[TowerTalk] Aluminum Masts

Robert Chudek - KØRC k0rc at citlink.net
Sun Aug 20 13:24:03 EDT 2006


We just had a discussion regarding masts on the Minnesota Wireless Assn 

You can use this on-line mast calculator to determine whether an aluminum or 
steel mast is needed for your specific situation:  It's provided by WD9P and 
you will
find it here: http://www.math.niu.edu/KARC/mast

In general, if you're not stacking large yagi's, and you don't live in a 
hurricane zone, aluminum can meet the task. But it's best to do a "worse 
case scenario" for your situation and then decide which way to go.

BTW, the 35,000 psi figure in the calculator for aluminum is conservative, 
6061-T6 is about 42,000 psi (a pretty common alloy) and the 7075 alloy (if 
you can find it) is over 70,000 psi. Chrome-molly steel is generally 110,000 
psi. It's best to ask the supplier for the exact specifications of their 
material but you can do a Google search to get a "feel" for reasonable 
figures to use in your calculations.

The calculator is *fun* to do some "what if" scenarios... What if I pushed 
that TH-11DXX (12.5 ft^2) antenna up from 1 foot to 15 feet above the top of 
the tower?

73 de Bob - K0RC in MN

> Message: 1
> Date: Sun, 20 Aug 2006 04:13:15 -0700
> From: "Bill" <w7vp at comcast.net>
> Subject: Re: [TowerTalk] Aluminum Masts
> To: "JC Smith" <jc-smith at comcast.net>, <britech at earthlink.net>,
> "'Tower Talk Reflector'" <towertalk at contesting.com>
> Message-ID: <031d01c6c449$a2a84030$6601a8c0 at attorneyg97r4a>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> reply-type=original
> Allen
> There are two primary issues to consider between steel and aluminum.  They
> are torsional rigidity and yield strength.  Since aluminum has about 1/3 
> the
> Young's modulus of steel it will require a thicker tubing for the same 
> outer
> dimension to obtain ths same torsional rigidity.  Aluminum is also 
> generally
> much lower in yield strength than steel too (although there are weak 
> steels
> and storng aluminums) so  the amount of torque that will induce a 
> permanent
> set in the mast will also depend on the cross section being used as well 
> as
> the yield strength.  Each of those questions would need to be answered in
> order to make a comparative determination.  I have used both successfully
> but each situation needs to be considered individually.
> 73
> Bill
> W7VP
> ----- Original Message ----- 
> From: "JC Smith" <jc-smith at comcast.net>
> To: "'JC Smith'" <jc-smith at comcast.net>; <britech at earthlink.net>; "'Tower
> Talk Reflector'" <towertalk at contesting.com>
> Sent: Saturday, August 19, 2006 8:09 PM
> Subject: Re: [TowerTalk] Aluminum Masts
>> Sorry, that was a bit blunt.  What I meant was you need to calculate your
>> load and see what kind of mast will handle it.  Obviously, "regular"
>> aluminum (like 6061-T6) won't handle the load steel will, size for size.
>> OTOH, if you really need aluminum for some reason, there are some really
>> strong alloys that will (at a price) match, and even outperform, some
>> steels.  I bought a military surplus, telescoping aluminum mast at a
>> swapmeet many years ago.  Have no idea what the alloy is, but it's one
>> heavy-duty chunk of metal.
>> Steve, K7LXC, who sponsors this reflector, has a nice little program
>> called
>> MARC (Mast Antenna Rotator Calculator) that will help you figure out what
>> you need.  You might check it out at:
>> http://www.championradio.com/misc.html
>> 73 - JC, K0HPS
>> -----Original Message-----
>> From: towertalk-bounces at contesting.com
>> [mailto:towertalk-bounces at contesting.com]On Behalf Of JC Smith
>> Sent: Saturday, August 19, 2006 7:52 PM
>> To: britech at earthlink.net; 'Tower Talk Reflector'
>> Subject: Re: [TowerTalk] Aluminum Masts
>> "Expert" opinion:  do the math.
>> Link to aluminum masts: http://www.texastowers.com/aluminum.htm
>> 73 - JC, K0HPS
>> -----Original Message-----
>> From: towertalk-bounces at contesting.com
>> [mailto:towertalk-bounces at contesting.com]On Behalf Of Allen R. Brier
>> Sent: Saturday, August 19, 2006 6:36 PM
>> To: 'Tower Talk Reflector'
>> Subject: [TowerTalk] Aluminum Masts
>> Sometime recently, someone provided a source for aluminum masts. I would
>> like to get that information again, please.
>> Also, what "expert" opinions can I get from the group on using aluminum
>> masts vs. steel?
>> 73,
>> Allen Ross Brier, N5XZ

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