[TowerTalk] Antenna Modeling

[Tom Hellem]

Dear Fellow TT'ers:
I am about to begin construction of a 10 meter 4 element beam which I
modeled using EZ-nec.
It will be made from aluminum salvaged from an old Telrex TB-6 so the
elements will step down in diameter several times from 1-1/2" down to 5/8"
o.d. The questions that have come to mind are these:
1. Does anyone know how accurate the stepped-diameter correction factor in
EZ-nec is? Can I    build the beam exactly per the model and expect the gain
and f/b figures to agree?
2. How can one test the antenna without a test range? Can I just point it at
a friend say 5 or 6 miles away and get a decent approximation of the f/b and
gain from s-meter readings alone?
3. I plan to build another 4-el beam later which I plan to stack with the
first one. It will be of similiar design but the element diameters will
probably not be exactly the same because I will be scraping the bottom of
the scrap aluminum barrel. Do I need to worry about phasing differences in
the stack because of the disimiliar element diameters? (Elements in the
second beam will probably be made up of 7/8 through 5/8 dia. tubing).

I have noticed that several of the regulars here on TT have mentioned their
experience with antenna modeling so am hoping someone can shed some light.
73 to all.
Tom K0SN


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