Message-ID: <479654C2.2010208@ukonline.co.uk>
Date: Tue, 22 Jan 2008 20:40:34 +0000
From: Peter Dodd <g3ldo@ukonline.co.uk>
User-Agent: Thunderbird 2.0.0.9 (Windows/20071031)
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <000501c85c3d$4fa2f820$0b01a8c0@weazle> <20080122135712.5D7C8F3862@smtps02.kuleuven.be> <4795FD3B.603@telia.com>
In-Reply-To: <4795FD3B.603@telia.com>
Subject: Re: LF: Fenceline longwire
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


EZNEC 5 shows the 1200 fence (3ft hi) antenna to have remarkable receive 
properties
If terminated with 400ohms it produces a polar diagram not unlike a 
3-element Yagi with a maximum gain of -17dBi and a F/B of 14 dB.
The maximum elevation gain is 37 degrees although the elevation gain is 
within 2dB from 20 to 50degrees.
The antenna current shows a classic corkscrew current distribution of a 
travelling wave antenna.
If unterminated it loses its travelling wave characteristics and 
directivity.
EZNEC can use real ground or MiniNEC. I have used real ground with a 
conductivity of 0.005S/m and a dielectric constant of 13.
It would need matching. The calculated Z is R11 -j518.
The 2000m antenna is something else!

Regards

Peter, G3LDO
> 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.
>
>
>