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[TowerTalk] Need recommendations for a 40-10m. Yagi

To: <towertalk@contesting.com>
Subject: [TowerTalk] Need recommendations for a 40-10m. Yagi
From: "Jim Thomson" <jim.thom@telus.net>
Date: Sun, 6 May 2018 09:44:03 -0700
List-post: <mailto:towertalk@contesting.com>
Date: Sat, 5 May 2018 17:34:33 +0000 (UTC)
From: Timothy Coker <n6win@yahoo.com>
To: <kstover@ac0h.net>,  <rlvz@aol.com>,  <towertalk@contesting.com>
Subject: Re: [TowerTalk] Need recommendations for a 40-10m. Yagi

<I could be wrong... but I believe your not looking at an apples to apples 
windload between the two.
<I?m seeing 16.5 sq ft for the JK Mid Tri w/40m and 17.8 sq ft for the 
Optibeam. Notice how Optibeam only lists one rating where as JK lists three 
which can confuse things in that Ken is giving more information.
<As for the aluminum being the same... way smarter guys here than me. I?ve been 
curious of late if that?s really the case... I?ve been reading about some boom 
failures at other stations of late and there are some very adamant hams talking 
about the quality <differences in aluminum used. Could just be angry folks, I?m 
no mechanical expert.
<If the original op is saying he?s mainly into the contests he?s probably going 
to want to keep his contest yagi?s as clear of his WARCs as possible in order 
to avoid possible interaction so that he obtains better performance during the 
contests.
<I first started out trying to do everything I could on 10 feet of mast 
sticking out of Rohn 25G. Who knows what was happening with a TH7DX at the 
thrust bearing, an A3WS/30m 5? above and a XM240 driven element at 10? above. 
Oh and toss in an 80m <inverted V a foot below it all! :)
<Going forward I?ll put my WARCs on separate structures or as temporary wires 
as needed. Just less for me to worry about when people aren?t returning to my 
CQ?s.
<That?s me though. Try to make it so the scores aren?t so much limited by 
hardware and more by me.
<Tim / N6WIN.

## The  JK Mid tri  with 40m  IS   24.75 sq ft of projected area.    Projected 
area  means   length  X width  for each ele.  Then total up all the areas of 
all the elements.     The  16.5 sq ft for the mid tri  with 40m is the old  C 
spec.... no longer used. 
The old C spec took the projected area.. then multiplied it by .666   to get... 
effective area.   This is what F12,  hy gain, etc used...and plenty of ant 
makers still use the old C spec.   To get from old  C spec ratings.. back to 
projected area,  just multiply   by  1.5.     EG:   10 sq ft projected =  6.666 
sq ft  using c spec.    6.666  X 1.5  = 10 sq ft.   For all you folks using 
yagis  with the old C spec ratings.... multiply by  1.5  to get reality. 

##  16.5  X  1.5   =  24.75  sq ft projected... which is what the mid tri + 40m 
actually is. 

##  I would not even mess with the F or  G spec,  too convoluted and requires 
the actual installed height to be factored in, plus a ton of other variables, 
including wind exposure etc.   IE, buried in a forest of trees, in the middle 
of a wheat field, on a ridge, or next to salt water, etc.   

##  When the projected area is run through the mech software, to calculate  max 
wind rating,  like when using DX engineerings ...Yagi mechanical,   it will 
spit out max wind survival for any spec you want, including  F, G,  C.... and 
also UBC-97..with its  associated  A, B, C, D.. wind exposure.   It will also 
spit out.... No  spec.     No spec is what you get when using a wind tunnel... 
which is good enough for myself... and is a bit more stringent vs the old C 
spec.  If  you installed a wind speed indicator at the top of your mast,  you 
will get the same results as using a wind tunnel.   Yagi mechanical will also 
spit out the ele deflection at any wind speed you want, from 0  up to max wind 
survival.   Ken uses  NO spec to calculate the max wind survival ratings of his 
yagis.   Its very conservative imo.  Also when the eles  deflect, the tips shed 
wind, aka reducing the loading.   That alone will add an additional safety 
buffer on top of what the NO spec spits out.   40M el
 es  will deflect more than a 20M ele, and unload even more.  The  JK 40M els  
dont sag, and  dont require a truss.

##  Several folks have had  severe issues with the way  optibeam splices their 
square boom sections  together.   I dont like their  boom to mast assys, it 
uses  2  x muffler clamps for the mast.  Nobody uses  muffler clamps for 
anything these days, esp the types with sheet metal saddles, as depicted. 
https://www.dxengineering.com/parts/dbo-ob12-4w-p      JKs  version wont budge 
or slip on any mast.   Optibeam uses  METRIC  tubing sizes for the 
elements..and also the square and also their round booms. 
Unlike  6063-T832,  39 ksi yield strength......  or  6061-T6, which uses  40 
ksi yield strength..and both using standard tubing sizes and wall thickness,  
METRIC tubing does not telescope with a snug fit.  They make a sloppy fit and 
have to be either shimmed, or swaged.... pita.   The deal breaker for myself is 
that  METRIC  tubing is a bitch to find in Both Canada..and the USA.  A buddy 
finally found one source for metric tubing in the usa....and it was special 
order, and expensive.  That may have changed.    So even if you can find 
replacement METRIC  tubing in the usa, next up you will have to get the ends 
carefully swaged.  Any swaging process has to be done dead one.  Too little or  
too much, and you are in trouble..esp if too much.

##  If you are hell bent for the optibeam,  even if you ordered it  asap,  it 
wont  ship from Germany until  August  13, 2018.   $3378.00   vs    $2695.00  
for the JK.    The  $683.00  difference is not exactly chump change either..and 
better put towards the JK-801.  The optibeam uses an included  2:1  balun.  
That would kill it for me right then and there.   The JK uses a simple 1:1  CM 
choke for the 20-15-10m  portion....  and a 2nd  1:1  simple CM choke for the 
40m portion. 

## JK WELDS the ends of their  40 loading coils,  made from solid .25 Al rod, 
comes in large rolls.   Zero resistance connections.   I would install the jk 
mid tri with 40m just a few inches above the top of the tower, and the 801 
towards top of mast..then call it a day. 

Jim   VE7RF

        

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