[TowerTalk] Modeling Rohn 25G in K6STI's AO
Mark - N5OT
r-emails at n5ot.com
Sat Oct 23 10:49:49 EDT 2021
Roger on all.
It is very hard to keep me off the air. I know almost all the tricks.
But sooner or later I have to put up something more on the permanent
side, where I feel like additional improvement is not worth the effort.
I am thinking "this may be the year."
Thank you for such excellent detail on the trap pros-and-cons. The trap
idea may be such a challenge that putting up a separate 80 meter
vertical may make more sense, plus add flexibility with regard to being
on both bands concurrently (i.e. more along the lines of SO2R).
If I get anything up by tonight it won't have a trap in it :-)
I have a bed of radials in place, so that's not a concern. I just keep
taking down and putting up radiators depending on multiple factors/du joir.
/N5OT is also the headquarters of:
Matching Networks R Us
House of Matching Networks
Matching Networks Unlimited
So whatever the radiator, I can make the transmitter happy and work
people. frankly I'll be more limited by what I can /hear /tonight,
since I don't have my RX antennas up yet.
////
73 - Mark N5OT
On 10/23/2021 8:52 AM, Haring family wrote:
> Mark,
>
> I presume your tower is around 70'. Unless you have a lot of ground
> loss, your feed resistance should be pretty low... like around 15
> ohms. On 160 of course, that's no big deal with a tuner. I aimed a
> friend across town toward using a 4:1 (50:12.5) Unun there, which
> seems to have worked well for him.
>
> If you want the pre-Stew, you might just start without the trap... add
> that after the contest...
>
> regards,
>
> Dave N3AC
>
> On Sat, Oct 23, 2021 at 9:47 AM Mark - N5OT <r-emails at n5ot.com> wrote:
>
> 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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> >
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