NEC-LIST: Modelling GP Antenna Arrays

Hello,

Yes certainly you can use MININEC (I have used the ELNEC version) to model
vertical GP type antennas --- monopoles or half-loops --- but click the
real ground option, otherwise you will calculate unrealistic gains.
MININEC is sort of equivalent to a GP antenna over a very good ground
system (infinite number of radials), with real ground in front of the
antenna. The far field pattern is calculated by Fresnel reflections.

One can use NEC-2 (I use EZNEC pro) to more realistically model monopole
arrays, all tower driven or one tower driven and others parasitically
excited, by using, as I have said before *resonant* radials. For 3.75 MHz
I use radials at a height of 1 metre, For other frequencies simply scale
in accord with frequency.

Use NEC-2 to establish the resonant length of the radial wire. Take a
dipole antenna and place it at the height you want to place the radials.
Vary its length to achieve *exact* resonance for the reference ground
parameters. The half length of the dipole is the resonant radial length.

Use 4-radials for each monopole. Rotate the radials so that the radials
connected to adjacent monopoles are separated symmetrically by as much as
possible. If you run two radial parallel with each other you end by
cancelling current on those radials --- so you might as well not have
them!!! If you have a unidirectional array, radials (2- or 3-radials)
arranged in a crow foot way, pointing in the direction of fire will do the
trick. Here we are "simulating" ground connection. But real antennas can
be built that way.

73, Jack, VE2CV

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Date: Mon, 23 Jun 1997 07:33:23 -0400
From: john.bartucci_at_lmco.com (John F. Bartucci)
To: nec-list_at_ee.ubc.ca
Subject: Re: NEC-LIST: ELNEC and verticals

Hi

I've tried using NEC for that purpose but I'm not sure I trust the
results. The gains derived are too good.

You MUST use the SOMNEC ground model and you must supply the ground as
separate wires. I designed a simple two element array elevated .5m
off the ground with an elevated feed to match 50 ohm coax, each element
with four radials. The gain was given as over 5 db. Seems unrealistic
to me. I'd be very interested if you get any other responses possibly
not through the mailer.

regards

John, K8JB

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Date: Tue, 17 Jun 1997 21:53:24 -0700
From: Kelly Taylor <ve4xt_at_mb.sympatico.ca>
To: nec-list_at_ee.ubc.ca
Subject: NEC-LIST: ELNEC and verticals

Hello.

Does anyone know if ELNEC would be useful for modelling ground-mounted
vertical parasitic antenna arrays? (Picture a vertical ground plane
antenna with parasitic reflectors and directors.)

If anyone can offer any advice, please e-mail address below. Thanks.

kelly taylor
ve4xt_at_mts.net

----------------------------------------------
John S. (Jack) Belrose, PhD Cantab, VE2CV
Director, Radio Sciences
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2308
FAX 613-998-4077
Received on Mon Jun 30 1997 - 11:03:01 EDT