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Re: [TowerTalk] mast material

Subject: Re: [TowerTalk] mast material
From: "Roger (K8RI)" <>
Date: Wed, 06 Aug 2008 16:26:57 -0400
List-post: <">> wrote:
> Julio:
> I don't totally agree with all your statements regarding top rails.  I've 
> used them very successfully in the past.  Since this goes back a few years, 
> my memories a bit fuzzy.  But, I seem to recall that there might be a heavy 
> duty top rail which is "just slightly" under 2 inch OD and not much smaller 
> as you mentioned.  I'd have to go out back and measure one to determine the 
> actual size.  
The top fence rails/pipe vary widely in strength but all I've seen had 
much more spring/give than structural steel tube.  IOW they would spring 
much farther than the steel without taking on a permanent set/bend.  
Around here what ever size fits the top of a 25 G would comfortably 
handle a small to medium size tri-bander as long as it was no more than 
about a foot above the top of the tower.  It'd also handled an array of 
144 and 440 arrays if they weren't large, BUT they would move around a 
*lot* when it'd get windy. I use a piece of    1 1/2" in my gin pole and 
its handled up to 200#. I've seen the top of that at least 2' out of 
plumb but I take great pains to avoid that situation.
It's not a material I'd recommend but it can be used with forethought as 
you've shown.

Speaking of unsuitable materials, I've even welded up "H-frames" for UHF 
quadrature arrays out of EMT and they held up just fine even in 60 Plus 
MPH winds.<:-)) OTOH they weren't overloaded and I'd not resort to doing 
that for large arrays using long 2-meter antennas.
> In several cases, I used 12'ish foot lengths for yagis mounted at the top of 
> the tower with the rotor recessed 10 foot into the tower.  In one case, I had 
> a full 20 foot length with a custom-turned insert placed down into the top 
> rail.  This one had a big  6 element 10 meter beam on a 3" boom at the very 
> top (10 foot out of the tower).  I can't count how many ice and snow storms 
> that combo survived.
> If any mast material's overloaded, it will bend.  Doing the analysis is the 
> first best step.  
> 73 charlie, k1xx

Roger (K8RI - ARRL Life Member)
N833R (World's oldest Debonair)


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