[TowerTalk] Mast Material EMT

[Timothy A. Holmes]

Ok cool, I'll have to do some figuring, but that sounds good!  I have 20 
feet of mast that is alread in use, its a bit gnarly, but I think i 
could extend it with the emp inside the tower

TIM
W8TAH

On 3/12/2016 10:42 PM, Wilson wrote:
> I use EMT exactly this way.
> There is NO issue within the tower, just a modest compression load and a tiny torque.
> I use the splices made for the EMT, but I drill 3/16” holes through the EMT so the screws thread through the coupling and into the EMT.
> I’m sure these will eventually wallow out, so you might want to drill an additional pair of holes in the couplings.  With an A-3 tribander, I see no problem after a couple yrs of near daily use.
>
> I use a centralizer at each tower joint.  The ends of RG-6 cable spools fit perfectly within 25-G, not quite a foot in diameter, I think, and make fine centralizers when heavily varnished.
>
> Your problem is above the tower.  EMT comes in 10’ pieces, AFIK, and the couplings wouldn’t begin to take the bending load due to even one Yagi .
> You need at least two feet within the tower, leaving eight feet for the stack.  Not near enough!
> The EMT will obviously stand up fine, until you have serious wind.  Maybe you can find a mast calculator that will estimate a design speed.
> It seems to me that your stack is an overreach for any reasonable mast, in terms of antenna separation, but you can get a 20 or 22 foot mast if you want to go for it.  Then you could splice the big mast onto EMT within the tower.
>
> What you can get away with depends upon your wind exposure and how frequently you are willing to replace the mast and maybe repair antennas.
> WL
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