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[TowerTalk] Optibeam OBLY14-5

To: <towertalk@contesting.com>
Subject: [TowerTalk] Optibeam OBLY14-5
From: "Jim Thomson" <jim.thom@telus.net>
Date: Fri, 16 Nov 2018 07:36:07 -0800
List-post: <mailto:towertalk@contesting.com>
Date: Thu, 15 Nov 2018 10:42:45 -0800
From: JVarney <jvarn359@gmail.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Optibeam OBLY14-5

<I bought a used OptiBeam 11-3.  Your post probably explains why the
<previous owner replaced all of the original elements with DX
<Engineering tubing.

<Kurt has noted -- and I've seen -- some wear issues where the
<square U-bolts for the elements meet the square boom. The sharp
<corner of the boom causes a stress concentration at that point.
<There are some places where the U-bolts have worn a groove into the
<boom corners.  I could see where in the long run this could initiate
<a stress crack in the boom and could eventually lead to boom failure.


<I'm not too concerned about it, but then I have the luxury of a tower

<friendly location where high winds are very rare and there's no ice.


<73 Jim K6OK

##  I dont  see  any advantages to the use of square booms.  Optibeam uses 
round 
booms on a lot of their other yagis, go figure. 

##  My problem with the tubing optibeam uses  for eles  is, its all metric  
tubing,
unobtainium  anywhere in NA.   And none of it neatly telescopes. 

##  6063-T832  is  1/2 the price of 6061-T6, and is nearly the  same yield 
strength,
39 ksi  vs  40 ksi,  big deal.  6063-T832 in any diam, is readily available 
from DX eng.  
My understanding is the metric tubing used in EU, is a lower ksi rating than 
the more common
39 / 40 ksi material used in  NA. 

##  For  boom material,  6061-T8, available from DX ENG is superb material.   
Comes
in  .120 wall, which means it all telescopes  nicely.  6061-T6 boom material on 
the other hand,
comes in .125 wall, which does  NOT telescope, pita, and requires  .005  to be 
turned down
on a lathe.. more pita. 

##  The newer  6061-T8 boom material,  in .120 wall, is also readily available 
from DX eng, along 
with every type of  SS u bolt and solid saddle combo you can think of. 

##  If you really want to go crazy, and  HD,  channel aluminum in various  
widths is also readily available 
from any local metal shop.    Channel aluminum is ideal for mounting els to a 
round boom,  bomb proof. 
Back in the late 70s,  I saw a fellow use channel Aluminum for mounting els to 
a round boom.... but in a 
unique fashion.   Half  round holes  were cut on both sides of  the vert  walls 
of the channel Aluminum. 
The half round holes, were of course the same diam as the diam of the boom.   
The half round holes
on both vert walls of the channel aluminum  were  dropped over the boom, then 
welded.  This process was
done on a dead flat table..and repeated  for  each  element location.    The 
actual ele is then simply
U bolted to  the   channel Aluminum  flat portion, at each end. 

##  End result is the channel aluminum boom to ele assys   are bullet proof.   
They cant and  wont break.
And no need to spend a lot of time trying to align brackets to a boom.   Draw 
back is, the ele positions 
are now permanently fixed. 

## Channel aluminum comes in various  widths and also various  vert wall  
heights.  The last stuff I bought
was  4 inches wide x   .250  inches thick.   The pair of vert walls  were  2.0 
inchs tall x .281 inch thick..
and made  from 6061-T6.     You can also get the vert walls  in 2 inches   tall 
  x .25 inches thick. 
Several versions are readily available  for the  4 inch wide channel Al, like  
4 x .187  with  a pair of 1.625 tall  x .25 thick  vert portions. 

##  You can also get  channel aluminum in 2 and  3 inch widths..and also  6 and 
8 inch widths.   They typ come in  10 and  20 foot long lengths . I just
get em to cut to the desired length I want.   Typ   4 inch wide  x   8-10 inch 
long for  20m els.  And a lot longer for  52-59 foot long
40m shortened els,  like   16-24 inches long.    I used  16 inch long pieces to 
retrofit onto my  F12  340N  yagi.  The oem  F12 flat plates
on mine were all slightly bent in the middle.   F12 had used a flat plate 
bolted to the underside of their ....wrap around bracket. 
Part of the problem was the flat plate they used, ends up with a slight gap 
between top side of plate and  6 oclock position
on the boom, hence the flat plate bending at the same point.   Flat plates  
tossed and replaced with channel  Al..and a lot longer,
problem solved. 

##  I bought a lot of  4 x 2  channel aluminum from the metal scrap dealer, in 
pristine  shape.... in   6-10 ft long 
lengths.    I then just cut it up to  desired lengths.  They were used on a 
long boom 20m yagi back in the late 70s,
and also  a long boom  10m  yagi   in the early 80s.  Those designs back then,  
I just used a pair of  U bolts to bolt
the channel al  to the boom.... NO mouse holes or  welding. 

Jim   VE7RF         



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