> I know Bob W7LR is using 90 ft verical for both bands but maybe its
> better /for 80m/ to use "isolating trap" between the hat and the top of
the mast?
> I will build in a Summer so I still have a time but its important for me
to know
> what the height will be the best so which construction to choose.
Rys,
The performance difference between a base loaded 90 ft vertical and top
loaded is unimportant if the ground system is good. Loading location is not
so important.
With noticeable ground losses, you would want radiation resistance as high
as possible. That occurs when ampere-feet of antenna is as large as
possible, so you want current maximum over the length of the antenna as long
as that does not increased loss in a loading coil or something similar.
The problem is mostly on 80 meters. I have had poor results with 1/2 wl
verticals on 80. Even on 160 my 318 foot tower is not much better than a 1/4
wl vertical, and gives up a good amount of performance at modest distance or
at sunrise or sunset.
On 80 meters, I have found this worse. Some of my poorest 80m verticals have
been 1/2 wl or taller verticals.
If you find performance on 80 lacking, you could use a 1/4 wl skirt for 80
meters and feed it. Then you do not need traps, and the bandwidth would be
much wider. But I would still try the vertical and see how it behaves for
you without anything special. You could install the skirt, and not connect
it unless needed. It would allow you to do an A to B test and tell us all
the results.
73 Tom
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