If your BalUn has already done the bigger job of turning a High Z to a
modest one, the common logic for the need for twin line has also been
diminished.

Yes but my question regarded the advantage of twin-lead vs. coaxial in that
particular application where impedance is uncontrolled.

73

Tony I0JX

On Mon, 5 Oct 2009 21:17:26 +0200, "Antonio Vernucci"
wrote:

Yes but my question regarded the advantage of twin-lead vs. coaxial in that
particular application where impedance is uncontrolled.

http://www.vk1od.net/calc/tl/twllc.htm

73's
Richard Clark, KB7QHC

"Antonio Vernucci" wrote in
:

If your BalUn has already done the bigger job of turning a High Z to
a modest one, the common logic for the need for twin line has also
been diminished.

Yes but my question regarded the advantage of twin-lead vs. coaxial in
that particular application where impedance is uncontrolled.

Tony, it depends on the details of your scenario, and may be different at
different frequencies.

Unless you believe in the myth that ladder line is *so* low in loss that
you *never* need to consider it, you need to calculate it out to really
know... it is not a no-brainer as we say, in fact it is a quite complex
problem to solve (mainly quantifying the loss and transformation in
transformers which both Roy and I have mentioned in this thread).

BTW, from time to time I see articles that recommend twin line for direct
feeding a ground mounted vertical (ie without using a balun at the feed
point). It is as insane as using a 4:1 voltage balun with coax at the
base of such a vertical, because both types of feed drive substantial
common mode current on the feed line. A review of such an article is at
http://vk1od.net/antenna/multibandun...tical/BSUM.htm , this one
using a magic ingredient, Belden 8222 twin feedline which Belden ceased
manufacturing. But... I am sure some hams have got the QSLs to prove that
it "works real good".

Owen