And yet with coax there is no "inside or outside". The shield wires are
woven and pass over and under each other. No different than at a connected
junction with a connector.
The fields are still maintained separately.
jim ab3cv
On Wed, Oct 1, 2025 at 2:52 PM Wes Stewart via TowerTalk <
towertalk@contesting.com> wrote:
> Jim,
> I think you're missing Jack's very interesting point. I've used an open
> ended cable as an example, but a mated pair of your favorite connectors is
> no different.
> At the very end of the cable (or connector) there is no inside and outside
> of the outer conductor, there is just the conductor, hence there is no skin
> effect at that point. I'm not smart enough to figure out how far down the
> cable the skin effect develops. But this raises a question in my mind.
> We've all seen a thousand times the drawing of a coax-fed dipole, where
> current is "spilling over" the open end and becoming a common-mode current
> on the outside of the cable. A smarter mind than mine needs to 'splain
> this to me.
> Wes N7WS
>
>
>
> On Wednesday, October 1, 2025 at 10:28:53 AM MST, Jim Brown <
> jim@audiosystemsgroup.com> wrote:
>
> On 10/1/2025 7:46 AM, Jack Brindle via TowerTalk wrote:
> > Connectors are very important in this system. They must be added to the
> analysis. Without them, we have to question the validity of the tests.
>
> No. Common mode and differential mode currents are a characteristic of
> transmission lines, and common mode can be present on 2-wire lines if
> the system that includes the antenna, the transmission line, and
> termination in the shack has imbalance. The mechanism by which common
> mode in coaxial line is on the outside of the shield is skin effect, and
> it's present in those connectors.
>
> Soldered or crimped, the connector(s) is/are simply part of the
> transmission line, carrying the differential and common mode current
> that is in that system (antenna, line, shack). Depending on their
> construction, they can introduce some discontinuity in the differential
> circuit.
>
> 73, Jim K9YC
>
>
>
>
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