This true story may help others to avoid trouble in
the future. It may also bore you - my apologies in
advance :-)
About a year ago, we bought a cabin in northern
California on a site with a decent take-off towards
the U.S. I installed a 70 foot self-supporting tower
with a 24 foot mast, and brought in a crane to mount
a C-31XR at 72' and a 2 element 40 meter yagi that I
designed at 80'. The 2 element yagi uses capacity
hats consisting of crossed 6' long .177" aluminum
rods to shorten the elements by about 15% and to move
the secondary resonance out of the 15 meter band to
reduce interactions with the C-31.
A series of mistakes and bad decisions related to
this project have cost me a bunch of trouble and time.
First of all, when I placed the hole for the tower
base, I was a bit sloppy. I didn't actually
calculate the turning radius of the 40 meter yagi, I
just picked a spot that looked to be about in the
middle of the meadow, and dug the hole. After the
fact, I measured the distance from the hole to some
nearby redwood trees, and decided that there was
barely enough room. I was wrong.
When we actually put the antennas up on the tower, it
became clear that while they would probably clear the
trunks of the trees, the 40 was going to get caught
up in the branches of the redwoods. No problem I
thought, when I get a chance I will have a tree guy
come in and trim the branches back. Until then, I
just won't rotate the antennas through the trees. My
second mistake.
I am always in a hurry when I am doing radio stuff,
because my family isn't very patient with me. When I
put the antennas up, I put a 1/4" bolt through the
mast at the rotor - but I didn't take the time to
tighten the U-Bolts on the rotor-to-mast mount. I
meant to come back and do it the next day, but of
course I forgot. I figured at the time (incorrectly,
as it turns out) that a 1/4" bolt was plenty strong
enough "for now".
Of course, last winter a storm came through and broke
the 1/4" bolt. The antennas free-wheeled in the
wind, and crashed into the redwood trees that I
hadn't bothered to trim yet. The capacity hat on the
40 meter yagi got all bent up, and one spoke broke
off of one hat. Even with all that damage, the
antenna still worked in the SSB segment, so I
operated a bit this spring before the weather got
good enough to fix the antenna.
Last weekend, I climbed the tower, rotated the 40
meter yagi's boom so that the elements pointed up and
down, climbed back down to the level of the lower
tips of the elements, reached out from the tower with
a 'gaff' and pulled each element tip in turn in to
the tower so that I could bend the hat spokes back
into place. I figured the job would take me 3-4
hours.
What I found was that the spokes were not only bent,
but that the brazes that hold the spokes to the
elements had broken. Since I had operated with the
hats in this damaged condition, they had arched and
there was soot all over the element/hat joints. I
ended up having to remove each hat from the element
(which means drilling out rivets at 55'), lower them
to the ground, rebraze the spokes, raise them back to
the tower, and reinstall them on the elements. 8
hours into the mission, and I'm about 2/3's of the
way done. I expect to spend another 2-3 hours on the
job this weekend. What a mess.
So a sequence of poor decisions conspired to cost me
over a day of heavy climbing work. If I had placed
the hole for the tower correctly, it wouldn't have
happened. If I had trimmed the tree as soon as I saw
the problem, or if I had tightened the U-bolts on the
rotor when I should have, it wouldn't have happened.
If I hadn't put RF into a damaged antenna, I would
have had an easier time because there wouldn't be
soot all over the place. It wasn't really any one
thing - it took at least three mistakes to get me in
trouble - but trouble I am in nonetheless. Tall
towers and big antennas are not very forgiving.
Sloppy work costs you dearly, as I am learning the
hard way.
If it wasn't for the invaluable help and education
that all of you have provided me over the years, I
could never have attempted this project in the first
place. I hope the story of my folly can help someone
else avoid a similar fate.
***dan, K6IF
|