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

[Mark - N5OT]

Thanks Dave.

My old 40 meter elements all have big fiberglass rod insulators, so that 
is what will insulate the stinger.  We're on the right track.

I appreciate all the detail in your email.  K6STI allows me to place a 
simple source at the bottom and leave it there.  I need to review how to 
add a lump capacitance at the base, since the resonant frequency will be 
little lower than the operating frequency.  I figure I can dial in the 
resonant frequency with a variable capacitor but the model will get me 
in the ballpark as far as the range of the capacitor I will be looking 
for in the junk box.

The guy wires will all be insulated less than a foot out.  I'm ignoring 
them in the model.

On the right track here.  I might be on for the stew tonight after all :-)

73 - Mark N5OT



On 10/23/2021 8:16 AM, Haring family wrote:
> I haven't used that program in a long time, but here are some comments 
> which might be helpful:
>
> 1. 8-1/2" effective dia works fine.
> 2. Use full dia or 2" only. On top, use 2/3 of taper length at full 
> diameter, and add the rest of the taper length to the 2" stinger. I 
> believe for singers and cap loading you are supposed to use pretty big 
> segments compared to the rest of the antenna.
> 3. Full dia for the base.
> 4. Build your model from ground - not from insulator/feed point.No 
> taper or taper adjustment.
> 5. Are you cap loading with a beam or wires?
> 6. Presuming 80 meter band, are your 2 or 3 sets of guys Philly or 
> steel? Insulated? I've included brackets and starts of guys before, 
> when steel and connected to the tower.
> 7. In EZNEC, source placement can be annoying. Build the vert as 1 
> element and you have to watch the segmentation carefully to know where 
> your source is. If you want to be sure, in EZ I'd make the model with 
> a bottom stub of length to the insulator, and build the top part 
> electrically connecting from there. You would feed at that junction as 
> a split source (SI); I don't remember that sti didthat though. The 
> only down-side: segmentation on both sides of the SI need to be the 
> same length.
> 8. EZ 6.0 must use Mininec for that type of antenna, and I believe STI 
> also uses MiniNec. You need to estimate reasonably accurately your 
> effective ground loss for your radial field. Much less accurate than 
> the rest of the model.
>
> I responded to your other email first... definitely use fiberglass, 
> not pvc or Teflon, for insulator up top.
>
> regards, Dave N3AC
>
> On Sat, Oct 23, 2021, 07:48 Mark - N5OT <r-emails at n5ot.com> 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?
>
>     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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