Dave,
I have two concerns.
1. The ability of EZNEC to properly predict the impedance of your vertical,
without you having to actually measure it and "warp" your model to mimic the
real world.
2. How you modeled your radials, if using NEC-2.
The well known "trick" of my article is not my idea, of course. The
technique has been used for along time. Just so the members understand I
was not doing anything new.
But I would suggest you model the vertical, fully tapered, with radials 1
foot above ground using the radial generation facility of EZNEC (NEC2)
Then for the feedpoint use a 1 foot wire (3 segments inside it) between the
radials and the vertical "wires. put your LOAD ( the shunt inductor in the
center segment of the wire.
First just put your source at the center segment and see if it looks like
your measured impedance at the vertical plotted over frequency. If not,
then you will need to tweak your model to get it close.
Since you are able to use a 4:1 UNUN for your match it must be near 12.5
ohms? If so you, are must be using a shortened vertical.
Your "LC" network will be different then mine of course. So using L network
software available on the web you should be able to describe the inductor to
EZNEC pretty easily plugging in the apparent "C" you get from your model.
But instead of going through all that work, why not just go out with an
inductor and some alligator clip wires, and shorten your vertical and make
the match?
Jay
-----Original Message-----
From: antennaware-bounces@contesting.com
[mailto:antennaware-bounces@contesting.com] On Behalf Of David Gould
Sent: Tuesday, August 17, 2010 7:14 AM
To: antennaware@contesting.com
Subject: [Antennaware] Topband vertical matching.
For the last few years I have just been matching my topband vertical
or inverted L antennas by using a 1:4 UNUN
I have just seen the following article by Jay at Array Solutions..
http://www.arraysolutions.com/images/Tuning_160m_Vertical.pdf
where he resonates the antenna at 1.9MHz which gives a capacitive
reactance at 1.83 (which becomes a phantom part of the L-network) the
other part being a real inductance to earth. I like the look of this
arrangement because of its simplicity and the fact that there is a DC
connection to ground.
I would like to try and model this directly in EZNEC, but not quite
sure how to define the load components and the source in this case.
1) Can I just specify a load of L+R (where R is the simulated earth
loss) and the source in the lowest segment?
2) Should I put the L+R in the lowest segment and the source in the
next segment up?
3) Or is there a better way?
I would appreciate any advice from anyone with a bit more experience
than I have.
73,
Dave, G3UEG
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