Jim,
with respect to keeping the system all balanced and running the balanced
line through portals along with metal objects,
you can simply make a length of shielded balanced line using two pieces of
coax with the braids connected at each end and connected to shack ground on
the inside end. It becomes a shielded balanced line of twice the coax Zo and
can be directly inserted into the transmission path with no problems.

Check out "Some Aspects of Series and Parallel Coaxial Cable Assemblies" at
Cebik's site, in particular the "Series-Connected Coax" section

http://www.cebik.com/spcoax.html

73,
John



wrote in message
oups.com...
Greetings
I have been using balanced line for many years and am convinced of its
virtues, particularly since I use a single tuned doublet for multiband
use.
The question I have never been able to get a clear answer on is this;
How critical is it for the balanced line to avoid metal objects?
Specifically, I now use about 6 feet of LMR 400 coax from a Radio Works
remote balun into my shack where I tune the antenna from either a
manual tuner or the auto tuner in my FT920. In order for me to run the
twinlead all the way into the shack there will be about 18 inches where
the twinlead will share a portal that I constructed to get my grounds
and other cables in and out of the shack. Now I always thought this
was a problem area for twinlead, hence the use of the remote balun.
I am considering the purchase of a new tuner and was thinking I would
like a Palstar Balanced Tuner. But can I use it? Would I be better of
with a T match and a short length of coax to a balun, or would a
balanced tuner be better even with the 18" or so of twinlead coming in
close proximity to the other conductors?
I really can not bring the twinlead in without it crossing paths as I
desribed.
Is a balanced tuner all that better than a T match anyway in terms of
antenna performance or loss?
What say?
Thanks