[TowerTalk] Tribanders on 12m/17m

[W5CPT]

Rick brings up a good point.  Years ago I was given a Hornet 3L Tribander because it was "dead". It would not show a decent SWR 10, 15 or 20M.  I opened the traps, the only common failure point I could figure, and the traps in the driven element were gone.  The Hornet had plastic forms with heavy wire (about 10GA) coils wound around them.  The plastic forms were so brittle they would crumble in my hand.  The wire for the coils was burned open in few places and there was evidence of arcing inside the trap covers.  The traps in the reflector and director were in better shape but still junk.  When I asked how much power the previous owner had run through it he said only 100W but on 17 & 12M.  He admitted it failed while working 17M.  You can develop some very high voltages in the traps in places where it was not designed to be.

I made an nice 15M beam out of it, fed it with a HyGain BM86 balun, and pointed it fixed toward Europe. 

The above is one reason there is a 5 band LPDA on my tower.

Clint - W5CPT

  ----- Original Message ----- 
  From: Rick Stealey 
  To: towertalk at contesting.com 
  Sent: Wednesday, September 23, 2009 3:35 PM
  Subject: Re: [TowerTalk] Tribanders on 12m/17m





  ----------------------------------------
  > Does it show gain or loss ....

  The pattern is largely influenced by the height above ground. I used a model of a 20 meter beam, and changed the frequency to 18 MHz and the pattern is essentially the same as a dipole gives. At 70 feet height it has three lobes, at 10, 35 and 60 degrees above the horizon, with a huge amount of power radiated straight up and looking down on the antenna from above it looks just like a dipole. 
  In my opinion you are going to get no advantage at all over a simple dipole. In fact be careful driving a trapped yagi on other bands, especially if you are running power - the traps may not take it.

  Rick K2XT
         
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