[Antennaware] 80m antenna for DX
dave at g3ueg.co.uk
Sat Dec 16 07:20:46 EST 2006
Would you be able to lay a reasonable number of radials? at 15m to
25m length, 60 plus would be good.
If so I would suggest a vertical. Its height perhaps depending on
what you feel the neighbours would tolerate. With good engineering
it is possible to put up a self-supporting vertical for 80m. I
think *NOT* having guy ropes would help the visual impact.
A typical 1/4wave vertical would be 20m (66ft)
If you can go taller to around 23m (75ft) then the feed impedance
would be around 50 + jXX and you can then tune easily with a series
variable capacitor bandwidth which would be good because of no lossy
inductors and easy to adjust.
If you have to go shorter than 20m, it is best to load with a
capacity hat, at or near the top but this does tend to make the
mechanical side a bit more difficult.
Another option if you have suitable supports is to use a T antenna
where the top of the T acts as the loading but still gives a good
If you have to use inductive loading try if possible to put it a half
to two-thirds up the vertical. Try to make the loading coil as good
as possible use thick wire or small diameter tubing (see that used
for gas supply in caravans or mobile homes) and make the length
approx equal to the diameter. Base loading is the least efficient but
generally easiest, as they say there is no free lunch!!
Going up from this there is always a four-square!!!
To get some ideas have a look at
www.spiderbeam.net (fibreglass poles)
There are a couple of others which I will try and remember and post
to you later
>Good day to all,
>I am new to the list and hope I am not flogging an old horse. I want to put
>up a dedicated 80m antenna for DX work.
>I have reasonable space but do not want to annoy the neighbours too much.
>Have excellent take off -360 deg. Have no idea what the electrical
>properties of the ground/soil is like. My QTH is on the east cost of South
>Africa about 30 km south of Durban and about 1.5 km from the coastline at
>about 85m elevation. Full frontal sea view so salt deposits during summer
>might be a consideration.
>Any advise would be welcome.
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