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

[Mark - N5OT]

Thanks Jim.

I was hoping someone had done this the easy way - Dave says "8.5 inches 
should work" and I'm getting predictable and usable results at the 
moment using 10 inches.  Mostly I'm trying to get a reality check at 
this point on the lengths of the top load wires. Certainly if I can get 
it to accept the 160 meter energy it will radiate it. I'm getting 
wrapped around ropes and wires.

73 - Mark N5OT


On 10/23/2021 10:05 AM, Lux, Jim wrote:
> 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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