[RFI] Low Voltage light RFI

dgsvetan at rockwellcollins.com dgsvetan at rockwellcollins.com
Fri Jul 11 17:19:05 EDT 2003

The last line is the whole point:  there are 2 reasons that come to mind as
to why these turkeys are on the market - 1) they are being sold without FCC
certification, which I think is a non-no if the switching frequency is > 10
kHz, or 2) they are legit, but since they are intended for outdoor use, it
is possible that these systems may be run under Class A emissions
requirements, as opposed to Class B.  Perhaps someone on the list knows the

Pete was lucky to get "magnetic transformers" for his lights.  They are
becoming a scarce breed, since the costs of cores and windings continue to
rise.  Noisy, sleaze-ball switchers are very low cost to produce these
days, especially if you don't bother to clean up their radiated and
conducted mess.  On the other side of the coin, I recently purchased an
Astron SS-30M switcher power supply to replace the old Astron RS-20 that
has been running for more than 20 years (and darn near causing hernias each
year when lugging it to/from Field Day).  Members of this list may recall
that the Astron switchers were top performers when QST tested switching
power supplies a couple of years ago.  After I opened up the SS-30M
(approximately 2 minutes out of the box - after verifying operation, of
course), I could see why:  real chunks of ferrite (2 big cores) on the
output leads, including the meter, fan, and thermostat lines.  There is
also a substantial common mode filter assembly on the power line input side
of the pc board, plus the 3-pin IEC connector for the power cord is part of
yet another line filter assembly.  In short, they did very well.  Sadly,
not many consumers would buy the decorative lights if the power source
alone cost more than the lights themselves.

Good luck.  Any attempts to clean up these types of power supplies should
apply the "cures" as close to the power supply as possible.  For extreme
cases, a combination of common mode filters and by-passing may be needed on
both the input and output sides of the supply.  It might help to place the
power source into an all-metal enclosure (one that provides some
ventillation) and then filters can be installed within the box.  Of course,
the box must be connected to the AC line safety ground via a 3-wire cord,
the shorter the better.  Good luck.

73, Dale

                      <kelly at thejohnson        To:       rfi at contesting.com                                                            
                      s.ws>                    cc:                                                                                     
                      Sent by:                 Subject:  Re: [RFI] Low Voltage light RFI                                               
                      rfi-bounces at conte                                                                                                
                      07/11/2003 03:33                                                                                                 

On Fri, 11 Jul 2003 16:12:10 -0400, Pete Smith wrote:

> At 01:24 PM 7/11/03 -0400, KE2N at cs.com wrote:
> >I ran into this same problem when I installed some halogen "puck" lights

> >in the kitchen. Switching supplies wiped out HF reception.  For the new
> >house, I specified the "magnetic transformer" option for the lights and
> >is RFI-quiet.
> >
> >Imagine: magnetic transformers - what will they think of next!
> Funny, I have three sets made by GE - 8 lamps total - that use some sort
> switching black lump, and they are totally RF quiet.  The only problem is

> that something -- probably their overtemp sensing -- is unduly fussy, so
> the darned things keep shutting themselves off...
> Wouldn't something like this be soluble by the same sort of filtration as

> other switching power supplies?

Probably, but it is easier to replace the power supply :-)  Since they
belong to me it's pretty easy for me to replace the supply.  I can't say
I've had a lot of luck in the past eliminating RFI with filters.  I still
have a TVI problem that I've never been able to solve, except by moving
the antenna to a less optimal location :-(

These supplies are incredibly noisy.  What if they belonged to my neighbor
instead of me and my neighbor didn't like me?  My question is: why are
like this allowed to be sold?
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