[TowerTalk] U.S. Tower 71 foot crank up mast

[Dick Green]

I always hate to disagree with K7LXC, but I think he thought you were
referring to the triangular crankup tower. The title and wording of your
message suggest that you are actually thinking of buying the MA-770 or
MA770MDP crankup tubular mast. If that's the case, there's no top shelf,
thrust bearing, rotor plate or 6-8 inch pipe. Instead, there is simply a
length of pipe inserted into the top section and welded to it (the top
section is square, unlike the three lower sections, which are cylindrical.)
I don't know how long the pipe is (i.e., how far down the top tube it goes.)
About 6-8" of the pipe sticks up above the lip of the top section and has
two set screws that hold the mast. You shove the mast down into the pipe and
tighten the set screws to hold it.

I used a 5-foot mast, purchased from U.S. Tower, to which I attached my
TH-7. Three feet of the mast sticks up above the antenna (required for the
boom guys) and two feet of the mast are inside the top section pipe. In
other words, the TH-7 boom-to-mast bracket rests on the the aforementioned
pipe coupling at the top of the tower -- no need to add any bending moment
to a tower so close to its rated windload max.

Note that I have the rotating base, so the rotator is mounted on a shelf at
the bottom of the tower. I'm not exactly sure what you do if you buy the
fixed base and want to put the rotor at the top. I seem to recall that U.S.
Tower sells a rotor shelf that mates to the pipe at the top of the tower,
but I can't find anything like that in the catalog. Maybe it comes already
welded to the top section. If not, another option would be to insert a short
piece of mast into the pipe coupling descibed above and mast-mount the rotor
(assuming you have a model with a lower set of mast clamps.)

You can find a little info at:

http://www.ustower.com/index.html

I'll be happy to answer any questions I can about the MA-770MDP.

73, Dick WC1M


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