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oh7ug Equipment

Broken 18m Spiderbeam Pole

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The 18 m Spiderbeam pole mast is made from telescoping sections which are secured with clamps. There are 12 sections each 150 cm when extended. I'm using it as 80 m vertical antenna. The pole is fastened up 2 meters to the house wall, tip being at 20 m level. The guy attachments were above 4th, mid 6th and above 9th sections, or 8m, 11,75m and 15,5m levels from ground. The guy wires are 3 mm Dyneema (similar to Spectra) yacht racing wire, being in place for nearly 4 years, so pre-stretched.

This weekend we had extremely high winds with gusts reaching well above 20m/s speeds. I saw the pole wobbling between guying levels in the gusts.

On one of the gusts the pole suddenly bent about 90 degrees, most of the pole above the first guy level being about horizontal (I saw it happen). I had seen this before with two sets of guys (above 5th and 9th section), and had added one more set of guys to stabilise the pole.

Spiderbeam 18 m pole broken due gusty wind

The pole broke at three points. At lowest guy point above 4th, 1/3rd way up 6th and just above sixth section. The first one to go may have been the 1/3rd way up 6th section and the two joints breaking caused by the collapse and the pull shock from guy wires.

It looks like the 7th section had slid down about 5-7 cm due to wind stress and perhaps the clamp not being tight enough. Both this and the wobbling may have caused guy wires to slack a bit too much and allowed the pole to bend in the wind gust. The guy wires were intact and none of them broke.

I will replace the pole, but I'm considering to move to use the new 26m pole instead and take the top 4 sections off.  Alternatively I could take the bottom section and three top ones off. I am worried of the 18 m pole being too flexible and wobbly in gusts.

Using the the 26 m pole for 80m full size means to reduce it to 20m tall, but I could leave the bottom section on ground level instead of lifting up 2 meters (as with the 18m pole). We'll see. But now I will be QRT for a few weeks :o(

Last Updated on Sunday, 23 January 2011 19:27  

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