Hi Dave,
To: <towertalk@contesting.com>
>Date: Sun, 07 Nov 1999 22:18:29 -0500
>From: Dave Jordan <wa3gin@erols.com>
>
>Hi Folks,
>
>I've mounted a Butternut HF6V dead center on top of a 40ft by
>25ft by 16ft high steel quonset hut.
Well, you sure put that vertical in the right place! From that
mount, its efficiency will be as high as it can be. You won't be
loosing much to near field losses (beyond what is lost in the
antenna itself that is).
>Eight foot ground rods every 8ft on both side of the building,
>tied to each other and to the building.
These ground rods and connections are irrelevant for the
consideration of radiation takeoff angles.
>Anyone got a modeling program that can calculate the effect (if
>any) of the curved steel building on the take-off angle of the
>vertical on 80-20m.
My initial guess is that the building is not really large enough
to strongly affect the shape of the far field pattern. But if
the antenna is physically small enough, I suppose it _could_. I
am not intimately familiar with the HF6V. I'm assuming that it
is a base fed trapped six band vertical. But I have no idea of
its dimensions. Can you tell us what its effective length
(feedpoint to trap or end of element) is on each band of
interest?
Also, do you have any idea what the ground constants are in your
area? I used to live in the N.MD / S.PA area. Outside the
mountains, the earth was fairly poor even though it was usually
wet. I think it came in around 3 milliSiemens conductivity with
a dielectric constant of 13 or so in most places.
I can't directly model the building shape with the software I
have available at home. But I can easily determine if the
building is large enough that modeling it makes sense. If it
turns out to be a factor, you can post a more specific request
with more of the necessary details (possibly to the antennaware
reflector).
73, Eric N7CL
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