[TowerTalk] Ground Plane Model Problem

[w3kl at w3kl.com]

Tom.  I've modeled a 1/4 wave gp with one resonant radial (1/4 wavelength) using the dimension you provided using NEC4 and it yields an impedance (real part, at resonance) of 40 ohms. BTW, you didn't specify what diameter conductor you're using for the radials, so I assumed 1 mm wire.
 
How many radials are you modeling and what are their lengths (in wavelengths)?  The impedance will decrease as the number of radials increases.
 
If I use four radials the impedance at resonance is now 35 ohms.
 
Also, what kind of ground properties do you use with the model?  I used average ground.
 
73, Jeff

Jeffrey K. Okamitsu, PhD, MBA
+1-609-638-5402

--- On Tue, 11/18/08, K0SN <k0sn at czo.net> wrote:

From: K0SN <k0sn at czo.net>
Subject: [TowerTalk] Ground Plane Model Problem
To: "Towertalk submit" <towertalk at contesting.com>
Date: Tuesday, November 18, 2008, 10:44 PM

Gentlemen:
I have been modeling a ground plane vertical antenna with elevated radials.
It's made of 3" aluminum tubing at a base height of about 15 feet.
My problem is EZNEC is reporting the feedpoint impedance to be
around 10 ohms, which disagrees with the conventional wisdom that
says it should be in the vicinity of 50-75 ohms. Any suggestions? Has
anyone encountered a similar problem while running EZNEC or another
modeling program? Any input would be appreciated.
Tom K0SN
Porterfield, WI

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