[TowerTalk] Tower Base Technology

[David Siddall]

Mike -

I've put two HDBX-48 towers up.  One was in sand (on Cape Cod) but about 5.2 cubic yards held it even through a hurricane (with Ham-IV, TH5DX 2' above top (50' above ground).   (The base is still there in HyannisPort if anyone looking to buy a house up there with the base already installed . . . .) 

Other was in rocky soil in West Virginia, again I used just a little over 5 cubic yards with no problem.  In sand, it was held pretty much purely by the weight of the concrete; in WV, I dug a ridge about 6 inches into the rock/soil around bottom; and also made to bottom a little larger than the top to provide a little better hold.  

Bottom line is, the recommended 5 cubic yards (this is my memory of being equal to slightly exceeding spec) will hold it in just about anything; that is, at least until the torque starts popping rivets on your top section with that antenna. . . but screws can fix that if watched.  [ Mine was fine until I put a KT34XA on it - knowingly serious overload - and steady winds of 70 -80 miles caused a little damage.  If you know W9LT, he could tell you about that  - it happened on a November contest weekend when he was single op'ing, up on the mountaintop.  But that was serious torque, a 34-foot boom being substantially greater than the recommended 10-foot one.  The 18-foot TH5DX came through even high winds without damage.  One thing about Rohn - I have always found them  conservative on their ratings.  Now that I am older, however, I follow them closer.  And I always exceeded on bases and anchors for simple safety reasons. ]

Dave K3ZJ   

>>> "Mike Foerster" <mike.foerster@home.com> 08/10/00 08:58PM >>>

Guys,

I'm new to the group, got a reference to ask the TowerTalk bunch my
question.

I just purchased a used (6 year old) 48ft Rohn HDBX 48, TH11DX and
Tailtwister rotor.  Had to take it down and it was in dire need of some boom
to mast repairs.  I've got that taken care of.

Now for the question.  The mfg. specs call for a big block of concrete
buried in the ground.  Brute force style.

Has anyone done any engineering using some technology to help to keep the
tower erect safely, other than just the big block?

    *Something like digging post holes in the bottom 4 corners of a bit
smaller pit and putting in some re-bar and then pouring concrete

    *Or perhaps a "+" shaped hole to use more of the dirt/clay to press
against vs the big block effect.

    *Is one shape (square, round, tall, short,tapered, etc.) better than the
others?

    *Differences in the ground makeup (sand, clay, rock)?


This (Rohn) tower technology is about 20 years old  (as is the book that
tells me how much concrete is required).  There has to be a better way

I know about following the mfg. specs, liability, warnings about twist, etc.

    I'm just asking...

Mike





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