[RFI] Looking for explanation...

[Gary Peterson]

Periodically, I have been plagued with RFI from an unknown source.  It sounds like a washing machine, as far as the cadence is concerned, with a swish, swish, swish sound.  It will show several tracks on the 80 meter waterfall.  It will end abruptly.  Every previous time it has come on, it has quit before I could get to my gear together and DF it.  I had my equipment ready to go and when it came on and I dropped what I was doing and went outside.  My loop gave me a beautiful, deep null toward the neighbors house, about 300 feet away.  

I gave my neighbor a call and told him what I discovered and asked him if he had been running any appliances a few minutes earlier.  He told me his main squeeze had been on the treadmill.  My neighbor is a ham, who has not been active for about a decade.  He turned on the treadmill and there it was!  Source found.  The treadmill is a PowerTread, I was told.

I gave him an EMI filter to try, that I had found in a box of assorted electronic parts purchased some time ago.  The filter is a TDK, model ANF-106U.  My neighbor plugged it into the outlet and plugged the treadmill into the EMI filter.  The filter knocked the RFI down by a couple of S units, but I could still hear the swishing.  Next, he plugged the treadmill, via an extension cord, into a different outlet, without the EMI filter.  No interference whatsoever was heard or seen on the waterfall.

Is it possible that the wiring from the nearest outlet, back to the service panel, is resonant on 80 meters?  Or, is it more likely that a connection might need tightening in the outlet box or breaker panel?  He does not know whether the troublesome outlet and the good outlet are on the same circuit or not.  I had him check both outlets with an outlet tester, thinking that he might have a mis-wired outlet.  Both checked OK.  He is afraid to get into the troublesome outlet box or his electrical panel.  I volunteered, but he doesn’t want me to take the risk.  When I was in broadcasting full time, I was inside more electrical panels than I can count, but I respect his wishes.  Before I hire a licensed electrician to check my neighbor’s wiring, I would like to have a better handle on the probable cause.

Any thoughts as to the explanation for this rather odd behavior will be most appreciated.

Gary, K0CX