"Ed_G" wrote in
.91:


Ed, you would be Much Better Off, if they would allow you to use (2)
runs of Coax, side by side up the mast, and connect only the Center
Conductor of each, to the tuner, with the shield left open on each
end and sealed against water intrusion.

What does this do, what does it achieve?

Owen



My expertise is weak in this area, but just guessing.... using
twin
coax in the above configuration, if the shields were grounded, would

But that is not what was said. I read it to say "with the shield left
open on each end".

allow the feedling between the antenna coupler and the feedpoint to be
'balanced' and yet the shields would not radiate as they would with a
single coax run.

Bunk. The only reason the shields would not radiate would be if they
carried equal but opposite currents. That is most unlikely in this case.

Let us just consider a simple example. Assumption is that skin effect on
the coax is fully effective, a reasonable assumption at HF.

Make a quarter wave vertical of a piece of RG213 supported on sky hooks.
Make no connection to the shield at either end, and connect the feed line
between a ground plane / counterpoise / whatever and the centre conductor
of the vertical piece of coax.

What current flows on the outside surface of the vertical coax?

The current on the outside surface of the vertical coax adjacent to the
bottom end of the isolated shield is the same as the current flowing on
the inner conductor adjacent to the same end of the shield.

Does the outer conductor 'shield' the vertical so that it will not
radiate?

No, the outside surface of the shield is the radiatior, it just has a
quarter wave o/c stub in series from the feedline to the radiating
element.



Perhaps others, here, will either expand on this, or correct my
misconception.


Owen