Dishwasher QRN to my K2 sn 1031

[Kenneth A. Christiansen]

I bought a Frigidaire dishwasher made by Elecvtrolux in January of 2005. It
is a model gld2450rds0. I did not realize it at first but it is the source
of my high QRN. I used my IC-746PRO to make the following observations
because it will pick up AM but the interference is just as bad on my K2 sn
1031. The background noise was S5 on 20 meters with the AM mode, 9 kHz
filter and a dead frequency of 13990 selected. All cycles of the dishwasher
except the wash part have a noise level of S6 to S7 which is still something
I could live with. Every time the actual washing starts the noise jumps to
10 DB over S9 and stays there until it shuts down to pump out,  add water or
dry. I looked at the output of my IC746-PRO with the water fall of Digipan
and see a consistent pattern from about 300 Hz to 1500 Hz but while there
may be more 120 Hz spaced peaks in places on the spectrum there are also
other spacing. The peaks do not move as I change the VFO on the ICOM so it
is a broadband noise. I have a portable radio and find noise all the way
from 2 mHz to 20 mHz. The noise seems to get into the wiring and plumbing of
the house and drops off rapidly if I take the portable radio outside. If I
use Digipan with the  SSB mode then I do not see the peaks. I just see white
noise across the entire receiver spectrum.

Now I am hoping someone on this list may have some information about curing
the noise from this dishwasher. Can some sort of beads be added around the
power line or is there a filter that can be added. The dishwasher draws 9
amps so any filter would have to be able to handle the high current.

My K2 and I have been having trouble with this noise since January of 2005.
The noise is so much stronger than almost every signial on the band that the
band sound as though there is no activity. The reason we did not figure it
out sooner is that just starting the dishwasher does not start the noise. It
doesn't happen except when it is in the actual wash parts of the cycle.

Thank you for any help.

Ken Christiansen W0CZ
[hidden email]

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Jim Brown-10]

On Wed, 13 Apr 2005 14:29:46 -0500, Kenneth A. Christiansen wrote:

>is a broadband noise. I have a portable radio and find noise all the
way
>from 2 mHz to 20 mHz.

Some thoughts. First, this issue has been discussed on the RFI list, and
there are some RFI specialists who hang out there. A study of their
archive is in order.

Second, there are two basic ways the RF can be getting out of the washer
-- radiated directly from an unshielded cabinet, and conducted on the
power wiring. I suspect the power wiring.

The first solution I would try with that is to form a common mode low
pass filter on the power line. The easiest way to do that is wind as
many turns of the power cord as you can around a 2.4" #43 toroid
(commonly called an FT240-43), AND add bypass capacitors (around 0.05uF)
from both sides of the AC line to the ground, and make sure the chassis
of the machine is tied to this same ground.

So, coming out of the machine, there's the choke, followed by caps to
ground. That is, the caps are on the LINE side of the choke. AND there's
a bond that does NOT go through the choke between the washer and the
equipment ground at the outlet. This bond should be as short as
possible, because it can be carrying some of the trash, and that trash
can radiate.

As to the number of turns: you probably can't put too many on it. I
would aim for at least 7 turns, and try for a few more. What happens
when you do this is that the ferrite choke develops a broad peak in its
impedance that is actually a resonance between the inductance and the
stray capacitance, and with the resistance of both the wire and the
ferrite thrown in. With more turns, that resonance will move down in
frequency. I've been working with Mike, W4EF, on a research project on
these toroidal chokes, and will publish the work this fall. Mike's data
shows that anything from about 7 to about 10 turns is ideal for 3.5 - 20
MHz, and the greater number of turns will help things on 80 and 160.

If this solution doesn't make a dent, the trash is getting radiated. In
that case, I would call the mfr and tell them to fix it.

Jim Brown  K9YC


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Ron D'Eau Claire-2]

Jim makes excellent suggestions.

If you have a battery powered radio, you can tell if the RFI is arriving
through the power line. One thing that I'd check before going too crazy
chasing possibilities is to be sure the metal frame and cabinet is grounded.
It should be, but sometimes the ground has to be attached during
installation and it gets left off. A quick check between a known grounded
outlet and the case with an ohmmeter should show a ohm or two at most.

Ron AC7AC


_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com