Al,
Tower makers aren't going to take on the liability risks of providing
guidance for house brackets. I do see that Rohn now specifies a minimum
of 815 pounds horizontal support force. "design by others".
I did a house bracket in EMA for a TH7DX, a big triband yagi on 20' of
Rohn 25 and up 15' on 2" x 3/8 thick wall 6061-T6 tube as the mast.
The hinged base was on my back deck so that yielded 7 more feet to the
top so it nicely cleared the roof. The mast was Al to minimize the
hoist moment load, which needed 3 sheave blocks and help to pivot it up.
The block attachment was a forged eyebolt thru the wall below the the
house bracket to the inside bracing.
In the attic is best place for your house bracket reinforcement. I
nailed a 2x10 across the studs for 6' with all thread holding the house
bracket. Then added a 3/4 inch plywood flooring and used two ~ 5 ft
long steel angle irons bolted/lagged between the all thread and the
plywood. IIRC I had to cut the ply to 2x8' to get them into the attic so
staggered 3 pieces across 12' of joists.
The idea is an eve end of a house is not structural and it is held only
by stud top and bottom toe nails. It's not too hard to pull it out. So
a membrane (3/4 plywood) structurally nailed (shear wall nail pattern)
on the structural joists can better transfer the load to the house
structure.
Attaching to the floor membrane in finished space is better
structurally, but usually not XYL survivable.
Maybe overkill back yard engineering, but this rig survived 2 major
hurricanes, local winds in excess of 80mph.
Unbelievable luck, the buyer was a ham unknown to me and required the
antenna be left intact.
Grant KZ1W
On 6/19/2020 10:32, Al Kozakiewicz wrote:
Until I can purchase the parcel of property next door, I'm limited in setbacks
and height to a 35' bracketed tower that will hold an M2 5el 6m Yagi and a
cheap Hy Gain 2m Yagi for 6m VHF contests and local repeater access.
I decided on an Ameriite (American Tower) 30' 25 series bracketed to the house
in one location. AFAIK this tower is essentially a knockoff of Rohn 25G.
I can't find either on the American Tower site nor Rohn's site the details of
the proper house structure required for attaching the bracket. Contacting the
manufacturer got me the foundation pland but not the bracket. I'm going to have
to cut through drywall for either the outside wall or access to the attic and
I'd like to know what prep I'll have to do before I undertake erection. Of the
tower.
Al
AB2ZY
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