Date: Thu, 18 Mar 2010 19:12:25 -0400
From: "Roger (K8RI)" <K8RI-on-TowerTalk@tm.net>
Subject: Re: [TowerTalk] 2" O.D. Pipe???
Stan Stockton wrote:
> Just my opinion.... 1.5 inch schedule 40 may be fine if you have some
> big tribander or 35 foot monobnder and it is mounted right above the
> top bearing. If you are stacking antennas on the mast, forget it.
http://www.rogerhalstead.com/ham_files/Tower29.htm shows a tribander at
100', 7L 6-meter Yagi at 115 and a 14' cross boom at 130' holding a pair
of 11L on 440 and pair of 12L 144. That all on 2" schedule 40 but it's
structural steel. It's a bit flexible with the top looking like a blue
gill rod that just tied into a big Bass, but it's withstood over 70 mph
winds and many occasions.
## sched 40 pipe doesn't come in a 2.0" OD. It's is 1.9" OD,
with a .145" wall.
## You mean to tell us that you have 30' [thirty feet] of mast,
sticking out the top of the tower ??? Do you ever get ice...
or ice + wind ?
I'm going to a heavier wall DOM so it doesn't beat the antennas to
death, but strength wise it seems to have been more than sufficient.
OTOH it's not ordinary schedule 40 pipe which is relatively soft and
## Regular sched 40 pipe would have been toast, long b4 now.
## 1026 DOM comes in 60 ksi, to as high as 90 ksi.
## IMO... for ants mounted way up a mast, you had better [A] run the
numbers through the spread sheet.. and [B] make sure the mast you buy
has paper work with it. Inform your steel supplier, that it's a legal
issue... and guess who's liable? As far as wind speeds go.... unless you
have a wireless wind speed indicator, at the top of the tower, you are
guessing. If it's 56 mph at grnd level, it could easily be 70 mph at the
top of the tower. Talk to anybody who has a wireless wind speed indicator
at both the top of the tower.. and also at the 15' level. You will get an
## all of this mast issue is really a no- brainer. Stuff the numbers into
spread sheet, and see what spits out.
## estimate the max wind speed gusts for your area.... then add a MIN
of 25% " to the speed [and pref a lot higher... like 30-50%]. Then procure
the correct mast. These 1 in a 100 yr wind storms are too plentiful these
and ditto with ice storms, seismic events, and heavy rains. WX patterns are
changing.. for the worse. OK, so you buy a mast that's overkill, so what?
Ham's spend $12K on a xcvr, without blinking an eye. When you get the
crane bill, to remove the destroyed ant's, coax, etc... the pricey mast
will look cheap.
later....... Jim VE7RF
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