This might be of help:
http://www.ebay.com/itm/301819075388?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
and/or see if you can find an AB1386/u crank up antenna mast which reaches
32 ft. Seller j5w233 sells them on Ebay. He doesn't have any listed right
now, but if you search on ab1386/u and then look at the sold listings you
can get a place to send him an email or note. Last I checked he had 40-50
of them in his warehouse in Pennsylvania. Seller beltfed34 sells ab1386/u
parts and antenna mounts for them on Ebay.
Gary J
N5BAA
-----Original Message-----
From: Kirk Kleinschmidt via TowerTalk
Sent: Sunday, May 15, 2016 2:26 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Tilt-Over Rohn 25?
Hi gang,
After 12 years in a condo with attic antennas, I will soon have a "short"
acre on which to farm some antennas. I expect to try a few low-band types
that are new to me, and will be looking for some feedback and input. :)
This might get a bit windy, so please bear with me.
First up -- Tilt-over mount for Rohn 25:
In central MN, when I was a new ham in the '70s, because we were in a
"fringy" area for TV reception, MANY homeowners had 50-foot tip-up masts to
support big TV Yagis and small rotators. Back then, the 2- to 4-inch steel
pipe required to construct these tip-ups was reasonably trivial in cost. A
50-foot single mast was made from several "telescoped" sections of steel
pipe, welded or bolted together. Two parallel steel pipes were sunk into the
ground and cemented in place, with 10 to 15 feet of the vertical supports
sticking out above ground. The vertical tip-up mast was centered in the two
fixed uprights, and a top-mounted pivot allowed the mast to be raised and
lowered with a bottom-mounted winch.
All or most of you know what I'm describing, so I will now stop! My point
is, the steel with which to make such a tip-up mast now far exceeds the cost
of buying abandoned or unused Rohn or Rohn-style towers. The question is,
how do I make a reasonably priced tip-up or tilt-over mount for these
things?
At my new QTH, I have four Rohn towers to play with. All were donated to my
cause, purchased for $100, or were "free if you'll just take the thing down
and haul it away." I have two 40-foot Rohn 25s with 3-into-1 top sections,
one BX64 (that will probably stop at 48 or 56 feet for improved wind load
capacity [to be discussed later], and one 40-foot BX40.
My "benchmark" antenna over the years has been a full-wave horizontal loop
(triangle shaped) cut for about 5 MHz, fed with open-wire line and a
ground-mounted autocoupler. And because of the lay of the land at the new
place, I plan to install three towers in a triangle configuration (no mature
trees). The "big" tower (if you can call a 48-56 footer big :) will be near
the house. It will eventually host an HF beam. It will also hold up one leg
of the horizontal loop.
The BX40 will go next to the garage and will host beams for 6, 2 and TV.
The two 40-foot 25Gs (the second and third skyhooks for the triangle loop)
will go in the back yard. They will be 70 to 90 feet apart. In addition to
holding up their respective loop legs, I'm hoping to make each tower (and
the mast on top) into verticals -- perhaps phased in some way (more on that
later).
So, my thought process is, if I want to have the most flexibility in tuning
and loading these identical verticals on multiple bands, it would be handy
to have them sufficiently insulated from the ground. A grounded tower can be
shunt fed, but I think that's pretty much a monoband solution...
I also don't want to climb towers unnecessarily, so I was thinking about how
to make an insulated tilt-over mount for the 40-foot 25G towers. My best
idea so far (!) was to sink a salvaged 25-foot telephone pole into the
ground (15 feet above ground, with help from a private utility contractor),
or sink a 20-foot pressure treated 8 x 8 beam into the ground, with cement,
like a tower base (14 feet above ground).
In either case I'd have about 15 feet of "heavy timber" on which to build a
plate-steel "tip down" or "lay down" mount. With a lay-down mount, the
bottom of the tower would be attached to the timber via a typical triangular
plate steel base with massive hinge/pivot. This allows the tower to "lay
down" near ground level. At the top of the vertical timber would be a winch
or a pulley (for the raising cable) and a retention bracket to keep the
tower locked and upright when it's vertical.
Will such a tower be sufficiently insulated from ground for use as a
multiband vertical?
Will a telephone pole or a pressure-treated timber handle the stresses of
raising and lowering (and of simply remaining upright)? I could also guy the
tower (NOT in the way I'd guy it if I were to climb it, but something
similar, but much less expensive).
Will the tower handle being raised and lowered by a winch, and where/how
should I attach the raising cable?
If a single timber isn't rigid enough, perhaps I could build a box beam or a
twin-rail I-beam from four 20-foot 2 x 12s?
Remember: This tower won't be climbed and won't have any antennas on top. It
will simply have to keep itself upright, hold up one leg of a lightweight
wire antenna, and/or be used as a vertical (eventually phased). And handle
occasional raising and lowering.
I don't know any mechanical engineers or "strength of materials" folks, but
I am interested in finding one or two who might be able to help me with load
and stress analyses -- and with materials.
I might also be able to use a dual-attachment system for the raising cable.
One end of a short cable would connect near the top of the tower, with the
other end connecting near the midpoint. This "tower-side loop" would attach
to the raising cable by way of a pulley, so as the tower is being raised and
lowered from the 15-foot mast, the loads would spread out along the length
of the tower a bit.
Saving grace: These things are in the back 40...and can't fall on the house,
roads, etc.
Am I way off base here, or might this arrangement actually work?
As always, thanks,
--Kirk, NT0Z
My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
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