[TowerTalk] Modeling Rohn 25G in K6STI's AO

[Lux, Jim]

On 10/23/21 4:48 AM, Mark - N5OT wrote:
> Hey youall,
>
> I want to model Rohn 25G as a transmitting antenna.  Has anyone 
> learned how to do that fairly accurately in K6STI's AO program? In 
> addition to some length of regular straight sections, my tower has a 
> factory 8' tapered top section which I would extend with a 2" stinger 
> and a single-point pier base that is basically a 10 foot section with 
> 3 feet of taper to a flange added.  It appears to be "factory" 
> although I have never seen one in person and it could be a one-off.
>
> 1. How do I model these tapers?
>
> 2. How do I model the tower itself?  Do I call it "10-inch diameter 
> steel?"  Larger?  Smaller?

For NEC (you'd have to ask Brian if AO works the same way, I think not, 
though)

What you want is a "wire" that has similar electromagnetic 
characteristics in terms of diameter, conductivity and permeability per 
unit length.  So you could put a 10" diameter wire, but you'd need to 
scale the conductivity down so that it matches the tower (i.e. it's not 
solid steel) - Don't forget that since it's steel, the skin depth is 
quite shallow - Someone may have figured out the magic numbers to 
match.  You might be able to use a single smaller wire that's "close 
enough".  It kind of depends what you're doing with the model - 
sometimes, a simple approximation works for a sensitivity analysis.  You 
put the wire in, get some data, take the wire out, get some data, decide 
that since the data didn't change very much, you neglect the effect of 
the wire.  Putting the wire in and then changing the diameter or 
conductivity is a similar exercise.

NEC doesn't model the currents flowing "around" the wire - Maybe you 
could model three parallel wires for your corner tubes and start with that.

Or, you just model the entire lattice (writing a short program to grind 
out all the segments is how most people do this kind of thing).  Of 
course, you will potentially wind up with "segment very much shorter 
than a wavelength" kinds of issues, but that's more a numerical 
precision thing.



>
> 3. Do I have to re-learn calculus?
>
> I would love to hear from anyone who has either done this or knows how 
> it is done.
>
> Thanks in advance.
>
> 73 - Mark N5OT
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