[TowerTalk] Feeding one antenna in a stack
n4zr at contesting.com
Sat May 31 09:01:18 EDT 2003
At 07:31 AM 5/31/03 -0400, K3BU at 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
>hardly any F/B or pattern - almost perfect "3 el. omnidirectional array".
>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
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