Rick wrote in
:


I'm planning a dipole installation fed with ladder line and a
wide-range antenna tuner.

I'd like to be able to use it on 160 through 10. A half wave at 160
meters is a bit under 260 feet. Is there any particular reason I
should limit its length to 260 feet? I have enough room to make it
about 320 feet... any particular reason I shouldn' t do that?

Thanks...

Rick

Rick,

It seems most people want to discuss optimum feedline length, though that
was not your question.

It turns out that it is quite challenging to obtain good efficiency from
a dipole less than about 35% of a wavelength long in the type of
configuration you propose. That sets a practical lower limit to the
length of the radiator.

On the other hand, the pattern changes with longer length. Probably the
most significant change occurs at greater than about 1.25 wl where the
pattern breaks up into additional lobes. Another respondent suggests such
pattern changes occur at greater than 0.5wl, but that is wrong. So, this
effect might set a practical upper limit if the pattern is an issue on
160m or a higher band if you intend multi-band operation.

So, if you made the dipole 320', it is 0.58wl on 160m, and 1.17wl on 80m.
The pattern will have two clear major lobes on both bands. You can't make
it short enough to avoid pattern break up on 40m without degrading
efficiency on 160m (though by only a small amount if you used 1.25wl on
40m).

As far as feedline loss, you know whether it is insignificant when you
have calculated the magnitude. Though others suggest that ladder line is
(always) insignificant, it is the loss in the ladder line that drives the
35% minimum practical length discussed above.

So, the choice depends, and probably mainly on whether you want to use it
also on 80m and 40m, and whether pattern is an issue.

Owen