If both shields, ( ungrounded ) are tied together, and the two

At both ends?

This is the first mention of shields tied together, I certainly didn't
read that into Bruce's "with the shield left open on each end
".


That's because I added that to the mix. Bruce's comment was a
suggestion for me. I have not done this yet, but my original post
under this thread was solliciting comments on using twin coax to feed a
balanced antenna, or using a single coax feed under the specific set of
circumstances I outlined.


About the common mode current.... please explain how this would be an
issue with the outer shields of two coaxes, shields tied together but
going nowhere ( no ground ), and the balanced antenna fed by the two
center conductors. I do not see common mode current being a factor, but
I'm willing to listen and learn.


Ed