"rickman" wrote in message
...
Why is a guyed ladder a "Rube Goldberg contraption"? All that matters
is the strength of the materials and the mechanics of the design. I
expect a ladder designed to carry 250 lbs of person to be more than up to
the task of holding a 15 lb antenna. Likely much more so than most of the
antenna towers that would be used for similar applications.


For short time usage such as field day I am sure it is ok.
For long term usage at home I don't think I would do it with a very large
antenna. Ladders are designed to lay on a wall at a certain angle. That is
why the legs are sort of an I beam type of construction. They are not made
to take sideways torque like a large beam would put on with the wind load.



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On 10/9/2014 10:19 AM, Ralph Mowery wrote:
"rickman" wrote in message
...
Why is a guyed ladder a "Rube Goldberg contraption"? All that matters
is the strength of the materials and the mechanics of the design. I
expect a ladder designed to carry 250 lbs of person to be more than up to
the task of holding a 15 lb antenna. Likely much more so than most of the
antenna towers that would be used for similar applications.


For short time usage such as field day I am sure it is ok.
For long term usage at home I don't think I would do it with a very large
antenna. Ladders are designed to lay on a wall at a certain angle. That is
why the legs are sort of an I beam type of construction. They are not made
to take sideways torque like a large beam would put on with the wind load.

I'm not sure what "sideways torque" is exactly, but an I beam is an I
beam. I don't think a ladder has any inherent weaknesses that would
preclude it from being used as a mast. Masts often have a rather
smallish diameter pipe at the top. The structure of a ladder is much
more substantial than that.

With adequate guy wires I expect a ladder would make a very good mast.
The only real issue is that of cost and convenience. I haven't priced
tower sections but I know long ladders are not cheap.

--

Rick

"rickman" wrote in message
I'm not sure what "sideways torque" is exactly, but an I beam is an I
beam. I don't think a ladder has any inherent weaknesses that would
preclude it from being used as a mast. Masts often have a rather smallish
diameter pipe at the top. The structure of a ladder is much more
substantial than that.

With adequate guy wires I expect a ladder would make a very good mast. The
only real issue is that of cost and convenience. I haven't priced tower
sections but I know long ladders are not cheap.

You will probably pay around $ 100 or more per 10 foot section of Rohn 25G,
one of the most common towers or about 30 to 40 dollars for a used section
in good condition.

If you look at a ladder, you will see the sides of it are made of sort of an
H section . The middle part is much larger than the side pieces. That
gives it the strength when it is laying against a wall as designed to be.

If the ladder is very long and a beam is mounted to the top of it, when the
wind blows it will tend to twist the ladder. The narrow sections of that H
form are not designed for much twisting. A 3 element beam can cause a lot
of twist in a 40 or more MPH wind .

A pipe will tend to resist twisting. Just look how small the drive shaft is
in most cars that have the rear wheel drive.



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On 10/9/2014 1:53 PM, Ralph Mowery wrote:
"rickman" wrote in message
I'm not sure what "sideways torque" is exactly, but an I beam is an I
beam. I don't think a ladder has any inherent weaknesses that would
preclude it from being used as a mast. Masts often have a rather smallish
diameter pipe at the top. The structure of a ladder is much more
substantial than that.

With adequate guy wires I expect a ladder would make a very good mast. The
only real issue is that of cost and convenience. I haven't priced tower
sections but I know long ladders are not cheap.

You will probably pay around $ 100 or more per 10 foot section of Rohn 25G,
one of the most common towers or about 30 to 40 dollars for a used section
in good condition.

If you look at a ladder, you will see the sides of it are made of sort of an
H section . The middle part is much larger than the side pieces. That
gives it the strength when it is laying against a wall as designed to be.

Actually you have this backwards. The middle part is called the web and
is there to support the two ends as well as add strength to bending in
one direction. The ends are called flanges and are where much of the
strength come from. They are separated from the center of the shape and
so have a large moment of bending. Even when the amount of material in
the flanges is less than the web, they add more strength because the
difference is more than offset by this larger distance. The ends also
resist bending in the other direction.


If the ladder is very long and a beam is mounted to the top of it, when the
wind blows it will tend to twist the ladder. The narrow sections of that H
form are not designed for much twisting. A 3 element beam can cause a lot
of twist in a 40 or more MPH wind .

