At 10:06 PM 5/6/03 -0400, Lee Scott - AA1YN wrote:
>First, consider your tri-bander is going to look like ground plane as far
>as the other two antennas.
This is an old wives tale that simply does not have any technical merit. I
once got into a similar discussion about stacking tribanders and loaded 40M
beams for HF contesting (i.e., which goes on top) and the "lower beam acts
as ground" statement was being used to support one particular
position. Sorry folks, the computer model shows negligible, if any, change
to the radiation angle of the upper antenna if the lower antenna is added
or removed, or which one was on top.
This result should not be surprising when you consider that it's not the
ground under the antenna which sets the radiation angle, its where the main
lobe strikes the ground, reflects off, and combines with the direct ray
from the antenna. If you're on perfectly flat ground, the height under the
antenna and where the reflection occurs is the same, but if you're on a
mountaintop (or, heaven forbid, in a steep valley) they're not.
I am not saying that yagis mounted near each other will not interact, but
these are detuning effects, not changes in the radiation angle. Getting
around detuning effects is a different story.
Dave/K8CC
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