Lostgallifreyan wrote:
wrote in news
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.


I imagine the simplest way (the way I'd do it if I was coding EZNEC myself
(as if I could!)), I'd allow the user to set the segment count not by direct
number, but by limiting angle to dictate segment length before generating a
new segment automatically, that way ANY curve will be met with an appropriate
array of segemnts, and changing the angle changes count, process time,
accuracy...

There is an add on for EZNEC call AutoEZ that basically allows you to
define an antenna using an Excel spreadsheet.

Which means you can define an antenna in terms of equations and/or
variables.

See:

http://ac6la.com/autoez.html


--
Jim Pennino

wrote in :

Lostgallifreyan wrote:
wrote in news
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.


Precisely so. Let me guess, at around 24 segments for a circle, it gets
pretty good?

A quick run of a 4, 8, and 16 sided loop shows:

gain impedance
3.07 126
3.34 136
3.41 139

So it appears that by 8 sides you are already pretty close.



Excellent. I thought the count would be very low. I sort of intuited it
partly based on what people have said about radial counts for good effect in
a ground. A bit of a reach, but the proportionality felt similar to me.

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.


--
Jim Pennino

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.

wrote in :

I imagine the simplest way (the way I'd do it if I was coding EZNEC
myself (as if I could!)), I'd allow the user to set the segment count
not by direct number, but by limiting angle to dictate segment length
before generating a new segment automatically, that way ANY curve will
be met with an appropriate array of segemnts, and changing the angle
changes count, process time, accuracy...

There is an add on for EZNEC call AutoEZ that basically allows you to
define an antenna using an Excel spreadsheet.

Which means you can define an antenna in terms of equations and/or
variables.

See:

http://ac6la.com/autoez.html


John S just posted about that too. I don't run Excel though. I use GScalc,
hopefully there's enough comptibility there.. Failing that, if we can write
things to plug into EZNEC the way Ruby scripting extends Sketchup, that can
work.

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

On 10/14/2014 2:19 PM, wrote:
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?

Good point. I've heard that .1 lambda is sufficient. I would normally
use half that. The best way to know is to model it.

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

One of the examples in AutoEZ is just that.

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

Indeed. I have a ways to go to be able to do that with AutoEZ, but I'm
sure it will come with practice.

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.

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.

Hey, guys. Starting with a loop is a great idea! Make a loop and then
delete all but the wires that would closely resemble a catenary. What do
you think?

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.

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.

Hey, guys. Starting with a loop is a great idea! Make a loop and then
delete all but the wires that would closely resemble a catenary. What do
you think?

Except that a circle has a constant radius and a catenary has a constantly
changing radius.

Which means a circle would be close in the middle but crap at the ends.

A simple V would be close at the ends and crap in the middle.


--
Jim Pennino

On 10/14/2014 3:38 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.

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.

Hey, guys. Starting with a loop is a great idea! Make a loop and then
delete all but the wires that would closely resemble a catenary. What do
you think?

Except that a circle has a constant radius and a catenary has a constantly
changing radius.

Which means a circle would be close in the middle but crap at the ends.

A simple V would be close at the ends and crap in the middle.

I don't know how crappy a circle would be since I think the sag is not
so great. Note that grinding a reflecting telescope lens results in a
spherical curve rather than a parabola. Also, according to
http://en.wikipedia.org/wiki/Catenary, a parabola is very close to
being a catenary. By extension, it may be that a circle segment is close
to a catenary. Probably not worth the effort anyway.