Date: Tue, 30 Sep 2025 21:22:23 -0700
From: Jim Brown via TowerTalk wrote:
The shells and center conductors of connectors splicing two sections of line
exhibit skin effect just like any other conductor. The only difference are
the dimension of the shield as it goes through the connector(s).
73, Jim K9YC
Exactly, following EM theory the energy is contained in the interstitial space
between the inner and outer conductor. The CM currents are due to potential
difference between the outer surface of the shield and the capacitance with the
environment. This is why EM fields in the environment cause CM currents to
flow. CM Chokes therefore reduce external pickup from the coax in receive.
The reciprocal is true in transmit.
If you look at the magnitude of CM currents using an inductive pickup on
feedlines as I have you will see both CM chokes and grounding can reduce CM
currents at the shack, but the grounding is perhaps more problematic given it's
variable impedance as part of the changing environment. A well designed CM
choke as Jim well describes in his documentation can provide reliable CM
attenuation regardless of ground impedance I have such chokes on my single
feedline at the feedpoint, where it hits ground level and in the shack.
Cheers & 73,
Howie / WA4PSC
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