Thanks for the input so far.
Ed K4SB asked how I determine the L-match components.. I use the
following website to match what the model gives me to 50ohms. The
network I use is the second down on the right. You do need to watch
the units ie frequency as 10.125e6 and the results give inductance in
nanohenries.
http://bwrc.eecs.berkeley.edu/Research/RF/projects/60GHz/matching/ImpMatch.html
The antenna is a 48ft vertical, 2.5inches at the bottom tapering to
2inches at the top.
For the 10MHz example I am working on, that gives me
A coil of 4.3uh (X=274) from bottom of antenna to earth.
A series capacitor 90pf (X= -175) from bottom of antenna (top of
coil) to feed line
I just went ahead and modelled it in EZNEC (V3) as I
described... And it gave absolute rubbish... (I am NOT blaming the software!)
The feed impedance was given as 220 - j18,000.
I think this proves that my model is far from correct, but I don't
know what to change to make it a true representation of my real life antenna.
I am happy with the physical implementation of the antenna, I just
want to play about with the model so I can get some idea of what
effect different coils (of different Q) and different earth losses
make to the antenna efficiency and SWR bandwidth.
73,
Dave, G3UEG
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