Why would the wind tend to twist the ladder? Is your antenna highly
asymmetrical? I would be more concerned by the bending forces which can
be very high if the antenna is a considerable distance from the highest
guying point. If there are guy wires immediately below the antenna this
can be minimized.

There is only so much torsional force which will be applied. The ladder
is supplemented in resisting torsion by the guy wires if they are
properly done. There are the I beams of the side rails of the ladder,
but the ladder is also a larger I beam made up of the rungs and the side
rails. This adds extra strength.


A pipe will tend to resist twisting. Just look how small the drive shaft is
in most cars that have the rear wheel drive.

Yes, a pipe is an good shape to resist torsion, but this depends on the
thickness and diameter. The drive shaft of a car is *very* much larger
and thicker than any antenna mast likely to be used by a ham. The
weakness of a pipe is to bending. So a pipe must also must be guyed
extensively.

I had no idea tower sections were so expensive. A ladder is looking
better all the time.

--

Rick

In article ,
Ralph Mowery wrote:

If the ladder is very long and a beam is mounted to the top of it, when the
wind blows it will tend to twist the ladder. The narrow sections of that H
form are not designed for much twisting. A 3 element beam can cause a lot
of twist in a 40 or more MPH wind .

The twisting torque could also stress or break the junctions between
the ladder uprights and the steps. Once that starts to happen, the
ladder's structural integrity is going to go to hell... it could twist
more easily, or want to "rack".

For small light-weight beams with a very modest wind surface area, the
old-style telescoping "push-up" antenna masts aren't bad - they do
need to be guyed. You can get 'em with two, three, four, or (I think)
even more sections (about 10' each).

A friend of mine swears by the use of threaded electrical
conduit... not the light-weight "EMT" stuff, but the heavier
pre-threaded type (about three times the weight and three times the
cost of same-diameter EMT).

Rohn tower certainly has a lot going for it... and if I could figure
out a place to mount one at my house that wouldn't put the antenna too
close to the power lines or reaching over the property line into my
neighbors' airspace, my friend would gladly hand me two or three
sections of Rohn 25 for the asking. Sure would be nice... and it's a
lot more robust than any aluminum ladder would be.

rickman wrote in :

Why would the wind tend to twist the ladder? Is your antenna highly
asymmetrical? I would be more concerned by the bending forces which can
be very high if the antenna is a considerable distance from the highest
guying point.

Even if the antenna were not symetrical, that bending would cause enough
assymetry to be bad. The only thin tall antenna mast I ever put up long term
was a receiving dipole for VHF, based on a thin angle-section scrap peice
from a a very long discarded shop front sign. It was as thin as a reed, and I
figured out that if I guyed it such that the flex above was countered by the
bowing below, then few gusts would ever cause it much risk. It twisted a lot,
but very gracefully, and despoite storm force widns it stood for fifteen
years until it rotted where it stood. The wind never harmed it, but
corrosion eventually did.

"rickman" wrote in message
...
I had no idea tower sections were so expensive. A ladder is looking
better all the time.


A truck took out a 100 foot tower for a repeater I keep up. Rohn makes
'kits' for various heights of tower. This is a base plate, sections , guy
wires and ground rods and wires for them. Maybe a few other things that are
needed. Total cost about 3 years ago was around $ 4500 not counting
shipping if I remember correctly.

I put up a 60 foot one for a lot less than that at my house. Found some
used tower that looked very good for $ 35 per 10 foot section. About $ 150
for a rotor plate and thrust bearing and plate. About $ 120 for 500 feet of
guy wire. Around $ 200 for 50 bags of sackcreet mix for the base of 3 feet
each way. Another $ 200 for 3 pieces of pipe about 3 or 4 inches in
diameter and 9 feet long. Used them for the anchors and left about 5 feet
out of the ground as I did not want to have to mow under wire going all the
way to the ground. And a joint of 1 1/2 inch pipe for a mast.

Antennas, coax , rotator, and a few other things to put it up not included.

The tower is about 3 feet in the ground and guyed about 30 and 55 feet as
per Rohn booklet.

