Even if one knows the capacitance of a top-hat it's of no use unless one
also knows the value of the inductance associated with it.

If the dimensions of a top-hat are tediously experimentally varied until the
antenna is tuned to resonance then one still has no idea either of the
capacitance or inductance. Not that the values would be of any use to
anybody after the job is done. And in all likelihood the experimental
procedure would not result in an optimum configuration.

What is needed are the means of *predicting* top-hat capacitance even before
construction materials are obtained. Optimum construction, or suitable in
some sense, could then be chosen.

Readers may wish to be reminded, from given dimensions program TOPHAT2
computes the performance of top-capacitance-loaded vertical antennas, not
necessarily very short as for mobile operation. In the process various data
of interest are produced including capacitance of the top-hat.

The top-hat consists of N radial wires optionally surrounded by a wire ring.
As N is increased capacitance increases until it is the same as a disk of
the same diameter. Capacitance also depends to a limited extent on height
above ground.

For good measure the program also computes L and C values of the base
matching L-network to 50 ohms.

Download in a few seconds from website below self-contained program TOPHAT2
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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