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#2
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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 |
#3
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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. |
#4
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The catenary effect
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#5
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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 |
#6
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The catenary effect
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