Jim Lux wrote:
MTV wrote:
Allodoxaphobia wrote:
On Sat, 07 Mar 2009 15:03:33 -0600, MTV wrote:
Phase 2 was first digging the 36' x 36" x 45" hole for the base,
then securing the tower rod base and pouring the concrete.

A 36 foot deep hole ought to hold up a freestanding 100' tower --
or more! :-)


It's actually 52" deep; the tower mfgr said min. of 45"; ARRL handbook
says 6' but only 30" sq, depending on the type of soil.

I don't know that I'd use the ARRL handbook as a source for
structural/civil engineering data. The figures in the "assembling a
station" chapter in my 1990 handbook are just an example for a TriEx
LM-470 or for a Wilson ST-77B, not a general recommendation for all
towers. In fact, the last sentence in the section is:
"Once you have that information, contact the engineering department of
your tower manufacturer or a civil engineer"

Following the mfr recommendations is probably the best bet. (and that's
if they're the *current* recommendations.. engineering and construction
standards are always evolving, what was acceptable in 1960 might not be
acceptable today)

That said, there's a lot of possible tradeoffs in tower bases, even for
the same kind of tower in the same location. skinny and deep vs wide and
shallow is one. If you're not taking the manufacturer's recommendation,
then you probably need to get someone with some engineering expertise to
tell you whether what you want to do is reasonable.

My thoughts, too, to use the mfg recommendation (45" deep) so I made it
52" deep. I can't see it not doing the job. Tower is HD aluminum and I'm
staying within all specs. Rated for 12 sq ft @ 87 mph; my wind load is
about 10 sq ft. Highest winds we had w/Hurr. Ike were between 85-90 mph.
The tower, however, will be protected by trees up to about 40', I
could lower the antenna before a storm, and I have a house brace I'll
probably use at 10'. The "Handbook" I referred to is a 2009 ARRL Antenna
Book.

Today I was trying to spot the 3 guy wire supports. Have a problem with
one, so I'm thinking of using 4. Instead of all being 120 degrees, one
would be 90 degrees; other three 30 degrees apart. Problem is that one
of the 120 deg's would be right into my RV pad - not possible. An
alternative to four would be to run one onto the end of the house roof,
which I suspect would not be as sturdy as it should be?

Marv