On 7/10/2020 10:56 AM, Michael Aust via RFI wrote:
CorCom filters take care of Sym (In-Phase) & ASym (Out of Phase) RF EMI Issues which
can be betterthan ferrite type 31 cores on AC lines try to justattenuate Common Mode
suppression !MikeWB6DJI RF EMI Engineer
In my experience, common mode is dominant from an RFI perspective. When
a traditional AC line filter like Corcom products fixes an RFI problem,
it is when the filter is installed in such a manner that it causes the
Green wire to be properly terminated at the noise source, wheras without
the filter it would not be, due to th design of the fixture.
The principle here is that common mode is what radiates. A definition is
appropriate. What EMC regulations define as common mode is voltage
between neutral and the Green wire. What RADIATES is the common mode
current on the three wires, and most of this is on the Green Wire due to
it's improper (or non-) termination within equipment. The Green Wire
passes through traditional line filters, so they do nothing to suppress
this current.
Another fundamental principle is that twisted pair (or triplet)
inherently suppresses differential mode radiation, and, in my
experience, also helps with common mode. When I lived in Chicago, I
solved a lot of RFI from VHF TV transmitters to home stereo systems by
replacing the zip cord feeding the loudspeakers with twisted pair.
73, Jim K9YC
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|