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Author Topic: Tower House Bracket (good/bad idea)  (Read 6870 times)
KC4MOP
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« on: May 22, 2012, 05:34:52 PM »

OK I'm a lazy person at times BUT do to laziness and not wanting to dig a 4 foot hole for a meager attempt to have a 30 foot tower, I am thinking of pouring a small concrete pad 5x5 Feet maybe 12 inches thick with some rebar in the center for support. The 30 foot tower holding a rotator and 6M 3 element beam would sit on top of the proposed pad and I would use house brackets designed for the tower (Rohn 25G) and attach to the house near the top, and about half way up from the bottom.
A friend told me that eventually the house brackets would "work" the wood. The 2X4's within the walls that are part of the house framing. This is going through the vinyl siding. There is a way to measure where the studs are from inside the house, I try to find the desired stud outside and attach to that.
My friend's meaning of "WORK" the studs, is that over time the forces of the tower and its load would eventually cause severe damage to the structure of the house. As I'm typing this, something hit me to try to go in between two studs with a 4X6 straddling the studs and run long nuts and bolts through the wall and do it that way. This is in a garage and will not be seen in a living area BTW.

OR get busy and get a bottom section and just dig a dam 4 foot deep hole 4 foot square...............and sink it the old fashioned way.
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AA4PB
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« Reply #1 on: May 22, 2012, 05:47:43 PM »

The problem with using a 12-inch thick slab is that if it settles due to the weight of the tower then the house brackets will be pulling downward on house framing. If you use the proper, specified depth of concrete base for the tower then the base will support the total vertical load without moving and the house brackets will only need to support the horizontal load. In addition, the bottom of the base will be below the freeze level (depending on where you are located).

I think you'll find a non-guyed, non bracketed 25G will be kind of shaky when climbing it to do antenna work. I'd use a 25G short base in the specified 4-foot depth of concrete plus one house bracket near the top of the house. Add some 2x4 or 2x6 bracing inside the garage to attach the bracket. That also gives you some leeway in case you decide to add another antenna.


« Last Edit: May 22, 2012, 05:49:48 PM by AA4PB » Logged
W6CD
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« Reply #2 on: May 22, 2012, 08:08:36 PM »

Hire a day laborer to dig the hole...
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K9KJM
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« Reply #3 on: May 22, 2012, 09:40:34 PM »

 A standard Rohn CB-1 (Concrete Base) is 3 feet deep, By 3 feet by 3 feet.  One cubic yard of concrete.
That base will easily support a 30 foot tower with the wind loading you propose in most any normal soil.

(The hole usually needs to be dug by hand so the concrete is poured against undisturbed soil only. (NO below grade forms)   
Your 5 X 5 X one foot thick idea uses almost the same amount of concrete, But as pointed out, At that depth is subject to frost heaving, Which would cause problems with a house bracket.

I dug lots of those holes back in the 1970's, In most normal soils, The hole could be dug in one hour.
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KC4MOP
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« Reply #4 on: May 23, 2012, 03:29:37 AM »

Thanks guys,
VERY good info that never would have entered my "short-cut brain'. The heaving ground during freeze/thaw would definitely put a strain on the house brackets.
We have a lot of Amish folks around and I could ask if there is someone available that would just handle digging the hole and mixing the concrete and setting the bottom section into the ground, keeping it plum, of course.
Good thing I posted this before going on with my thought......
Thanks
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KD8KCH
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« Reply #5 on: May 27, 2012, 01:16:54 PM »

I have had a 60" tower for TV antenna setting on a cement block 30" down with a house bracket at 27' for 21 years now with no problems. With the bottom of the legs open like this never any water standing inside the tower legs to freeze and bust like so many that I have seen that were put in with concrete that split an rusted out after 10 to 15 years.
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VE3FMC
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« Reply #6 on: May 27, 2012, 03:52:26 PM »

I have two 30 foot towers attached to the house with no problems. Plus I have 18 feet of tower above the attach point. That is about the limit you want to go though. Anything above that you better guy it.

One of those towers has been attached to the house since 1992 and has not sunk, moved etc. I check the lag bolts holding the brackets once a year and tighten them if needed.

I have currently had a 8 foot mast out of one of the towers with a small tv rotor on that and a 3 element 6 meter beam mounted on the rotor.

The other tower has about 10 feet of mast out of it with a T bar mounted at the top. I have a 40 meter delta loop and an 80 meter dipole hanging off that cross bar and a 6 meter vertical above that. Again no problems with the tower sinking etc.

