The catenary effect
 

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)

The catenary effect
 

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.



--
Jim Pennino

The catenary effect
 

John S wrote in :

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)


No worries, I'm willing to accept that, now and as of last night's talk too.
This is useful to me as it is, it gives a good example of diminishing returns
in some lines of exploration.

The catenary effect
 

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.

The catenary effect
 

John S wrote in :

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


I've started reading the manual, I suspect there's little danger of that. :)
At least with EZNEC+ 4 onwards, not sure about standard version. I suspect
like curves built in segments in Sketchup, or the straight bars in the chains
of the Clifton Suspension Bridge, the amount of fine tuning you'll get in
using more than about 24 segments for a catenary might be an exercise in
diminishing returns, and that even just 3 to 5 might be adequate, if the
deviation from straight is small.

The catenary effect
 

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.


--
Jim Pennino

The catenary effect
 

The catenary effect
 

The catenary effect
 

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.

The catenary effect
 

Lostgallifreyan wrote:
wrote in :

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.


--
Jim Pennino

The catenary effect
 

Lostgallifreyan wrote:
wrote in :

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

The catenary effect
 

The catenary effect
 

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

The catenary effect
 

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.

The catenary effect
 

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.

The catenary effect
 

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

The catenary effect
 

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.

The catenary effect
 

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?

The catenary effect
 

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

The catenary effect
 

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.

The catenary effect
 

The catenary effect
 

Lostgallifreyan wrote:
wrote in :

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


If you can do a parabola that could be close enough. Not the same as a
catenary but a damn sight closer than a circle's arc, and much more likely a
form for a tool specialising in projecting energy to be able to do.

I just don't see the issue with a catenary.

The equation for a catenary is y = a * cosh (x / a).

All spreadsheets have a hyperbolic cosine function and can produce graphs.

Back in ye olden days we would use a math table and graph paper to plot
the function then use a ruler to get a straight line approximation.


--
Jim Pennino

The catenary effect
 

The catenary effect
 

In message ,
Lostgallifreyan writes
John S wrote in :

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


I've started reading the manual, I suspect there's little danger of that. :)
At least with EZNEC+ 4 onwards, not sure about standard version. I suspect
like curves built in segments in Sketchup, or the straight bars in the chains
of the Clifton Suspension Bridge, the amount of fine tuning you'll get in
using more than about 24 segments for a catenary might be an exercise in
diminishing returns, and that even just 3 to 5 might be adequate, if the
deviation from straight is small.

I did a simple sagging 40m dipole on MMANA using the wire editor with
9 wires. I had a 3m sag in the middle . I ran the optimiser for best
match. The impedance worked out at 69 ohm and the gain was 2.06dBi. The
model reported a lobe elevation of about 8 degrees. There was a
vertically polarised component at 90 degrees to the horizontal lobe at
-15dBi.

You'd expect something like this to happen since there is part of the
antenna in the vertical plane.

Brian GM4DIJ
--
Brian Howie

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

The catenary effect
 

On Monday, 13 October 2014 18:14:13 UTC+1, 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)

I did a simple sagging 40m dipole on MMANA using the wire editor with 9 wires. I had a 3m sag in
the middle . I ran the optimiser for best match. The impedance worked out at 69 ohm and the gain
was 2.06dBi. The model reported a lobe elevation of about 8 degrees. There was a vertically
polarised component at 90 degrees to the horizontal lobe at -15dBi.

You'd expect something like this to happen since there is part of the antenna in the vertical plane.

Brian GM4DIJ

The catenary effect
 

On 10/16/2014 3:29 PM, Brian Howie wrote:
In message ,
Lostgallifreyan writes
John S wrote in :

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


I've started reading the manual, I suspect there's little danger of
that. :)
At least with EZNEC+ 4 onwards, not sure about standard version. I
suspect
like curves built in segments in Sketchup, or the straight bars in the
chains
of the Clifton Suspension Bridge, the amount of fine tuning you'll get in
using more than about 24 segments for a catenary might be an exercise in
diminishing returns, and that even just 3 to 5 might be adequate, if the
deviation from straight is small.

