Date: Tue, 22 Jan 2008 15:58:05 +0100
To: rsgb_lf_group@blacksheep.org
From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
In-Reply-To: <4795FD3B.603@telia.com>
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 <4795FD3B.603@telia.com>
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Message-Id: <20080122145654.1993E31E702@smtps01.kuleuven.be>
Subject: Re: LF: Fenceline longwire
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Johan,

indeed there are some limitations to MMANA. And when getting a 
negative radiation resistance one should get cautious.
But for small verticals and small loops MMANA seems to work OK. I am 
using version 1.0.0.65 of MMANA-GAL.

73, Rik ON7YD

At 15:27 22/01/2008, you wrote:
>Rik Strobbe wrote:
>>It seems that (at least in theory) even 1200 foot is too short to 
>>be long  on 500kHz ...
>>Or does MMANA not work properly ?
>
>Hello Rik,
>
>MMANA works very well for free space models but since it is based on 
>MiniNEC, it does not properly model how the "real world" ground 
>interacts with the near field. As far as I know, it uses the ground 
>parameters for the far field calculations only. In other words, I 
>don't think MMANA is able to make meaningful performance predictions 
>for small antennas close to non-perfect ground.
>
>I just put a 2000m horizontal wire into MMANA and tried different 
>heights from 1cm to 1m on 500kHz with real ground. Both gain and 
>impedance figures were ridiculous, >600dB gain difference and 
>sometimes the real part of the impedance was negative! :-D
>Beverages rely on non-perfect ground to work so I saw no reason to 
>trust the radiation patterns either.
>
>73
>Johan SM6LKM


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