One hint for putting together many antennas with clamps so they stay
together (whether stamped or hose clamps, e.g HyGain, CC, etc).
One poster said his TH7 fell apart. I've had two which survived 5
serious hurricanes between them without any problems. What I found was
the clamp forces relax after the initial tightening. HyGain stamped
element clamps or telescoping tube hose clamps, it makes no difference.
So after the initial torque of the bolts, let the antenna stabilize for
a few days. Best if it can be exposed to temperature cycling, e.g. hot
day sun and cool nights. After several cycles go back and torque all
clamps and fasteners, it is amazing how much they relax. (don't forget
to lube stainless bolts or the torque is meaningless if they seize).
Of course, it's best to use a calibrated means of torque setting, but
those aren't in many ham toolboxes for smaller than 1/4-20 fasteners.
One commercial product I was responsible for had required clamping
forces near the yield points of the very high strength fasteners but the
parts would still move in service. So we set up temp cycling
ovens/coolers to cycle the assembly and then a final torque to the limit
solved the relaxation problem.
http://www.mountztorque.com/learning-center/article/techniques-reduce-joint-relaxation-fastened-joints
Grant KZ1W
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|