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Re: [RFI] Variable speed drives

To: "Kelly Johnson" <n6kj.kelly@gmail.com>
Subject: Re: [RFI] Variable speed drives
From: dgsvetan@rockwellcollins.com
Date: Tue, 27 Mar 2007 09:36:38 -0500
List-post: <mailto:rfi@contesting.com>

Judging from the other posts, your comments about the LG pair got a lot of
attention.  That's great to know and thanks for passing along the model
numbers in your latest post.

You are mostly correct with your comments below.  I say "mostly" because,
to be honest, the fundamental electronic generation of the variable speed
drive power is, by design, an RFI generator.  (The drive electronics use
switchmode technology, with a variable frequency, the create the varying AC
drive power for the motor(s).  If true linear power amplifiers were used
[very inefficient!}, then there would be little or no RFI.)  As the LG
design seems to show, the "hash" can be reduced to acceptable levels if the
correct engineering and production techniques and materials are used.  So,
I agree that these devices do not need to cause RFI, but most do because of
little or no concern over the RFI issues.

Academic question for thought: one has to wonder if the reduced RFI from
the LG machines has anything to do with the fact that LG also markets TV
and audio equipment, as well as cell phones.  Maybe they actually have some
EMI/EMC engineers on their staff?  Inquiring minds are curious.

73, Dale

             "Kelly Johnson"                                               
             .com>                                                      To 
             Sent by:                  rfi@contesting.com                  
             rfi-bounces@conte                                          cc 
                                       Re: [RFI] Variable speed drives     
             03/26/2007 06:24                                              

Variable speed motors don't necessarily have to cause RFI.  I bought
an LG High Efficiency Washer/Dryer pair 1.5 years ago.  It clearly
uses this type of microcontrolled technology and it is RF quiet.
There is less RFI from these devices than from my 13 year old CRT
television.  My tower is only about 30 feet away from the washer/dryer
and 65 feet tall.  I've never heard a peep from them.  My FT-817
doesn't register anything on the S-Meter until it is about 12 inches
from the front panel where, I assume, the micontroller is.  My FT-817
registers noise from my TV at about 24 inches.

Some manufacturers cut corners and build junk and others know how to
shield things properly.  Variable speed motors aren't the problem.
Bad engineering of whatever technology is the problem.

What we really need (and will never get) is an FCC requirement that
manufacturers fix, replace, or refund money for any device found to
cause harmful interference.  The real problem is that there isn't
enough incentive on the manufacturers to clean up their act.  There
aren't enough hams to make it an issue.  The manufacturer just tells
your neighbor that "it's that ham operator's fault".  If the consumer
could force the manufacturer to resolve the issue (or refund your
money) things would be much better.  Unfortunately, it will never

On 3/26/07, dgsvetan@rockwellcollins.com <dgsvetan@rockwellcollins.com>
> All,
> Knowing the many previous posts on this reflector regarding variable
> drives for home applications, here is an article that probably will not
> make you rejoice.  There is a lot of interesting information, but I am
> you all will note the complete non-mention of RFI.
> 73, Dale,
> http://www.electronicproducts.com/ShowPage.asp?Filename=irf.aug2006.html
> _______________________________________________
> RFI mailing list
> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
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