One thing I'd add for replacing tower brackets with something *really solid
is to build an "A-Frame" out of one inch square steel tube. You can
get it in everything from about 16 gauge to on the order of 3/16ths inch
wall which is heavy.
The easiest is to make a mock up of wood first and then cut the steel to
size. If you can weld it really helps, but it can be bolted together.
*Most* towers have the single leg on the house side and the two legs away
from the house as a pivot, or hinge.
There are several ways it can be done, but I would "U-bolt" a straight piece
across each face of the tower toward the house. This means they will cross
about an inch or two from the single leg. Cary them on up to the side of
the house.
At the house two routes are presented. Have a "foot" plate welded on the
end of each piece and lag bolt it to the "face plate" such as a 2 X 10 or 2
X 12. (don't forget the backing plate on the inside). If the tower is 18
inches from the house this gives a healthy foot print against the face
plate. You can also have a piece of tube welded from the end of each
straight piece with a "foot plate" on each end. Just remember there will be
about an inch and a half off set due to the pieces crossing next to the
tower.
Instead of crossing you can cut one side (leg) and have it welded so the
whole thing forms an X with one side much shorter than the other with the
tower legs "U-bolted" to the shorter legs.
I hope I made this clear. There is a lot of room for improvisation, but if
need be I can put up a simple drawing. The shorter the tower the less the
wind load and the lighter the construction can be and the less strain on the
end (or side) of the house.
The wider foot print, heavier material, and much wider foot print makes this
a very rigid attachment. Just be careful that it's not made too heavy and
that it is attached to a well fortified area. (wall plate on the inside
across the studs and surface plate on the outside for the most strength.)
If it goes it'll take the whole end of the house with it. Unfortunately
I've seen more than one home where it would do just that. The tower would
be serving as a reinforcement for the end of the house instead of the other
way around.
Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com
>
>
> Bob,
>
> Some factors to consider:
>
> * Rohn rates 25g for 2 sq ft. 30' above a house bracket.
> at least, that's what I recall. It was published in
> their commercial catalog, some years ago.
>
> * I would recommend using 45G, if you can find it, although it
> is heavy. An 18" face is lots easier to climb on.
>
> * I had 50' of rohn 45g house bracketed @ 5' and 15', in Vermont,
> for several years. It had a 10' mast out the top, and a 10
> element lpda on top, plus an r7000 vertical on top of that.
> It was solid as a rock. (and it was sitting on a rock...about
> 2' down. No concrete.)
>
> * My house bracket system used wood. pressure treat 2x8,
> which spans at least 3 joists. details follow:
>
> A 5' 2x8 plate is either lag-screwed into joists, or thru-
> bolted to a backing plate inside the building. (preferred)
> The plate needs to be longer than 48", so you can tie into
> the three joists.
>
> If you lag-screw in, you must drill pilot
> holes sized to provide maximum thread depth, and you must
> get them centered in the joists if you're going in end-on.
> (no small task!) I used 12" lag screws. Undersize the holes
> and split the joists...so be careful.
>
> The tower is centered on the backing plate, and held laterally by
> two 2x8 pieces, one on either side, sized to provide a tight fit
> against the tower legs.
>
> The lateral plates are held by carriage bolts which come from
> the back side of the backing plate...lateral plates are drilled
> for clear fit, and bolted down. I usually countersink these
> bolts, so there's no interference with the next layer, the TOPPING
> plate.
>
> A topping plate goes through the tower, and is held in
> place on either side by longer carriage bolts, also coming from
> the back of the sandwich. This plate must extend as far as possible
> along the length of the backing plate.
>
> The result of this system is that the tower is held close to the
> house, with no moment arm. It can't wiggle.
>
> This obviously won't work if you have to stand off from an eave.
> In that event, you have to use Rohn's bracket...even though it's
> much less sturdy, and doesn't spread the load enough.
> Those brackets can wiggle and produce creaking noises.
>
> All bolts are 1/2" zinc plate, by the way. Stainless is hard to
> come by. Use flat washers on ALL surfaces, and split washers under
> all nuts.
>
> * If you use 25g, I would anticipate guying it, in some fashion. Even
> if it's non-optimal, given the load you're anticipating.
>
> * If you need to get a building permit for this project, forget about
> what you're thinking. You won't pass, and Rohn isn't here to help
> you square away your engineering submission.
>
> I got away with mine because I was in Vermont, and simply didn't
> ask.
>
>
> N2EA
> jimjarvis@ieee.org
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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