The shield has to be modeled as a wire in it's own right. It's in the
other element's fields. If you break the shield connection at the
relays then it's short, nonresonant and of small effect. Otherwise
it's a wire connected to one of the same size (via the shield
connection) on the other side, connected to the feedline to the shack,
possibly the tower, not short, and in play.
73, Guy.
----- Original Message -----
From: "Pete Smith" <n4zr@contesting.com>
To: <K3BU@aol.com>; <towertalk@contesting.com>
Sent: Saturday, May 31, 2003 8:01 AM
Subject: Re: [TowerTalk] Feeding one antenna in a stack
> At 07:31 AM 5/31/03 -0400, K3BU@aol.com wrote:
> >See if you can model feedlines from antennas that are connected by
their
> >shields (as just about all antenna switches do) and their centers
open and/or
> >shorted, and the combinations.
>
> I don't know how to do this, but agree that it would be a closer
simulation
> of the real world. I've seen models of dipoles with transmission
lines
> attached, where the physical shield is represented by a wire
connected to
> one side of the dipole, with the other end floating. I don't know
what
> would happen if you connected the "free" end similarly to another
dipole,
> as if it were the driven element of a second yagi. It's something
to try.
>
> >
> >
> >Similar situation presented problem when I tried to use WX0B
StackMatch to
> >feed three vertical triangular array, which uses "disconnected"
feedlines to
> >make two radiators act as a reflectors. Contrary to WX0B claims it
didn't
> >work,
> >hardly any F/B or pattern - almost perfect "3 el. omnidirectional
array".
> >Some
> >Eu hams had similar experience and found that you need to
disconnect the
> >shields too (StackMatch connectors are all mounted on the metal
box).
>
>
> My 4-element lazy-vee array is also built this way, in a plastic
box, with
> both the shields and the center conductors floated. I did it this
way,
> even though it is a pain in the neck, because it's what K3LR said
one
> should do, but don't understand the theory. I would have thought
that an
> open stub with its shield grounded at the open end and connected to
the
> shields of other similar stubs would still have functioned as an
open stub,
> but don't know. Can anyone explain?
>
>
> 73, Pete N4ZR
> The World HF Contest Station Database was updated 9 May 03.
> Are you current? www.pvrc.org/wcsd/wcsdsearch.htm
>
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers",
"Wireless Weather Stations", and lot's more. Call Toll Free,
1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
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