Re: [RFI] Smoothfitness 6.25 Treadmill RFI

[Jim Brown <jim@audiosystemsgroup.com>]

The AC line filter ONLY works on differential mode signals, and the 
ferrite choke ONLY works on common mode signals. So yes, both are present.
Remember that what the power world calls "common mode" is voltage 
between neutral and green. Our definition of common mode is the complex 
sum of the current on all the conductors, and in most products, that's 
on the green wire, because it's not terminated properly inside the 
equipment. The green wire goes past commercial line filters, so they 
have no effect on it.  The exception would be a commercial line filter 
that physically mounted (and bonded) to the shielding enclosure of the 
noise source, which is likely to be effective.
73, Jim K9YC

On Tue,9/13/2016 10:56 AM, Lionel Booth wrote:
> Don,
>
> It was my experience also with the Delta line filter on the 
> NordicTrack.  Installing it made a dramatic improvement.  That said, I 
> added toroid cores per Jim, in and out, and virtually eliminated the 
> problem.  The toroids alone helped quite a bit but it took the Delta 
> to really kill the problem.  In the case of this treadmill I'd say 
> that the power supply is adding the every 17 Khz, (these seem pretty 
> much constant with speed but change a bit with load) or so spikes and 
> the PWM driver is the wideband perpetrator.
> I have spectrum display captures from SDR if anyone is interested.
>
> But I think if the noise is CM conduction on the AC Line then perhaps 
> the AC line filter wouldn't be effective, yet is seemed to be.  Could 
> it be not strictly CM?
> Both approaches seem needed.  These are tough cases but at least in my 
> house.
>
> > From: wd8dsb@gmail.com
> > Date: Tue, 13 Sep 2016 13:36:52 -0400
> > To: jim@audiosystemsgroup.com
> > Subject: Re: [RFI] Smoothfitness 6.25 Treadmill RFI
> > CC: rfi@contesting.com
> >
> > Jim (K9YC) and gang,
> >
> > Based on my experience with treadmills, a commercial AC line filter 
> is not
> > a waste of time, but normally it needs to be used in conjunction with a
> > K9YC type toroid core choke to have maximum reduction in RFI. As an
> > example you can check out the youtube video at :
> > http://www.youtube.com/watch?v=VO5DcVSw3M0 which I created a few 
> years ago
> > demonstrating treadmill RFI and the elimination of it.
> >
> > (I really need to go back and update this video using a spectrum display
> > captured with an SDR receiver).
> >
> > I would also not characterize the treadmill noise as coming from a SMPS,
> > but rather originating from a variable speed drive (same issue regarding
> > high speed switching, but calling it a SMPS is probably too much of a
> > generalization).
> >
> > I've also found commercial AC line filters very useful in reduction or
> > elimination of other equipment that contains variable speed drives
> > (injection molding machines, HVAC systems, etc.).
> >
> > Don (wd8dsb)
> >
> >
> >
> > On Tue, Sep 13, 2016 at 12:52 PM, Jim Brown <jim@audiosystemsgroup.com>
> > wrote:
> >
> > > On Tue,9/13/2016 8:44 AM, Lionel Booth wrote:
> > >
> > >> My question to the group is whether there is any specific 
> experience with
> > >> this manufacturer as guidance when I rip into this monster?
> > >>
> > >
> > >
> > > Lionel,
> > >
> > > The noise is produced by a switch-mode power supply inside the 
> unit, and
> > > is probably radiated as a common mode signal by the AC wiring. 
> That part of
> > > it can be killed by winding the power cord through one or more #31
> > > Fair-Rite cores to form a common mode choke. Follow the guidelines in
> > > Chapter 7 of k9yc.com/RFI-Ham.pdf for the bands where you hear the 
> noise,
> > > and for coax the size of the power cable. That is, if the power 
> cable is
> > > the diameter of RG59/RG8X, use the guidelines for that coax.
> > >
> > > There may be more noise radiated from internal wiring. For that, 
> you'll
> > > need to go inside the box.
> > >
> > > AC line filters are a waste of money for this sort of problem.
> > >
> > > 73, Jim K9YC
> > >
> > >
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> > >
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