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[email protected] · October 14th 14, 08:19 PM posted to rec.radio.amateur.antenna

John S wrote:
On 10/14/2014 1:41 PM, wrote:
John S wrote:
On 10/14/2014 12:18 PM, wrote:
John S wrote:
On 10/13/2014 12:38 PM, wrote:
John S wrote:
Jim is right. There is almost no difference in a V and a catenary as far
as the antenna is concerned.

It would really wind up being an exercise of "can we really model a
catenary?"

If anyone disagrees, we will do it. (NOTE: I said "we", not just me)

It depends on how close you want the model to be, but in general all you
do is break the catenary, or any curve you want, into a series of
straight line segments.

Yes, of course. And, with the free version of EZNEC, one must be careful
not to exceed the max segments allowed.

Not really a problem as it does not take many segments to represent the
ends, which has a slow change, as the center part with a more rapid
change.

If I were going to do it, I would use something like a spreadsheet
to plot the curve then draw straight line segments on the curve and
plug those directly into EZNEC.

Interestin that you suggest that. See below. Note that I am not
affiliated with EZNEC in anyway other than as a very satisfied user.

The extreme case is modeling a loop as a geometric figure with straight
side.

EZNEC will generate loops with whatever number of sides you want and
thus it is fairly easy to see when increasing the number of sides
gives diminishing returns in the difference between the loops.

While checking the EZNEC Web site to see if I had the latest version two
days ago, I discovered a dynamite Excel spreadsheet application. It is
called AutoEZ. Just today I learned how to use it to generate a curve of
antenna efficiency vs permeability of the wire.

I also was able to reproduce the list I posted earlier of efficiency vs
antenna length in a matter of seconds. I am flabbergasted with this tool.

It seems to have an optimize tool that I have yet to explore.

There is a free version with limitations.

Yeah, I am aware of it and have been concidering buying it.

The rub is I would also have to buy Excel and the machine I run EZNEC
on only has OpenOffice and then only to read the occasional Microsoft
file.

Bummer! You don't seem to suffer from it, though.

Until AutoEZ I haven't found anything I can't do with OpenOffice.

My main interest in AutoEZ is the ability to change things and plot
the data.

Examples:

You model a reflector as a number of wires. How close do the wires have
to be in wvelengths to approximate a solid reflector?

You model a beam consisting of double diamond structures. How does the
gain, impedance, and F/B vary with reflector size and spacing?

While you can do both manually, it is a bit arduaous.

--
Jim Pennino