[RFI] AC Line filters- Direct-Drive Washers

Jim Brown jim at audiosystemsgroup.com
Fri Apr 4 12:40:50 EDT 2008

On Fri, 04 Apr 2008 08:22:12 -0600, Larry Benko wrote:

>Perhaps it is now too late but why not return the offending appliance?  
>I bought a new large screen TV recently and told the store that I would 
>return it if it produced interference to the HF spectrum.  I even wrote 
>that condition on the sales slip prior to signing it.  Then of course 
>purchase with a credit card.  Fortunately the TV I bought was clean.  As 
>consumers our ultimate power is in the "pocketbook". 


>The first words uttered, were "look, we're exempt from 
> certification with that product." 

These words deserve to be shoved you know where. Returning the defective 
product is the only way I can think of to do that.   

>As an aside, since most of the interference produced by these appliances 
>is common mode current on the AC power cord and it should be fairly easy 
>to take a clip on current probe and connect it to a small hand held 
>receiver before purchase (if the store has the appliances powered). 

If it is, indeed, common mode on the power cord, that's pretty easy to kill 
with a good multi-turn ferrite choke on the power cord. No certification 
issues at all -- a common #18-3 IEC power cord can easily fit at least 7 
turns through a 1.4" i.d. toroid (I've done more) or a 1" i.d. "big 

>This solution has other problems in that if there are 100 other 
>appliances all plugged in the common mode current you measure may be 
>from some of them.  Still an S9+50 signal should jump out with this test.

The QRM of those other appliances will also mask direct radiation from 
internal wiring that is poorly shielded. And this lack of shielding is 
virtually impossible to fix short of a major science project.

>Perhaps we could really use a database of appliances that are "clean" 

I think this is a VERY good idea. There are no liability issues I can think 


Jim K9YC

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