Dave-
One piece of info that figures heavily into this equation-
What are you using for fasteners to attach the legs of
the tower to the roof rafters, how many, and if they are
some type of lag screws, are you sure they are all into
solid wood, and not, for example, screwed into the joint(s)
between the double and triple members?
Tom
K0SN
On Sun, Apr 6, 2025 at 1:31 AM Dave WB2PJH <wb2pjh@gmail.com> wrote:
> Hi Jon,
>
> There is a lot of expertise in this group but if you wouldn't mind looking
> over my plans and letting me know if I'm FUBAR or OK, I'd sure appreciate
> it.
>
> My plan is to the following: I have an existing GM RT-832 roof tower with a
> G800DXA rotator and Yaesu GS-065 thrust bearing. It's currently holding a 5
> el 6 m and 70 cm yagi on a 10 ft length of 2" aluminum conduit. The roof
> joists are doubled or tripled where the mounting feet are located. I just
> replaced my roof and don't want to trash it by doing anything stupid like
> overloading this light duty roof tower and taking my $20K roof out.
>
> I bought a 2 inch 12 ft 15 lb 6061 mast and want to install a Hy-Gain 2 el
> trap TB, 20 lbs, 3 sf, 14' radius, an M2 6m 5 el yagi, 2.2sf 13 lbs, 11 ft
> radius, and, if possible my 2 meter M2 9 el, 1.2 sf, 6 lbs 8 ft radius on
> top (very optional). The 70 cm is coming down and will be sold.
>
> The K factor in the Yaesu manual is for this rotator is 180. If I only put
> the 2 el HF yagi and 6 meter on the mast the calculated K factor is 231, 51
> higher than recommended by Yaesu. If I add the 2m then I'm over by 77. The
> Yaesu manual equation doesn't count wind resistance, just antenna and mast
> weight and turning radius. The thrust bearing takes most of the weight of
> the mast and antennas but there's nothing in the manual to account for
> that.
>
> I'm OK on weight for the GM roof tower but the manual calls for no longer
> than a 9 ft mast, and the rotator plate is 6 ft from the top, not much room
> for antennas! I think I'll be OK with 12 ft even if I add the little 2
> meter yagi at the top, but the tribander and 6 meter both have to go on the
> mast and the 6 meter won't be anywhere near the top since it's a big
> antenna.
>
> I got a 12 ft mast because that's what my friend had in his garage - if he
> had 9 ft or 11 ft it wouldn't make much difference to me since I won't have
> enough room for optimal spacing in any case..
>
> In your collective experience, am I cutting things too close for comfort?
> I have a TA-33 but I think it's too much antenna for this roof tower and
> rotator with a K of 262 which is why I'm going with the 2 el Hy-Gain,
> lightweight with low wind resistance.
>
> Most of this project except for the roof tower and meter M2 yagi are used
> items from from fellow hams who are trustworthy.
>
> Thanks for your assistance.
>
> 73,
> Dave WB2PJH
> FRC, CWOPS
>
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