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John S · October 15th 14, 03:33 AM posted to rec.radio.amateur.antenna

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.