[RFI] Low voltage lighting solid state "transformers"

Steven Farmer wa5rpf at gmail.com
Sun Dec 17 15:23:30 EST 2006


The lights are exterior low-voltage halogen accent lights.  The source of 
the rfi is the so-called "transformer" which converts the 120v a/c to 12v 
a/c (pretty sure it's a/c anyway).   These "transformers" are actually 
made-in-china switching power supplies.  If they have any filtering at all, 
I can't tell it.   Intense noise is present from the am bc band all the way 
through 11 MHz.  It's particularly strong on 80 and 40 meters.   Checks with 
a handheld shortwave radio show that the a/c wiring is hot with this rf, 
not only in their building, but in ours and in the single-family home next 
door to us.

Operating from a condo is a character-building experience.


Steve WA5RPF

----- Original Message ----- 
From: "Dave, K2DP" <k2dp at charter.net>
To: "Steven Farmer" <wa5rpf at gmail.com>
Sent: Sunday, December 17, 2006 12:41 PM
Subject: Re: [RFI] Low voltage lighting solid state "transformers"

> Steve,
> Am interested to learn more about your source of RFI. Would you be kind 
> enough to describe exactly the type of lighting device you are referring 
> to so that I can add it to my list of "rfi sources". I tracked down a 
> dilly of one here in my neighborhood a couple of years ago........we live 
> "in town' in an old area of St. Louis, so homes are 15-20 feet apart from 
> side to side. My next door neighbor had an "air purification system" 
> installed on the forced air HVAC system. The purifier used a black light 
> and some other lamp, which generated RFI from 3 - 20 mhz and was radiating 
> BACK out of the neighbors house all over the power lines. Fortunately, the 
> manufacturer replaced the unit under warranty and when the new one was 
> installed, I noticed that they had implemented a significant design change 
> which seems to have cured the problem !!!!!
> 73 and good luck with your noise problems,
> Dave, K2DP, ST. Louis
> ----- Original Message ----- 
> From: "Steven Farmer" <wa5rpf at gmail.com>
> To: "RFI List" <rfi at contesting.com>
> Sent: Sunday, December 17, 2006 12:07 PM
> Subject: Re: [RFI] Low voltage lighting solid state "transformers"
>> Jim,
>> 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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