[TowerTalk] Sorry to bring up an oldie - Mast Material

[K8RI on TT]

On 3/9/2011 4:24 PM, K7LXC at aol.com wrote:
>
> In a message dated 3/9/2011 12:01:25 P.M. Pacific Standard Time,
> towertalk-request at contesting.com writes:


As Steve says, the tripod mount is likely the weak point and not the 
current mast.
I purchase 6061-T6 in 24' lengths with 1/8", 3/16" and 1/4 wall. No, I 
would not recommend a 24 footer be used in your tripod.  I'm looking for 
some stronger alloy and temper.

As for your system I'd not go more than a few feet above the tripod, 
unless the roof is reinforced under the tripod and the tripod is bolted 
to/through the reinforcing and not just into the rafters.

Wind is strange as to what survives and what fails.
I used to install TV antennas as a sideline back in the 60's and early 70's.
At home I had a 5L 20 meter KLM on a 40' tower, a 6L 15 Meter KLM on a 
40' tower and a 7L 10 Meter Wilson (39' boom) on a 40' tower. These were 
relatively light steel towers on dirt bases and 3 way guyed just below 
the top of the tower.  Yes I needed larger towers but that is what I had 
at the time.

I installed a new, fairly large TV antenna just above the top of a roof 
mounted tripod. This tripod had two lag bolts in each leg that ran 
nearly through the respective rafter in pre drilled holes so they 
wouldn't split the rafters.  Just a day or two after installing the TV 
antenna (remember I did a lot of these) we had a rather strong 
thunderstorm. It literally split the rafters pulling the bolts out and 
took the tripod right off the roof, destroying the antenna in the 
process. Yet the wind did no damage to any of the big antennas on the 
40' towers.

Just because a lightly built system survives a big storm, does not mean 
that system will normally, or can normally be expected to survive 
another storm of the same intensity. Nature is fickle!

73

Roger (K8RI)

>>   Im really confused.  Id like to buy Local, because  the mail order
> houses have
> Really high prices and high shipping
> plus  they only do 5 or 10ft intervals.
>
>>   I have a Glen Martin 9ft  roof mount tower.  Its just shy of 4ft from
> the rotor
> to the top of  the tower.  Right now I have
> a 2 1/2" Fence Post mast (really heavy  wall) that I hold an A4S up with.
>
>>   A4 is going bad so I  decided to get my dream antenna the standard
> SteppIR 3
> element beam and  nothing else will go on the mast.  I would
> like to get 8ft as that  will give me 4ft above the tower, I can put the
> antenna
> at 2 - 3 feet and  be ok.
>
> Hiya, Scotty --
>
>
>      The 3L SteppIR isn't appreciably bigger than the  A-4 you're currently
> using. Go ahead and use what you've got.
>
>      If you want to go a little higher, use 1.5"  galvanized pipe (that's
> the ID measurement - the OD is 1.9"). The SteppIR  U-clamps are very snug for
> a 2" mast so they'll work FB on a 1.9" piece of  steel.
>
>      The main factor is that it's going on a  roof-mounted tower. The tower
> will likely blow off the roof before the mast  (whatever it is) bends.
>
> Cheers,
> Steve     K7LXC
> TOWER TECH
> and
> _www.championradio.com_ (http://www.championradio.com)
>
>
>
>
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