[TowerTalk] Modeling Rohn 25G in K6STI's AO
Mark - N5OT
r-emails at n5ot.com
Sat Oct 23 11:54:53 EDT 2021
Thanks Joe, I was thinking about this but I had the models constantly
blow up. However, I was attempting to connect the wires together at the
top, which may have interfered with the "fatness" of the tower
"conductor" at that point . You are not suggesting this these wires be
connected together. Should they be left open?
Also, at the bottom, this cage could be brought to a separate feedpoint, no?
73 - Mark N5OT
On 10/23/2021 10:16 AM, Joe Subich, W4TV wrote:
>
>> 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).
> It would not help with SO2R but I would simply hang three pieces of
> 1.25" PVC off each face of the tower and run wires parallel to the
> tower and spaced 3' or so away. Trim them to a quarter wave on 80
> and connect them back to the bottom above your insulator (assuming
> this is base fed). You will need a second set on stand offs at the
> bottom and one or two sets along the way depending on the spacing,
> tension and expected winds.
>
> You can do it with just one wire but I like three to make it a
> nice "fat" structure with wider SWR curve.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 2021-10-23 10:49 AM, Mark - N5OT wrote:
>> 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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>>
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