My thoughts:
When I see the specs on clamping wire rope, phillystran and EHS, I have
to wonder if they are talking about using one clamp, or three as is
suggested for the Phillystran boom truss? I believe The jacket
thickness of the little "stuff" is a much smaller % of the cable
thickness than it is for the 4,000# and 6,000# strength (and larger)
cables. If that is correct, then the saddle clamp use would be much
more damaging on the larger cables than on the small stuff used for a
boom truss..
Three clamps on phillystran, do not need to be tightened near as much as
one. Three clamps tightened to snug will likely give more holding power
than one tightened to destroying the Phillystran jacket. Anyone up to
testing this configuration. They also reduce the "creep" of the Kevlar
core inside the jacket.
I've seen tests run with figures, but I couldn't find a listing anywhere
as to the number of clamps. Most I've seen listed only used one saddle
clamp.
I much prefer wire rope over EHS. I admit to being prejudiced against
EHS. Yes, it's strong for its size, but I've found working with it to
be a royal PITA. Wire rope is more flexible and much easier to work
with. As far as that goes, I much prefer Phillystran over either, but
installed with the Big Grips.
When we figure the loads on the tower, we take into consideration, the
angle and resting tension of the guys. Don't forget the weight of the
guys. A horizontal guy would impart half its weight to the tower base,
A vertical guy would impart 100% of its weight to the tower base.
Neither angle is practical, but the least weight imparted to the tower
is 50% of the guy's weight. Using 1/4" EHS on a 120' tower would add
substantial weight to the tower base. OTOH that weight is a fraction of
the load imparted to the base by the guy tension.
The longest booms I've used were 42 feet of 3" on a 5L 20 meter
monobander and a 6L 15 meter monobander,. The boom truss on these could
be held with one hand, or more precisely, two fingers IF the truss
anchor points were high enough to provide the proper offset. Yes, the
really big antennas do have a substantial load on the truss, but often
the excess truss load comes from the truss offset being too low, as in 3
feet for a 40 or 50 foot boom. I use 3 feet for the lightweight 7L C3i
6-meter Yagi with a 29'6" boom.
Ice in the area? You might better raise the support a few feet instead
of beefing up everything else.
73
Roger (K8RI)
On 11/27/2015 4:04 PM, kr2q@optimum.net wrote:
I've received several replies so far and thanks to all for those.
I guess that I need to specify that in this case, I am referring to the SteppIR
antenna.
It uses Phillystran for the boom truss and Dacron rope for the element trusses.
While the instructions say to tighten again after 20 minutes, that doesn't give
me the warm/fuzzy.
One the antenna is "up," I can't really tighten them again after 30 days
without taking it down.
Hence my question.
On the Dacron rope truss, I think I actually (already) ran out of thread when
tightening down.
I think these just keep the rope from slipping out of the thimble at one end and are not
really used to hold anything "solidly." I could be wrong.
But the boom truss is a different story.
And thanks for the "data book" (120 pages) on using Crosby clamps. Wow....who
knew?
Keep the suggestions coming.
Thanks so much!
And for those of you partaking in the CQWW in 3 hours...best of luck and much
FUN!
de Doug KR2Q
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73
Roger (K8RI)
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