It's perfectly feasible, but depending on your plan for handling the guy
wires, may not save all that much time over dropping the mast with
antennas into a short larger pipe stuck in the ground, dropping the top
section, and popping up 4 new sections one of which has the new guy set
already attached, and dropping the loaded mast back into the tower (all
done with the crane).
If you do it *your* way, whatever your guy plan is (extending the
existing guys and just adding new ones for the the new lower bay(s)?)
you should have absolutely Everything possible prepped in advance.
And the crane should be large enough so that if the tower spins while
it's hanging the antenna elements don't bang into the crane boom.
A calm day would be nice (not like today here in the Midwest).
-Steve K8LX
On 11/18/2013 10:34 AM, Richard Thorne wrote:
I have a 77' Rohn 45g tower installed with a large tribander and 4 element
30/40 combo installed. The tribander is about 1' above the tower and the
30/40 combo is 6' above the tower. Total mast out the top is 15' or 9' of
mast above the top antenna.
I want to take the tower to 117'.
What I would like to do is leave the antenna's installed and have a crane
lift the entire tower up 40+ feet then slip 40' of tower below and reset the
original 77' on top of the new 40'. I could remove the antenna's if
necessary, but that add's crane time.
The crane would attach at the very top of the tower.
My estimates have about 225 lbs above the top of the tower (the crane
attachment point) and 600 lbs for the tower and rotor and a % of the mast
below the crane attachment point.
So the question (I'm an accountant not an engineer) will the tower stay
straight up and down or will it tilt due to the weight above the tower/crane
attachment point? I honestly don't know what the affect will be since the
antenna's have the weight distributed along the boom, not directly above the
fulcrum.
I'm also assuming that the double bolt system on each tower leg will hold
the tower together safely.
This may sound crazy to some, but it's difficult to get tower help. I've had
very good success with the local crane company. I get a crane operator and
a rigger for assistance. That's how I installed the tower/antennas in the
first place. It's safe and quick.
You can check out the tower on my qrz.com page.
Thanks,
Rich - N5ZC
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