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@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@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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