Message-ID: <001601bf01ad$d5b2d460$eb97b38f@w8k3f0>
From: "Dick Rollema" <d.w.rollema@gironet.nl>
To: rsgb_lf_group@blacksheep.org
Subject: Re: Fw: LF: LF-antenna with top load
Date: Sat, 18 Sep 1999 10:13:37 +0200
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

>From PA0SE

Dave, G0MRF, wrote:

>I recently installed a small broadcast transmitter on 1350kHz which was
>licenced for a maximum antenna height of 10m.
>
>After some time we managed to get a 10m glassfibre mast errected with a
small
>top capacity hat,  inductive loading at the centre (Litz), together with an
>element of distributed loading in the top section between the loading coil
>and the top hat.
>
>When examined by the authorities the efficiency was around 7%.
>
>A rough calculation would suggest that the Rrad of a 10m vertical is no
>greater than 0.1R, on 136k.  The computers perfect ground assumption could
be
>affecting the ability to compare the effects of different arrangements for
>top loading.  Is it EZNEC which has poor / Avg / good / perfect  /  ground
>models?


Dr. Dave,

The program AO by Brian Beezley, K6STI, indeed has the option of different
type of grounds (dielectric constant and conductivity). But that is only
used in computing radiation patterns and gain. And - as mentioned before -
these are not even applicable to the surface wave.

The impedance in the feed point is computed over perfect ground.

I have also the program NEC/WIRES by K6STI and this uses real ground also
for  feed point impedance computation. But only for antennas that are not
fed angainst ground, dipoles etc. So not for Marconi's, inverted L and the
like.

I do not have EZNEC myself but I think that program can use real ground for
feed point impedance calculation of antennas fed against earth. .
Perhaps someone  familiar with EZNEC can confirm.

73, Dick, PA0SE