John, N9JG wrote:
What do you mean by optimum length since open-wire feedline has minimal
loss?

By "optimum length", I mean the length where you can
switch your antenna tuner into bypass mode and obtain
a 50 ohm SWR of less than ~1.6:1. For any dipole that
is 1/2WL on the lowest frequency of operation, that
will be at an SWR current maximum point making the
antenna plus tuned feeder system resonant without a tuner.

On 20m, for example, if one can vary the ladder-line
length by plus or minus 15 feet, one can always locate
the SWR current maximum point and usually bypass the
antenna tuner. I have a 20m 1/2WL dipole that I use
on 20m, 17m, 15m, 12m, 10m, and 6m without a conventional
antenna tuner by simply varying the length of the
300 ohm ladder-line.
--
73, Cecil http://www.w5dxp.com