Date: Fri, 26 Aug 2011 11:27:13 -0400
From: "Tommy Alderman" <aldermant@windstream.net>
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!
73,
Tom - W4BQF
## what mechanical designer's ? Optibeam is a one man show, I know the
fellow,
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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