SMØIMJ wrote:
Hi all,
Anyone that have an idea about a wire antenna (folded dipole, trapped
something, etc.) that can be used on a limited space (e.g. on a smaller roof
11*6 meter)?
I mainly use verticals but need something for local (national) 80m QSOs.

cheers,
Hans / SMØIMJ

Paul's idea for the inverted-L is good, but I have found that length of
wire isn't effective use on 80 Meters. You could probably make it work
but there is no telling how well it will work.

I had one once that was a similar arrangement. Fed at ground level it
first went up about 30 Ft., then east for about 20 feet to a tree
branch, and then south for the rest of the run. Overall it was about
96 feet long. I fed it with a small choke on 40 meters and added a
series capacitor (250pF variable) on 80. A little pruning got SWR
down on 40 meters and the variable capacitor took care of 80. I
buried about 5 randon length wires (20-30 Ft) under the feed point.

Cecil suggested a loaded dipole and John suggested a trap dipole.
Both give a shortening effect and the trap dipole gives you more bands
to work. I used a home made trap dipole for 10-15-20-40 for many
years and it worked great. Once it was set up there was no tuning
on any of the bands. The only drawback is that in order to set it up
right you should have a grid dip meter and a antenna analyzer on hand.
You can do it with out them but it's much more difficult. It's usually
easier to borrow the necessary equipment from a friend. I would expect
that the tuning for 80 meters would be a little touchier than the
higher bands.

To help increase your available space you could raise the center of
the antenna in an inverted-v. Instead of having only 5.5 meters each
side of center, a 5.5 meter mast would extend that to about 7.5 meters.
Not a huge gain, but with the longer length, the coil for a loaded
dipole could be smaller making it more efficint.

--
Martin E. Meserve

http://www.k7mem.150m.com