[TowerTalk] IARU Team Stations and Portable Towers

Wilson Lamb infomet at embarqmail.com
Sun Jul 29 09:14:56 PDT 2012


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


More information about the TowerTalk mailing list