I did a simple sagging 40m dipole on MMANA using the wire editor with
9 wires. I had a 3m sag in the middle . I ran the optimiser for best
match. The impedance worked out at 69 ohm and the gain was 2.06dBi. The
model reported a lobe elevation of about 8 degrees. There was a
vertically polarised component at 90 degrees to the horizontal lobe at
-15dBi.

You'd expect something like this to happen since there is part of the
antenna in the vertical plane.

Brian GM4DIJ

Excellent info, Brian. Thanks for that.

Cheers,
John KD5YI

The catenary effect
 

On 10/16/2014 3:29 PM, Brian Howie wrote:
In message ,
Lostgallifreyan writes
John S wrote in :

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


I've started reading the manual, I suspect there's little danger of
that. :)
At least with EZNEC+ 4 onwards, not sure about standard version. I
suspect
like curves built in segments in Sketchup, or the straight bars in the
chains
of the Clifton Suspension Bridge, the amount of fine tuning you'll get in
using more than about 24 segments for a catenary might be an exercise in
diminishing returns, and that even just 3 to 5 might be adequate, if the
deviation from straight is small.

I did a simple sagging 40m dipole on MMANA using the wire editor with
9 wires. I had a 3m sag in the middle . I ran the optimiser for best
match. The impedance worked out at 69 ohm and the gain was 2.06dBi. The
model reported a lobe elevation of about 8 degrees. There was a
vertically polarised component at 90 degrees to the horizontal lobe at
-15dBi.

You'd expect something like this to happen since there is part of the
antenna in the vertical plane.

Brian GM4DIJ

By the way, Brian, do you have data of the non-sagging model for
comparison? Don't do it unless it is fun for you. The data looks just
about the same for a non-sagger anyway. A comparison would show the
small differences.

Super work! Thanks.

The catenary effect
 

In message , John S
writes
On 10/16/2014 3:29 PM, Brian Howie wrote:
In message ,
Lostgallifreyan writes
John S wrote in :

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


I've started reading the manual, I suspect there's little danger of
that. :)
At least with EZNEC+ 4 onwards, not sure about standard version. I
suspect
like curves built in segments in Sketchup, or the straight bars in the
chains
of the Clifton Suspension Bridge, the amount of fine tuning you'll get in
using more than about 24 segments for a catenary might be an exercise in
diminishing returns, and that even just 3 to 5 might be adequate, if the
deviation from straight is small.

I did a simple sagging 40m dipole on MMANA using the wire editor with
9 wires. I had a 3m sag in the middle . I ran the optimiser for best
match. The impedance worked out at 69 ohm and the gain was 2.06dBi. The
model reported a lobe elevation of about 8 degrees. There was a
vertically polarised component at 90 degrees to the horizontal lobe at
-15dBi.

You'd expect something like this to happen since there is part of the
antenna in the vertical plane.

Brian GM4DIJ

By the way, Brian, do you have data of the non-sagging model for
comparison? Don't do it unless it is fun for you. The data looks just
about the same for a non-sagger anyway. A comparison would show the
small differences.

Super work! Thanks.


I design and build antennas for fun, but mostly VHF and UHF. However my
last one was 5ft screened Rx loop for 472KHz.

The non sagging one was 72 Ohms impedance and a gain of 2.13dBi . The
main lobe was horizontal. Plain vanilla dipole figures and
surprisingly much the same for the sagging one

Above a ground 20m up it has a gain of 7.1dBi and a lobe elevation of
29.6deg and an impedance of 73.6ohm

Now the sagging one 20m up at the ends

82.5ohm impedance, gain 6.23dBi and a lobe elevation of 33.8deg. The
vertical component was 12dB down.

The upshot is that a bit of sag isn't going to impact performance. It is
going to give mechanical problems due to wind sway.

73 Brian GM4DIJ



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The catenary effect
 

On 10/17/2014 1:23 PM, Brian Howie wrote:
In message , John S
writes
On 10/16/2014 3:29 PM, Brian Howie wrote:
In message ,
Lostgallifreyan writes
John S wrote in :

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


I've started reading the manual, I suspect there's little danger of
that. :)
At least with EZNEC+ 4 onwards, not sure about standard version. I
suspect
like curves built in segments in Sketchup, or the straight bars in the
chains
of the Clifton Suspension Bridge, the amount of fine tuning you'll
get in
using more than about 24 segments for a catenary might be an
exercise in
diminishing returns, and that even just 3 to 5 might be adequate, if
the
deviation from straight is small.

