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From: "Reg Edwards"
Subject: Program TOPHAT2
Date: Fri, 4 Oct 2002 16:52:48 +0000 (UTC)
Organization: Private individual
NNTP-Posting-Date: Fri, 4 Oct 2002 16:52:48 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Program TOPHAT2.exe is an improved version of TopHat1.
Part of introductory notes -
"PERFORMANCE OF SHORT, VERTICAL, TOP-CAPACITANCE-LOADED ANTENNAS
Capacitance loading of a short vertical antenna can improve radiating
efficiency better than inductance loading. Best possible improvement for a
2/3-height loading coil relative to base loading is typically 3 dB. But a
large top hat can improve performance by more than 6 dB. In this program
the hat is a number of horizontal radial wires or rods optionally surrounded
by a wire circle.
Top-capacitance loading improves radiating efficiency in two ways -
(1) A more uniform distribution of antenna current versus height results
in an increase in radiation resistance for no loss in the top-hat. Whereas
the high loss resistance of a raised coil can outweigh the benefit of
increased radiation resistance.
(2) A tuning coil is always necessary. But its inductance is less when a
capacitance hat is fitted and if overall coil dimensions are unchanged then
loss in the coil is much smaller. A more uniform current due to a top hat
lessens the advantage of fitting the coil part-way up the antenna. The coil
can then be combined with the Z-match network located between antenna and
the transmitter as in this program."
Download in a few seconds program TOPHAT2 from website below. Run
Regards from Reg G4FGQ
Free Radio Design Software
Go to http://www.g4fgq.com
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