|To:||"Bill Coleman" <email@example.com>|
|Subject:||Re: [TowerTalk] My Tower cost|
|From:||"Tower (K8RI)" <firstname.lastname@example.org>|
|Date:||Wed, 25 Aug 2004 13:27:55 -0400|
Ahhh... No, the old "fence post" which is still often used had the guys connected to the base right at the ground. I used one set at the top and another around 12 feet down. They were very effective.
While such shoddy engineering practices may have been common practice years ago, they are not advisable today.
Who would they hit? This was out in the country and no one would be in the garden or out in the yard during high winds any way. Those would occurr during thunderstorms or during the winter.
Climbing them was like climging my 45G, but not as convenient. The old American Steel had cross rungs every two feet. They were solid when climbing.
The tower base was the one that came with the towers and was designed for dirt. Set in clay they never moved.
Yet they withstood 70 MPH wind gusts on quite a few occasions over something like 12 to 15 years with no damage.
Back then there was no such thing as properly, or improperly engineered towers way out in the country, at least not little 40 footers.That was also over 35 years ago.
Certainly. There were 3 per leg. That was the recomended mount for the TV tripod. They didn't even recomend the 2 X 6 backing plates I used.
I'm just saying you can pour as much concrete into the base as you wish without any permit in this area.
You can see how I installed mine which did require an inspection.
Today, in many areas I see ham tower instalations that make my old installations look over engineered. 30 and 40 foot towers I wouldn't climb even when I was younger.
Fortunately I've been asked on quite a few occasions what I thought of what some one was planning and was able to give some input. Invariably these were not the 30 or 40 towers, but big heavy towers or the smaller 25Gs going to 90 feet plus.
In nearly every instance they had good basically good ideas, but had neglected at least one issue that would render the system unsafe.
In one particular instance a ham was going up 100 feet with 25 G and following the book for guying. Good base, good anchors, and it was going to support a substantial 144/440 array within it's capabilities. He wanted to reduce the twisting moment on the tower and was planning on putting the rotor down at the base where it would be easy to get at and also reduce the twisting moment.
Unfortunately mounting the rotor just two feet above the base puts all that twisting moment against a short piece of tower that is pretty much rigid and eliminates the spring in the overall tower. Not a probelm with small antennas, but it could have been a problem with the array. The big problem came from the mast that went from the rotor to the antennas. He was using chrome molly tube which was a good idea, BUT it was 1 1/2 inch tube with half inch wall. I could barely lift one end of a 20 foot section off the ground. Each 20 foot section weighed well over 300#. He had 6 sections for a total of 1800# in addition to the tower weight and guy tension. He had planned on using 1/4 inch EHS.
We went through the calcs a week of so back as to the pressure on the base and even the little 25 G can support phenominal loads when they are evenly distributed and in the vertical plane.
OTOH many of the TV type towers used for ham antenna systems have no where near that strength.
This tower could have supported the additional load and even the extra tension from the 1/4" EHS, but the specs call for 3/16" EHS at 3 levels. He was still within load limits, but any shift due to wind allowed by the catenary could put a single leg beyond the design limits. This doesn't take into sonsideration the extra 1800# on mass added to the twisting moment transfered to the base. Nearly all antennas stend to swing a bit in wind and nearly all rotors have at least a little give. With the spring in the tower unavailable to take up the torque, I doubt that base would have survived 30 MPH winds if the array started to oscillate.
OTOH all he needed to do was install a larger concrete base so it supported the rotor on stand offs. It would have removed the extra load and all the twisting moment of the antennas and mast from the tower base.
I find, in general, it's the little things in the larger systems that tend to scare me rather than the little systems. True I may not be willing to climb most of the light duty systems, although the "dirt base" rarely plays a part in that. More often than not it's the way the tower is assembled, its condition (rust, bent, cracks), or loose guys. Most of those little systems can be put up with no climbing which is good as you'd never get me on one.
The taller and heavier the installation the more critical the safety issues.
A group of us recently took down a 32 foot tower with a small tri-bander on top. It was... well... not exactly a solid instalation. The tower was similar to an HBX series The bolts had loosened, the guys were very loose, and it didn't have a dirt base, the bottom was just set into the sand about a foot. Basically it was like a wet noodle. That "system" had been up over 15 years and withstood winds that took down nearby trees. Six of us, more or less just picked it up and laid it down over a step ladder to remove the tribander. Had it fallen over in the winds the most that would have happened would have been his wife's flowers.
OTOH that 25 G installation could have cut a house right in two.
I have some photos of a 60 American Steel tower that went down due to the high winds in a blizzard about 20 years ago. The tower was guyed at two levels and bracketed to the peak of the roof some 30 feet up (two story home with high pitched roof) It had a tribander, and some VHF antennas on top. It was guyed with the typical 3/16" hardware guy line which is soft steel. A set of guys broke and it bent the tower right over the top of the house and left the top section with antennas hanging down the north side of the house.
I went up to the peak and sawed the tower in two so the top part could slide off the roof.
BTW, there was no damge to anything other than the one tower section and the antennas.
It didn't even hurt the roof.
If I had to guess, I'd say that the installations most of us have that frequent this group and not typical of ham installations in general. Were I to bet, I'd say that maybe 10% are actually engineered while the other 90% are much closer to what I've described.
I purchase good materials and adhere to the books. I also use good safety equipment and pratices.
N833R, World's Oldest Debonair (S# CD-2)
First one off the assembly line. http://www.rogerhalstead.com/833R/833R_frame.htm
The airworthyness certificate says September 11, 1959. The airframe log shows 30 hours of pre production flight testing. It still has slightly less than 4000 hours and I've put over a 1000 of those on it.
It's a hybrid consisting of a V-35 fuselage, but with a 33 empenage (conventional tail) grafted on. It was called a 35-33 for the first few examples and then changed to a 33.
Roger Halstead (K8RI, EN73 & ARRL Life Member) N833R, World's Oldest Debonair (S# CD-2) www.rogerhalstead.com
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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