I spent yesterday with the crew at W3BP's qth putting up 140 feet of AB105
with 4 element 40 meter and 6 element 20 meter OWAs on it. A few suggestions
while the experience is fresh in my mind.
As W5VX suggested, a crane operator worth his salt can get the antenna
pretty much where you want it, but there are some caveats.
1. With a decent operator and crane you can't expect him to get the holes in
the mounting plates perfectly alligned. One way or another you will need
some the ability to move the antenna somewhat vertically and horizontally.
2. We used two different processes yesterday. With the 40, we brought the
beast up to our working level with the crane, and then transferred it from
the crane to a come-along. The reason we resorted to the come-along, is the
reach of the crane allowed us only a foot or two of crane cable between the
jib and the antenna. That made it very difficult to get any lateral movement
to line up the holes. The second problem (and I'm not sure if this was a
function of the crane or the operator) was the ability raise or lower the
antenna by a matter of inches once it was close to the working level. With
the come along one can perfectly align things horizonatally. With ten feet
of tower above our working level and the cable of the come-along almost
fully extended, it was fairly easy to move the antenna from side to side to
get the holes aligned.
2. With the 20, we lucked out and the operator got it real close. Because
the antenna was lower on the tower the operator was also able to give us
more cable between the top of the jib and the antenna which made swinging it
laterally easier. While one of us pulled and lifted a skosh, the other was
able to get the first bolt in. After loosely running the washer and nut up
on it, getting the second bolt in was fairly easy.
3. A key in getting this sort of thing done is how level you can have the
antenna once it reaches the mounting point. First you should use a yoke that
keeps the boom level. Then how you tie the yoke to the boom is going to help
determine how level the elements remain as it rises. In some cases one may
need to adjust where the yoke straps are tied around the boom so the tips of
the elements tip up slightly to clear guy wires as it goes up. In general if
you can attach the yoke so the boom and the elements remain level with the
ground, it's going to take less horsing around to get the thing mounted.
There's absolutely no question that with what we were doing yesterday, a
slightly taller crane would have made the job much easier. Then again going
with a slightly taller crane would have cost considerably more. Then again
the complexity of having a crane that was "just adequate" increased the
amount of time it was needed, so I'm not sure where the break point would
be. The taller crane would probably have meant less time for the crew on the
tower.
Whether using a crane or tramming, it's usually much easier to transfer the
antenna to a come-along that to try and force it into position from where
there crane gets it or where it stops on the tram.
As you work with larger antennas, you'll probably learn to appreciate these
two statements yelled from the guys on the tower to the ground crew:
"Got the first bolt in"
"Got the second bolt in"
Plan carefully and be carefully up there.
73 de Larry K7SV
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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