PDA

View Full Version : Rohn 25G install plan?



WX0C
05-27-2012, 07:07 PM
I managed to nab myself 50' of Rohn 25G from a little old lady for merely the cost of having a tree service drop the tower. I'd like to erect this thing back at the home QTH, but have questions on how I should do my base concrete and how high I can go. I want to bracket it to the side of the house. Where the base will be measures 20" wide with plenty of depth and length to use. I was planning on bracketing the tower to the house about 15' up. Antennas will be 24' fiberglass vertical, an 80m Windom, and a ladder line 2m/70cm Slim Jim.

How long and deep should my pad be? Is 50' asking too much? Our neighbor sits in a weird little 50' depression so that might shield us from heavy winds a little. I apologize for the wrong attached thumbs. I grabbed the wrong pics and it won't let me delete them.

93961
93962

WX0C
05-27-2012, 09:00 PM
Im almost thinking of burying a 10' section in the cement and ending up with a 36' finished product with a section left over. Seems like people say they get a little scary at tall heights. Kinda funny though because the thing was standing 50' unguyed for many years.

WB2WIK
05-27-2012, 09:09 PM
All base construction details are on line at Rohnnet.com; look for "guyed towers," then click on "25G." It's all there.

Do you need a permit for the tower? If so, that usually involves a site inspection or two (often two: one for the base excavation and installation, and a second one for the fully installed tower). And if so, follow the Rohn blueprints exactly as doing otherwise will often cause an inspector to fail it.

WX0C
05-28-2012, 01:50 AM
Ya, I checked out the information over at Rohn. My application doesn't exactly fit nicely with the specs. I don't have space for a 4x4 pad for free-standing, and don't have the space to throw down guy wires. The best I can do is a bracket at 15' and or a rectangular base. I'm not sure what I can do safely. I don't wanna have the bracket rip out of the side of house or have the tower fold.

WA7PRC
05-28-2012, 02:18 AM
Your local building authority may require wet-stamped plans from a licensed Structural Professional Engineer. The first step is to find out what is allowed and the permit requirements, if any. The second step is to secure a copy of Up The Tower (http://www.championradio.com/UP-THE-TOWER-The-Complete-Guide-To-Tower-Construction.1) by Steve Morris K7LXC. It answered all the questions I had, and some I didn't know I had.

W9GB
05-28-2012, 02:28 AM
How long and deep should my pad be? Is 50' asking too much? Our neighbor sits in a weird little 50' depression so that might shield us from heavy winds a little.
Jim -

1. Follow to the letter, the Rohn 25G base construction. IF you can't, MOVE ON.
Does Sioux City require building permits for antenna towers?
Do they require inspection of that tower base?

2. You can use the Rohn house attachment bracket near top of your house, you can go 20 feet above that bracket without guy wires.

3. Rohn 25G ten foot sections are too expensive to bury on part way for a base. Buy the 5 foot foundation base as well as other parts you I'll need. Hill Radio in Bloomington, IL will have the lowest prices for drop ship to your residence.
==
BTW, since the 1970s municipalities and many counties,
as well as CC&R and HOA with real estate, have adopted stringent rules.
IF you don't have these -- you are very fortunate or have been lucky
These changes happen over past 50 years, for many reasons:

+ Post-1970s CB-Craze response by communities (neighbors don't want a CBer next door)
+ Reaction to 1980s nationwide Cellular telephone tower build-out (installation accidents, deaths)
+ Anti-technology and anti-science (radio in this category) by some religious and national groups
+ P&C Insurance industry, due to earlier insurance claims (or lawsuit payments)
traced to improper installations.
+ Katrina hurricane, and increases in property damage from tornadoes -- have triggered nationwide changes in wind loading regulations for ALL new tower construction (Florida has the most stringent).
+ Legal community, their participation in lawsuits for damages from tower collapses,
with loss of property and life.

w9gb

WA7PRC
05-28-2012, 02:33 AM
Jim -

1. Follow to the letter, the Rohn 25G base construction. IF you can't, MOVE ON.
Does Sioux City require building permits for antenna towers?
Do they require inspection of that tower base?

