> My modeling exercises suggest that a grounded metal mast will
> degrade the pattern significantly. It will still have some F/B, but
> the peak F/B in the null will be reduced.
What spacing do you have between the mast and the antenna element,
and how tall is the mast Gary? I've never seen that effect either in
a model or in real-life antennas.
I just checked one random old model of mine using a 60 foot long
antenna, and when I stay within the guidelines of Elnec I see a
deterioration from 32.1 dB to 31.34 dB F/B when I add a 2-inch
grounded metal mast that is within one foot of the #12 antenna wire.
Tweaking the termination restored the insignificant change.
I'm puzzeled by the large reported change, since it also makes no
sense from a theoretical standpoint unless the mast is a significant
fraction of a wavelength tall, perhaps .1 wl or more. But then there
is always something to learn, if you can get to the bottom of
disagreements. 73, Tom W8JI
W8JI@contesting.com
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