[TowerTalk] 2" OD pipe.. again

[Michael Ryan]

Really much-a-do about nothing here for 24 hrs at least. I REALLY HOPE these
guys use their water pipes, pipe cleaners, or pool cleaners, or whatever, to
prop up their antennas. It will sooner or later amount to fewer guys in the
pileups.  - Mike

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Thomson
Sent: Friday, March 19, 2010 1:30 AM
To: towertalk at contesting.com
Subject: [TowerTalk] 2" OD pipe.. again

Date: Thu, 18 Mar 2010 19:12:25 -0400
From: "Roger (K8RI)" <K8RI-on-TowerTalk at 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 
easily bent.

## 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
liability 
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
really 
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 
earful.

##  all of this mast issue is really  a no- brainer.  Stuff the numbers into
the 
spread sheet, and see what spits out.
http://thebont.com/spreadsheets/AnalysisOfAntennaMastStrength.htm

##  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
days
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  



>   
>   

73

Roger (K8RI)
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