The below url pdf explains the 222-G spec in detail.
http://www.towernx.com/downloads/TIA-222-G_Explained.pdf
Vortex shedding is well known. Eles vibrate up + down like crazy, like 6
Inches in total,
in just a light breeze. Ask anybody who own a 204BA or any wilson product.
Those swedged eles are a pita..and so is
having to put rope inside the eles..which is still in the current Hy-gain
204-BA manual.
Where the software falls down is when long eles bend at the tips. In extreme
winds, F12 el tips will bend straight back, so
the ele looks like a U. I call that...shedding wind. If you side guy the
elements, and or construct them so the horz deflection is far less,
then you also increase the load on the tower..and mast.
Then there are other issues, like Torque imbalance...which is my favorite pet
peeve. Easily rectified with either a counter weight,
or a Torque compensation plate. Why antenna manufacturers dont incorporate
TQ balancing techniques is beyond me.
Perfectly Torque balanced... and you dont need huge amounts of torque in the
rotor. Almost like dragging a parachute behind your
car, then having to up the engine HP to compensate.
Some other issues are how ele sections are joined, and how various boom
sections are spliced or joined. I fabricate my own
boom to mast plates similar to the F12 easy on double plate concept, but use
.375 thick plates, and DXE hardware. Then its dead
simple to install the yagi... plus it wont slip on any mast, not with the use
of those DXE heavy duty mast clamps. Muffler clamps with
the sheet metal saddles have been fubar since day 1...good riddance. Other
yagi issues include overhead truss lines
on booms, typ they dont terminate high enough above the mast. Putting a
cross bar part way up the mast, with 2 x truss lines for
each half of the boom is another wasted effort, it buys you nothing..and wont
decrease the horz deflection one bit.
Most these days are using the sum total of all the projected areas of the
eles on a HF yagi..which is typ greater than the projected area of the boom.
VHF + UHF yagis are typ the opposite in some cases..with the boom having more
area. If you have something like a 80m rotary dipole stacked above a
3 el 40M yagi, then you have to calculate the sum total of the 3 els..... vs
the sum of the 40m boom + 80m dipole. Since the 80m dipole is oriented
in line with the 40m boom, you have to calculate both scenarios.
If you have a f12, M2, mosely, hy-gain product..they have used effective
area, and not projected area. Multiply X 1.5 to get reality. Better yet,
enter
each elements taper into either DXE yagi mechanical or Kurts yagi
stress.... to do the calcs. They can also easily be done on a calculator.
Ice..and Ice + wind never appears on any yagi spec..dunno why not...nor heavy
wet snow. You can enter any amount of ice in the above software. It will
spit out the Vmax
for any thickness of ice. DXEs will also spit out horz deflection in any
wind..with or without ice. And also vertical sag deflection..again, with or
without ice. I have had
a few cases where heavy wet snow fell off one half of the ele. Meanwhile, the
other half of the ele is still at least 6 inchs OD, weighs a bunch...and puts
stress on any
ele to boom assy.
I have seen pix or heard about almost 3 dozen bent mast horror stories since
1970. A partially bent or folded over mast..with yagis mounted at different
levels along the mast is an absolute disaster....2nd only to the tower
falling over. 1.9 inch OD sched 40, 36 ksi pipe does not work with a big
ant mounted
8-10 ft above tower. But folks keep on trying.
On contesting.coms home page...under strays last week, is a pix of an old 4
el, 40M KLM...where the boom had rotated 90 degs..so all 4 els were vertical.
Great, now the total windload is the els + the boom combined = disaster. Seen
the same thing happen on a F12 620 / 340 yagi. Muffler clamps with
sheet metal saddles dont work folks.
222-G is one thing..but how the yagi is put together is another issue.
Jim VE7RF
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