[RFI] Trane Furnace RFI

Dale Svetanoff svetanoff at earthlink.net
Sat Oct 3 13:52:17 PDT 2009


Welcome to the reflector!  From prior postings seen on here from other
people who have had to deal directly with equipment manufacturers, I would
say that you did pretty well in talking with Trane about the problem.  As
you are learning, variable speed AC drives might be wonderful for boosting
efficiency, but they are not electromagnetically friendly.  I am impressed
that Trane did provide a kit to reduce the interference effects.  One
question about the filter kit: did the filter kit get connected to a good
ground when the installer added the kit?  A "good" ground would be a solid
connection to the metal chassis or cabinet of the furnace.  If the kit is
supposed to be grounded (likely) in order to work properly, lack of a good
ground (because of painted metal) could render the effects of the kit to be
minimal.  I would hope that Trane gave the installer a clear set of
instructions for installation of the kit.

At this stage, I think a worthwhile question to ask is:  by what means is
the remaining RFI propagating?  You have the AC power line, of course, but
you also have the wires to/from the thermostat that can act as a radiating
antenna, and then there is direct radiation from the wiring within the
furnace itself.  (There have been several posts in recent months about
radiated RFI from the wiring in variable speed laundry equipment -
especially from the control panels, which are largely unshielded.)  I think
it is interesting that the problem only exists when heat is on, not A/C. 
Assuming that the same motor is used to run the air mover blower whether in
heat or cooling mode, can you determine why the motor is "quiet" when
cooling?  I am thinking that maybe the motor runs at a constant speed when
cooling.  Alternatively, maybe the culprit is something other than the
blower motor.

I'd like to suggest that you rig up a "snooper loop" of some sort as a
detecting antenna.  This could be a 6" diameter loop of wire rigged with a
coax connector and connected to one of your HF receivers.  Put the receiver
into whichever receive mode gets hit the worst (probably SSB or AM) and
tune for max noise.  Then, move the snoop loop antenna around all parts of
the furnace to see if you can find a really hot spot from which the most
amount of noise is coming.  

Incidentally, keep one more thing in mind: this problem is occurring at a
relatively low frequency, not at VHF.  "Ferrites", as such, will probably
not do a lot for you.  If the problem can be helped with added materials,
you are likely to need special mixes designed for lower frequency
applications.  But that comes later ... for now, see if you can determine
the source and why only on heat cycle.  Best wishes.

73, Dale

> [Original Message]
> From: Pawlak, Dan L. <Daniel.Pawlak at gd-ais.com>
> To: <rfi at contesting.com>
> Date: 10/3/2009 10:27:55
> Subject: [RFI] Trane Furnace RFI
> Hi,
>      I'm new to this list. I have a problem with my furnace.
>      I bought a new Trane furnace 2 years ago (model # 2TXCB036BC3HCAA)
and complained to the installer that I was having problems with RFI on the
ham bands. Some bands had more RFI than others. I contacted the
manufacturer directly and they worked out a dealer with the installer to
add a filter to my furnace (Variable Speed Inducer Kit #KIT14688). It was
installed on the ac line inside the furnace, but did not cure the problem
completely. I didn't take any S-meter readings before and after it was
installed, but it did help somewhat. The RFI only happens when the furnace
is running and not the a/c. Has there been any experience with this model
furnace? Are there any other measures, like adding ferrite cores, that
would help?
> TIA,
> Dan Pawlak KF4KKF
> Manassas, VA.
> _______________________________________________
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> RFI at contesting.com
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