TopBand: Light Dimmer Noise

[Garry & Yelena]

Chip Owens wrote:
> 
> My neighborhhod is full of light dimmers that are
> making reception on 160M and 80M next to impossible.
> 
> I have tried shielded loops, both horizontally and
> vertically polarized. These don't help much.
> 
> The noise blanker in my OMNI-V helps some, but still
> the average noise level hovers around the S-7 level.
> 
> Has anyone had any success in minimizing the effects of
> light dimmer noise using the DSP boxes? or by other
> means?
> 
> Chip, NW0O
> 
The DSP boxes are of limited use for that purpose--the algorithms are
for white noise.

The JPS ANC-4 is an analog combiner at the feedline. A noise antenna's
output is subtracted from the RX antenna's output. Effective operation
requires experimentation to determine an optimum noise
antenna--excellent cancellation of almost any single source can be
obtained. However, it is relatively ineffective against multiple
sources.

If your neighborhood is full of dimmers, the best course is to attack
the problem directly:

1. Find a source of "clean" dimmers--these usually have internal
filtering--beads, etc. To determine which are clean, invest in one-each
of several brands from different hardware/electrical stores; get the
single-pole model that advertises RFI protection, whether it is a
push-and-turn model or one that looks like a conventional switch. You
will note that these cost a buck or so more than the cheapest,
unprotected ones--which is why people buy them. Set up a jig with a 100W
bulb and all your dimmers, so you can switch or connect each in turn. I
made one out of a couple of pieces of scrap wood. Place your AM portable
nearby and do a comparison test. The differences should amaze you. Then
go buy a bunch of the quietest ones. One possible problem is that some
of the big chain hardware stores buy product from several sources, and
private brand-them, so you may not get the same unit next time around.

2. Locate the offending units by walking the neighborhood with an AM
radio--a little portable with a loopstick antenna. Its directionality
can be used to advantage. Tune it to a clear spot near the top of the
broadcast band. Often, walking past a house with a rotten dimmer will
really ring its bell.

3. Negotiate with the homeowners/renters to selectively kill breakers to
localize the culprit and to replace their offending dimmers. This can be
a great way to meet your neighbors, but beware if you have TVI. Some
will tell you to go perform an impossible anatomical act. Others will be
happy to cooperate--especially if you can convince them that RFI is a
serious and dangerous defect. Sometimes, the offending dimmer will be a
double-pole model and you will have to repeat step 1. While it is not a
good idea in general to go tinker with other people's houses--the
lawyers will tell you not to do it--you have little choice here, if you
hope to hear anything on 160. If you do not know how to replace a
dimmer, you are an appliance operator and probably should stick to 20m
SSB nets.

I found a Lutron D-600, sold by WW Grainger, the clear winner in the
group I compared. But it was not a complete sample and your mileage may
vary. If you find one BETTER than the Lutron, please let me know!!!!

Garry Shapiro, NI6T
Visit the Northern California DX Club home page:
http://www.ncdxc.org

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