To all and sundry.

You can't locate a loading coil at the top of a short antenna because
it requires infinite inductance.

Before it gets to the top it resonates with its self-capacitance,
becomes a parallel tuned circuit, and isolates itself from the
antenna. The antenna then reverts to an unloaded rod.

The 'mechanism' is modelled in program LOADCOIL, which alows the
loading coil to slide up and down the antenna to find maximum
radiating efficiency.

There is enough information available to further calculate the angles
of the bottom section, the coil. and the top section if you are
prepared to find the time and think about it. But I can assure you
angles take no part in the internal calculations of the program except
perhaps in calculating efficiency. They are just a distraction.

Just enter diameter of bottom section, length and diameter of the
coil, and diameter of the top section and slide the coil up and down
to see what happens with constant overall height at a given frequency.
As a free gift you also get the number of turns on the coil. Its been
some time since I used the program myself. It might even tell you the
wire gauge.

Download program LOADCOIL in a few seconds from website below and run
immediately.
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Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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