I am considering putting up a ground mounted vertical antenna, based
on using telescopic aluminum tubing such as is available from Texas
Towers or DX Engineering. Tubing available ranges from .500 inch to
2.125" with corresponding increase in price as diameters increase.

My vertical should be limited to a maximum of 30 feet, but preferrably
around 23 - 25 feet. I will feed it with an SGC coupler at the base and
operate 80M - 10M.

My question: Using the 6' long aluminum pieces, what is the minimum
diameter sizes I should start with to enable the antenna stand up to a
75mph wind UN-GUYED. Also, how much "overlap" should I use in the
telescoping pieces?

I will consider alternative means of building the vertical, but I
really wish it to be unguyed .

Any info or recommendations appreciated. TNX

Ed K7AAT

Here's one data point:

I've had four unguyed verticals about 32' high in my back yard for over
20 years. They've survived gusts of at least 75 mph in a couple of
storms, but we've never had sustained winds of that level while they've
been up. They're made from 6061-T6 aluminum, 1-1/4, 1-1/8, and 1 inch
diameter. The pieces are 12 feet each, so the overlap is about 2 feet.
For mounting, I drove an 8 foot chain-link fence line post 4 feet into
the ground, then clamped the antenna to it with muffler clamps -- long U
bolts. Some pieces of 1/4" wall PVC pipe sawed lengthwise are used for
insulation.

A 30 foot antenna will have a high angle of radiation -- about 40
degrees above the horizon at maximum -- on 10 meters. A 23 foot antenna
will have a high lobe on 10, but decent radiation at lower angles also.
A few minutes with any antenna modeling program including the free EZNEC
demo program from http://eznec.com and the Vert1 example file will give
you a good idea of what to expect.

Roy Lewallen, W7EL

Ed wrote:
I am considering putting up a ground mounted vertical antenna, based
on using telescopic aluminum tubing such as is available from Texas
Towers or DX Engineering. Tubing available ranges from .500 inch to
2.125" with corresponding increase in price as diameters increase.

My vertical should be limited to a maximum of 30 feet, but preferrably
around 23 - 25 feet. I will feed it with an SGC coupler at the base and
operate 80M - 10M.

My question: Using the 6' long aluminum pieces, what is the minimum
diameter sizes I should start with to enable the antenna stand up to a
75mph wind UN-GUYED. Also, how much "overlap" should I use in the
telescoping pieces?

I will consider alternative means of building the vertical, but I
really wish it to be unguyed .

Any info or recommendations appreciated. TNX

Ed K7AAT

Roy Lewallen wrote in
treetonline:

Here's one data point:

I've had four unguyed verticals about 32' high in my back yard for
over 20 years. They've survived gusts of at least 75 mph in a couple
of storms, but we've never had sustained winds of that level while
they've been up. They're made from 6061-T6 aluminum, 1-1/4, 1-1/8, and
1 inch diameter. The pieces are 12 feet each, so the overlap is about
2 feet. For mounting, I drove an 8 foot chain-link fence line post 4
feet into the ground, then clamped the antenna to it with muffler
clamps -- long U bolts. Some pieces of 1/4" wall PVC pipe sawed
lengthwise are used for insulation.

A 30 foot antenna will have a high angle of radiation -- about 40
degrees above the horizon at maximum -- on 10 meters. A 23 foot
antenna will have a high lobe on 10, but decent radiation at lower
angles also. A few minutes with any antenna modeling program including
the free EZNEC demo program from http://eznec.com and the Vert1
example file will give you a good idea of what to expect.

Roy Lewallen, W7EL


Thanks for that info, Roy. I will finally download that demo software
and try it within the next 24 hours. Also, I appreciate the comments on
the other. While I can't easily get 12 foot sections, I'm sure I'll do
ok with the 6 foot sections. Here on the Oregon Coast we get storms with
sustained winds exceeding 75MPH sometimes. I would lower any antenna if
NWS were to suggest such a storm was approaching, but I'd like to have
confidence with the antenna if some gusts reached that speed on rare
occasion.

The high takeoff for 75M would be fine as most of my work in that
band would be within the State of Oregon, anyway.

