The base for my LM470, is the first base where I've used rebar.
The guyed 100' 45 G has a minimal (~1.5 sq yds) high strength base in
hard clay. 3' in dia and a bit over 5'6" deep.
I've had 50 and 60' guyed, ROHN 25Gs mounted on dirt bases for over 25
years (some with relatively large antennas) with no problems.
I had the antennas and 50 to 60 feet was all I could afford.
We had an ice storm that had the element tips of my 5L 20 meter KLM
pointed at the ground. Fortunately it warmed enough for the ice to fall
off before the wind hit. The wind removed a large Winegard VHF/UHF TV
antenna off off the roof. That antenna was hag bolted into a thick
wood plate under the roof boards. I was on the roof at night, in
torrential rain and high wind, pumping Silastic RTV into the holes left
by those lag bolts. At least there was no lightening, but that rain
sure was cold. Calking gun in one hand and a flashlight in the other.
There was no damage to the big antennas or towers which had dirt bases.
BTW, when the ice fell off those 20 meter elements, they all went back
to where there were supposed to be. I figured I was going to lose that
antenna when I saw the ice.
73
Roger (K8RI)
On 1/5/2016 Tuesday 3:09 PM, jimlux wrote:
On 1/5/16 9:42 AM, Ken wrote:
I am totally amazed at how concrete has weakened over the years.
More that people care more about edge cases and unlikely scenarios.
All the changes in regulatory codes are usually in response to some
"bad event" and a desire to "make sure that can't happen again".
In a commercial environment (which is what Rohn, et al, design for and
what local codes contemplate when making tradeoffs), the incremental
cost of a cubic yard of concrete against the total job cost (including
labor!) is pretty small.
By and large, businesses and regulators don't contemplate "homebrew"
implementations with self provided labor when making the tradeoffs.
You see this all the time with building codes.
When I put up my 64' UNGUYED Heights tower in 1970, 4'x4'x4' was all
that was required and that held a tribander and other antennas for
years (rebar wasn't mentioned and it was hand mixed concrete). For
a 50' guyed tower, all I used was 30" square and 8" deep.
But that was back before we had modern computers to tell us it
wouldn't work.
Ken WA8JXM
On 1/4/16 12:59 PM, Jim Brown wrote:
Rohn recommends more. 3 ft x 3 ft, 4 ft x 4 ft. More mass in the
ground is better when the wind blows.
73 Roger (K8RI)
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