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Re: [TowerTalk] EZNEC- needs improvement

To: towertalk@contesting.com
Subject: Re: [TowerTalk] EZNEC- needs improvement
From: Steve Hunt <steve@karinya.net>
Date: Mon, 06 Apr 2009 09:40:27 +0100
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Jerry,

My head is spinning after 30 minutes of trying to compare our figures. 
I'm sure you wont believe this, but I believe there is a bug in EZNEC.

I loaded up the vertical model I was using last night - 132ft over 
Real/MININEC average ground, Aluminium Wire Loss, and re-ran the 
figures. My numbers were several dB higher than yours. I then switched 
to Perfect Ground and Zero Wire Loss to check my Average Gain figure - 
it was very low. Then I switched straight back to Aluminium Wire Loss 
and Real/MININEC ground and got a completely different set of figures - 
very close to yours.

I repeated the exercise from a "cold start" (closing down EZNEC and 
restarting it) about 6 times and consistently saw the same thing - an 
erroneous set of figures at first, and then a correct set once I'd 
swapped to Perfect Ground and back. I was trying trying to bottom-out 
exactly which change caused the change in behaviour, when it stopped 
doing it and I now can't reproduce the effect.

I wonder if anyone else has ever seen this?  Please don't suggest it was 
"operator error" - once I'd first identified the effect I was very 
careful to check and double-check every setting.

Steve G3TXQ


K4SAV wrote:
> G3TXQ wrote: Are we sure we're looking at the EZNEC results carefully 
> enough.
> If I compare a 160m half-wave at 300ft with a ground-mounted
> quarter-wave vertical, over average ground, the vertical has the
> advantage at take-off angles under 10 degrees by as much as 8dB.
>
> Well Steve it's obvious one of us is not looking close enough.  I 
> can't get that.   Are you sure you're not using a perfect ground for 
> the vertical?  When I said no near field ground loss, that implies a 
> Mininec ground.
>
>     

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