[RFI] RFI Digest, Vol 42, Issue 1

Lee Hill lhill at silent-solutions.com
Fri Jun 2 16:53:15 EDT 2006

The noise source is either from the PWM motor control or the microprocessor.
The path is out the long AC power cable.  Twisting the wires won't help the
unless there was an unlikely huge design oversight with the placement of
return wires.  Beads won't help nearly as much as the line to line and line
to chassis capacitors inside the AC line filter.  The beads that most hams
have peak Z at 100-200 MHz, and will present maybe 10 to 50 ohms max at
20m, and probably much less at 75m.

If the AC power line filter doesn't fix it, it is possible the control and
power wires leaving the microprocessor board are the radiating antenna, in
which case the unit is probably exceeding FCC limits, since the radiating
antenna is so small and noise being detected is so big. And this problem is
non trivial to fix unless you work on EMI problems all the time. Much more
likely the AC power cord is the path/antenna between the source and the
rig's antenna.


-----Original Message-----
From: Leigh L Klotz, Jr. [mailto:Leigh at WA5ZNU.org] 
Sent: Friday, June 02, 2006 4:38 PM
To: Lee Hill; rfi at contesting.com
Subject: Re: [RFI] RFI Digest, Vol 42, Issue 1

In mine, the control and power lines are not beaded, and are not 
twisted.  The control lines are a random jumble of ribbon cables, all 
tied into a single wiring harness.  It may be that the signals are 
differential, but I doubt it.
On Fri, 2 Jun 2006 10:09 am, Lee Hill wrote:
> They are using PWM motor control to run the high speed motor.
> The problem is likely to be low frequency noise coming out the AC line 
> cord.
> I would buy a high performance AC line filter for a few bucks off ebay. 
> It
> will work tremendously better than even a correctly selected ferrite 
> alone.
> Mount the filter body directly to the washer, remove some paint so you 
> get
> direct contact. Use very short (less than 6 inches, this is only 75mto 
> 20m
> not 2m) wires between the line filter and the AC input of the washer. 
> Then
> use a different power cord to go into the line filter. Beware this 
> could
> void your warranty.
> Keep the wires between the washer and the filter far away from the AC 
> input
> cable and where it connects to the "line" side of the filter. The 
> "load"
> side of the filter connects to the washer. Make sure the filter current
> rating is above the max listed on the washer. Peak current can reduce 
> the
> performance of the filter.
> Insulate and cover the thing properly/securely so no kids, animals, or
> objects cause fire or electrocution.
> 73
> Lee
> -----Original Message-----
> From: rfi-bounces at contesting.com [mailto:rfi-bounces at contesting.com] On
> Behalf Of rfi-request at contesting.com
> Sent: Friday, June 02, 2006 12:00 PM
> To: rfi at contesting.com
> Subject: RFI Digest, Vol 42, Issue 1
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> Today's Topics:
>    1. Re: Washer RFI/EMI (Paul Christensen)
> ----------------------------------------------------------------------
> Message: 1
> Date: Thu, 1 Jun 2006 20:25:14 -0400
> From: "Paul Christensen" <w9ac at arrl.net>
> Subject: Re: [RFI] Washer RFI/EMI
> To: <rfi at contesting.com>
> Message-ID: <008301c685db$04d2e560$033ca8c0 at Dorm>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> 	reply-type=original
>>  I've had no RFI problems with my LG High Efficiency Washer/Dryer.
>>  It's quieter than my CRT television.
> I have +40 dB/S9 noise on 75M from a new GE Harmony Washer and can be 
> heard
> all the way up through 20M.  The dryer appears to emit no RFI/EMI.
> Is there a common cure among the newer generation of washers?
> Paul, W9AC
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