Hello everyone,

I'm contemplating putting up a vertical antenna for HF use. I'm looking
at an approximate height of 30 feet or so. I am thinking of using
aluminum tubing (0.058" wall) in a 'telescoping' manner. Here are my
questions (so far):

1) Diameter. For wind resistance, should I start with something like 1
inch diameter and work down to 3/8 inch? Would the antenna be stronger
if I started with 2 inch diameter and worked down to 1-3/8 inch?

It would seem to me that the larger diameter might be better able to
withstand wind but it would also offer more resistance to wind possibly
negating the additional strength. But, I have no experience to draw
from. So, fat or slim?

2) I am planning a set of guy ropes at about the 12 foot level, a bit
over 1/3 height. Is there a better height for guy ropes? I can put as
much concrete in the ground as I like, and a very robust mount system is
possible. Is there any way to make an unguyed 30 footer that isn't a
tower form factor? Something like making the bottom 12 feet or so from
2 inch diameter, 1/4 inch wall tubing and then light weight tubing from
there up to full height?
--
73, Hank

Hank Zoeller wrote:
Hello everyone,

I'm contemplating putting up a vertical antenna for HF use. I'm looking
at an approximate height of 30 feet or so. I am thinking of using
aluminum tubing (0.058" wall) in a 'telescoping' manner. Here are my
questions (so far):

1) Diameter. For wind resistance, should I start with something like 1
inch diameter and work down to 3/8 inch? Would the antenna be stronger
if I started with 2 inch diameter and worked down to 1-3/8 inch?

It would seem to me that the larger diameter might be better able to
withstand wind but it would also offer more resistance to wind possibly
negating the additional strength. But, I have no experience to draw
from. So, fat or slim?

2) I am planning a set of guy ropes at about the 12 foot level, a bit
over 1/3 height. Is there a better height for guy ropes? I can put as
much concrete in the ground as I like, and a very robust mount system is
possible. Is there any way to make an unguyed 30 footer that isn't a
tower form factor? Something like making the bottom 12 feet or so from
2 inch diameter, 1/4 inch wall tubing and then light weight tubing from
there up to full height?

When I bought my aluminum tubing from Texas Towers, they had
a computer program that calculated and specified all of the above.

http://www.texastowers.com
--
73, Cecil http://www.qsl.net/w5dxp

The windload on a piece of tubing of a given height is proportional to
the radius, but the stiffness of a piece of tubing is proportional to
the fourth power of radius.

So, as you make the tubing bigger, the stiffness goes up much much
faster than the windload, so bigger tubing will always be stronger
unless you make the wall very, very thin compared to that of the
smaller tubing.

Now, the weight of the piece goes up too, and the price is proportional
to the weight, so you don't see a lot of antennas made of 5 inch
aluminum tubing when they don't need to be.

For a freestanding vertical, you're going to get the best results with
a taper. It's good for the tubing to get thinner as you go up, because
the big problem with a freestanding pole is that the wind is trying to
tip it over. The mount at the base has to be strong enough to take
this torque. The wind has more leverage when it's acting on the tip of
the vertical than when it's acting further down, so having the vertical
thin at the top helps reduce the load on the base.

Cecil's suggestion about the Texas Towers calculator is a good one.
Also, after you put up a vertical you'll have more intuition about
this. I wouldn't make it a 1 inch vertical all the way up :-).

I had a 40m vertical, 4 elevated radials at 15 feet and 1 inch tubing
from that point up to about 25 feet, with smaller tapered tubing and
rod above that. It worked OK, but had to be guyed in two places! It
also snapped in half in a windstorm. Bad mechanical design, but I made
do because I had the tubing. It would have been a much nicer antenna
if I'd purchased the proper materials.

73,
Dan

How are you planning on mounting the alum. tubing at ground level?
And what, if any, means are you considering to provide for tipping it
over?
I wonder if it is practical to install say, 4X4 posts in the ground
about 5 inches apart, with another 4X4 as the vertical support for
the aluminum pole. The aluminum pole bolted to the 8 foot long 4X4 at
about the 6 foot level. Would the wood detune the antenna?

Rick K2XT

Rick wrote:
How are you planning on mounting the alum. tubing at ground level?
And what, if any, means are you considering to provide for tipping it
over?
I wonder if it is practical to install say, 4X4 posts in the ground
about 5 inches apart, with another 4X4 as the vertical support for
the aluminum pole. The aluminum pole bolted to the 8 foot long 4X4 at
about the 6 foot level. Would the wood detune the antenna?

