At 08:50 PM 6/18/2006, NØATH wrote:
>Is there a Yahoo group or any location anybody knows of that
>would help a fellow with any of the antenna modeling programs?
What's the question? You might ask it here.
There's the NEC-List which sporadically has useful stuff.
http://www.robomod.net/mailman/listinfo/nec-list
If you're using 4nec2, Arie Voors(the author) answers questions sometimes,
depending on what they are.
http://home.ict.nl/~arivoors/Home.htm
Likewise Roy Lewallen (W7EL) answers questions about EZ-NEC. Try
http://www.eznec.com/
These two, however, are more focussed on software usage issues, rather than
antenna modeling, per se.
L.B.Cebik's (W4RNL) web pages (http://www.cebik.com/) are quite useful and
ham oriented, and has a wealth of information on practical modeling.
> >From a thick headed kid from the country.
>Dave / NØATH
>
>
>----- Original Message -----
>From: "Bill Coleman" <aa4lr@arrl.net>
>To: "Bill Turner" <dezrat@copper.net>
>Cc: <towertalk@contesting.com>
>Sent: Sunday, June 18, 2006 5:20 PM
>Subject: Re: [TowerTalk] re Radials
>
>
> >
> > On Jun 17, 2006, at 1:08 PM, Bill Turner wrote:
> >
> >> At 05:55 PM 6/16/2006, Bill Coleman wrote:
> >>
> >>> Horizontal antennas, like dipoles, make great antennas, but they are
> >>> affected by proximity to the ground. They have to be at least 1/4
> >>> wave above ground before the radiation pattern is anything but
> >>> straight up.
> >>
> >> *********** REPLY SEPARATOR ***********
> >>
> >> So you are saying that a dipole at less than 1/4 wavelength high
> >> has *only* straight up radiation?
> >
> > To make sure I have my facts straight, I've gone and modeled a 20m
> > long dipole at heights of 10m, 20m and 30m at a frequency of 3.6 MHz
> > (which is darn close to resonance at low heights).
> >
> > At 10m high, the main gain lobe is at 90 degrees. At 30 degrees, the
> > gain is about 3.7 dB down from the peak, and it falls down very
> > quickly from there.
> >
> > At 20m high, the main gain lobe moves to 57.4 degrees, although the
> > 90 degree point is only a few tenths down. At 30 degrees, the gain is
> > down 1.5 dB, and it falls off quickly below 20 degrees.
> >
> > At 30m high, the main lobe moves to 36.6 degrees, the 90 degree point
> > is down almost 4 dB from the main lobe. Gain falls off rapidly below
> > 10 degrees.
> >
> > It's pretty evident from modelling that my statement above is true --
> > you have to get a horizontal antenna higher that 1/4 wave above
> > ground before the majority of your signal isn't going straight up.
> >
> > Did I say that there's no radiation or pattern in other directions?
> > No, I didn't say that. Even a dummy load has some radiation or
> > pattern -- it's just not efficient.
> >
> > Does that mean a low dipole won't work? Heck, no, because EVERYTHING
> > works. Some antennas work better than others, but if you have enough
> > patience and put in sufficient effort, you can work DX with any antenna.
> >
> > Bottom line, if you want to get your radiated signal from a
> > horizontal antenna below 30 degrees -- the angles at which the DX
> > signals arrive and depart -- you need to get it 3/8 wave or higher.
> > On 80m, that's 30m high, or 100 feet. For 160m, double that.
> >
> > THAT's the reason many hams choose to use verticals for the low
> > bands, despite all the hassle of putting down radials. They just
> > don't have the mile-high supports necessary to do a good job with a
> > horizontal antenna.
> >
> > Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
> > Quote: "Not within a thousand years will man ever fly!"
> > -- Wilbur Wright, 1901
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
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> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
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