Does the G5RV require a tuner for one or both bands?
80 / 40 dipoles can be made independent of each other
by placing them at right angles to each other with a single
feedline. As the wires come closer to each other, there
will be coupling effects which may require retuning,
especially on the 40M wires.
Assuming there is a LOT of metal in / near the roof, the
effective height of the dipoles OVER the roof will be the
height above the roof, i.e., it would be good to have 30 ft
masts for support which will reduce coupling effects to
the structural metal while still directing the signal UP for
high angle local coverage.
One DXpedition to SE Asia reported using dipoles over a
roof on 80 / 40. They had the WEAKEST 40M signal I
have ever heard from SE Asia on 40M (339 vs 559 signals
for 100W and vertical stations) and they had amplifiers.
They were ESP on 80M except for one isolated transmission
where their signal came out of the noise enough to verify their call.
Dipoles OVER a building roof are NOT good DX antennas
unlesss they are elevated well above the structual metal.
de Tom N4KG
On Wed, 31 Jan 2001 "Ted Leaf" <tleaf@hotmail.com> writes:
> Hi Guys,
>
> We are thinking of replacing our old G5RV at the hospital with a new
> G5RV or two dipoles on a common feed point cut for 40 and 75M.
> We want this for
> local emergency communication among the islands out to 250 miles.
> We have a tuner. Antennas will be above the 3rd story roof.
>
> Any recommendations?
>
>
> 73, Aloha
> Ted Leaf, K6HI
> Kona, Hawaii
> <tleaf@hotmail.com>
>
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