In article ,
Owen Duffy wrote:

A simple program or spreadsheet ought to be able to do the necessary
calculations... try every wire length from 66 feet to 132 feet and see
if you can find a length which is a comfortable percentage away from
an even multiple of 1/2 wavelength on each frequency. Or,

You probably mean't any integral multiple of a half wave.

You're right... integral multiple of a half-wavelength, or even
multiples of a quarter-wavelength are two alternative ways for stating
the lengths to be avoided (high feedpoint Z).

alternatively, iterate through each frequency, calculate the
1/2-wavelength multiples, and "blacklist" every possible length which
is too close to these multiples.

I have done just that, and searched for "sweet" wire lengths that aren't
within say 5% of band edge for all HF bands. It sounds like a solution to
the problem doesn't it. (5% implies that you have a pretty determinate
scenario, which is a big assumption. IIRC 10%+ will not give a practical
result on the higher bands.)

Problem is that it probably unecessarily constrains the solution.

Entirely possible!

The input impedance and the feed point voltage of an end fed wire at its
higher parallel resonances falls, so that whilst you might want to avoid
the first such resonance, the impedance (and feed point voltage) at the
third or higher resonance might well be low enough to not worry about it.

And, even if it was a bit high, you might not need to be more than a
couple of percent away from it to get it down to a length that might
work.

Odds are that some amount of experimentation is going to be required,
at any given installation, to find a wire length which tunes up well
with these ATUs. The orientation of the wire (vertical, inverted-L,
etc.), height about ground, presence of trees and metallic objects,
and (perhaps most importantly) the details of the ATU's grounding
system, are likely to change the impedances around enough to make the
"textbook" answers less than completely effective.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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