80 Meter Stinger Version 3.0

As I wrote several days ago an ice storm damaged my 80 meter vertical yagi. Weight of ice on the catenaries ropes supporting the parasitic wire elements was too much for the stinger at the top of the tower driven element. Unequal ice weight on the four wire elements was a factor, probably a result of partial tree cover on the southeast element and the variety of rope diameters being used.

This is the second stinger to fail. The first one failed due to expedience: I made a couple of poor material choices because I was in a rush at the time. The second stinger survived winds well over 100 kph last summer and I thought it was strong enough to last a while. However ice is often a greater hazard than wind, and around here ice is more common than high winds. Obviously I did not design the stinger well enough.

The stinger failed where the 1.5" OD tube joins to the 1.9" OD pipe below it. This is a high stress point. After tearing the antenna apart and lowering the broken version 2 stinger I inspected the break.

I thought I had used 0.095" wall tube for this section. Turns out it was no more than 0.065" wall. Thinking back to when I built it I remembered that the 1" PVC pipe above it was slightly too large at 1.315" OD to fit inside the 0.095" wall 1.5" tube so I substituted a thinner wall tube. Amateur forensic analysis of the bent tube leads me to believe that this surplus tube is not 6061-T6 unlike the standard pipe sizes I've accumulated over the past few years.

We just had two days of balmy 5° C weather that was perfect for tower work. I dropped other projects to focus on repairing the 80 meter yagi. As the sun set on the second (and last) mild day the antenna was back in service. I had to work fast and not make the same expedience driven error I made the last time.

The version 3 stinger is exactly the same length as version 2. This is important since now that the antenna is tuned and the matching networks are fixed changes would consume far too much time and be very uncomfortable in our winter weather.

I reused the lower 1.9" OD pipes since they were undamaged. The lower pipe was left on the tower. The broken 1.5" tube required effort to remove since it was distorted by the bend. It was replaced by a 1" schedule 40 6061-T6 pipe and reducer already fabricated for another antenna project.

I slipped it into the 1.9" pipe and drilled the new pipe through the outer pipe's existing splice holes. This was quick and allowed the stainless hardware to be reused. Beware cutting debris on stainless threads since that is guaranteed to seize and destroy the fasteners. I learned this the hard way some time ago. Brush the threads clean before tightening.

The 1" pipe is shorter than the old 1.5" tube. I cut the undamaged top end of the 1.5" tube to reused the PVC top support and make up the missing length. The top segment of catenary ropes could be left in place which saved a lot of time.

With the broken tube as a length guide the tube and pipe were drilled and screwed together. Now all I had to do was install the new stinger. This is the most difficult part of the repair job.

Despite a couple of fumbles the new stinger was installed in a couple of hours. The dangling ropes inevitably tangled and had to be carefully separated and then held apart while I went up and down the tower attaching and suspending the four parasitic elements.

With that done I pushed the stinger to its full height and tightened up the tower clamps. Some lateral adjustment was needed since the force of the ice pushed the clamps out of vertical alignment.

Back on the ground I walked back and forth among the four element anchors carefully pulling them to working tension. It is important to do it in steps so that the stinger is not put under bending stress. It's tedious but necessary.

Finally it was done as the sun set. I cleaned the site, put away my tools and went indoors to check it out. The SWR was perfect in all of its directional and omni-directional modes. Mission accomplished.

Losing this antenna worried me because it keeps me competitive on 80 meters. The high inverted vee performs poorly on paths longer than 2000 km.

Now I have to hope for the best with stinger version 3.0. It is stronger but still a concern since it is quite tall and under stress during adverse weather events. Ideally I would like to increase the tower height and use a short stinger. It's in my plan though perhaps not this year.

All the ice storm damage to my antennas has now been repaired. It could have been worse and for that I'm thankful.