Think about all the tv towers that are attached to houses in North America. Most of them have no concrete pads at the base. They are simply sitting on the ground with the 3 metal stakes pounded into the ground at angles. Survived for years  Wink
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K9KJM
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« Reply #7 on: May 27, 2012, 10:03:36 PM »

Quote: "Think about all the tv towers that are attached to houses in North America. Most of them have no concrete pads at the base. They are simply sitting on the ground with the 3 metal stakes pounded into the ground at angles. Survived for years"

Yeah, Not for very MANY years though!

Around here with deep frost,  ALL of those "cheapo" tower jobs we did back in the 1970's (Drive in stake kit from Rohn, Rohn 20 tower sections, House bracket kit) NONE are now standing! (Although we did not do very many of them....)

Where the Rohn 25 towers we did with a standard CB-1 3 foot by 3 foot by 3 foot concrete base are all still up except the ones taken down on purpose!
 
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KC4MOP
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« Reply #8 on: May 28, 2012, 04:23:41 AM »

Thanks for these replies. I can get a little pick and shovel action going here and just do it right. CB-1 base or a bottom section. There's a fester in Butler Pa. (June) and I'll be looking for a used CB-1 or a short section to be used for the bottom.
The tower I have must be a look-a-like to the Rohn. The cross members are not Rohn, but I'll check against the dimensions shown from a 25G PDF to make sure the pieces will fit. I do not want to sink what I have in a hole and lose 3 feet of height into the ground.
I know, guys, Rohn doe not recommend mixing their tower components with look-a-likes. But this is only going to be 30 feet. A very minimal tower for a 6 Meter station.
I might start another thread entitled, "30 foot Tower for 6 Meters,,,,Is it worth it"?
My readings tell me that it will work, but don't expect to bust through a lot of grid squares.........who knows?
Yagis for HF and 6M and, UHF, of course, love to be 60 feet high
Thanks again
Fred
« Last Edit: May 28, 2012, 08:03:39 AM by KC4MOP » Logged
K1ZJH
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« Reply #9 on: May 28, 2012, 01:59:04 PM »

When the band is open having your beam up 30 feet will be fine on six meters.
More important is not having the beam pointing into a building or thick grove of trees.

Pete
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KC4MOP
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« Reply #10 on: August 07, 2012, 03:38:47 AM »

Hello Gang,
I am bringing this back to the top to announce, that after the entire Summer of avoiding to address this tower problem or other solutions to raise a 6M antenna, has been solved.
I am glad I took to heart the responses to "do it right"
A contractor was using some excavating machines on the property next to us to prepare for building.
I asked if it were possible to dig a 3X3X3 foot deep hole. He said no problem and asked for $25.
In 10 minutes it was over. The machine was like a large back hoe.
Concrete company said they would be happy to deliver a small order of 1 cu yd. $150. Better than yankin' my back with a pick and shovel and lifting 80 lb bags of concrete!!\
It does pay to wait. Thanks.
The tower will be installed properly.
Fred
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K1CJS
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« Reply #11 on: August 07, 2012, 04:48:05 AM »

You've had enough feedback on the base, but almost none on the house attachment.  If not done properly, the house bracket attachment will indeed 'work' the wood causing damage.  To do it properly, you have to get the tower bracket firmly against the house, and that sometimes is a problem with siding installed over foam insulation.  The insulation will tend to get squashed, causing loosing of the bracket--and an unsightly distortion of the siding. 

The proper way to install such a bracket on a house with siding installed over styrofoam insulation is to remove the siding and insulation to fit a two by four or a two by six firmly against the house, then to reinstall the insulation and siding around it.  The block of wood can be covered by the siding type that is used to cover the trim around the house.

Then bore the holes to attach the bracket through and back the inside attachment with another two by six to distribute the strain of the mounting bolts evenly inside the house woodwork.  If done in that manner, and with yearly checks of the tightness of the mounting bolts, the house attachment point will be strong and sturdy, and you won't have to worry about loosing of the bracket attachment because of the pancaking of the insulation--if your house has that foam insulation under the siding.  73!
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AA4PB
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« Reply #12 on: August 07, 2012, 05:26:38 AM »

Since it is a garage and presumably unfinished on the inside, you should have plenty of options for reinforcing the bracket on the inside. Consider placing the bracket high enough that you can tie the support back to one or two roof rafters while maintaining overhead clearance.

Back when I had a house bracket I placed it high enough that I could access the inside of the location from the attic. I used a 2x6 between the studs and tied it back to three roof rafters with 2x4s. I still had, over time, some nail pops on the drywall on that wall and the "clank" of the rotor brake could be heard inside the house because of sound transfer through the bracket.
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K7KBN
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« Reply #13 on: August 07, 2012, 09:53:18 AM »

The August 1996 issue of QST has a well-written article on using a Rohn house bracket and suggestions on beefing up the attic structure of the house or building to add even more stability.
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73
Pat K7KBN
CWO4 USNR Ret.
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