Pix of antenna on qrz at my call KU4PT.





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On 10/9/2014 3:50 PM, Lostgallifreyan wrote:
rickman wrote in :

Why would the wind tend to twist the ladder? Is your antenna highly
asymmetrical? I would be more concerned by the bending forces which can
be very high if the antenna is a considerable distance from the highest
guying point.

Even if the antenna were not symetrical, that bending would cause enough
assymetry to be bad. The only thin tall antenna mast I ever put up long term
was a receiving dipole for VHF, based on a thin angle-section scrap peice
from a a very long discarded shop front sign. It was as thin as a reed, and I
figured out that if I guyed it such that the flex above was countered by the
bowing below, then few gusts would ever cause it much risk. It twisted a lot,
but very gracefully, and despoite storm force widns it stood for fifteen
years until it rotted where it stood. The wind never harmed it, but
corrosion eventually did.

I think you are getting confused. If the wind makes the antenna bend,
any asymmetry would be along the direction the wind is blowing and so
have no torsional force.

Or are you saying the antenna would bow of it's own weight? That is a
flimsy antenna. I think if you put this on top of a ladder you don't
need to worry about the ladder being the first thing to go.

--

Rick

On 10/9/2014 5:10 PM, Ralph Mowery wrote:
"rickman" wrote in message
...
I had no idea tower sections were so expensive. A ladder is looking
better all the time.


A truck took out a 100 foot tower for a repeater I keep up. Rohn makes
'kits' for various heights of tower. This is a base plate, sections , guy
wires and ground rods and wires for them. Maybe a few other things that are
needed. Total cost about 3 years ago was around $ 4500 not counting
shipping if I remember correctly.

I put up a 60 foot one for a lot less than that at my house. Found some
used tower that looked very good for $ 35 per 10 foot section. About $ 150
for a rotor plate and thrust bearing and plate. About $ 120 for 500 feet of
guy wire. Around $ 200 for 50 bags of sackcreet mix for the base of 3 feet
each way. Another $ 200 for 3 pieces of pipe about 3 or 4 inches in
diameter and 9 feet long. Used them for the anchors and left about 5 feet
out of the ground as I did not want to have to mow under wire going all the
way to the ground. And a joint of 1 1/2 inch pipe for a mast.

Antennas, coax , rotator, and a few other things to put it up not included.

The tower is about 3 feet in the ground and guyed about 30 and 55 feet as
per Rohn booklet.

Pix of antenna on qrz at my call KU4PT.

Wow, $880 not including the labor. I guess the $210 for the tower is
not so big a deal. Actually, I expect 60 foot of ladder would be just
as much if not more.

--

Rick

On 10/9/2014 3:04 PM, David Platt wrote:
In article ,
Ralph Mowery wrote:

If the ladder is very long and a beam is mounted to the top of it, when the
wind blows it will tend to twist the ladder. The narrow sections of that H
form are not designed for much twisting. A 3 element beam can cause a lot
of twist in a 40 or more MPH wind .

The twisting torque could also stress or break the junctions between
the ladder uprights and the steps. Once that starts to happen, the
ladder's structural integrity is going to go to hell... it could twist
more easily, or want to "rack".

For small light-weight beams with a very modest wind surface area, the
old-style telescoping "push-up" antenna masts aren't bad - they do
need to be guyed. You can get 'em with two, three, four, or (I think)
even more sections (about 10' each).

A friend of mine swears by the use of threaded electrical
conduit... not the light-weight "EMT" stuff, but the heavier
pre-threaded type (about three times the weight and three times the
cost of same-diameter EMT).

Rohn tower certainly has a lot going for it... and if I could figure
out a place to mount one at my house that wouldn't put the antenna too
close to the power lines or reaching over the property line into my
neighbors' airspace, my friend would gladly hand me two or three
sections of Rohn 25 for the asking. Sure would be nice... and it's a
lot more robust than any aluminum ladder would be.

Yeah, no doubt. I put up an antenna tower once on a job. It was just a
TV antenna some 15 or so feet above the house, but that tower was pretty
solid. It could be climbed without any trouble... once it was guyed.
But I do recall it was an expensive tower compared to the usual pole
sticking up from the chimney.

--

Rick