At 06:33 PM 6/27/2005, Art Boyars wrote:
>On the CQ-Contest Reflector K7QQ said: "You have to keep in mind that the
>best antenna doesn't exist. You can only get up what you can and it is
>never enough." Well that's where I am, but I'd like advice from you
>experts on how to improve my antenna, within my personal constraints.
><snip>
<snip>
>I've pulled the ends of the dipole as far as I can into the trees (maybe
>too far), but it still sags quite a bit -- 5 to 10 feet, by eye. Some of
>the sag is probably from the weight of the antenna wire and the feedline,
>but I think a lot of it is simply from the dipole's being longer than the
>span between the trees.
Doesn't take much weight in the middle to pull it down, even with thousands
of pounds of tension. It's that 1/sin(theta) thing.
>I have two seat-of-the-pants concerns. First, I may be getting losses
>from having the ends of the dipole in the foliage. Second, the vertical-V
>might be more NVIS-like than Iis good for me. Obvious solution is to
>shorten the dipole a bit, but that would make it even shorter than the
>recommended 100-ft minimum. So, first question for the experts: Do you
>think I'll do better to shorten it, or should I leave the ends in the trees?
My own experience has been that keeping the ends out of the trees, and
using a tuner to compensate for the non-resonant length, has been
better. The ends of the dipole are a high voltage point, and aside from
the arcing problem, the high voltage leads to higher losses in the leaves.
>Second-order solution and question: If it turns out that the feed line is
>weighing down the center, would I be better off to let it sag than to
>change to something more like TV twin-lead? (I recall some discussion
>here about Radio Shack selling a twin-lead with heavier-than-typical
>conductors.)
Let it sag... the radiation properties aren't all that much different
between a dipole with the angle being 120 degrees between the wires and 180
degrees (perfectly flat). However, if you do happen to have a resonant
length, 120 degrees included angle will be closer to 50 ohms than perfectly
straight (which has an impedance of 72 ohms).
>Thanks for your help.
>
>73, Art K3KU
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