At 12:19 PM 6/18/01 +0200, Arie.Voors@ict.nl wrote:
>For a periode of time now I am trying to modell a vertical with a two
>spoke top
>hat (80 m dipole) and a radial ground screen.
>
>The actual (burried) ground screen consists of about 20-30 copper wires with
>lengths between 1/8 and 1/4 wavelengt;
>some without, but mostly with one or two copper ground stake pipes (5 meters
>long).
>
>The measured impedance is about 45 + j 400 ohms.
>
>The modelled antenna, using a 20 radial ground screen elevated 20 cm above
>ground, gives me an impedance of 22 +j 150 ohms
>
>I can not beleave that my ground (screen) has such a 'big' impedance of
>about 23
>ohms.
>
>My modelling of antenna systems, not using a ground screen, works very well.
>
>The question is, is it possible with nec-2 to model such a vertical antenna
>system
>by using a ground plane elevated above ground, or do I have to use nec-4 ?
>
>Is it possible for 'normal' people, not connected to any official company
>or so,
>to get a PC based nec-4 executable ?
>
>Another question is, if there are people who have succecfully modelled a
>vertikal antenna with
>a burried ground screen using nec-2 ?
>
>If so, is it possible for me to recieve a copy of this model ?
It sounds as if you are using MININEC to model your antenna. If this is the
case, you will not get accurate results for the "elevated" radials. NEC-2
is more accurate for low elevated radials, although NEC-2 is not capable of
modelling buried radials accurately. NEC-4 can model buried radials. One
of the versions of EZNEC-PRO (http://eznec.com) can run NEC-4, but requires
you to buy the license for NEC-4 separately and it's not cheap. The EZNEC
software and NEC-4 license will run over US$1000, I believe. Perhaps there
are EZNEC-PRO/NEC-4 users here who can comment.
73, John W1FV
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