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Author Topic: Rohn 20g tower  (Read 2972 times)
FIGUSMAKEM
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« on: April 01, 2010, 04:02:34 AM »

Hi all, Ive just purchased a rohn 20 g tower at a fair price used. My question is can I use this tower un guyed at about 35-40 ft? I will have it bracketed at about 10 ft. (My 1 story house is only 10.5 ft. at the peak) I will only have a di pole attached to it at the moment because of neighborhood restrictions, but I want to get higher in the air. These seem to be very elusive when it comes to finding this type of info.
       Thanks for the help, Mike
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KAISERSOUSE
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« Reply #1 on: April 01, 2010, 04:53:13 AM »

You can find the 20G guides fairly easy online.

I have the 20g and the instructions I found said you guy it at 30' and I believe 75' (I have 80' tower).

That said its still in a heap behind the garage because:

1) I havent rented the digger to dig the 5'x5'x5' cube for the base (have to do other stuff with the digger as well)

2) I don't know if I can afford the concrete for the base right yet

3) I'm too much of a wuss to climb it

In my minds eye however, its a beautiful tower and a wonderful addition to my backyard antenna field.

Anyways...yeah guying it at 30 - 35' ft sounds about right.
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W5RB
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« Reply #2 on: April 01, 2010, 05:05:06 AM »

Even the current Rohn web site doesn't offer much on this . The 20 series was designed for exactly what you describe , a bracketed installation  of 40 feet or less , back when most homes had a TV antenna . Be sure to bracket to something substantial , not just a facia board .  I'd hang a pulley or two on it , so you can pull wire antennas up and down with no climbing .  3'x3'x3' is plenty of concrete for a base . A link to the Rohn page for 20g is below . Stay well clear of wires and never work alone . Good luck with your project .

Russ , W5RB

http://www.rohnnet.com/rohn-20g-tower
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W8JI
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« Reply #3 on: April 01, 2010, 09:07:25 AM »

Rohn 20G can be bracketed, but Rohn says it should NOT be guyed. This is because the legs are thin and the braces are small and far apart compared to 25G.

You actually can guy it, but the guy lines cannot be real big. The tower won't take a lot of outward pulling on the legs. I would not put anything big on 20G, TV sized antennas or most wire antennas are OK.

Also if you are installing a 5x5X5 base on 20G you are wasting money. In normal soils, 20G will break long before an 18" diameter 5-foot beep base will shift! I would never bother sinking a 20G base that big. I would would do a proper Rohn 25G base section and bolt the 20G to it.  Then, when the 20G fails or gets replaced, or if you want to guy it, you have the 25G base.

It is good tower, but the 20G is a BRACKETS only TV type tower.

Tom
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K9KJM
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« Reply #4 on: April 01, 2010, 11:42:32 PM »

VERY GOOD advice from W8JI.

NEVER put a Rohn 20 in your concrete base!  Spend a few bucks and get at least a short section of Rohn 25G to put in the concrete!
By doing so you could always upgrade to an entire Rohn 25 if you wanted to do so sometime in the future. Putting the 20 into the concrete would really limit what you could do in the future!

The "standard" Rohn base is one cubic yard of concrete as pointed out. 3X3X3 feet, Hole dug so the concrete is poured against undisturbed soil.  A little gravel under and around the tower legs for proper drainage.

JI is also correct that the lightweight 20 was never designed for guy wires, A house bracket only. ( But I too have seen many 20's  with the lightweight steel clothesline type guy wire that have been up many years with no problems)
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KAISERSOUSE
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« Reply #5 on: April 02, 2010, 05:15:03 AM »

How does one tell if they have a 20G versus a 25G? Is there a difference in the cross-bracing on the tower sections and/or a difference in the leg-tube diameter?

If I have 100' of 20g then I guess I'll have 3x 33' towers (since guying a 20g in 2 places doesn't seem like the best engineering practice in the world).
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KAISERSOUSE
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« Reply #6 on: April 02, 2010, 05:28:09 AM »

Think I found my "answer"...

