Allen,
We just had a discussion regarding masts on the Minnesota Wireless Assn
reflector.
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@comcast.net>
> Subject: Re: [TowerTalk] Aluminum Masts
> To: "JC Smith" <jc-smith@comcast.net>, <britech@earthlink.net>,
> "'Tower Talk Reflector'" <towertalk@contesting.com>
> Message-ID: <031d01c6c449$a2a84030$6601a8c0@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@comcast.net>
> To: "'JC Smith'" <jc-smith@comcast.net>; <britech@earthlink.net>; "'Tower
> Talk Reflector'" <towertalk@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@contesting.com
>> [mailto:towertalk-bounces@contesting.com]On Behalf Of JC Smith
>> Sent: Saturday, August 19, 2006 7:52 PM
>> To: britech@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@contesting.com
>> [mailto:towertalk-bounces@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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