I would recommend NOT using baluns in connection with open wire line.
It's hard to guess what impedance they would see at a particular
frequency location along the line, and they do not work well nor with
low loss when they are mismatched. In general, they will always be
mismatched in your situation! For the coaxial sections you contemplate,
use one short coaxial cable for each side of the balanced line, tying
the shields together at the ends. Seal those ends against the
weather. These transitions maintain balance with relative immunity from
proximity to external conductors. You will have large mismatches at
those junctions, which is why you use as little coax as will reach. You
will tune out the mismatch with a tuner in the shack anyway, so small
consequences if any. It's best to use a truly balanced tuner for
balanced feedlines for the reasons mentioned above. In such a
well-designed setup, the necessary balun is at the INPUT of the tuner,
contrary to manufacturers with a few exceptions. Hope this helps and
good hunting! 73 de Allan, W1AEL in Tennessee, USA.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|