Ed K7AAT

Ed wrote:

Thanks for that info, Roy. I will finally download that demo software
and try it within the next 24 hours. Also, I appreciate the comments on
the other. While I can't easily get 12 foot sections, I'm sure I'll do
ok with the 6 foot sections. Here on the Oregon Coast we get storms with
sustained winds exceeding 75MPH sometimes. I would lower any antenna if
NWS were to suggest such a storm was approaching, but I'd like to have
confidence with the antenna if some gusts reached that speed on rare
occasion.

The high takeoff for 75M would be fine as most of my work in that
band would be within the State of Oregon, anyway.

Ed K7AAT

Doesn't aluminum corrode pretty fast at the coast? My parents lived in
Yachats, and aluminum didn't hold up very well at all -- although I'm
sure that some alloys would be better than others. At best, you'll have
to make heroic efforts to avoid electrolytic corrosion. I'll bet Danny,
K6MHE could add a lot to this.

Roy Lewallen, W7EL

Ed,
I'm certainly no expert on wind loading, so don't take any of this
as 'gospel'. Having said that, I've found that winds in the 75 mph
range can tear up almost anything, even if it is guyed. That's from
living in "Tornado-Alley" and seeing things laying on the ground that
shouldn't be. I figure guying is at least a sort of good insurance
thingy.
If you get a lot of salt water where you live, I'd also take a few
precautions about treating the antenna in some way to help prevent
that corrosion. No ideas about that since I don't have much salt
water where I live. There has to be something that will help at any
rate.
And lastly, your vertical at 20-30 feet tall just ain't gonna work
super-well on the lower bands where it's not going to be sort of close
to 1/4 wave length (mobile 80 meter antennas come to mind). If you
are happy with that performance, then big deal, who cares, it works.
- 'Doc

(None of these thoughts are all that 'fantastic', mostly just 'what-
if's and 'common sense'. Also probably included in that list of
mistakes I've made before.)

In article . 196,
Ed wrote:

I am considering putting up a ground mounted vertical antenna, based
on using telescopic aluminum tubing such as is available from Texas
Towers or DX Engineering. Tubing available ranges from .500 inch to
2.125" with corresponding increase in price as diameters increase.

My vertical should be limited to a maximum of 30 feet, but preferrably
around 23 - 25 feet. I will feed it with an SGC coupler at the base and
operate 80M - 10M.

My question: Using the 6' long aluminum pieces, what is the minimum
diameter sizes I should start with to enable the antenna stand up to a
75mph wind UN-GUYED. Also, how much "overlap" should I use in the
telescoping pieces?

I will consider alternative means of building the vertical, but I
really wish it to be unguyed .

Any info or recommendations appreciated. TNX

Ed K7AAT

a couple of points come to mind here. First, Your not going to get much
out of a 30 Ft Radiator tied to an SGC Autotuner, UNLESS you have a
REALLY LOW Impedance RF Ground for you Antenna System. Radiator is just
to short. It would be a lot better is it were 70 Ft tall.
Second, there are, what is Known in the Marine Radio Trades,
"Pre-corroded Aluminum Alloys" that already have an Aluminum Oxide
coating on the interior and exterior surfaces. Then the trick is, to
get a good Metal to Metal Bond between the joints of the separate
tubing pieces. Usually done with Threaded Bolts, in Drilled and Taped
holes, and coated with Ú, or other such conductive substance.

--
Bruce in alaska
add path after fast to reply

Ed wrote:

Thanks for that info, Roy. I will finally download that demo
software and try it within the next 24 hours. Also, I appreciate the
comments on the other. While I can't easily get 12 foot sections, I'm
sure I'll do ok with the 6 foot sections. Here on the Oregon Coast we
get storms with sustained winds exceeding 75MPH sometimes. I would
lower any antenna if NWS were to suggest such a storm was approaching,
but I'd like to have confidence with the antenna if some gusts reached
that speed on rare occasion.


We live in a similar situation, about two miles from the south-west
coast of Scotland. After a period of strong winds, everything is
plastered with salt spray.

