Antenna Tower

[WA6DJM]

I am getting ready to raise a 30' maybe 40' Rohn 25g Tower for a 4 element triband hf Beam. I don't want to cut up my patio to replace it with a 3'x3'x3' concrete block supported by rebar plus placing ground rods etc. Since we rarely see high winds here in San Diego California would it matter if I placed concrete anchors inside the patio concrete for the mounting plate, plus secure the tower to the center roof support beam then include guide wires? Would this be sufficient stability for this project? I can drill holes and place grounding rods 3' apart in all corners surrounding the tower this should sufficiently provide a good grounding potential for my tower and my equipment. Any Comments or suggestions will be welcome.

David (WA6DJM)

 

[acyddrop]

Though this doesn't answer your question at all you might want to be aware that if you are putting the tower yourself that your home owners insurance might not cover any damages that might occur should it fall down or damage your home. That was the case with my towers so I had to have mine installed professionally. While that was always my intention it's an important thing to consider.

But I also highly doubt that your patio concrete is deep enough to support your tower even with anchors on your house. Since even small winds will generate high torsional force on the tower. But I'm a bit of a neophyte on the subject.

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[AK9R]

Though this doesn't answer your question at all you might want to be aware that if you are putting the tower yourself that your home owners insurance might not cover any damages that might occur should it fall down or damage your home.

Or, worse yet, would the homeowner be covered for damages if the tower fell down and damaged a neighbor's property?

 

[mmckenna]

I am getting ready to raise a 30' maybe 40' Rohn 25g Tower for a 4 element triband hf Beam. ... Since we rarely see high winds here in San Diego California would it matter if I placed concrete anchors inside the patio concre
David (WA6DJM)

While certainly not ideal, it would likely work. I had a neighbor who did a similar install on the side of his house with a 40 foot Rohn 25, and he didn't have any issue. Unguyed, it did fine. The anchor at the bottom and the roof peak were about 20 feet apart. This left about 20 feet above the roof peak.

He only had a vertical and a TV antenna, so you would need to carefully consider how much wind loading your tri-bander will put on it. Make sure you research the specifics on that tower and how much it can hold unsupported for 20 feet.

Ideally, if you could, guying the tower would be your best bet if you can't sink the big foundation.

I've got a Rohn 25 supporting 2 repeater antennas on one of the buildings at work. About 15 feet of it is above the last bracket holding it to the penthouse. It's holding 2 large 800MHz antennas and a tower top amplifier, so quite a bit of wind load. It occasionally sees some high winds (70MPH or so) and has lasted 20 years now.

 

[N0IU]

It doesn't matter what anyone here thinks. The only thing that matters is the building code for your county. I suggest you get a permit and have the installation inspected before you put up your tower. If your installation does not meet code, your insurance company won't pay for damages to anything it falls on.

But go ahead and do it your way. I just hope you have deep pockets!

 

[acyddrop]

Or, worse yet, would the homeowner be covered for damages if the tower fell down and damaged a neighbor's property?

Well having it professionally installed I'm covered now, I'm glad I caught this bit of wisdom before I even started the tower installs, a bit of due diligence goes a long way.

 

[acyddrop]

It doesn't matter what anyone here thinks. The only thing that matters is the building code for your county. I suggest you get a permit and have the installation inspected before you put up your tower. If your installation does not meet code, your insurance company won't pay for damages to anything it falls on.

But go ahead and do it your way. I just hope you have deep pockets!

I doesn't matter what anyone thinks, but you're wrong if thinking just having the inspectors come out to look at it will cover you. All many (and by many, I mean most) insurance companies need to hear is "I put this here tower up myself!" and they will deny coverage, many won't even insure it seperately at xxxx rate. So if and when it does fall down, you are going to be stuck holding the bag for whatever damages you incure, be it to your home or someone elses (and by home, that also includes tree damage, out bulding damage, etc etc etc).

When we live in Florida, the many hurricanes that hit us in 2005 did a number on our home. To repair it was a significant amount ($50,000USD+) now if you have that kind of money just laying around by all means do it yourself. I for one was happy our homeowners insurance covered it.

 

[n5ims]

I am getting ready to raise a 30' maybe 40' Rohn 25g Tower for a 4 element triband hf Beam. I don't want to cut up my patio to replace it with a 3'x3'x3' concrete block supported by rebar plus placing ground rods etc. Since we rarely see high winds here in San Diego California would it matter if I placed concrete anchors inside the patio concrete for the mounting plate, plus secure the tower to the center roof support beam then include guide wires? Would this be sufficient stability for this project? I can drill holes and place grounding rods 3' apart in all corners surrounding the tower this should sufficiently provide a good grounding potential for my tower and my equipment. Any Comments or suggestions will be welcome.

