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.

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

wrote in :

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.


Fair point. I dare so it's native to math.c too, though I haven't looked.. I
just figure than if it were not ready at hand, a parabola might be. Judging
by the small number of segments needed to converge pretty well, I'd not worry
about the different between catenary or parabola, but reach for whichever
came easiest at the time.

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

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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

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

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.

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



--
Brian Howie

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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

"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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