[TowerTalk] Looking for good source of 20 ft mast

[Jim Thomson]

Date: Mon, 14 Sep 2015 13:33:37 -0400
From: Stephen Davis <sdavis at davisrf.com>
To: "towertalk at contesting.com" <towertalk at contesting.com>
Subject: [TowerTalk] Looking for good source of 20 ft mast

Hello all

Specs :   20 ft. 2" O.D. .50" wall chrome moly

Yep, .5 "  !

Tnx a lot.  73. Steve. K1PEK

Steve Davis
Senior RF Cable Design Engr.
& Founder
DAVIS RF Co. a  division of
Orion Wire Co., Inc.
Tel: 978-369-1738
     ALSO: Davis Rope & Cable             Assembly Co., LLC:
      Design Engrs, Distribution

# A  2.875  or 3 inch OD cm mast with just a .25 wall is one helluva lot stronger
vs a 2 inch mast with a .375 wall......yet they all weigh the same....and cost the same ! 
You can see all of that on the arrl mast software at a glance.  Huge difference in strength. 

##  as soon as u exceed .25 wall, you are essentially wasting your time and $$. At that point, 
the OD needs to be increased.   A 2 inch mast with a .5 wall  will only be a tiny bit stronger than
a .375 wall.   A 2 inch solid mast will gain you nothing....but weight + $$. 

##  in my case, the HDX-689 was all setup for a 2 inch OD mast so I was screwed.  My only option 
was to use a 2 inch x .375 wall CM mast.   Another option if u are stuck with a 2” OD mast is to
insert a 2nd tube inside the 1st one, close fit...then weld the base.   

##  for folks that actually have a choice of mast OD, always use a 3 inch OD, 4130 CM  mast...or a 2.875
inch OD  DOM mast....and both in .25 wall. 
DX eng sells the 3 x .25  CM masts.   Array solutions sells the 2.875 x .25 DOM masts. 

##  Dunno which idiot decided to standardize a 2 inch od mast for ham radio use, but it was fubar. 
I have been collecting bent and broken mast pix since 1977..think its now up to 36 or 37.   Removing
mast bent at a 90 deg..with yagis  still on it is beyond extremely  dangerous.    In many cases, a crane
cant be used, or will not fit the space, to get at them. Then what ?  Ever see one fall and slice the guy wires below it. 
Then the tower comes crashing down. 

##  use the freebie  ARRL mast software to plan your install....and also allow for future expansion. 
Sure, a 2 inch od x .25 wall CM or  DOM mast sounds wonderful, till u find its maxed out when u go to stack
your shiny new 40m yagi parked right at the top.   If a single yagi is  mounted within a few feet of the top of the
tower, anything will work, including plane jane 35 ksi water pipe, in sched 40 or sched 80.   Again the software 
will tell u at a glance if its even doable for XXX  windspeed.   

##  IMO, the mast is the most important thing up there.   It has to be the strongest component in the mix.  A mast
failure should  not even be a remote possibility.    But if you are stuck with a 2 inch od mast, your only option is DOM, and if that’s
not up to the task, then  CM.   If CM in .25 isnt up to the task, then  thicker wall CM, like .375 or perhaps .5 thick is an option.

##  hams have been cheaping out on masts since day 1...and are still doing it to this day.   Better to pay once, cry once, and buy the 
real deal..and have it hot dipped galvanized too. Use the dx eng handy cap for the very top, to keep water out of the inside.
I kicked myself many times for not buying a good mast  35 yrs ago...when they were  a lot cheaper.   A good mast will easily last a lifetime,
and have good re-sale value.   Section modulus x yield strength =  max bending moment.   Bigger OD + thinner wall results in a bigger section modulus
vs smaller diam + thicker wall. 

sri for the riot act.