At the Johnson Space Center ARC, one of our towers as an ex-Air
Force we acquired many years ago through our then-MARS
affiliation. It is a 50', free-standing, three-legged tower with
a leg-spread at the base of about 6 or 8 feet and tapering to
about 18 or 24" at 30 or 40 feet, at which point the taper stops.
The top of the tower is a flattop with a thrust bearing (sorry,
Ken, but that's the way it arrived.). It's a stout tower on an
incredible concrete base. I have never felt any movement at the
top even in breezy weather.
On the tower we have what may be a 12 to 15 ft mast (material
unknown), an A3WS (3-el, triband WARC beam) and an A3S (3-el,
triband 10/15/20m beam). The rotor is on a rotor plate about 3
or 4 feet below the top.
This antenna array has been up for about six or seven years now
and has had no problems, other than a cratered rotor.
I have a couple of issues I am seeking the reflector's collective
intelligence and help on:
1. When I replaced the rotor about a year ago, I found that the
array is one heavy sucker. It's also very tippy! The mast at
the rotor got away from me (looking back, I have no earthly clue
as to why it was free and not secured in some way). I think I
was very lucky in that the lower mast end was stopped by the leg
and leg rung. However, I recall hearing the sound of rushing
water. I looked down and my pants were dry, so I could only
conclude that the water was in the boom(s) of one or both of the
antennas.
We have end-caps on the booms. Maybe we shouldn't. I know N5RP
is (among other things) a propounder of no end-caps. I'm
curious about this: The element traps have drain holes. Why not
the boom ends? Is there any problem in doing so? Has anyone
done it? Would it be simpler to just leave the end caps off? It
may be an opportunity for wasps/hornets, etc, to make homes in
the booms, but there are plenty of other openings on a tower that
they never set up residence in, so that may not be a factor.
Recommendations?
2. The A3WS is about a foot above the tower top. The A3S is at
the top of the mast. Standing on the tower top, my hand reach is
about three or four feet short of the A3S. Guess which antenna
needs service?
LIke I said above, I don't know what the mast is made of. Is
there a way to tell by looking or some kind of scratch test or
something else to determine the hardness of the mast? I can
probably measure the thickness of the wall at the rotor. Given
the fact that the array has been up and on the mast for a number
of years with no problems, should I install a mast step and press
on to climb the mast and lower the A3S?
That question may be moot. But, I'd still like to hear
ideas/comments.
As I was gassing up the car the other day, a large bucket truck
pulled in to gas up. I asked them the extension of the bucket
and their rates and they said 70 feet and $68 and hour. That
seems pretty reasonable to me.
With a bucket truck, we could have the antenna down in a couple
of minutes, check it out, maybe even fix whatever needed fixing,
and have it back up all within an hour. The tower is located
directly adjacent to the employee recreation center parking lot,
so the truck's access to the tower shouldn't be a problem
Has anyone used a bucket truck to take down antennas? We used
one at TDXS Field Day one year, but my attention was diverted to
collection and recycling of the leaking hydraulic fluid (probably
the major reason why we didn't use it the next year), so I didn't
really pay close attention to the mechanics and problemmatic
aspects of using the bucket truck. Is it as much of a snap to
do as I think it is? Are there any hidden or unexpected things
to prepare for or look for when lowering/raising an antenna on
the bucket?
Thanks and 73,
Dale Martin, KG5U
kg5u@hal-pc.org
http://www.hal-pc.org/~kg5u
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