Wednesday I discovered my top 6 element 15 meter yagi was suddenly resonant
at 20.7Mhz. It is an OWA design (close spaced 1st director, 50ohm feed).
I went up there today intending to swap out the balun and the coax which I
did. This did not cure the problem.
In the process of tipping the antenna down and back up again I noticed that
the SWR curve was normal again when I tipped the antenna up toward the sky
or down toward the ground. Somewhere around a 45 degree angle produced a
normal SWR curve. When it approached flat, the SWR went up again. I can't
for the life of me figure out what could be causing this problem. I
checked all of the hose clamps on the elements and they were solid.
I've taken the antenna down to the ground and tomorrow I will rebuild it.
If anyone has any ideas about what the cause could be, please drop me a line.
73
Bill - W4AN - K4AAA
Bill Fisher, W4AN (EX KM9P)
http://www.contesting.com
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|