In the two years since I started putting up antennas, experience with
corrosion has been varied. The cast aluminum housing of the Hy-Gain
rotor has become very heavily corroded. Antennas have fared better, and
the Optibeam is immaculate.

Least corroded , of course, of all are my fiberglass poles with
insulated wire taped up the outside. If corrosion is a worry, you might
consider one of the Spiderbeam poles, which are made in Germany and are
much stronger than regular fishing poles:
http://www.shop.dx-is.com/product.sc?categoryId=5&productId=11

A friend put up an 80m 4-square at about the same time, and at a similar
distance from the sea. He found that although the tubing was OK along
most of its length, there was extensive internal corrosion at the
joints, due to the custom-made couplers that had been machined from a
different grade of alloy. They wouldn't have lasted through a third
winter, so he is changing to 40ft Spiderbeam poles mounted on 2in metal
poles.



--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ed wrote:

I am considering putting up a ground mounted vertical antenna, based
on using telescopic aluminum tubing such as is available from Texas
Towers or DX Engineering. Tubing available ranges from .500 inch to
2.125" with corresponding increase in price as diameters increase.

My vertical should be limited to a maximum of 30 feet, but preferrably
around 23 - 25 feet. I will feed it with an SGC coupler at the base and
operate 80M - 10M.

This is basically what I had.

The length is adjusted to be resonant on 40M.

It worked fine on 80M through 30M, OK on 20M (compared to a real 20M
vertical) and goes downhill from there, though it is usable all the
way to 10M.

I later modified it by adding a base loading coil switched in and out
with a relay that made it resonant on 80M with the coil in.

It now works pretty well on 160M and tunes up on 80M a lot faster,
though there doesn't seem to be any performance difference.

20M and above were not effected.

It is in the middle of a watered grassy area with radials.

When I first put it up I thought I could get away with not using
radials since the ground is allways moist; wrong thought.


--
Jim Pennino

Remove .spam.sux to reply.

Ed wrote in
. 192.196:


I am considering putting up a ground mounted vertical antenna,
based
on using telescopic aluminum tubing such as is available from Texas
Towers or DX Engineering. Tubing available ranges from .500 inch to
2.125" with corresponding increase in price as diameters increase.

My vertical should be limited to a maximum of 30 feet, but
preferrably
around 23 - 25 feet. I will feed it with an SGC coupler at the base
and operate 80M - 10M.


I know you didn't ask about the radio performance of the proposed design.

Nevertheless...

It is challenging to achieve good efficiency from such an antenna (ground
mounted unloaded vertical, earth system, impedance matching at the base)
at less than about 17% of a wavelength in height. My article
http://www.vk1od.net/multibandunload...ical/index.htm models an
unloaded vertical of 10m (about 30') in height, and also considers a
better configuration (13m).

The article may interest you because it questions whether a 30' vertical
is a good antenna at 3.6MHz, or above 18MHz.

In any event, the bigger issue is what is under the ground rather than in
the air.

Owen

My thanks to those who have responded so far. Much food for thought.
Roy, I downloaded the demo program.... BUT.... I'm going to have to
spend some time learning its operation... it appears to have a
considerable learning curve, which I'm sure will be well worth the
time.... when I get it.


Commets on salt water corrosion have been noted. I'm about 1/4 mile
from the nearest salt water.... and down wind. My mobile RV vertical
antenna has been parked here for about 3 months now and is already
showing early signs of the corrosion.

My thoughts at the moment are I can either easily remove the aluminum
elements and clean them every 6 months or so, OR perhaps I should use
an insulated wire supported by a fibre glass support. I note someone
mentioned the DX-IS poles out of Georgia. Although I swore I would stick
to only the vertical I originally spoke of, the idea of a quality
fibreglass mast does seem to have benefits for my location. If anyone
else can recommend other sources, or their opinions of robust fibreglass
masts, I'm receptive. Given the comments on projected poorer
performance of a 30 foot vertical, I suppose I need consider one that is
higher, but I have CC&R's, and while not enforced, I do not wish to
draw attention to myself.

Thanks to all, so far.

Ed K7AAT