[LCC] Sharing the wealth

[Randy Prewitt]

This is forwarded from Tom Webb, W4YOK in Plano, TX. Of course -- it's in reverse order with
Tom's inital email to the ARRL last on the list.  It concerns RFI from his new washing machine.
Randy K4LJA

----- Original Message ----- 
From: Thomas Webb 
To: Jack Hudson ; Jim Moore ; Larry Yates ; Randy Farmer ; Randy Prewitt ; Skip's Shack ; Wood DaveW 
Sent: Friday, July 30, 2010 1:28 PM
Subject: FW: RFI problem


I contacted ARRL about my washing machine RFI problem and received the following response.  My RFI isn't all that bad, so I'm not sure I'm going to do all of this stuff, but I thought it might be of interest to some of you.

 

Tom

 

From: Gruber, Mike W1MG [mailto:mgruber at arrl.org] 
Sent: Friday, July 30, 2010 1:15 PM
To: Thomas Webb
Cc: Hallas, Joel W1ZR
Subject: RE: RFI problem

 

Tom,

 

As Joel points out, there are certain absolute emissions limits that the manufacturer must meet.  If and when interference does occur from an otherwise legal device, it becomes the responsibility of the user to correct it or cease using the device.

 

As for a cure, Stu Cohen, N1SC was able to solve a similar washing machine RFI problem as follows:

 

1)  Add a common mode choke with a FT-240-31 or equivalent toroid core to the power cable where it enters the back of the machine.  Wind approximately seven turns of the cable around the core.  Keep the first and last turn on the core separated as much as possible.  This is to minimize any capacitive coupling in the choke.  (Note:  The maximum number of turns possible is limited by the size of the plug. You may want to remove the molded plug, wind the toroid with as many non-overlapping turns as possible, and then re-attach a screw-on 3-wire

plug.)

 

2)  Add a second common mode choke about six inches up the cable.

 

3)  Add a third and fourth common mode choke to the cable.  This may require (as it did in my case) an extension cable that I made to accommodate the chokes.  I used 12 gauge 3-wire cable and added the appropriate plug and socket to the extension. Be sure to observe proper polarity!

 

4)  For additional suppression, plug the cable into a brute-force AC line filter, such as the ICE Model 475-3 AC Line filter that appears on the Short Takes column in the March 2005 issue of QST.  Look for it on page 48. The filter wasn't necessary in my case; the four toroids were sufficient, but "your mileage may vary."  (Note:  If you use this filter, you may wish to experiment with the ground on connection on the filter for best results.)

 

In Stu's case, this cured the problem.  Good luck, and please let me know how it works for you if you try it.

 

Thanks,

73,

 

Mike Gruber, W1MG

ARRL EMC Engineer

 

ARRL - The national association for Amateur RadioT

225 Main Street, Newington, CT 06111-1400 USA 

Telephone: (860) 594-0392 

FAX: (860) 594-0259

Email: w1mg at arrl.org

World Wide Web: http://www.arrl.org/


--------------------------------------------------------------------------------

From: Hallas, Joel W1ZR 
Sent: Monday, July 26, 2010 11:59 AM
To: 'Thomas Webb'
Cc: rfi
Subject: RE: RFI problem

 

Tom,

 

The FCC does restrict the emission levels of "unintended emitters" in Part 15. Your manufacturer may or may not have a cure available, however, the ultimate responsibility to avoid interference may rest with you, the device user. 

 

I am copying ARRL Lab RFI Engineer Mike Gruber, W1MG, in case he has any additional, or different, information.

 

Regards, Joel

 

Joel R. Hallas, W1ZR

Technical Editor, QST

ARRL, the national association for Amateur RadioT

MTh;  860-594-0393

Tu,W,F(morning); 203-226-7353

 

From: Thomas Webb [mailto:sam9lives1 at verizon.net] 
Sent: Saturday, July 24, 2010 3:16 PM
To: doctor
Subject: RFI problem

 

Our new Kenmore Cabrio washing machine puts out rough-sounding pulses over most if not all of the HF spectrum, about 16 KHz. apart.  Do FCC regulations allow this?  Has anybody figured out how to fix it?

 

Tom Webb, W4YOK

ARRL Life Member

Plano, TX

 
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