Thanks for the great shots of the temporary tilt bases!
It's good to see others showing how ridiculous are the monster concrete bases
in the ROHN catalog, which I'm sure keep many hams from having towers.
My club uses a very similar arrangement for a 40 footer, except the tilt base
is bolted to the rear end of a 16' flatbed trailer.
The tower is raised by an electric winch on the front end, normally used for
loading logs and cars.
The falling derrick is a triangle of 2X6 wood that rests on the trailer and
supports the cable until the tower is up to about 45 degrees.
The only tricky part is that once the cable gets above the derrick the system
becomes laterally unstable and the tower must be kept lined up with the two
outer guys. The winchline serves as the third guy, although its angle is quite
steep.
Really, at 40', the loads are negligible. Our guys are climbing rope, rated
for a few hundred pounds.
The greatest load occurs as the tower is lifted from the ground, which I've
calculated to be 800-1000 lb. No prob for the 6000 lb winch.
I built a wooden crutch to hold the tower while the beam is installed, so it's
rock solid and the workers don't have to depend upon the winchline for safety.
This year we added a 30' tower for 10m, which we manhandled up. 30' is trivial
for three people on the tower and two on the guys. One moves to the back guy
as the tower gets near vertical.
The base for that one is a standard Rohn base, pinned to the ground as shown in
the pictures, except I bought 4' rebar at Home Depot and welded old nuts onto
it at about six and 10 inches below the "top" ends. There's an electric demo
hammer in the club which has had a tubular sleeve welded to a bit. That is a
great rig for driving the tower base pins and the many ground rods we use each
year. The pins and rods are pulled with a farm jack onto which KR4UB welded a
fork that grips the upper of the two nuts on the rods/pins.
The tower guy stakes are mostly old harrow axles which are about 1" square,
three feet long, with a head on one end, like a carriage bolt.
In the ground around here, 2' of the axles in the ground will hole more than
we'll ever need!
Instead of the four pins shown, we only used two for the 30' tower and they
were more than adequate.
We have some pictures at DFMA.org in the Field Day and Gallery sections.
Here's one of the falling derrick and the tower being assembled. It travels as
two 20' sticks lying on the trailer.
http://www.flickr.com/photos/14790531@N08/5879063531/in/set-72157626940733947
The rotor is near the bottom, in case adjustments are needed to align the beam
and rotor.
I'm sure a 40 tower could be manhandled with several good lifters and three
people on the guys. A vehicle pulling on the back guy would be a big help, if
the afomentioned lateral instability is thought about and the two front guys
kep taught, with the tower kept strictly online.
The fab work on the championship bases is great. Someone is obviously a good
designer/welder!
I'm about to put up a 40 footer bracked to my chimney at 21', just above the
middle joint. It will have the very same type of base pinned to the ground.
We should all keep in mind that even a 30' tower is more than capable of
hurting/killing people if it falls/is dropped.
At least one or two people involved in these installations ahould have some
experience with rigging/knots/etc AND they should be prepared to issue orders
as necessary, including bring everything to allstop if necessary to restore a
safe environment. You CANNOT count on the average inexperienced ham to known
when the sky is going to fall!
Nice job and I'm looking forward to the article.
Wilson
W4BOH
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