[TowerTalk] Rope breaking strength vs working strength ???

[Pete Smith]

At 08:48 PM 8/21/00 -0400, Tom Rauch wrote:
...
>And remember if you set tension BEFORE the antenna is out near 
>the center of the span the tension will skyrocket when the antenna 
>hits anywhere near the midpoint.
>
>The force multiplication can be tremendous if nothing gives!
>
>It is important to always have enough sag in the line that the angle 
>of V when the load is at the center of the line does not become too 
>shallow. As that angle (when the load in the center of the line 
>cause the line to V) approaches 180 degrees (a perfectly straight 
>line) on the line, the tension in the line will approach infinity!  

This is painfully true, as a friend found when his 2" .25 wall steel mast
bent under the load imposed by a 100-lb antenna on a trolley line of 3/16 EHS.

It's also a truth worth remembering for slopers and K8UR-type arrays.  They
work best if you have a LOT of ground around the tower, because if you try
to take too much of the sag out of the line supporting the elements you
quickly run into that infinite-tension conundrum.  It's best if you can
pull the ropes supporting the elements out to ground level at ~1.5 times
the tower height, to keep the tension on them down to a reasonable amount
while still getting the elements out at an angle of ~45 degrees.  Actually,
best of all is to build the elements into your guy wires, but that takes
more forethought than I usually exhibit.

73, Pete Smith N4ZR

The World Contest Station Database 
is back up and running at
http://www.qsl.net/n4zr 



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