I love radio and TV towers, as do probably you too, and I started wondering about the ground aspect of a tall tower.
I love radio and TV towers, as do probably you too, and I started wondering about the ground aspect of a tall tower.
I am not talking about transmitter radial grounding, I mean the foundational base required below a tower to keep it standing stable and firm.
The weight of the tower, all downward to one point of earth, plus the downward pull of the heavy guy cables, no doubt places huge stress on the earth beneath a tower. If there were a cavity in the earth the tower could puncture right through like a spear thrown by an Olympic giant from 700 B.C.
So, then, therefore, what is down there, at the foot of a tall tower, to keep it soundly in place?
A Big Thing
Usually a mass cement block. If there is a chamber below…well then in my opinion…they should have picked a different site!
Then again…who is to know when a sink hole is right under your feet!
RFB
A Giant Tortoise
Carl, at the base of broadcast towers which I have visited there was a huge concrete pad usually about 25 X 25 feet. I have no idea how deep they went but it was prabably a few yards.
I helped a fellow ham install a free standing 40 foot tower and recall that the base required a cubic yard (3 x 3 x 3 feet) of concrete. I suppose larger towers require more.
Neil
That’s Major
Radio8z, 25 X 25 is a major chunk of concrete. How high do you estimate these rise from ground level?
Small Tower Didn’t Require Much Footing
Carl, my 55 foot tower has no concrete at the base. I dug a hole a little over 3 feet deep and placed a brick under each leg to distribute the weight of each leg. I filled the hole with dirt.
I did put brackets at the peak of the roof at 20 feet, one on each of two legs to offer some lateral support. And, about 2/3 up the tower I attached 3 guy wires.
In the 25 or so years it’s been standing firm and hasn’t sunk at all.
When I was younger, living at my parents, I had a free standing 30 foot tower. The base was set in concrete. The hole was 4 feet deep and about 20 inches in diameter.
Obviously, a commercial broadcast tower requires some serious engineering to keep it up.
Cutting Corners
“Obviously, a commercial broadcast tower requires some serious engineering to keep it up”
Even serious engineering, when done half arsed, ends up in things like THIS happening.
An incorrect type u-bolt (cheaper) was used instead of the proper ones.
A tower has more chance of coming down due to things meant to keep it up failing, or incorrect/inadequate things used to build it.
There has never been any case documented where a tower fell or sunk because of the lack of a sufficient base.
And although not exactly the same…do not let synchronicity become part of the project KDX.
(Tower in video was the KDXH TV tower)
RFB
Tower
Radio8z, 25 X 25 is a major chunk of concrete. How high do you estimate these rise from ground level?
Carl, the tower I had in mind when I posted earlier was the WLWT tower in Cincinnati. This is a four legged self supporting tower which explains the size of the pad and I would estimate the height was near 900 feet. This is based on knowing the height of a repeater antenna our group installed on the tower at 660 feet which was about 2/3 of the way up. The tower legs were secured to the pad with the biggest bolts and nuts I have ever seen. At all four corners there were large (guessing 6″ wide and 1″ thick) copper straps which disappeared under ground.
This tower was rather new at the time and was located next to the old tower. The old tower is the one which was made famous as the “WKRP in Cincinnati” tower since it was used in the shots for that program.
One thing which is perfectly obvious once one thinks about it involves installing the hardline for the antenna but it can be a nasty surprise otherwise. The line was to be installed on one leg of the tower, lashed in place with #12 wire every 3 feet. Sounds simple until one realizes that 660 feet of line weighs 500 pounds. This is the weight of the line which has to be hoisted up the tower leg so doing so by hand was out of the question. We arranged for a professional tower crew to do the work.
It began with a man climbing the tower to the 660 foot level. He carried a pulley and messenger line up with him and rigged the pulley and looped the line back to the ground. He came down and they attached a heavier line to the messenger and used a winch mounted on the back of a truck to pull the heavier line through the rigging. Next they attached a platform which was about two foot square with a pole vertical from the center. The pull line was attached to the pole and the hardline was attached to the bottom of the platform. One of the crew men then sat on the platform holding the antenna and his tools and rode the platform winched up the tower, installed the antenna, detached the pulley and let the pull line fall to ground. He then climbed down the tower lashing the feedline to the leg as he descended. This whole process took less than two hours. These guys really knew their business.
Our first contact was a station about 80 miles from the site. Not bad for a 220 MHz repeater.
