On 12/5/2020 5:37 AM, David Aslin G3WGN wrote:
I note that the capacity hat extends to a significant distance down the
vertical section. It's my understanding that will shield some of the radiation
from the upper part of the vertical.
Yes and no. The sloping hat reduces the effective height, which reduces
the radiation resistance, thus the feedpoint impedance, but most of the
radiation is from the part of the antenna where current is greatest,
which is at the base.
There are many ways to match it, as shown by other responses in this
thread. Remember also that coax loss on 160M is small, so unless the run
is quite long, the major concern is whether the power amp is happy with
the load it sees. My 87As are picky, my KPA1500 is not.
And no matter the details of the vertical radiator, a serious
radial/counterpoise is critical to minimize losses in the soil.
73, Jim K9YC
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