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[TowerTalk] Antenna location for hurricane

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Subject: [TowerTalk] Antenna location for hurricane
From: "Jim Thomson" <>
Date: Fri, 26 Aug 2011 09:21:59 -0700
List-post: <">>
Date: Fri, 26 Aug 2011 11:27:13 -0400
From: "Tommy Alderman" <>
Subject: Re: [TowerTalk] Antenna location for hurricane

I think it is silly to listen to what 'some xxx user' says! How the heck do
they know? The only thing they did was fork over the bucks to buy the
antenna. Listen to what your manufacturer tells you to do because his
mechanical designers most likely know better than 'some xxx user'. The
Optibeam designer says to point the end of the elements into the wind, so
that is what I do with my two Optibeam yagi's. Irene just passed about 300
miles east of my QTH in south Georgia and nothing but a slight breeze from
the east. 

Good luck to those further up the best coast! Hihi!

Tom - W4BQF

##  what mechanical designer's ?    Optibeam is a one man show, I know the 
and that's before he got into the ant business. He's an accountant by trade.   
The reason the
els  are pointed into the wind [boom broadside to the wind] is simple.  The 
boom is stronger than
the els.  The flip side to that argument is also simple, most yagi's are not 
torque balanced.  IF the
yagi is NOT torque balanced, you are better off to point either end of the boom 
into the wind.
IF the yagi is not torque balanced, and you place the boom broadside to 
the...100 mph wind,  you 
will be in for a rude awakening, as your boom to mast clamps will slip, and if 
they do hold, the next to go
is the mast to rotor clamps.  Most rotor clamps are a poor joke at best.  Using 
U bolts  for the boom to mast
connection is also poor eng practice.

##  The best I could come up with is, use a torque compensated yagi, then use  
DX engineering jumbo proper boom
to mast clamps [ like 3 of them].. they come in 2", 2.5", and 3" only.  They 
have a textured finish on the insides, and use a pair of
G-8 armour plated bolts. They will NOT slip on a mast.      I use a K7NV small 
prop pitch with the
mating K7NV mast clamp. [ he makes them in 2" and also 3"..and will make custom 
sizes].  Those clamp assemblies
use G-8 hardware, and trhe mast barely slides into the K7NV steel mast tube.  
His mast tube is slit  down one side, with a 
welded lip on either side of the slit.   The 5 x G-8 bolts [ with nylocks]  are 
 torqued down,and the mast is not about to slip,
since  the assy has loads of  surface area to grip any mast. 

##  I use a HB  version of the infamous  F-12  double plate boom to mast assy.  
 Except my plates are thicker, 3/8"  thick
6061-T6.  They are also slightly bigger, 8" x 17", and 2 of them, one for boom, 
one for mast., and 3 of the dx eng super mast
clamps. [2 at the top, one at the bottom].    You can also use those super mast 
clamps to  hold the boom to the plate if you want to. 
they are the real deal.   The dx eng SS U bolts  and solid saddles are also 
superb, a lot better than using typ F-12  plated steel U bolts  and
no saddles at all.  k7NV and other's have software that  will  design the 
torque compensation plate for any yagi..and also the 2nd method, 
designing the counterweight to stuff into the light end of a boom. 

##  I used his software to design a TQ comp plate for a buddy across town, who 
has a hb yagi, with a lot more boom on one side of the 
tower  vs the other.   We tested the TQ plate, by temp installing the yagi on a 
short, 30' tall, freestanding tower.   In a 35 mph wind, he could
climb up there and turn it by hand. [ no rotor,coax used for this test, just 2 
x thrust bearing, mast + yagi].   Without the TQ comp plate,
 the boom would weather vane in the wind, and chewed up several rotor's.

## using the same software, it's pretty easy to design any yagi eles to handle 
100++ mph winds, boom included.   You can also stuff ur
existing yagi ant tubing schedule into the software, and see at a glance, where 
all the weak points are.   The fix for them is straightforward,
either change the tubing schedule/ and or  use doublers inside the existing 
weak spots.  Most ant makers  will offer their products in
 a wide variety of wind survival ratings.   A bare min of 100 mph [no ice]  
will cover most needs, and a 120 mph version  doesn't weigh, or cost
much more, and is a good investment.    6061-T8  with a 50 ksi yield strength 
rating is readily available  for boom material  from dx eng  and
other AL  sources.   The T-8 version is aprx the same price, and is 25%  
stronger than the more common T6  version [40 ksi yield]. 

Later... Jim   VE7RF     

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