Topband: Elimination of Treadmill RFI on 160 meters

[Tom W8JI]

> are talking about current that is flowing in the same direction on three
> conductors."  In my case the additional Toroid core choke had a very
> noticeable impact, and I now can't tell when the treadmill is on when 
> using
> the combination of both filters.
>
> P.S. I sent an e-mail to the manufacturer of our Treadmill, and they never
> responded.  I am now going to call them on the phone in an attempt to get
> in touch with their design engineers, and likely will also file a 
> complaint
> with the FCC regarding treadmills in general.  There are a couple more
> treadmills near my home that generate very strong RFI, but fortunately 
> they
> normally use their Treadmills during the day, and I operate mostly at 
> night.

The FCC requires testing of power line conducted emissions with a line 
sample unit that connects from each conductor to ground. One LISN is 
specified to go from each current-carrying conductor to ground. The safety 
ground, since it does not carry current, is grounded.

The flaw in this system is that differential voltages between current 
carrying wires are not measured, and anything on the safety ground isn't 
measured.  Noise voltage is only measured from individual current carrying 
conductors to ground, and the safety ground is grounded and not measured.

Filters inside devices and many outside filters often route the noise right 
out on the safety ground, in differential to the equipment case (if large it 
acts like a groundplane) or other connecting wired systems like a Telco line 
or data interface cable.

Since the FCC mandates the safety ground and other grounds be grounded to 
the test equipment RF measurement groundplane, that path or ground loop 
paths are not measured. This allows some pretty ratty stuff to pass FCC 
tests.

The FCC should have created a better test, instead of assuming all grounds 
in the real world were common-connected with near zero impedance.

73 Tom