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
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