"Brian Kelly" wrote:

A shallow concrete slab will not support any
tower unless the tower is well bracketed to
the house. There are only two choices: A large
block of concrete for the base or a slab with
a house bracket.


The word "slab" was probably a poor choice. I was mainly referring to the
width, not depth, of the concrete. The concrete will pretty much fill the
entire hole below the ground surface.


Use a mast made from steel pipe. I've used 'em
several times, works fine. Assume the bottom
section of the mast is made from a full length
of standard 2.5" Schedule 40 galvanized steel
pipe x 21 feet long. Top the base section with
a couple 10-12 foot lengths of smaller diameter
pipe and assemble the mast & antennas. Drive a
five foot length of 3" pipe into the ground,
clean it out, raise the mast to a vertical
position and drop it into the 3" pipe. (snip)


To make it freestanding, one would have to use some fairly thick steel
pipe (both wall thickness and pipe diameter), especially for longer lengths.
And pipe that heavy would almost require a crane to move it around. Because
of that, steel pipe might be fine for shorter masts (or guyed taller masts
using thinner pipe), but wouldn't really be feasible for a taller
freestanding structure (unless one owned a crane, but then the crane itself
could just be used to support the antennas).


Dwight Stewart (W5NET)

http://www.qsl.net/w5net/

Dwight Stewart wrote in message ...
"Brian Kelly" wrote:

A shallow concrete slab will not support any
tower unless the tower is well bracketed to
the house. There are only two choices: A large
block of concrete for the base or a slab with
a house bracket.


The word "slab" was probably a poor choice. I was mainly referring to the
width, not depth, of the concrete. The concrete will pretty much fill the
entire hole below the ground surface.

OK.

Use a mast made from steel pipe. I've used 'em
several times, works fine. Assume the bottom
section of the mast is made from a full length
of standard 2.5" Schedule 40 galvanized steel
pipe x 21 feet long. Top the base section with
a couple 10-12 foot lengths of smaller diameter
pipe and assemble the mast & antennas. Drive a
five foot length of 3" pipe into the ground,
clean it out, raise the mast to a vertical
position and drop it into the 3" pipe. (snip)


To make it freestanding, one would have to use some fairly thick steel
pipe (both wall thickness and pipe diameter), especially for longer lengths.

That's nonsense. If you want a properly-designed pipe mast you do it
by the numbers, not with amateur "eyeball structural engineering"
and/or broad-brush statements like "have to use some fairly thick
steel pipe . . ". You won't know a thing about any pipe sizes until
and unless you run the numbers. A 40 foot pipe mast analysis is as
simple as it gets in the field of applied mechanics, any sophomore
student in any engineering discipline including the EEs who brought
you your HT can handle the job. A pipe mast is just a classic
cantilever beam.

And pipe that heavy would almost require a crane to move it around. Because
of that, steel pipe might be fine for shorter masts (or guyed taller masts
using thinner pipe), but wouldn't really be feasible for a taller
freestanding structure (unless one owned a crane, but then the crane itself
could just be used to support the antennas).

You gather up five buddies. You hang a pulley near the house bracket.
Run a rope from the ground, thru the pulley then down to the midpoint
of the mast. There's your "crane". Three guys walk the mast up and two
pull on the rope and up she goes.

Dwight Stewart (W5NET)

http://www.qsl.net/w5net/

w3rv

w3rv

"Brian Kelly" wrote:

(snip) That's nonsense. (snip)


Not in an area with relatively routine tropical storms and the occasional
hurricane.


Dwight Stewart (W5NET)

http://www.qsl.net/w5net/

Please see comments below.
--
J. Mc Laughlin - Michigan USA
Home:

"Brian Kelly" wrote in message
snip

That's nonsense. If you want a properly-designed pipe mast you do it
by the numbers, not with amateur "eyeball structural engineering"
and/or broad-brush statements like "have to use some fairly thick
steel pipe . . ". You won't know a thing about any pipe sizes until
and unless you run the numbers. A 40 foot pipe mast analysis is as
simple as it gets in the field of applied mechanics, any sophomore
student in any engineering discipline including the EEs who brought
you your HT can handle the job. A pipe mast is just a classic
cantilever beam.


I agree with the essence of Brian's observation. However, I offer two
additional observations:
1. The engineering understanding of tall columns using steel has gone
through quite an evolution in my lifetime. Buckling of a vertical
cantilever beam (A.K.A. a column) is a different issue from the breaking
of an actual cantilever beam. Need to study the latest steel handbook
and the tower standard and use an appropriate safety factor that is
larger than 1. [Yes, the latter is a snide remark. People do sell
stuff with specifications that are accurate for a safety factor of one!]
2 The engineering understanding of the effects of wind has also
undergone quite an evolution. See the tower standard (222F, I think is
the last one published). Any simple relationship between "miles per
hour" and pressure is almost certain to be inappropriate. [Do not
believe most antenna manufacturer's survival ratings in terms of MPH.]

However, for the heights being discussed, the "roughness" of a typical
urban neighborhood will significantly reduce wind loading from what one
would expect using weather wind info. That fact provides an additional
safety factor that just does not exist where I have placed antennas and
towers.

I give a big Amen to Brian's observation that even EEs should be able to
run the numbers AND a big Amen to the need to run the numbers. This is
an area where one wants to check twice - or more.
73 Mac N8TT