[TowerTalk] 2" OD Long Masts

[Roger (K8RI) on TT]

On 8/26/2014 9:23 AM, Byron Tatum wrote:

My experience:

I used 2" X 1/4" wall, with about 1.5" telescoped inside it.  Both masts 
are DOM 1/4" wall.
http://www.rogerhalstead.com/ham_files/Tower29.htm
The TH-5 is abt 2' above the top of the tower(100'), 6-meter 7L C3i at 
15' (~115') and the 144/440 arrays on a cross boom at 30' (~130')
Yes, it's too long, but never bent, even in winds approaching 70 MPH.  
OTOH  the cross boom and top antennas moved far too much to be useful in 
winds much over 25 MPH.  One of the 2-meter antennas ended up pointing 
about 30 degrees above horizontal.  It destroyed a TB-3 and a TB-4 in 5 
to 6 years. It also destroyed a couple Ham IVs and and HDR-300 rotator. 
I finally installed a PST-61 which worked for several, but water 
collecting on the top caused the shaft to rust, destroying the seals 
which let water into the housing and that destroyed the bearings.  I 
rebuilt the rotator and added protection for the top seal. 
http://www.rogerhalstead.com/Gears.htm   It's amazing that nothing broke 
on those antennas.

73

Roger (K8RI)

> Hello-
>    For years I have used the 2" OD, 6061-T6, 1/4" wall x 24' long aluminum masts to stack VHF and UHF antennas. I have seen these take a bend a time or two over the decades.
>    I wanted to ask:
>      1. If I was to switch to 2" OD steel, as a mast to extend about 15'-18' out the tower top for stacking VHF/UHF long boom yagis, what would be a suitable grade of steel, the finish and wall thickness?
>      2. I have heard of inserting a smaller aluminum tube inside the 2" aluminum mast, in the area where the mast exits the tower top and on above a bit. I wanted to ask if someone here has experience with inserting an aluminum tube inside the 2" OD mast? I would assume it would be 1-1/2" OD, of similar material and length and what wall thickness?
>    I guess reasons I have stayed with the aluminum masts is that they are lightweight and easy to handle, plus no rusting down in this Gulf Coast area.
>       Thanks, Byron WA5THJ
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73

Roger (K8RI)


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