On Wed, 6 May 2009 10:04:52 -0400, Dan Zimmerman N3OX wrote:
>No, cancellation is cancellation.
Think about where the magnetic flux is in a parallel wire line. It
is MOSTLY between the two conductors, but it also leaks out around
them. Now, wind that line around a core. Most points within the
ferrite core is closer to one conductor than the other, so it sees
more flux from that conductor than the other. In other words, the
flux in the core is not uniform, so locally, within the core, there
is not cancellation. If the core has significant loss, that
difference results in heating.
Coax is different. 100% of the flux associated with differential
current is contained within the coax dielectric. Only the flux from
common mode current is outside the coax and seen by the ferrite
core.
73,
Jim K9YC
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