There are two situations where a horizontal 1/2 wave and a vertical 1/2 wave
couple minimally:
a) where the center of the vertical is in the line which is the extension of
the line of the horizontal element off its ends. This gets to be a fuzzy
concept if the horizontal element is supported in the center and droops
significantly.
b) where the vertical is in the plane that is perpendicular to the horizontal,
and at its center. This is not sensitive to horizontal element droop.
In either case, miscellaneous semi-resonant conductors common to the near field
of both may accomplish a two-stage unwanted coupling. Such must be modeled to
see whether this coupling is large or small. This includes feedlines not
sufficiently isolated from the intended radiating conductors.
The b) situation fits your question, with a caveat for maximum separation:
since the yagi will be a bit offset to one side for the boom to mast bracket,
and the vertical will be offset by its mounting device, position the vertical
offset to place the vertical as close as possible to directly vertical over the
beam's boom.
That should remove (minimize) yagi front to side issues with an overhead
vertical.
NOTE: if you are really talking about a ground plane, as opposed to a coaxial
dipole, larger radial elements sometimes have unequal currents in the
individual radials. This will allow some degree of coupling to the horizontal
to take place.
Short tuning "radials" like those on an R8 actually have relatively small
current compared to the electrical center of the antenna, and are unlikely to
have any significant effect.
Good Luck.
>
> From: "JerryC" <jerryc@netscope.net>
To: <towertalk@contesting.com>
> Date: 2001/05/14 Mon AM 11:54:09 EDT
> To: <towertalk@contesting.com>
> Subject: [TowerTalk] Vertical over 4 el yagi
>
> After changing my mind several times I need advice. I was planning
> a 4el 10M yagi at about 40' (3' above the tower top) and wanted to
> install an imax 10/11M vertical at around 48' to 50'. I have seen this done
> with
> antennas on different freq. but am getting different advice on using both
> these for 10M. I don't think the yagi would affect the vertical but not
> shure about the other way around. I was told the gain would remain
> o.k. on the yagi but the side and rear rejection might suffer based on
> how far the vert. is mounted above the yagi. Any experience or ideas on
> this??
> Thanks
> JerryC
> jerryc@netscope.net
> no call sign yet (still working on the code)
>
>
>
>
>
>
> List Sponsor: Champion Radio Products - We'll be at the Dayton Hamvention
> with all of our safety equipment and other products. Stop by booth #559 and
> say hi.
> <A HREF="http://www.championradio.com";>www.ChampionRadio.com</A>
>
> -----
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>
>
>
>
List Sponsor: Champion Radio Products - We'll be at the Dayton Hamvention
with all of our safety equipment and other products. Stop by booth #559 and
say hi.
<A HREF="http://www.championradio.com";>www.ChampionRadio.com</A>
-----
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