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Re: [Antennaware] EZNEC modelling

To: Terry Conboy <>
Subject: Re: [Antennaware] EZNEC modelling
From: David Gould <>
Date: Mon, 20 Nov 2006 21:34:09 +0000
List-post: <>

Thanks very much for the model and the explanation and taking the 
time to do it...

I see what you have done,  in that the capacitor has gone to ground 
effectively in parallel with the coil.
My thinking is that the series C does indeed go to earth but 
**through**  the 50ohm resistive source impedance.
Is it just a convention that this resistance can be ignored in the 
model?  The proof is that it seems to work without it..

I have got TLW on a CD somewhere, I must look it out and load it onto 
this (new) PC.

I should just say that I made a small mistake in the previous post in 
that the vertical was only 37ft high (not 48) so that was why my 
L-match components were different from yours.  (I have been playing 
with several different models and got them mixed up)  I have modified 
your model to the correct values.

Thanks again for your help.

Dave G3UEG

>My EZNEC model may be a little different than yours.  I used 3
>sections of 16 feet each with 2.5, 2.25 and 2 inch  diameters (64
>segments each), then inserted a 0.25 foot section of 2.5 inch (1
>segment) at the base where I place the source.  With no matching I
>got 425.5 -j 536.7 ohms (MININEC ground).
>I put that into TLW, from the ARRL antenna book.  It produced a shunt
>L of 2.93 uH (Q=200) and a series C of 68.7 pf (Q=1000).  TLW says
>the loss in this network is 0.15 dB.
>I added a 0.25 foot piece of 2.5 inch conductor horizontal and a 0.25
>foot piece to ground, where I placed the inductor.  The series C went
>on the base segment along with the source.  The impedance was now
>47.4 -j 4.5 ohms.  The resonance occurs at 10.175 MHz, where the
>impedance is 48.9 ohms.
>One issue is that this antenna is very close to 1/2 wavelength long,
>and the impedance is very sensitive to segmentation, even without the
>matching network.
>Hope this helps.  I'll forward Dave a copy of my EZNEC file.
>73, Terry N6RY
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