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Re: [TowerTalk] 2" masts.. an eye opener !

To: "'Tower and HF antenna construction topics.'" <>
Subject: Re: [TowerTalk] 2" masts.. an eye opener !
From: "Julio Peralta" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Fri, 19 Mar 2010 16:52:35 -0400
List-post: <">>
Looks like what happened when I used the fence material.

Julio, W4HY

-----Original Message-----
[] On Behalf Of D Calder
Sent: Friday, March 19, 2010 8:20 AM
To: 'Tower and HF antenna construction topics.'
Subject: Re: [TowerTalk] 2" masts.. an eye opener !

Here is what "cheap mast" pipe did to me when the eye of Charlie came over..

I have since went to steel and it's done well.

The TV antenna mounted to the power weather head in the foreground, it's me
but a moron neighbor. FPL
has since made him remove it.

73 Dave n4zkf

-----Original Message-----
[] On Behalf Of Jim Thomson
Sent: Thursday, March 18, 2010 2:04 AM
Subject: [TowerTalk] 2" masts.. an eye opener !

Date: Wed, 17 Mar 2010 18:42:35 EDT
Subject: Re: [TowerTalk] 2" O.D. Pipe???

hi Ted, you can find it at _www.texastowers.com_ 
( .
Click on the on line catalog button and select steel masts.
Gerald K5GW

##  I used the  arrl  mast software, available free online at

Scroll down , till u get to  'download here' .   This is from the 2004 ch-22
of the arrl ant book. 

I got a REAL  eye opener, when plugging stuff into it !   I'm stuck using a
2"  mast on the HDX-689  I just bought,  since  conversion to 3"  is a
show.  The PPM, bearings, etc, holes in plates, etc,  everything is 2". 

That being the case, and wanting to install 3 x yagi's  on the mast + a 80m
rotary dipole, the  2"  mast demands  are enormous. 

I can get, locally, at any of our 4 x steel  supplier's... 1026 DOM.. in any
up to 12".   All their  1026 DOM is the same...  75 ksi.  AS  sells 1026
masts in 87 ksi.
4130 chromoly can be had in 104 ksi  from AS...25" thick.   4130 chromoly in
106 ksi
can be obtained from US Tower corp.... .375" thick.

Check out the below calcs. 

1.9" x .145"  wall  x 35   ksi =   42 mph  [sched 40]
1.9" x .200"  wall  x 35   ksi  =  47 mph  [sched 80] 
1.9" x .950"  wall  x 35   ksi  =  60 mph   [SOLID ! ] 
2"    x .25"    wall  x  75  ksi  =  78 mph
2"    x .25"    wall  x  87  ksi  =  84 mph
2"    x .375"  wall  x 75   ksi  =  87 mph
2"    x .25"    wall  x 104 ksi  =  92 mph
2"    x.375"   wall  x 106 ksi = 104 mph 

104 mph / 92 mph = 1.13     1.13 x 1.13 = 1.28 
The .375" thick chromoly is 28%  stronger, than the .25"  thick chromoly. 
Pressure goes up to the SQUARE of the wind speed, regardless of whose
you use. 

Here in Canada, all new tower /mast specs/ ant specs are done in pressure
[metric as well] 
Most are  converted to mph as well.... so we can relate to it... [ and lbs
per ft, etc]  

I just got  yet  3 x more pix  via e-mail... of masts  folded  right the last 3 x weeks ! 
Several more install's   I have seen... are just an accident waiting to

This has been going on since 1972, when I got my ham ticket.   Nobody seems
to... 'get it'.
No rocket science here.   Yield  strength x section modulus = max bending
moment of a mast. 
B4  pc's... I used a calculator by hand.. and the old EIA/rohn rs-222-C spec
"70 mph = 19.6 lbs per foot"
Calculate the Effective wind load of each yagi in flat plate eq.   [
projected area x .67]
Effective Wind load x pressure =  total  force on yagi.  
Total force x  height of yagi up the mast = bending moment at base of mast. 
Add in the bending moment of the mast itself. 

These days it's easier  with the various spreadsheets.   Now try and
explain to joe ham the above,
and they still  won't believe it.   Joe ham  doesn't  have a clue  what the
windload on his huge quad
actually is.  Any els  that are either vertically polarized, or on an
angle... have a huge windload. 
Point  a vertically polarized yagi in ANY direction.... and the els are
ALWAYS   broadside to the wind ! 
Same deal with a quad.   Now put the boom of the quad broadside to the
wind... yikes  look out.  

Mast selection is not to be trifled with.  Removing a bent mast is extremely
dangerous... esp  with
ants  still on it.  In some cases a  crane can't be brought in.. due to
power lines, etc, etc.  You take 
a heavy mast, loaded with ants... and it snaps off.... it can easily slice
polygon rod  + Phillystran ..
then down comes the entire tower! 

later......... Jim   VE7RF

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