[Antennaware] 80m antenna for DX

David Gould 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 
radiation pattern.

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.titanex.de   (verticals)
www.spiderbeam.net  (fibreglass poles)

There are a couple of others which I will try and remember and post 
to you later

Dave, G3UEG

>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.
>Kind Regards
>Andre Zr5AG

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