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

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

Using the center conductors of two pieces of coax, with shields bonded
together, does create a balanced transmission line. . .

There's a semantic problem here. I and many others consider "balanced"
to mean non-radiating, which requires that the two conductors carry
equal and opposite currents. Others call any physically symmetrical line
"balanced". As I explained in another recent posting (and in the article
at http://eznec.com/Amateur/Articles/Baluns.pdf), making a line
symmetrical doesn't make it balanced -- that is, it doesn't guarantee
equal and opposite conductor currents and therefore doesn't guarantee
that it won't radiate. A coax line can be balanced and a symmetrical
twinlead line can be unbalanced.

Roy Lewallen, W7EL