[RFI] Looking for explanation...

[Don Kirk]

Hi Grant,

Treadmills are notorious RFI generators due to their variable speed
drives.  I suspect you are onto something regarding what outlet it's
plugged into versus how long the run is relative to resonance.  On my wifes
treadmill I had to add a choke on the power cord for common mode rejection,
as well as a commercial input power filter for differential mode
suppression.  Here is a link to a youtube video showing my treadmill RFI
and the two filters I used.

I always knew when my old neighbor was on her treadmill, and had a lot of
fun telling her so.

73,
Don (wd98dsb)

On Fri, Jun 26, 2020 at 3:35 PM Grant Saviers <grants2 at pacbell.net> wrote:

> Any surge protectors on the problem circuit?  Degraded MOV's can cause
> problems.  GFI outlets also.
>
> Grant KZ1W
>
> On 6/26/2020 10:30, Gary Peterson wrote:
> > 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
> >
> > _______________________________________________
> > RFI mailing list
> > RFI at contesting.com
> > http://lists.contesting.com/mailman/listinfo/rfi
> >
> _______________________________________________
> RFI mailing list
> RFI at contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>