Ted,
I agree with the recommendations to go with two dipoles on a common feed
point. I have two 40/80 inverted vees like this, apex @ 45', one for each
radio, and they work great on just about anything west of the continental
divide. The vee's are regularly 20+ db louder on west coast signals than my
verticals. I used to run JA's on 40 with one because it was better than my
phased verts broadside to JA. The qth is 100' above the valley floor going
to JA, so it's probably cheating. The 40m 4 square is much better now due
to the terrific noise rejection. But I've kept the vees because they are so
simple and useful.
I found that you only need to get the wires about 40-50 degress apart from
one another to get them to tune properly, so don't worry a bunch if you
can't get them at right angles to each other. Cut'em long and prune them
in.
Have fun
73, Kurt, K7NV
EUGENE SMAR wrote:
>
> Ted:
>
> You and I have corresponded before on NVIS antennas. I agree with Tom
> that you ought to raise the antennas above the roof with masts, pous mount
> them at right angles to reduce coupling.
>
> However, you are not looking for this system to grab DX - you're
> looking for close-in comm during island emergencies. Having a set of low
> dipoles (low above effective ground) will give you the sigs you want and
> need for local and inter-island communications.
>
> In my Novice and General class days at home, I used a three-dipole
> spiderweb antenna on 80, 40 and 20 just as you're suggesting. I used a
> tuner in the shack but still worked some satisfying DX (for a kid with 60
> watts and a deaf receiver above 14 MHz.) Bottom line is it will work for
> your intended purpose.
>
> GL es 73 de
> Gene Smar AD3F
> -----Original Message-----
> From: n4kg@juno.com <n4kg@juno.com>
> To: TOWERTALK@contesting.com <TOWERTALK@contesting.com>
To: <towertalk@contesting.com>
> Date: Wednesday, January 31, 2001 8:16 AM
> Subject: Re: [TowerTalk] G5RV or Dipoles
>
> >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
> >
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