I have mine with the bottom mounted at 20 ft using 2x4s.
The tubing is isolated from the 2x4s by a sleeve of PVC
pipe. There is no noticeable detuning by the wood support.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
When I bought my aluminum tubing from Texas Towers, they had
a computer program that calculated and specified all of the above.

http://www.texastowers.com

Cool! Does it calculate the size to use based on expected wind speed?

I looked around on their web site and didn't find a calculator so it
must be something they do with you on the phone? I'll call 'em Monday
and see what they have to say.

Thanks for the tip!
--
73, Hank

wrote:
The windload on a piece of tubing of a given height is proportional to
the radius, but the stiffness of a piece of tubing is proportional to
the fourth power of radius.

Thanks, Dan, this is really useful info -- just what I was looking for.

What do you think of having the bottom 12 feet be 2" diameter by 0.25"
thick tubing? If I went up another say 16 feet with 0.059 thick tubing
properly telescoped do you think I'll need guy ropes?

I've been thinking of overlapping the thin tubing in such a way that
there would always be two layers of it for the entire length of the
antenna. It would seem to me it would be much stronger without
increasing the wind loading at all.

Thank you for your insights.
--
73, Hank

Rick wrote:
How are you planning on mounting the alum. tubing at ground level?
And what, if any, means are you considering to provide for tipping it
over?

I haven't yet decided how I'm going to mount this thing. Now, I'm
leaning toward (pun intended) a larger size of tubing than I initially
thought. Once I make a final determination on the tubing size then I'll
turn my attention to the mount.

Fortunately, I have a machine shop so I ought to be able to fabricate
something worthy.

As to the detuning, I'm not concerned at all about resonance as I'll
have a 1-kw antenna coupler mounted at the base of the vertical. I
would be concerned about other effects so I'll likely make the mount
with as small an electrical footprint as possible.

The fold-over idea is good. I think I'll probably make two of these
things, one about 30 feet high and another about 16 feet high for the
upper HF bands. It would be cool to be able to switch them out easily..
--
73, Hank

For about 20 - 25 years I've had four verticals of about 33 foot height
in my back yard. They're free standing, no guys. They went through one
wind storm with gusts in the 80 mph range, and all other weather,
without damage. Each is made of three pieces of telescoping 6061-T6
tubing, 1-1/4, 1-1/8, and 1 inch diameter. The support is an 8 foot
chain link fence line pole (about 1-1/2 inch diameter, steel), driven 4
feet into the clay ground. The antenna element is clamped to it with
muffler clamps, insulated with a couple of slices of thick wall plastic
conduit about 1/4 inch thick.

Roy Lewallen, W7EL

Hank Zoeller wrote:
Hello everyone,

I'm contemplating putting up a vertical antenna for HF use. I'm looking
at an approximate height of 30 feet or so. I am thinking of using
aluminum tubing (0.058" wall) in a 'telescoping' manner. Here are my
questions (so far):

1) Diameter. For wind resistance, should I start with something like 1
inch diameter and work down to 3/8 inch? Would the antenna be stronger
if I started with 2 inch diameter and worked down to 1-3/8 inch?

It would seem to me that the larger diameter might be better able to
withstand wind but it would also offer more resistance to wind possibly
negating the additional strength. But, I have no experience to draw
from. So, fat or slim?

2) I am planning a set of guy ropes at about the 12 foot level, a bit
over 1/3 height. Is there a better height for guy ropes? I can put as
much concrete in the ground as I like, and a very robust mount system is
possible. Is there any way to make an unguyed 30 footer that isn't a
tower form factor? Something like making the bottom 12 feet or so from
2 inch diameter, 1/4 inch wall tubing and then light weight tubing from
there up to full height?

Hank Zoeller wrote:
Cool! Does it calculate the size to use based on expected wind speed?

As I remember, you give them the wind speed and they give you
back the specifications. They ran the program for me while I
was standing there in the lobby wondering what size to buy.
I requested a self-supporting 33 ft monopole rated at 75 mph
but changed my mind when I found out what that required -
more than double the cost of a guyed monopole. Also building
it out of six foot sections instead of 12 foot sections reduced
the cost considerably. ME's probably understand why but, as a
EE, I was surprised.
--
73, Cecil http://www.qsl.net/w5dxp