When looking out of the window this morning I noticed something was wrong with the 4m/6m duoband antenna.
Half of the 4m reflector was missing. We had some large winds last night with heavy windgusts, very unusual for this time of year. It looks like the wind has found the weakest point. It is no problem to repair but takes time I do not have at the moment. The weather forecast is not as good either.
Found the missing part between our garden and our neighbour just at the border. But can't use it anymore. Bought a new tube today. I found a solution to make it mechanically stronger and probabely have to work on all radials in time.
Of course, now the antenna is out of order, we will have amazing ES propagation in the next few days...
Bas, this happened to me before with a 2-element Yagi for 70 MHz. The problem was that there was a mechanical resonance with the reflector and it would vibrate and 'sing' at a certain wind speed. That resonance finally resulted in the reflector snapping in two. When you put the antenna back up, listen for a vibration when there is a gentle breeze or look at the end of the reflector element and see if it is vibrating.
ReplyDeleteHello John, now you write this to me.....indeed I heard a vibrating sound. Couldn't see or locate what it was. Now the element broke the sound is gone. What did you do to prevent this? I will improve the reflector element mechanically now and turn my antennas 90 degrees from the winddirection. Hopefully this helps. Tnx, 73, Bas
DeleteI've heard that for HF Yagi's, they put a rope through the element and then tie it off. Anything to stop it vibrating.
DeleteHallo Bas, er stond een stevige wind 4 en 5 mei. En nog steeds fris voor de tijd van het jaar. Voorlopig blijft het koud voor de tijd van het jaar, van mij mag het wel wat warmer worden. Succes met de reparatie van je antenne. 73 Paul
ReplyDeleteHallo Paul, ja zeker stevig. Bij jullie was het nog heftiger zo te zien op de windkaart. Ik probeer zaterdag of zondag de boel weer te repareren.
Delete73, Bas
Die End Fed draad hangt er 10 jaar zonder problemen hier. Vangt niet zoveel wind. 73 Paul
DeleteSorry to hear about your problem, Bas - we don't have 70 MHz privileges here but I will monitor 6m for increased ES! Good luck getting it fixed quickly.
ReplyDelete73,
John
How annoying! I wonder what the securing bracket for that element looks like? Was it quite a weak design from the start? Resonance and vortex shedding can be a problem, but shouldn't lead to a breakage. I see it under winds of about 70km/h sometimes, but is not very common (this depends on spacing, environment, etc, of course).
ReplyDeleteHello John, to answer ur question. See:
Deletehttps://pe4bas.blogspot.com/2020/06/4m6m-yagi-some-progress.html
73, Bas
Certainly not a bad design. I wonder what happened?
Delete