What else that works instead of rope, is either .125 SS cable.... or .09375
SS cable..
or galvanized winch cable in the same 2 sizes. Then a SS hose clamp to hold
the cable
to the outside of the tip. IE: cable run down the inside of the entire ele,
then out the tips, then
folded back on the outside of the tips, then SS hose clamped down.
You need a bit of weight to kill the vortex shedding. A buddy across town had
his 204BA up
100 ft on 25G.... and when he finally took it down, all 8 x ele tips were
almost ready to pop
out the ends. The oem Hy – gain ele clamps did not do the trick. The winds
were strong up
there..and the tips and also inboard ele sections started to migrate outwards.
I had a 204BA with a wilson 5 el 15M yagi stacked.. plus a 5 el, forget the
brand name.. 10m yagi,
back in the 70s. No rope on any of them. Both the 20 + 15m yagis would
vibrate like crazy, in a
light breeze..but only when turned a bit at an angle to the wind. But the
vibration was aprx 6 ft
out from the boom, not the tips. They would both vibrate up 3 inches..and
then down 3 inches,
6 inches in total. Later, my hb 20m yagi did the same thing, but nothing ever
broke.
My 20 + 15m F12 yagis, plus my buddys F12 5BA never had a vibration / vortex
shedding issue,
regardless of wind speed, or yagi orientation to the wind. They just dont
vibrate... no rope or cable
required.
The F12 yagis dont have the swedged els. The 20m eles use a simple .375 - .5
– .625 – .750 – .875 – 1. – 1.125
taper to the eles. The 1.125 is double walled. For even greater wind speed
capability, the 1.00 section can be
double walled as well.
Baffles me why hy-gain et all, just dont re-design the ele taper on their
yagis..and eliminate the swedges.
You dont require the large OD sections in the middle, like the 1.25 sections on
the 204BA. You can run the
various tapers through either of the mech software programs to see the effects
right away. Even if you wanted
to use 1.25 tubing the center, you still taper off with the 1.125 – 1.00 –
.875 etc etc. Still wont vibrate.
Another fellow across town had his internal rope start to migrate out one ele
tip... with several inches of it
flapping in the breeze. It had cut loose at both ele tips..and was free to
migrate out either end. Be careful
with what rope you use, if exposed and folded back on the outside, some of it
can degrade with UV.
Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|