2. You can use the Rohn house attachment bracket near top of your house, you can go 20 feet above that bracket without guy wires.

3. Rohn 25G ten foot sections are too expensive to bury on part way for a base. Buy the 5 foot foundation base as well as other parts you I'll need. Hill Radio in Bloomington, IL will have the lowest prices for drop ship o your residence.

w9gb
Again, before doing ANYTHING, find out from the local building authority what is allowed and if a permit is required. And, if a permit is requried, whether wet-stamped plans from a Structural Professional Engineer are required. In my case, that's exactly what was required. They would not accept plans from the manufacturer, with an out-of-state engineer's stamp. Find out what is allowed/required before doing ANYTHING.

K9KJM
05-28-2012, 04:39 AM
The standard Rohn "CB-1" concrete base was a square 3 feet by 3 feet by 3 feet deep. One cubic yard of concrete.
There are many HUNDREDS of them around here that were installed in the mid 1970's to what was called a "50 footer" But was actually less height of the tower, Just over 3 feet of tower was in the concrete (Tape off the bolt holes, Put some gravel around the legs for moisture drainage) Which leaves 46 feet of tower "free standing" plus the mast and TV antenna. With a 10 foot mast, This did get your antenna up an actual 50 feet, Or slightly more. The only such towers that have come down that I am aware of, Were taken down and replaced by cable TV.
With a house bracket, The house bracket is actually doing all the "work" of supporting the tower. With smaller reasonable size antennas, A Rohn 25 will work well at these heights.
Six sections of Rohn 25 tower with 3 feet in concrete (56 feet of tower above ground) Will get "wiggly" and require almost yearly maintenance to keep the joints tightened, Especially near the ground. (This is well beyond Rohn specs, But proven to work well)
Seven sections of Rohn 25 tower with 3 feet in concrete (66 feet of tower above ground) "Freestanding" WILL COME DOWN in a strong wind! The tower itself is the failure point, Not the CB-1 base. Guy wires are required at these heights even for the smallest antennas.

K7MH
05-28-2012, 05:55 AM
I don't wanna have the bracket rip out of the side of house or have the tower fold.


When I had Rohn 25G for a tower, I used the house bracket. I lag bolted some reinforcement 2x6 just under the eve and attached it to that as opposed to just the house or the eve. The 2x6 (2 two stacked pieces) were about 3 or 4 feet long and bolted in different places to be very secure. It was a one story house similar to a rambler so the tower was only 30ft.

A friend had a much taller house and with some reinforcement, used two house brackets (one halfway up and one at the top) and put Rohn 25G up to either 40 or 50 ft., I don't remember for sure but I think it was 50.

Neither was ever a problem and were quite sturdy for tribanders and a 6 meter beam.

The reinforcement was a good idea and probably necessary. I have seen some where the reinforcement was done inside in the attic space as well.

WX0C
05-28-2012, 04:36 PM
Thanks for the help! I've gotten a lot of good advice. I think I will...

1) Inquire about the need for a permit
2) Dig a hole for 1yd of concrete
3) Go 40' up with a house bracket at 15'

I think this will be a very sturdy setup that might even support a small beam if the day ever comes. K9KJM pretty much describe the original configuration of this tower. It was 50' free standing in a concrete pad that was only 20" in diameter. I guess it was standing for ages. The tower itself is in excellent shape, but the base shifted and she was a doing the Tower of Pisa act.

K1ZJH
05-28-2012, 05:01 PM
The base isn't doing much work, since as others noted the house bracket as taking the brunt of
the lateral stress. Do not skimp on how that bracket is attached to the frame!!!! And don't
exceed the free standing height above the bracket per the Rohn guidelines.
Getting a permit and having it inspected is good advice--but based on my experiences many
building inspectors will rubber stamp the approval since they don't have a clue what they are
looking at.

