On 4/2/2014 11:07 AM, Grant Saviers wrote:
Most of what you need is in the Rohn 25 brochure
http://www.rohnnet.com/filedownload/downloadfile/fileid/17/filenum/0/src/@random48eced0c124b9
It appears to me from the Rohn specs, most 40m 2L yagis are within its
capacity if properly guyed. Texas Towers and others can supply what
parts you need. If the top section is the one with the 2" id tube
then you don't need a new top section and the problem is how to get a
mast into a erected tower. You can put a shorty mast (5'-10') by
armstrong + gin pole but a 20' will take a crane or boom lift.
I put a 24' 2" 1/4" wall, steel tube into mine (45G) with just a 16' gin
pole. I built my own gin pole. at the top I put a steel hoop/ring
about 10" in diameter. I raised the mast through the ring which kept it
from swapping ends. It did take two men on the 1/2" rope though. This
was a braided rope like climbers use. Don't use a rope with a twist as
in conventional ropes. On a 100' lift or even 60' lift, you will find
the load wants to rotate "many times" just going over pulleys.
Adding additional guys over the ROHN recommendations is not advisable.
It's often done, including larger guys, but it is very easy to add more
stress than the tower is rated for. Larger guys add a lot of weight and
when properly tensioned can multiply the vertical load. The 25G is a
relatively light duty tower. "Normally" it is better to go with a larger
tower (45G) than adding extra guys. I feel far more secure on a 45G than
a 25G.
As I said, it's done, but what about insurance? Calculate the vertical
load with all the guys (and antenna) in place at the designed tension.
Then wind load for the maximum gust in your area.
If you reach a point where extra guying is necessary, or considered
advisable, it's time to call an engineer if you expect your insurance to
cover it.
The base on a guyed tower is just to keep the tower from sinking, or the
base from sliding sideways.
73
Roger (K8RI)
Did you do the original installation? If not, hire the installer
again. You might have wind exposure that warrants a PE analysis and
better guying than in the Rohn catalog.
The G1000 is asking for trouble rotating a 40m beam, IMO.
Grant KZ1W
On 4/2/2014 7:23 AM, Michael Warren wrote:
Problem: I have a Rohn 25 G tower that I want to use with a 40 meter
yagi. I know that the tower needs some redoing to get it in shape. I
need the groups expertise to guide me through this redesign.
+++The Rohn 25G is at 65 ft, and it was was constructed of new
materials three years ago. It is used only as an internet tower in a
rural area to get above the tree tops.
+++The base is buried in 3X3x3 concrete. The top section is pointed.
There two levels of small gauge guy wire. There is a 4 in gray
plastic conduit runner from the base underground to house.
++++I have a Yaesu G-1000DX A, enough 7/8 heliax to run the 300 feet
down to the shack
++++ I want to update this tower so that I can put a 40 meter yagi.
Things I suspect that needs to be done.
Put on a heavy duty flat top section
Obtain a mast
The 40 meter yagi - used, but in good condition from a contester. I
have not pickup this yagi to determine the make or model yet, or wind
load. (Get it in shape to use)
etc.
***Could I get some help as to the planning, the obtaining of parts,
and possess of construction?.
tnx 73
Michael Warren
KA5REJ
"I'm a old school teacher, and I can still learn new things!"
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