[RFI] AC Line filters- Direct-Drive Washers
dgsvetan at rockwellcollins.com
dgsvetan at rockwellcollins.com
Fri Apr 4 14:14:32 EDT 2008
Sorry to hear about yet another QRN machine. Your experience does lead to
some questions, however:
1. Have you determined how the noise is propagated within your house?
(ie: Is it ALL power line conduction (and subsequent radiation off house
wiring), or could it be a combination of power line conduction and
radiation directly from the pc cards and drivers within the machine?)
2. What is the orientation of your 80m antenna relative to the machine?
3. What are the noise levels like on 40m and higher bands?
While I have no direct experience with the Harmony machiens, I do have
prior experience with their industrial bretheren, variable frequency AC
drives. Bad news.
It would not surprise me if the digital controller electronics actually
contain filters and design details that are necessary for the controllers
to even operate in such close proximity to the variable speed drive
systems. In any case, minimizing coupling between your antennas and the
machine/house wiring combination is a good place to start while waiting
for the warranty to expire. Another thing you can do while waiting is
prepare some "sniffer" probes to use with your receiver, a spectrum
analyzer (if you can get one), or an oscilloscope. The sniffers are
nothing more than insulated lengths of coax made to have anywhere from 1
or 2 inches of exposed center conductor to maybe as much as 5 or 6 inches
exposed. BTW: When I say "exposed", I mean without shielding braid. Be
sure to leave the center conductor dielectric in place so that you are not
probing around with a bare wire!
The idea is to set the machine into normal operation and "sniff" around
the power cord, control panel, and all around at cabinet seams and
openings to see where the strongest signals exist. Do that before opening
up the cabinet. Once you know the hot spots, then go at it, but be sure
you can reassemble that which you took apart. Don't be surprised if you
end with control boards and wiring all over the floor. The best news (for
you) would be to find that it's all in the power cord. That means you
could probably leave the machine alone and place a big hunkin' line filter
right at the cord entrance to the machine. (See K9YC's comments.)
If the problems are, in fact, from multiple sources within the machine,
you will probably need to use the "divide and conquer" approach to EMI
investigation, which means isolating the various sections or stages as
much as possible and then applying shields, filtesrs, etc, as required.
Keep in mind that you may not be able to kill it all to a point low enough
to preclude some interference. So, that goes back to either relocating
antennas or finding other activities when the laundry is being done.
Best luck and please keep us informed.
"Paul Christensen" <w9ac at arrl.net>
Sent by: rfi-bounces at contesting.com
04/04/2008 09:04 AM
<rfi at contesting.com>
Re: [RFI] AC Line filters- Direct-Drive Washers
For the past year, I have been fighting an issue with my own GE Harmony
direct-drive clothes washer. It's a great clothes washer, complete with
serial I/O port to the dryer and a touch-screen display. Unfortunately,
under 47 CFR 15.103(d) such appliances are still exempt from the specific
technical and certification standards, notwithstanding the general Part 15
requirement that a user of such a device holds no unconditional right to
use when it causes harmful interference to another service.
I suspect that the last time this section within Part 15 was revised, it
wasn't foreseeable that appliances like clothes washers could hold as much
processing power as a personal computer. The amount of RFI being
by this washer is mind-boggling. On 80M, it is producing signals at +50
dB/S9 every 50 kHz or so on my Icom 7800. If this RFI was loosely coupled
to a resonant dipole, I imagine that its effect could be heard to the same
extent as some QRPp transmissions -- it's that strong.
I have tried using some robust AC line filters on the line cord with zero
effect, but I know that I need to dig deep and attack the problem closer
the source. However, I need to first let the warranty period expire.
I had an opportunity to speak with two of the GE Harmony designers. They
were quite surprised when I found their direct inline-dial numbers on the
Internet. In fact, one of the engineers was responsible for the entire
digital interface. The first words uttered, were "look, we're exempt from
certification with that product." No further assistance was provided and
of course, this was the first complaint he had heard relating to the
Anyone have any similar experiences with the new direct-drive washers and
so, what specific remedy was used to mitigate RFI? I am completely
with the general concepts of RFI/EMI abatement, but I am looking for
case-specific solutions with actual experiences with direct-drive washers.
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