[CQ-Contest] An Antenna Riddle

Bruce Sawyer zf2nt at candw.ky
Fri Feb 18 19:31:33 EST 2000

This being the day OF the contest, I suppose it's natural that "interesting"
things should happen.  So here's a little puzzle I hope somebody can explain
to me.  Not that I'm going to be able to do anything about it before the
contest starts, but I'm still curious.

I have one tower with a Force12 4 element 15 meter beam at the top (about
56') and a second KLM 5 element 10m beam about 7' under it.  (A 10' mast was
the longest I could get down to Little Cayman.  It's not like I'm within
driving distance of Texas Towers.)  That KLM 10m beam has always been a
fantastic performer.  When it works, I love it.  The problem is that it's
built as though it came from Starkville, MS.  When I first put it up this
year, the SWR curve was shifted up from where it should have been by about 1
MHz, and the performance was lousy.  Then about two months ago, the
reflector suddenly worked loose and fell to the ground.  Instantly, the
antenna was doing great.  I used it in several contests, and it was
wonderful.  Of course, there was no F/B, but at least the nulls on the side
were deep.  Then yesterday--naturally, the day before the contest--a tip on
one of the directors worked loose and came to the ground.  The antenna was

This morning I pulled the antenna down and put the director tip back in.  I
also put the reflector back on the beam.  When the reflector came down
before, I noticed that the shorting strap between the two element halves had
broken due to metal fatigue.  (This antenna always vibrates furiously in the
wind.)  I assumed that the open between those two halves was the cause of
the problem I had before.  So after getting the beam back up in the air,
it's behaving just like it was in the beginning--SWR curve shifted up 1 MHz
and lousy performance.

So what's going on here?  I checked everything out on that beam before
putting it up again.  Climbing towers in the noon sun on a windy day on
Little Cayman is NOT how I choose to amuse myself.   Is it likely that the
beam is fine, but simply coupling with the 15m beam?  That 15m beam is
working great, by the way.

Bruce, ZF2NT

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