US Tower--What model?
At first thought that seems a little much (load) at the top of the mast
What model shorty forty?
I have a 21' mast(5' inside the tower), 4el SteppIR 1' or so above the top
plate and a XM240 shorty forty 12' above the SteppIR on a 54' Tashjian
crankup LM-354HD.
Generally you would want the most load closest to the top of the tower.
Reverse the antennas?
73 John wa5zup
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of kr2q@optimum.net
Sent: Saturday, September 12, 2009 10:23 AM
To: towertalk@contesting.com
Subject: [TowerTalk] how much mast out of the top?
I have a couple of crank up towers. I want to insert a 20' mast into the
top section.
I called US Tower since they sell 20' masts for this crank up (and other
models). They
replied that they only rate the tower, not the load on the mast. Thanks.
Anyhow, a concern is that with a decent amount of antenna load on the mast
(at the top)
is there a chance (I know, always a "chance")..a GOOD chance that the top of
the tower
section would get so torqued as to bend (the top of the tower section)?
My guts says NO because each telescoping section is held by only the top 3'
feet (or so) of
the next section down. By the time you get to the bottom, that is a LOT of
bending torque
at the top of the bottom section...and it does fine.
I am not concerned about the mast bending...that is not the question. I am
concerned about
"bending" the top of the inner-most (top) tower section.
The mast will be about 3' feet into the tower, the rest sticking out. I
want to put an OB11-3
at the top (9 sq feet) and a shorty forty just above the top plate of the
tower. So in a 70
mph wind, I guess this will be like 20x9 = 180# X the 17' of mast. The 40
just above the plate
should not add much additional torque at all, although it will add wind load
for the tower. But hey, it's a crank up, so in winds, it cranks down.
Another way to look at this is just laying the tower over (horizontally)
seeing if I can handle
180# weight at the end of the mast without the top of the top tower section
getting wrecked.
Any comments? Has anyone done the calculation or is anyone actually doing
this?
Tower is TX472.
Thanks!
de Doug KR2Q
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