Some people say 25g is 4 legs, 20g is 3 legs. However everything on Rohn's site shows the 25g being 3 legs.

Some people say if it has 7 horizontal braces its a 20g, while 8 means its a 25g. Then others say they've changed it and 25g and 20g >could< have identical numbers of bracing.

What EVERYONE seems to agree with, is that a 10' section of 20g weighs 32 pounds, while a section of 25g weighs 40.  

Guess I'll weigh a section tonight and find out.

/me gives thread back
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WT0A
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« Reply #7 on: April 02, 2010, 05:36:21 AM »

count the cross members
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W8JI
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« Reply #8 on: April 02, 2010, 09:37:24 AM »

Think I found my "answer"...

Some people say 25g is 4 legs, 20g is 3 legs. However everything on Rohn's site shows the 25g being 3 legs.

Some people are obviously just plain fools. :-) Four legs in  pig's eye.

Quote
Some people say if it has 7 horizontal braces its a 20g, while 8 means its a 25g. Then others say they've changed it and 25g and 20g >could< have identical numbers of bracing.

Some people are fools. They offer advice that can hurt people, or rip them off, when they clearly haven't a clue what they are talking about.

Rohn 20G ALWAYS has 7 horizontal braces per ten foot section. Always. No exceptions ever. It also always has thinner rod, always. It has 18 gauge legs. It also fits right on 25G.

Rohn 25G always has eight horizontal braces per ten foot section. Always. No exceptions. Rohn never made anything different.  It has thicker brace rods. It has 16 gauge legs.

Quote
What EVERYONE seems to agree with, is that a 10' section of 20g weighs 32 pounds, while a section of 25g weighs 40.  


The only reason everyone agrees on that is because the clueless people guessing and misleading people and making up wild stories never actually weighed the tower.

Quote
Guess I'll weigh a section tonight and find out.


You don't have to weigh it. Count the braces in a full ten foot section. It will never mislead you. No matter what anyone wants to pretend, if you count seven horizontal braces per ten foot section you have 20G. I've seen people pay for 25G and get ripped off with 20G. The sellers assure them it is 25G.

73 Tom
« Last Edit: April 02, 2010, 09:45:06 AM by Tom Rauch » Logged
KAISERSOUSE
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« Reply #9 on: April 02, 2010, 09:43:09 AM »

HAHA excellent. I'll do that this weekend when I drag it out from behind the garage.  Thanks!
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FIGUSMAKEM
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« Reply #10 on: April 02, 2010, 12:49:43 PM »

Thank you all for the great help and advice. I have looked everywhere on the net and can not find the manuals or any literature on the proper installation of a 20g,except that it should be bracketed only. After reading up here, I think I will go with the 25g base. That sounds logical if I intend to upgrade down the road.
     Thanks again guys, Mike
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N6AJR
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« Reply #11 on: April 02, 2010, 12:59:21 PM »

http://www.antennasystems.com/towers.html
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W8ATA
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« Reply #12 on: April 02, 2010, 06:44:20 PM »

Check out Norm's Fabrication in Adrian, Michigan. Norm, W8TTH makes all sorts of accessories for Rohn towers. I use his guying bracket for a 25 which will also fit a 20. It bolts around the tower and provides guy anchor points. It works as an integral unit and fits snugly around the tower. Your guys pull on it as a triangle and not the tower legs. Norm and Ginny his licensed XYL are good people to deal with. www.normsfab.com

73,
Russ
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K9KJM
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« Reply #13 on: April 02, 2010, 10:22:55 PM »

I did not point out in my post that Rohn 20 fits directly on to a Rohn 25G section........   They are actually interchangeable, Just that the 20 is much lighter duty tower, So if you do have the Rohn 20 sections, Do get at least a cut off short piece of 25G to put in the concrete.
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KJ4LCM
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« Reply #14 on: April 03, 2010, 06:06:31 AM »

I believe the Texas Towers website has a lot of info on towers. You might go there for more info.
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