David (WA6DJM)

The tower system (note the word "system" here, it's important) has design specs and those specs translate to how much load the tower can handle. The system includes not only the actual tower, but also the base and any additional supports (think house mounts and guy wires here) that tower may or may not have. A tower of a specific type, rated for a certain wind load capacity, would be for a tower with at least a certain minimum construction on the base, a maximum height, and a specified minimum guy wire configuration.

If you follow the design specs, it should safely handle that wind load. If you have less of a guy wire configuration, a smaller or more weakly constructed base it will no longer handle the specified wind load (perhaps it won't even handle the weight of the tower itself). Also be aware that the base design assumes a certain type of soil. Different soil types do require different base configurations so factor this into your specific design! Nice stable, well drained soil may use the minimum base design while shifting sands or other unstable soils may need a much more substantial base design to handle the same tower weight and load.

A patio slab may only be 4 or 6 inches thick, not much of a base when the specs call for a 3 foot thick base. Will it work? Perhaps. Will a bicycle tire work on an automobile? Also, perhaps. Either way, I wouldn't want to trust it if it was my tower, next to my house, that may crash down having a tribander element stab into my child's bedroom and perhaps even through his chest.

For the posts that say all you need to do is meet "minimum code". The key there is the word "minimum". Building codes are not there to guarantee that things are totally safe or even will work as intended. They are there for two very diverse reasons. #1 to cover the majority of the most basic installations so they're basically safe (think small TV antennas here, not large or even fairly small ham antennas). #2 to protect local businesses that have pull with the local government (e.g. you must use a certain type of connection that local contractors know and understand but those from outside the area wouldn't normally use and thereby will fail the inspections).

If you want a safe installation, use the manufacturer's guidelines on proper installation for the style, type, size, height, and windload you desire. Starting with the Rohn tower guidelines will be your best bet.

http://www.rohnnet.com/resourcesmodule/download_resource/id/654/src/@random4a982aa1bba7e/

 

[N0IU]

I doesn't matter what anyone thinks, but you're wrong if thinking just having the inspectors come out to look at it will cover you.

Its a moot point since he is going to have the tower professionally installed, but...

I did not say that he should just have the inspectors come out to "look at it". Inspectors don't come just to look at anything. They come out to make sure the installation meets the building code. When you get a permit (assuming it is even required where he lives), they inspect every aspect of the installation from start to finish. If it the inspector signs off that the installation complies with the building code in the area, it will be covered.

 

[n5ims]

Its a moot point since he is going to have the tower professionally installed, but...

I did not say that he should just have the inspectors come out to "look at it". Inspectors don't come just to look at anything. They come out to make sure the installation meets the building code. When you get a permit (assuming it is even required where he lives), they inspect every aspect of the installation from start to finish. If it the inspector signs off that the installation complies with the building code in the area, it will be covered.

But meeting the building code doesn't guarantee that a tower is correctly installed. Code here basically restricts the tower to a few percentages of being in the center of the lot (based on the tower being taller than the distance from that "center" and the closest property line). When the inspector came out to verify a friend's tower I helped put up, all they did was measure the distances from the tower base to the property lines and sign off on the project. They didn't check the base was correct for the tower (it was, but still they didn't verify that) nor did they verify that the guy lines were correctly placed (save a comment that it would be a good idea to flag or paint the one that was rather close to the roof and could be easily ran into by someone walking around on the roof).

 

[acyddrop]

Its a moot point since he is going to have the tower professionally installed, but...

I did not say that he should just have the inspectors come out to "look at it". Inspectors don't come just to look at anything. They come out to make sure the installation meets the building code. When you get a permit (assuming it is even required where he lives), they inspect every aspect of the installation from start to finish. If it the inspector signs off that the installation complies with the building code in the area, it will be covered.

Which is exactly what I said "come out and look at it", you know full well I didn't mean they were going to come to the house and just stare at it blankly, how foolish do you think I am or they are? But even if it's up to the building codes, doesn't mean it's up to the stresses set forth by the people who made the tower and established guide lines. But given the OP's statement, it would not of been up to snuff with loads and so forth, even if it was up to snuff with building codes. Honestly, what ridiculous comment.

 

[N0IU]

But even if it's up to the building codes, doesn't mean it's up to the stresses set forth by the people who made the tower and established guide lines.

That's why the manufacturer provides the specs for the base. It is the inspector's job to make sure that the base does meet the manufacturer's specs.