In a message dated 98-03-12 01:17:52 EST, rmidgett@edge.net writes:
> Each pipe is between 7 & 8 feet long, with 5 feet
> of the pipe in an eight inch diameter hole filled with Quickcrete to within
> 2-3" of the ground surface.
IMO putting concrete in a pipe is superfluous and doesn't add any
appreciable added strength to the pipe.. Say you have a column of concrete 4
inches in diameter and it's 3 feet tall standing vertically. What happens when
you let go and the concrete column hits the ground? Right - it shatters.
That's what it'll do if there's any compression when it's inside a pipe. It
doesn't really do anything.
> I plan to install 20' of Rohn 25G on top of this 130' & rotate the 25,
> using it as the mast for my VHF+ array; then I'll be able to climb my mast.
>
I've been through this analysis before since I thought it was a pretty
nifty idea too. The problem is that the 25G sections have a lot of windload
just by themselves. I don't have the numbers off-hand but they take up a lot
of the tower capacity with no antennas on them. Perhaps your VHF+ array is
small enough to make it worthwhile but it definitely isn't worth it for HF
antennas. BTW, a regular 15 foot two inch mast has approximately 1.7 sq.ft. of
wind load. I think the Rohn section was on the order of 3-4 sq.ft.
If you need to climb the mast, get some 12-18 inch pieces of L-iron or
aluminum. Get some appropriate sized muffler clamps (so you've got saddles)
and attach each step (after drilling, natch) to the mast. Then climb on up.
You can either leave them there or remove them when you're done. If you're
gonna leave them on the mast, soak them with cold galvanizing spray paint.
73 and GL, Steve K7LXC
TOWER TECH - professional tower supplies and services for amateurs
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