[RFI] Any Issues with newer heating cooling systems

Paul Christensen w9ac at arrl.net
Fri Aug 28 09:44:19 PDT 2009

> Modern variable speed motors are notorious for REALLY severe RFI.
> They work by first rectifying AC to get DC, then creating a chain of
> square waves whose width is modulated to control the motor.

And the worst part?  When these devices are used in "appliances," the entire 
appliance is exempt from certification and is also "exempt from the specific 
technical standards and other requirements..." under Part 15.103(d):

"Sec.  15.103  Exempted devices.

(d) A digital device utilized exclusively in an appliance, e.g.,
microwave oven, dishwasher, clothes dryer, air conditioner (central or 
window), etc."

I especially like the "etc." part at the end.  The unintentional radiator 
segment of Part 15 has not kept up with the times -- or perhaps it has and 
lobbying power between large appliance manufactures and the FCC has kept 
subsection (d) alive and well during these times of significant technical 
advancement of our household appliances.

In my own kitchen, every major appliance is now controlled through a 
computer or CPU of one form or another, including my dishwasher, 
refrigerator, microwave oven, and range.  Oh, and the huge RFI producing 
clothes washer (also an exempt appliance), produces +40 dB/S9 interference 
on 75m.   It's so pervasive, that remedial RFI abatement techniques are 
useless.   A large induction loop around the drum sprays RFI directly and 
also cross-couples to unshielded cabling throughout the washer. A total 
nightmare.  For once, I cannot wait for a major appliance to break down.  I 
am hearing reports that newer direct-drive clothes washers are getting 
better in this regard.

Perhaps the ARRL can begin keeping a database of "RFI-friendly" appliances 
for prospective purchasers like myself who do not want to live with severe 
RFI during the lifetime of the appliance?

Paul, W9AC 

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