I did a simple sagging 40m dipole on MMANA using the wire editor with
9 wires. I had a 3m sag in the middle . I ran the optimiser for best
match. The impedance worked out at 69 ohm and the gain was 2.06dBi. The
model reported a lobe elevation of about 8 degrees. There was a
vertically polarised component at 90 degrees to the horizontal lobe at
-15dBi.

You'd expect something like this to happen since there is part of the
antenna in the vertical plane.

Brian GM4DIJ

By the way, Brian, do you have data of the non-sagging model for
comparison? Don't do it unless it is fun for you. The data looks just
about the same for a non-sagger anyway. A comparison would show the
small differences.

Super work! Thanks.


I design and build antennas for fun, but mostly VHF and UHF. However my
last one was 5ft screened Rx loop for 472KHz.

The non sagging one was 72 Ohms impedance and a gain of 2.13dBi . The
main lobe was horizontal. Plain vanilla dipole figures and
surprisingly much the same for the sagging one

Above a ground 20m up it has a gain of 7.1dBi and a lobe elevation of
29.6deg and an impedance of 73.6ohm

Now the sagging one 20m up at the ends

82.5ohm impedance, gain 6.23dBi and a lobe elevation of 33.8deg. The
vertical component was 12dB down.

The upshot is that a bit of sag isn't going to impact performance. It is
going to give mechanical problems due to wind sway.

73 Brian GM4DIJ

That was my guess.

The mechanical problems must be handled via another route. There must be
some sag in order to keep the antenna from breaking in high winds.
Somewhere on VK1OD's Web site, he did such an analysis. I think he was
forced to change his call and his site, so you might find it at
http://owenduffy.net/blog/. His stuff is extremely educational and
well worth reading.

73 John KD5YI

The catenary effect
 

"Brian Howie" wrote in message
...
I did a simple sagging 40m dipole on MMANA using the wire editor with
9 wires. I had a 3m sag in the middle . I ran the optimiser for best
match. The impedance worked out at 69 ohm and the gain was 2.06dBi. The
model reported a lobe elevation of about 8 degrees. There was a
vertically polarised component at 90 degrees to the horizontal lobe
at -15dBi.


I know you did that for an example, but 3 meters of sag for a 40 meter
dipole is a lot of sag. I bet the ends were close together.
About 1 meter of sag would be more like it.




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The catenary effect
 

In message , Ralph
Mowery writes

"Brian Howie" wrote in message
...
I did a simple sagging 40m dipole on MMANA using the wire editor with
9 wires. I had a 3m sag in the middle . I ran the optimiser for best
match. The impedance worked out at 69 ohm and the gain was 2.06dBi. The
model reported a lobe elevation of about 8 degrees. There was a
vertically polarised component at 90 degrees to the horizontal lobe
at -15dBi.


I know you did that for an example, but 3 meters of sag for a 40 meter
dipole is a lot of sag. I bet the ends were close together.
About 1 meter of sag would be more like it.

Yes it is a lot of sag. It's 19.57m end to end. The unsagging one is
20.81, so there's more wire in the sagging one. Recall I altered the
length to get a good match. If you had a sagging dipole like that you'd
have to trim the length.

For a 1m sag the vertical component is below -60dB and it's close to
the unsagging performance.

I was interested in the catenary problem for a different reason.

http://www.bigskyspaces.com/w7gj/longyagi.htm

I toyed with the idea of making one of those at one time.

Brian GM4DIJ

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The catenary effect
 

"Brian Howie" wrote in message
...

For a 1m sag the vertical component is below -60dB and it's close to the
unsagging performance.

I was interested in the catenary problem for a different reason.

http://www.bigskyspaces.com/w7gj/longyagi.htm

I toyed with the idea of making one of those at one time.

Brian GM4DIJ


I have seen designs like that before. I always wondered if they really
worked out when carried out to the extream like the 100 foot long boom yagi
in that pix.

I would think that in real life things would fall off more than the model
would indicate, but maybe not.

