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Author Topic: Rohn 25G installed in a corner...which bracket should I use?  (Read 1042 times)
KB1TXK
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« on: April 15, 2013, 04:10:56 AM »

Putting up 40' of 25G behind the garage.  Garage has an add-on, so I was going to put the tower in that corner where the back wall of the garage meets the side-wall of the add-on (figured it would be better secured that way).  NOT guying it while its only 40'...will add guys when I add on next year.  

Going to hand-dig at LEAST a 3'x3' cube, want to try and do 4'x4' or more (yes, overkill).  Can bracket it up the wall the first 16'.  Don't have a base, but one section has a small rupture at the very bottom on one of the legs (1" split) so thats the one I'm submerging 4' down in the concrete.

Looking for advice on which brackets I should use? I assume as close to building as possible (more stable)?
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K1CJS
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« Reply #1 on: April 15, 2013, 04:31:15 AM »

Just my opinion, but I would center the tower in the block you're going to pour, not get it as close to the building as you can.  The main support of the tower will be it's base, not the bracket.  Once you find out how far the tower would be from the building, then you could either get a standard bracket or have one fabricated.  If you want more stability, why not bracket the tower with standard brackets to both the main building and the addition?

Just my .025 (inflation adjusted) opinion.  It seems like it would be better that way to me--and I may be wrong.  73!
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W5CPT
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« Reply #2 on: April 15, 2013, 05:58:43 AM »

Rohn makes a house bracket labeled the HBUTVRO - Texas Towers and DXEngineering both carry it (or can get it for you).  It is a Universal House Bracket meaning it comes in pieces and can be assembled in different configurations. It would take some modification, but you could split the back bracket and attach each half to one face of each wall and brace the tower from two different directions. I think it would be very well braced especially if you can get the braces at 16'.  I will caution to make sure that the structure (garage & add on) is well braced inside to withstand the load the tower will place on them.  Lag bolts into the fascia board will not suffice. 

You did not mention what you had plans of mounting on the tower when at 40'.  That will figure into your calculations of whether or not it MUST be guyed.

While not built to Rohn specifications, here in Rural West Kentucky there are many installations of Rohn 20G (one size smaller than you are planning to use) that rise unsupported well over 40' with very large TV antennas.  And while that is anecdotal and does not guarantee your installation will not fail, it does add testimony to the fact that Rohn specs have a considerable amount of safety margin built in.

Lastly the universal Internet disclaimer = YMMV.

Clint - W5CPT -
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AA4PB
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« Reply #3 on: April 15, 2013, 06:18:48 AM »

Unless you have a way to mfg and galvanize a custom bracket, I'd get the standard Rohn house bracket first and then figure out where to position the tower to use that bracket. Once you concrete the tower in place you may find it impossible to use the standard Rohn bracket if you haven't planned for it properly.
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KB1TXK
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« Reply #4 on: April 15, 2013, 08:02:15 AM »

All good advice!

1) yeah I should have specified a little better with the concrete.  I'd want it as close to the building while _still being centered in the concrete_.  I want as much concrete as I can pulling down on the tower, and I want that force to be straight down...so yeah absolutely centering it. 

2) I will definitely be reinforcing the structure where the brackets will bolt into.  2x4s added to the studs, large quality bolts through-and-through.  If this thing is going to come down, I want it to be because the entire garage wall came down.  Like I said, trying to overdo this a bit.  At first the 40' will have just an Opek UVS-200 on it (2m/440 base antenna).  Once I get the guy situation figured out and add the remaining 40' of tower (total of 80') it will have a UVS-300 (replacing the 200), Cushcraft A3S and a home-brew PVC+wire 6m Quad. If I don't have room for the quad, it will be a home-brew 6m beam (ABS or PVC). There WILL be a rotor on the final product as well.

3) I'll dig a hole and do a non-concrete markup to figure out what I need for bracket length. 
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AA4PB
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« Reply #5 on: April 15, 2013, 08:25:11 AM »

Be sure you leave gravel in the bottom of the hole so that the ends of the tower are open and can drain out any water condensation that collects inside the legs. Make sure the liquid concrete can't enter the ends of the legs.

When I did my bracketed tower I built it up to the bracket height, then got everything connected to the bracket and leveled before I poured the concrete. It's more important that the tower be level and properly aligned with the bracket than it is that it be "precisely" centered in the concrete. The base on a guyed 25G is intended to handle the downward force on the tower and prevent it from sinking into the ground. They guys convert the sideways pressure from the wind into a downward pressure. They guys also need to be properly tensioned (per Rohn specs) in order to prevent the tower from twisting with large boom/element antenns (the A3 for example). Rohn makes a tortion bar that helps prevent twisting - although it is probably not really needed with your planned antennas.

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KB1TXK
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« Reply #6 on: April 17, 2013, 03:51:43 AM »

As well as remembering the gravel....would it be a bad idea to ram an 8' rod in the bottom of the hole, right where one of the legs will be? Slide tower leg on it, weld outside of rod to inside of tower leg.  Direct connection between tower and ground, but plugs one of the tower legs. I can fill that leg w/ foam (from the top of ground rod to above-ground level, maybe there is an option for a _small_ hole to drain water at that point?  I feel this would be an improvement over copper strap at 90-ish degree angles connecting to an external ground rod (4' higher than in-hole rod).
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K1CJS
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« Reply #7 on: April 17, 2013, 04:19:30 AM »

...It's more important that the tower be level and properly aligned with the bracket than it is that it be "precisely" centered in the concrete....

Precisely?  Who said that?  All I said was centered--in other words you really don't want to pour a 4' x 4' block and have the tower legs inches from two sides--and two and a half feet (+/-) from the other two.
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K1CJS
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« Reply #8 on: April 17, 2013, 04:23:23 AM »

As well as remembering the gravel....would it be a bad idea to ram an 8' rod in the bottom of the hole, right where one of the legs will be? Slide tower leg on it, weld outside of rod to inside of tower leg.  Direct connection between tower and ground, but plugs one of the tower legs. I can fill that leg w/ foam (from the top of ground rod to above-ground level, maybe there is an option for a _small_ hole to drain water at that point?  I feel this would be an improvement over copper strap at 90-ish degree angles connecting to an external ground rod (4' higher than in-hole rod).

Not such a good idea.  Maybe the ground would be better, maybe not.  The real problem is that a _small_ hole will get plugged, maybe sooner, maybe later--and if you make the hole big enough to be sure it isn't, you're going to weaken the tower leg.  I wouldn't take the chance.
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AA4PB
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« Reply #9 on: April 17, 2013, 05:57:00 AM »

I said "precisely"  Grin  If I hadn't then someone here would have come back and said "the concrete may crack if you locate the tower only 2" from one side". My point was that (to me) it makes more sense to set the tower the proper distance away so that I can use a standard Rohn bracket rather than randomly setting the tower in place and then have to design and build a custom bracket.

As for ground rods, I would put in three, one connected to each leg and located a foot or two from the concrete base. I like to keep the connections and wire above ground where it's easy to inspect and ensure tight connections over the years.
« Last Edit: April 17, 2013, 06:00:08 AM by AA4PB » Logged
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