[TowerTalk] Aluminum Masts

[K7LXC@aol.com]

In a message dated 06/12/2000 12:06:38 PM Pacific Daylight Time, 
DAVED@ctilidar.com writes:

> I'm wondering what you guys think about long aluminum masts. I've got a 17'
>  GME roof top tower which puts my C3-S at about 42' in height with 2' of 
mast
>  above the tower. I'm thinking about getting a 20' aluminum T-6061 2.25"
>  diameter 0.25" wall mast to put in it with 10' sticking out the top, 10'
>  staying in the tower. I'll have to move the rotor bracket down from roughly
>  3' from the top to 10' from the top. The thinking is that this will
>  strengthen the already strong and stiff tower. I'm planning on putting
>  modest beams on it (C3-S) or home brew beams in the 30lb and <8sq ft 
surface
>  area class.
>  
>  Is this mast ok for this? 

     Like they say in engineering discussions - it depends. What state and 
county are you in? Or do you already know the county windspeed rating?

     It sounds like your requirement is pretty moderate so it might be okay 
but will need more info to see. 

> Will it be real noodley and spooky to climb on? 

     YES! I wouldn't climb it myself.

>  Is there something better for the same $.

     You've got two mast choices - aluminum or steel. Aluminum resides in the 
lower end of the yield strength spectrum - about 35kpsi. Steel pipe is that 
or less. Alloy steel tubing is that strength and up. The sometimes 
unacceptable stuff is cheap - the real stuff isn't; you get what you pay for. 

     I guess the real question is: Is another 9 feet of elevation going to be 
worth the expense, effort and extra stress on the tower system? You might see 
some small changes in antenna performance but it's only going to make a 
*small* improvement. You have to almost double the height to really see the 
benefit. Have you modeled this?

Cheers,   Steve   K7LXC

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