Back to Glen Martin rooftop towers:
I have the 17.5 foot unit on my roof, and it seems to be pretty good,
if scary (1). I have 2x4' rafters, but partnered several with 2x6's
(probably should have used 2'x8's), and then put in braces to a
load-bearing wall.
If I were to do this again, I'd consider puting one of the F12 12
foot crankups through the roof, based on that load-bearing wall. Then
the rafters would function as braces in compression.
Or, I would modify the top of GM the tower by replacing the top
horizontal braces (which are 1/2" tubing), with angle aluminum to
provide a third bearing mounting location, half-way between the two
provided. I'd put a MC-10 or equivalent mast clamp there, so that I
could lock the mast in place for rotator maintainance. My Ham-M
rotator (and I suspect most other units) must be installed by going up
from inside the tower. Another possibility would be to put a bearing
at the existing lower location, and add a rotator platform below that.
73, doug
(1) it shakes a bit when I'm up, even with my weight on the lashed-on
ladder, and if it falls, I'll fall the 20' to the roof, and
if not attached, then will roll down the roof and off to a further
25' drop to the ground. If the thing collapsed at the bottom,
it's not impossible that I'd get dropped over the edge of the roof
directly. So, I climb with a tether to the roof, and another to
the tower below the rotator, as well as my regular lanyard.
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