I did visit the WLW AM tower site in Mason, Oh. This is a guyed Blaw-Knox design and it literally stands on a small point at the bottom. The concrete pad for this tower was much smaller than 25 x 25 but I couldn’t get close enough to really judge the size. Approaching an operating insulated from ground tower for a 50 kW station is not a good idea.
But, I digress…
Neil
Most Do
Most professional tower crews do know their stuff. It’s the management department that can make things come tumbling down.
Good thing you guys choose the right route, meaning good management. Was not so for the seven tower workers who were forced to use inadequate rigging gear chosen by the management.
RFB
More my style
I wish I could find a pic with it lit up at night …
http://www.modestoradiomuseum.org/wooden%20tower.html
Lovely Sight
Ken, the largest wooden tower is beautiful to see. I had not heard about anything like that. I’ll bet it looks beautiful lit up at night.
Just yesterday, still obsessed by having a 50-foot tower for long wave, but afraid of a guyed tower because it could end up in a neighbor’s yard, I still fantasized about a fire-tower 50-feet high with an observation deck on top and stairs or ladder all the way up. Sitting up there could be fun for nature watching in the tree tops, but when helicopters came over it would be disturbing.
FAA Flight Level Minimums
Anyone who’s a pilot, helicopter or fixed wing, as I hold a private pilot’s license for both copters and fixed wing single engine planes, knows that you cannot fly at 50 feet AGL…PERIOD!
And any clear headed pilot would not even get anywhere near 50 feet AGL in normal flight anyway. Lot’s of unlit billboard signs and trees and high voltage power lines and poles also unlit that are out there.
Oh and need I forget, there are certain flight paths planes and copters must fly at specific altitudes over populated areas too!
Do you see any helicopters or airplanes buzzing about 50 feet above your head or house or neighborhood right now?
No you don’t!
About the only place your going to find an aircraft at 50 feet AGL is just before touchdown and just after take off, and that is usually at the airport runway or helicopter pad, not over your house or neighborhood!
Oh and BTW, minimum tower or antenna support structure ABOVE 150 feet must be lit up. Below that, they do not have to be. So 50 feet is WELL WITHIN the safety margin concern for aircraft.
The only thing I can see which is a valid concern is Carl’s about the 50 foot pole coming down onto his neighbor’s house or bopping them in the head! If you do not have the footprint area on the ground to adequately place proper guy and anchor points to keep that 50 foot pole up, then don’t put one up! Instead, run a slanted vertical or Windom wire antenna, or 50 foot long wire horizontal, though not as effective. Still the solutions are simple, which do not require needlessly complicated complex answers.
If it fit’s, wear it. If it don’t, don’t try to force it!
RFB
Tower materials,
Tower materials, construction, safety gear, wind factors, it’s all there:
http://k7nv.com/notebook/topics/TowerTips.pdf
MSAs, etc.
http://www.risingup.com/fars/info/part91-119-FAR.shtml
Having shown that, when I flew in the CAP, twice a year we flew military route certification (lots cheaper than regular Air Force), had to report any objects/structures estimated to be 100′ AGL or more not shown on current charts.
The joke was: Fly 50′ AGL; if we run into something, be sure to mark it on the chart ;D
Tower Talk
Last night a helicopter went over at what sounded like 2-feet above the roof. I always hope they haven’t had too much to drink.
That Tower How To Guide is great, I almost printed it out, but remembered that I might not need all that with a 10-footer.
I would like to be able to climb it, though, and that puts a lot more stress requirement into the structure. Maybe I should just seal the feet of a high aluminum ladder into a concrete block.
How about a circular iron staircase to nowhere that goes up 10-feet…. it would be helical.
There’s coffee……
Temporary High Tower Platform
Hey Carl,
What do you think of this configuration?
http://i40.tinypic.com/2nm1x7o.jpg
It’s totally legal as large Car Dealerships do it all the time. Except they don’t use them for radio communications. Ever see a small blimp hovering over your local car dealership? Just think of the savings over an actual high metal tower. If you use Mylar or Kevlar skin you don’t need to keep topping off the helium gas. You would need a electric wench to retract it tough. Harbor Freight sells 12v wenches for under $80 bucks.
SpookySR
K-BLIMP
I love the blimp plan, SpookySR!
Wow, I can imagine floating one of those in the dark with no lights, reaching coast to coast, and by morning over-sleeping and attracting a traffic tie-up with news helicopters and military patrols.
“Would you believe I’m a hobby car dealer?”
Up, Up & Away!
I always wanted to do a baloon/blimp supported antenna set-up, but then I priced blimps. $$$$$$$$!! Maybe a surplus weather baloon would do it?