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The catenary effect
 

"Ralph Mowery" wrote in news:kI-
:

I would think that in real life things would fall off

I'd be inclined to have stopped that sentence right there. :) It looks
awesome, but wouldn't this be like some of the early attempts at telescope
design? In the end people quit trying for really long ones, they found that
accurate forms for long range detection were more easily built in
surprisingly compact designs, most likely because that way they could control
the precision much more easily. Very different forms, sure, but still
directed at distant photon sources, so essentially similar I imagine.. Size
will change with wavelength, but I'm thinking the proportions for accuracy
and good yield might not, so much.

The catenary effect
 

On Fri, 17 Oct 2014 20:27:57 +0100, Brian Howie
wrote:

I was interested in the catenary problem for a different reason.
http://www.bigskyspaces.com/w7gj/longyagi.htm
I toyed with the idea of making one of those at one time.
Brian GM4DIJ

I built a "rope Yagi" like that for 2m long ago (1960 something).
Instead of 1/4" rod, I used #12 AWG solid electrical wire. I used it
as a hidden transmitter on a transmitter hunt where I pointed it down
a freeway. The signal was very strong on the elevated freeway, but
became extremely weak as soon as anyone left the freeway via an
offramp. It also had an impressive assortment of side lobes to
confuse anyone that got too close. We were eventually found, more by
luck than by technology or skill. A rope yagi has also been used on
very long range transmitter hunts. Mine was only about 20 meters long
yielding a theoretical gain of around 20dBi(?). Usable bandwidth was
very narrow (about 100 KHz as I recall) and difficult to tune
accurately. See antennas designed for EME for clues.

The antenna did droop badly in the middle. However, some crude
testing with extra ropes and poles in the middle didn't show much of
an effect on signal strengths until the elements were fairly close to
the ground. The only critical parts seemed to be the driven element,
reflector, and maybe the first 3 directors.

At some point in the past, I tried to do a model in YagiCAD or 4NEC2.
That's when I discovered that I needed an NEC4 calc engine to
correctly model it. Sorry, but no plot today.





--
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150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

The catenary effect
 

On 10/18/2014 11:30 AM, Jeff Liebermann wrote:
On Fri, 17 Oct 2014 20:27:57 +0100, Brian Howie
wrote:

I was interested in the catenary problem for a different reason.
http://www.bigskyspaces.com/w7gj/longyagi.htm
I toyed with the idea of making one of those at one time.
Brian GM4DIJ

I built a "rope Yagi" like that for 2m long ago (1960 something).
Instead of 1/4" rod, I used #12 AWG solid electrical wire. I used it
as a hidden transmitter on a transmitter hunt where I pointed it down
a freeway. The signal was very strong on the elevated freeway, but
became extremely weak as soon as anyone left the freeway via an
offramp. It also had an impressive assortment of side lobes to
confuse anyone that got too close. We were eventually found, more by
luck than by technology or skill. A rope yagi has also been used on
very long range transmitter hunts. Mine was only about 20 meters long
yielding a theoretical gain of around 20dBi(?). Usable bandwidth was
very narrow (about 100 KHz as I recall) and difficult to tune
accurately. See antennas designed for EME for clues.

The antenna did droop badly in the middle. However, some crude
testing with extra ropes and poles in the middle didn't show much of
an effect on signal strengths until the elements were fairly close to
the ground. The only critical parts seemed to be the driven element,
reflector, and maybe the first 3 directors.

At some point in the past, I tried to do a model in YagiCAD or 4NEC2.
That's when I discovered that I needed an NEC4 calc engine to
correctly model it. Sorry, but no plot today.



LOL, that reminds me of a time I was the fox back in Iowa. I backed
into a school loading dock, surrounded on three sides by building. To
the west about ten blocks away was a large water tower (the type that
was a solid structure all the way to the ground - not a tank on a small
stem) in a large shopping mall parking lot.

I then aimed a pair of phased 11 element beams at the water tower.

The signal was quite strong in the mall, and hunters were all over the
place looking for me. Some started to head east, but the signal quickly
dropped off due to the rolling land (not real hilly, but hilly enough).
It took them over 4 hours to find me. :)

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