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Author Topic: Urban restrictions - (new to HAM radio)  (Read 4545 times)
KD0TLI
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Posts: 42




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« on: October 16, 2012, 05:31:04 PM »

I picked up a used Rohn 25 with hinge plate, 4 sections, and top mast - so almost 50' of tower.
I was looking forward to having a nice high tower but then my balloon was popped.

After calling up to the city office to see about my local codes, I was dismayed to find out that
after all is said and done, I'll only be able to use about 20+ feet of my tower due ice/wind loading
restrictions (90 mph and 1/2" ice)- and my garage peak is already 15' high  Sad

I've called Rohn in an effort to figure out if this is correct, and is sounds like it is.

It doesnt seem logical to bury a huge chunk of concrete into the ground if I'm only going to get a few feet
above my garage peak ?

Any advice....?
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K7KBN
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Posts: 2782




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« Reply #1 on: October 16, 2012, 05:52:25 PM »

The scary word in this instance is "used".  It might look pretty on the outside and be rusted all to bits on the inside.
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73
Pat K7KBN
CWO4 USNR Ret.
AB4D
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Posts: 298


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« Reply #2 on: October 16, 2012, 07:00:55 PM »

Any advice....?

Unfortunately, Rohn 25G does not meet the newer TIA-222F standard (3 second gust@90 mph, with a 1/2 layer of radial ice) that most municipalities now rely upon when considering any tower installation.  Unless, as you note, the installation is limited to 20 feet or less.   You're going to need to move up to a stronger tower such as the Rohn 45 or even 55.  The first logical step into installing a tower is to decide how much load (wind loading and weight) you plan to install on the tower, including the mast and rotor, and then find a suitable tower to handle that load. The second step is to obtain the PE signed engineering documents from the manufacturer to support your permit.

Like any construction project, once you get the permit in hand, then you obtain the correct tower and begin construction.  You probably don't want to hear this, but I would sell the tower, perhaps someone in your area needs a couple of 20 foot tower, and then start from scratch the right way.

73



    
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N6AJR
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« Reply #3 on: October 17, 2012, 11:07:19 AM »

If you use a 3X3X3 foot base of concrete, and a bracket to the house, and a set of guys or two, you should be fine.  My 40 footer, is done that way and it meets our local  codes.
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W8JI
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« Reply #4 on: October 18, 2012, 07:02:41 AM »

I picked up a used Rohn 25 with hinge plate, 4 sections, and top mast - so almost 50' of tower.
I was looking forward to having a nice high tower but then my balloon was popped.

The hinged plate is a weak link, and negates the worry about significant concrete area. A hinged base is so weak that the guys or brackets are mandatory at any height. A proper bracket or guy system makes the base area a non-worry except for compression load.


Quote
After calling up to the city office to see about my local codes, I was dismayed to find out that
after all is said and done, I'll only be able to use about 20+ feet of my tower due ice/wind loading
restrictions (90 mph and 1/2" ice)- and my garage peak is already 15' high  Sad

I've called Rohn in an effort to figure out if this is correct, and is sounds like it is.

That sounds about right for 25G if you have a lot of antenna area at the top. It looks like you need to consult with a PE.

 
Quote
It doesnt seem logical to bury a huge chunk of concrete into the ground if I'm only going to get a few feet
above my garage peak ?

It is not logical, because a guyed tower places the base almost entirely under compression load. The only requirement is the base does not shift or sink. A PE should be able to advise you on the safe Rohn ratings, and even a safe base size. The most critical part is the guying. You might be surprised at the 25G capability if the antenna is not too large.
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K7KB
Member

Posts: 605




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« Reply #5 on: October 20, 2012, 06:58:48 AM »

According to TIA-222G, Class I (Amateur, CB) towers are exempt from the 1/2 inch Ice Loading requirement.  My county tried to impose the same restriction but once I showed them the information in the document that specifically states that, they dropped that requirement and issued my permit.

I have information I can send you concerning this if you want to send me an email at my QRZ.com posted email address.

John K7KB
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KB1GMX
Member

Posts: 748




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« Reply #6 on: October 20, 2012, 10:54:24 AM »

50ft is pushing with Rohn25 unless guyed on a non tilt base.

If your doing fixed base and bracketed to the peak then you can easily go 10ft higher than the last joint below the bracket. so about 30ft is doable.

You will still need 24"Wx 48"D concrete and dump the plate.  Use a partial section embedded in the
concrete as base per the ROHN Catalog find it on line for specs on the base and for ice/windload/height.

Follow all the installation details like insuring the legs can drain.

Generally used is OK, but inspect carefully.  Helps if you can get the age of the material.

Ham radio tower should not have to comply with more than TIA-222. Class 1 but know the
specification and what it says. I went through similar request for excess requirements until
I did my homework. 


Allison
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AB4D
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Posts: 298


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« Reply #7 on: October 20, 2012, 07:09:04 PM »

According to TIA-222G, Class I (Amateur, CB) towers are exempt from the 1/2 inch Ice Loading requirement.  My county tried to impose the same restriction but once I showed them the information in the document that specifically states that, they dropped that requirement and issued my permit.

I have information I can send you concerning this if you want to send me an email at my QRZ.com posted email address.

John K7KB



Hi.  When I tried to get 25G approved where I live. I proposed to my county, the ice rating requirment was not applicable to my proposed tower.  However, it was a no go even though I provided a copy of the various class ratings under TIA 222.  They didn't want to discuss the class ratings.  I suppose, because we have a significant number of ice storms in this county each winter.  Storms with a half inch or more of ice is not uncommon in certain parts of the county every several years.

They demanded engineering data signed by a PE that showed 25g can withstand the 90 mph gust@3 seconds with 1/2 radial ice.  I contacted ROHN, and they could not provided any engineering data for loading with ice. Therefore, without manufacturer support, I decided to obtain a heavier 72 foot crank up tower.  Oddly, even that tower only met the TIA-222 rating if it was cranked down below the 52 foot level, but that was good enough for the county.

The whole absurd thing in the state where I live, most of the counties here never ask what you are going to install on the tower.  I've put up several towers across the state.  Hypothetical speaking, you could mount a Volkswagen Beetle on top of a tower after the final tower inspection, and still be in compliance with your county building permit. 

Perhaps his building department will be more cooperative about the class ratings than mine. 

73
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KD0TLI
Member

Posts: 42




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« Reply #8 on: October 23, 2012, 06:41:33 PM »

Thank guys, appreciate the help.

I dont want to give the hobby a black eye, so I'll play nice with the city I live in and probaly get a better tower to get the height I want.

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