Tripod Roof Mount of TA33

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Mike Miller:
I'm looking for some advice (a fool hardy thing to do here!). I'm in the process of fixing a TA-33 with the planned installation on my roof (garage section) using a 10' tripod. (manufacturer unknown). I will have a Ham-M rotor mounted inside the tripod using the mast-mount attached to the bottom of the rotor, and a short 18" mast through the top and  using a thrust bearing (GS-50) mounted at the top of the tripod.

Question #1 How does the thrust bearing attach to the top of the tripod when the top is held together by a mast mount type clamp arrangement?

Not to be more complicated then this needs to be, but I plan on mounting the tripod on non-absorbing material - 1 per leg(4x4x 24" kilz painted and black painted blocks) per NEC Section Code 810. (June 05 rules).  Each block will have a Stainless Steel lag bolt in the center hole with a code 8 bolt through the leg+block+roof. Also at each end of the block, a 3/8" thread bolt with a washer+lock washer+nut arrangement through the block+roof and into a 2x6 board straddling at least 4 rafter struts each to spread the load of the tripod+rotor+antenna. Roof sealant where needed.

Question #2  Suggestions needed on guying?  I have pondered this:  use Kevlar from the top of the tripod to three points on the roof (rafter anchored) just as an extra safety measure; or use steel 1/8" cable (plastic coated to mitagate rust) tightened for little play. Guying does then add weight and torque to the tripod...do I gain anything or am I better to leave all of the guying off?

Location parameters:
Peak of roof where tripod (30" spread at bottom) will be mounted - 14 feet above ground
Antenna mounts 12" above thrust bearing.

House sits in a lower section of average terrain, with 60' trees to north (30') and others 100-150' away. Location is 7 miles due west of downtown Minneapolis.  Winds can exceed 60-70 mph with 50 inches of snow average during winter, and we do get occassional ice storms.

Your help and comments are appreciated!

Local- Twin City hams need not respond, as I am looking for other opinions and I already have yours! :)

Phil Salas:
I really recommend the Glen Martin 4-legged roof towers over a tripod.  They are very sturdy.  I had a Tennadyne T5 HF log periodic mounted on my Glen Martin tower and no guys were needed.  I used the 4.5-foot Glen Martin tower but used a 9-foot mast with it.  Here in Richardson, TX we have to have a PE provide calculations showing that the structure can survive 100 mpg winds.  Again, no problem in his calculations for the unguyed roof tower/mast/LP.

Phil - AD5X
ad5x@arrl.net
www.ad5x.com

Bob Lewis:
We really can't answer most of your questions because we have no real data on the tripod (strength, etc). If you have something like the Glen Martin roof tower then you shouldn't need any guying with the TA33 mounted within a few inches of the top of the tower.

It sounds like your tripod was not designed for a thrust bearing. You need a flat surface at the top of the tripod to mount the bearing. It sounds like some modification of the tripod will be required.

Steve Katz:
I'll third the vote for the Glen Martin Engineering 4-legged roof "quadpod" product, as opposed to a 3-legged tripod arrangement.

Not only is 4 legs a lot better than three, but the G-M products are specifically designed and manufactured for the express purpose of installing amateur antennas, so they come with an internal rotator mounting plate and a flat top mounting provision for a thrust bearing, so there is zero question about that.

The G-M roof tower products do not require guying, and I wouldn't bother.

I've had a few of these over the past several years, and definitely recommend them: Lightweight but very strong (extruded aluminum), easy to assemble, climbable, and with 4 legs they can "tilt" in any direction you want them to, based on how you install the mounting brackets to the roof.  Strong enough to tilt over the whole assembly after installation, so you can pull two bolts and lay the thing over for beam maintenance, without any helpers required.

And mostly: Designed and built to hold up ham antennas like the TA-33, so there are no questions about how to do that.

WB2WIK/6

Mike Miller:
I'm not 100% sure this is the correct Tripod, but it is of aluminum 1 1/4" tube and looks like the Rohn TRT122. It has 2 diagonal braces, and welded ladder braces up 1 side. I've sunk alot of bucks into the antenna and supplies, and while I would consider the G-M 4 legged 8 footer, I don't have the $$ for it.  (Poor in the wallet Ham!)  

Now I've also come to find out I need new plastic for winding the wire inside the traps (their cracked and separating).

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