[TowerTalk] Inverted vee mounted above HF Yagi

[Chuck Lewis]

Jack, for the past 10-12 years, our club has used a simple device for our 80M vee over a 20M quad for Field Day. We found a sealed automotive bearing whose O.D. was just right for slipping into the mast we use to hold the Vee above the quad (you'll have to do the math to figure out how high it needs to be to clear the A3WS). Slot the mast so the bearing can be FIRMLY clamped into the mast at the top. Find a 1/4-20 galvanized eyebolt about 10" long, and bend the threaded end, with heat, at 90 degrees to the 'eye-end'. Bend just enough of the threaded part to be passed through the I.D. of the bearing and be clamped in place by washers with nuts on top & bottom. We used the washers that are found at the top of automotive front shock absorber mounts (the ones that squeeze the rubber mounting washers). The nice thing about these washers (the metal ones) is that they are dished a bit and will self-center in or around the bearing I.D. while clearing the outer race. With the bent end in place in the center of the bearing, clamp the bearing O.D. in the mast using a S.S. hose clamp. Now you have a pivoting hanger that's offset from the mast by the unbent length of the eyebolt. It might be a good idea to use some cold galvanizing at the spot that was heated. 

When you choose the anchor points for the inverted vee ends, make sure they are not directly in line with the mast. There needs to be a little side-load on the eyebolt to keep it always on one side as the mast rotates under it. You'll have to adjust the antenna tension by watching the position of the pivot; pull one end or the other until the pivot is straight out from the mast and roughly 90 degrees to the plane of the vee. A loose wrap or two of coax around the mast will be sufficient. We use two 10' sections of cheap TV mast, but that's a Field Day approach and, besides, you might need more height to clear the yagi. We've always wondered about whether the threaded part in the bearing would remain lined up with the mast axis, but it has survived a LOT of Southern Summer thunderstorms and is still perfect. One weekend per year doesn't amount to a definitive test, even after quite a few years; but there's no evidence of degradation so far. I wouldn't hesitate to use it for a permanent installation, but your mileage may vary!  

Good Luck!


Chuck, N4NM


  ----- Original Message ----- 
  From: Jack White 
  To: towertalk at contesting.com 
  Sent: Wednesday, August 17, 2011 2:31 PM
  Subject: [TowerTalk] Inverted vee mounted above HF Yagi



  Hi Guys

  I have a standard 60ft Versatower with a Yaesu G-1000 and bearing mounted at the top, and just above this I have a Cushcraft A3WS (pic on QRZ). I want to extend the stub mast about 20ft above the A3WS to support the centre of a 160/80/40 trapped inverted vee. I'm looking for some type of mount that will allow me to mount the centre of the inverted vee at the top of the stub mast and remain fixed whilst the stub mast rotates. Ideas/advice would be great.


  73, Jack G8DX


         
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