Joe,
How about capacitive end loading for shortening your antenna? As far as I
know, it's the most efficient type of loading.
You could let the ends droop and attach basic spoke and perimeter wire hats.
Fashion the hub of each hat such that you can adjust its position on the
radiating wire for tuning.
I've made a shorty forty dipole with this method. I don't have anything more
than a gut feeling for the size you need. Since you have modeling software,
start with a 4 spoke hat, having a single perimeter wire of, say, 4ft
diameter.
I guess you would also want to have tag lines to stabilize the hats in the
wind, and minimize variable interaction with the suspending towers.
You could also possibly use forked ends on your wires, and vary the angle of
the fork with tag ropes to vary the capacitive effect. This might be easier
to model than the hat assemblies.
Some ASCII ART to illustrate:
end of horizontal radiator
-------------------------+
|
|
/^\ ends droop with fork
/ \
/ \
--...MARK_N1LO...--
Joe writes:
<<Jim and Tom, many thanks for your replies. Let me tell you what I'm up
to.
I would like to put up an 80M EDZ between two towers. However, my
towers are only 300' apart and I need about 340'. I have considered
drooping the ends vertically, but I thought either a folded dipole or
linear loading a few feet on the ends with ladderline would allow me to
fit it inside the 300' span. I use EZNEC 4+ for modeling.
I wonder if minimal lengths of ladderline for linear loading on each end
would provide the shortening while making the high resistance losses
arising from lower Q negligible? I haven't tried modeling it yet. I
thought I'd first see if anyone had successfully modeled ladderline as
an antenna element. 73, Joe >>
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