[RFI] Low voltage lighting solid state "transformers"

Steven Farmer wa5rpf at gmail.com
Sun Dec 17 13:07:56 EST 2006


Thanks for the helpful information.  I was delighted to have finally tracked 
down the source of my rfi problem,  but my happiness was short-lived.  It 
seems that all 3 units in the condo building in question use the offending 
power supplies.  Not only that, but the contractor who remodeled the 
building in question lives next door to me (in my building) and *he* has one 
of the crappy little boxes too.  They'll all have to be replaced or filtered 
to eliminate the problem, probably at my own expense.  We might understand 
that it's their responsibility to stop using any device that interferes with 
a licensed radio service, but they have trouble with that idea.  If I dig my 
heels in, I could be living with the noise for a very long time.

Things are a little simpler for you, since you own the devices in question 
and can apply whatever fix you can engineer.  I have to rely on a local 
electrician to obtain and install a cure.  These power supplies are housed 
in boxes the same size as you'd mount a single a/c recepticle or wall switch 
into, so the replacements will probably also have to be switchers rather 
than conventional transformers.  Since my rfi seems to be mostly a common 
mode problem, some sort of emi filtering at their breaker panel might also 
work.  So far, google has turned up only lighting "systems" and not any 
individual power supplies.  I don't yet know if replacements can be had at 
the local electrical supply house or not.  Anyway,  I'm still hopeful that 
someone out there can suggest a particular model or brand.

Thanks again,

Steve WA5RPF

----- Original Message ----- 
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: "RFI List" <rfi at contesting.com>
Sent: Sunday, December 17, 2006 9:23 AM
Subject: Re: [RFI] Low voltage lighting solid state "transformers"

> On Sat, 16 Dec 2006 19:59:57 -0700, Steven Farmer wrote:
>>Can anyone suggest a brand or manufacturer of _quiet_ 120 to 12 volt
>>switching power supplies for low voltage lighting?
> I have a half dozen or so of these little monsters in the home I bought
> in CA. I've done some things to suppress them, with varying degrees of
> success. The problem is physical space to mount either the suppression
> component or a real transformer.
> To put my comments re: the effectiveness of these filters in
> perspective, I live in a low population density part of a redwood forest
> north of Santa Cruz. I have one neighbor about 250 ft away, two at about
> 400 ft, and a half dozen that are probably 750 - 1,400 ft away. My noise
> level is usually fairly low, and at least 15 dB lower than what I had in
> a Chicago residential neighborhood. I can often copy a CW signal that
> doesn't move the S-meter on my TS850 with a 250 Hz filter. But when the
> XYL goes in the bathroom and turns on the LV lighting, I'm in trouble.
> Before I did the suppression, they gave me noise levels of 10 dB over
> S9.
> So far, I've come up with three solutions. The easiest is a commercial
> power line filter that fits in the backbox. I found a 3A Delta unit in
> their DK series at a local surplus house. They worked well enough that I
> bought all they had. I still hear a bit of noise from them on 160 on a
> vertical 25 ft away, but not on a dipole 100 ft overhead. Next time I
> open the backbox, I'll add 0.22 uF in parallel with the Line side of the
> filter.
> The first thing I tried works well electrically, but it doesn't fit in
> the backbox. It's 14 turns of #12 stranded THHN twisted pair wound
> around a #31 Fair-Rite 2.4" o.d. toroid (it might be called FT-240-31 in
> the ham world), with 0.47 uF on the Line side of the choke. This choke
> resonates around 10 MHz, so it is quite effective from about 20 meters
> down, but its effectiveness is reduced at higher frequencies. I hear NO
> noise on that vertical from the lighting with that filter in line. The
> resonant frequency could be raised a bit while still maintaining the low
> frequency performance by using smaller gauge wire. Nearly all power
> cords are #18. One surprise to me -- zip cord was far less effective in
> this filter.
> At one location, I have three of these little power supplies in line
> with the switch. I have the choke/capacitor in series with the first one
> (closest to the switch) shoved up into the ceiling. In each of the other
> two fixtures, I have smaller chokes using #16 twisted pair around
> smaller toroids (as I recall, 7 turns around 1.4" toroids). They fit in
> the backbox. This works fairly well below 20 meters -- I don't hear
> these fixtures on a 160/80/40 dipole that runs 100 ft overhead --  but I
> do hear them on a Beverage that runs about 50 ft away, and they are
> significantly increasing the noise level on 20M dipoles that are 100 -
> 200 ft away. My next move will probably be to replace the small chokes
> with the same commercial filters I used in the other fixtures.
> When thinking about wire size, remember that these fixtures are
> typically 40W fixtures, and you're on the 120V side, so some fairly
> small wire will do the job. All it needs is insulation rated for use on
> the AC line.
> I'll be interested to see what options emerge from this thread for the
> "transformer." So far I haven't found any. W8JI says he's used filament
> transformers to power lighting like this. All the 12V transformers I've
> found are far too large to fit in a backbox.
> 73,
> Jim Brown K9YC
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