Pete

W9GB
05-28-2012, 05:02 PM
Rohn 25G --- Product Page
http://www.rohnnet.com/rohn-25g-tower

Municipal and County/Parish governments are revising their permit process,
that require tower installation permits to address compliance with current TIA-222 standard.
Design Considerations Using The ANSI/TIA-222-Rev G Standard
http://www.rohnnet.com/resourcesmodule/download_resource/id/189/src/@random48eced0c124b9/


The tower itself is in excellent shape, but the base shifted and she was a doing the Tower of Pisa act.
That would be due to an improper base installation ... Not deep enough (your local frost line).
http://en.wikipedia.org/wiki/Frost_line

The frost line (depth) for your geographic area will be KNOWN by any contractor who performs foundation work (footings, basements).

As I remember, it will be at least 5 feet below grade for your area !!

Rohn sells short base sections that are set into a hole, with concrete poured around them.
The SB25G is 3 feet long. The SB25G5 is 5 feet long. The SBH25G is a hinged three foot section.
Your local hole depth (frost line) determines which one you use !!
http://www.texastowers.com/rohn_25gsb.htm

N5TGL
05-28-2012, 06:30 PM
I'd suggest a pinned base rather than embedding the 5' section. No worries about legs rusting out, and if you do, you can replace them. If the pier pin rusts out, you can remove it, and embed a new one in epoxy.

The base is actually doing a LOT of work. First, it's resisting the tower from sinking. Secondly, it's preventing wind loads from kicking the base out. With a bracket at 15', all the tower above that provides quite the lever against that base. I'd say it needs to be guyed at the very top too, but I'm sure someone will come in there with a story about their old uncle doodlebob who did it without guys and it was just fine. The question you have to ask is "do you mind 50' of tower coming down at a most inappropriate time?" :)

WB2WIK
05-28-2012, 11:04 PM
I'd suggest a pinned base rather than embedding the 5' section. No worries about legs rusting out, and if you do, you can replace them. If the pier pin rusts out, you can remove it, and embed a new one in epoxy.

Except he said he has no room for guys. I can't imagine using a pier pin base without guys, that was never the intention. A house bracket alone won't do this job without an actual concrete foundation (not a pier pin). Well, it might work with two brackets spaced 20' apart and secured to something very solid; but as stated here a few times now, if a permit and inspections are required, and the inspector knows how to read, he probably wouldn't approve that as it's not recommended in any of the Rohn engineering documentation.



The base is actually doing a LOT of work. First, it's resisting the tower from sinking. Secondly, it's preventing wind loads from kicking the base out. With a bracket at 15', all the tower above that provides quite the lever against that base. I'd say it needs to be guyed at the very top too, but I'm sure someone will come in there with a story about their old uncle doodlebob who did it without guys and it was just fine. The question you have to ask is "do you mind 50' of tower coming down at a most inappropriate time?" :)

Yeah, I agree with you. I think 25G is good tower, and I've seen them unguyed at 50' stand up for 30-40 years holding simple antennas like a TV antenna or a ground plane; but not with a rotator and HF beam. The torsion requirements to turn and stop something with long elements like an HF beam, or even the long boom of a high-gain VHF beam, are just too much. Every time you STOP a beam with any long members (elements, or boom, or both), you're trying to twist the tower into a pretzel, and eventually that will happen.

K1ZJH
05-29-2012, 04:25 AM
I'd suggest a pinned base rather than embedding the 5' section. No worries about legs rusting out, and if you do, you can replace them. If the pier pin rusts out, you can remove it, and embed a new one in epoxy.

The base is actually doing a LOT of work. First, it's resisting the tower from sinking. Secondly, it's preventing wind loads from kicking the base out. With a bracket at 15', all the tower above that provides quite the lever against that base. I'd say it needs to be guyed at the very top too, but I'm sure someone will come in there with a story about their old uncle doodlebob who did it without guys and it was just fine. The question you have to ask is "do you mind 50' of tower coming down at a most inappropriate time?" :)

I agree, I was careful to state that the bracket takes care of the lateral stress. My 64 Rohn
foldover is on a hinged base... with two sets of guys. The base is six cubic yards of concrete left
over from a HDBX tower that previously occupied the same spot.

Pete

ad: dxeng