly with rotary knobs and either push-in or crank-CCW
switches. I mounted them to a wood fixture and drove a 100W bulb with
each, in turn, using a cheap Radio Shack pocket AM radio as a detector.
A crude test, but with striking results--the dimmers varied ENORMOUSLY
in the amount of garbage radiated at 1.6 MHz--reasonably close to 160m.
As expected, the unprotected units were worst, but the protected ones
varied considerably.
A thorough test would require sampling multiple units of each dimmer,
from different manufactured lots, and as many different dimmers as could
be found. That would require more time and resource than are available
to me. I am not Consumer's Union and was satisfied merely to find one
type that seemed the most innocuous, of which I purchased a quantity
against future sweeps of the neighborhood. I have so far replaced 3
unprotected dimmers in one neighbor's rented home---it was a cheap fix
to the problem, when you think about it. I had found that source by
coasting by in my car, with the engine off, listening at about 1600 kHz
on the car radio. That neighbor was uphill, and virtually at eye level
with my 160m TX antenna, as well as in line with my east/west Beverage.
The dimmer I "liked?" An RFI-filtered Lutron D-600P. I purchased it at
W. W. Grainger, catalog item 4X603, $4.20 each in lots of 3. All of
Grainger's offerings are RFI-filtered, but then Grainger sells to the
industrial and commercial markets.
--
Garry Shapiro, NI6T
Editor, The DXer
newsletter of the Northern California DX Club
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