Thanks to John W1FV, George AA7JV, Rick N6RK and Rick W0RIC who came
back with useful information in private. I'll sum it up here for
anyone interested in building a (tall) vertical:
Rick N6RK wrote:
I have built a lot of verticals with irrigation tubing of 2, 3, and
4 inch diameter (50.8, 76.2 and 101.6 mm) and 30 feet long
(9.1 meters) with wall thickness of 0.050 inch (1.25 mm).
For 60 feet high (18 meters), the minimum construction that will stay up
is 3 inch diameter for the bottom 30 feet and 2 inch diameter
for the top 30 feet. For 90 feet high (24 m), the minimum construction
that will stay up is 4 inch diameter for the bottom 30 feet,
3 inch diameter for the middle 30 feet, and 2 inch diameter for
the top 30 feet. It is not advisable to try to use 2 inch diameter
tubing for the entire length of a 60 foot vertical, regardless of wall
thickness. This is because stiffness is proportional to wall thickness,
but is proportional to the cube of diameter. I use the "falling
derrick" method to raise the verticals. A 3 inch 30 foot derrick
should be used for the 60 foot vertical. For the 90 foot vertical,
a 4 inch 30 to 45 foot derrick should be used. Info on my web
site www.n6rk.com.
John W1FV wrote:
Attached is a diagram for a 1/4-wave vertical designed to resonate in
the
80m band. This is what I use on 80m and 160m (with loading). Its
dimensions are within the range you are interested in. The tapering
toward
the top makes it very easy to erect because it is not top-heavy like a
vertical made of tubing of constant diameter.
(I am sure John shares the diagram PDF if interested)
Rick W0RIC wrote:
I have 2- Phased 55 foot (16meters) verticals. They are tapered from
3" at the base to about 3/8" at the top. Very heavy duty walled and
guyed at 2 spots.
Geroge AA7JV also came up with some good ideas to protect the
Spiderpole that I think might be useful. (In my installation the fifth
section of the pole has broken twice due to mechanical deterioration
probably cased by a combination of the pole flexing in the wind and
weather)
I use a "hybrid" vertical here. It is 30 meters tall. The bottom 13
meters is aluminium and the top 17 meters is spider pole. There is a
40 uH loading coil at 16 meters.
Initially I had a lot of problem with the spider poles. The antenna
was not guyed and the spider pole would break in heavy wind. Also, the
outside of the spider pole would deteriorate (from UV), making the
fiberglass brittle, further weakening the antenna.
About one year ago I rebuilt the atenna: the bottom 13 meters is still
aluminium: 110 mm at the bottom tapering to 70 mm at the top. The 18
meter long spider pole consists of two poles slid into each other for
about 12 meters (to strengthen the spider pole). This then slides over
the top of the aluminium for about 1 meter (padded by duct tape
wrapped over the aluminium to make a tight fit). The loading coil at
16 meters is wound using teflon insulated silver plated 3 mmm multi-
strand wire (military surplus). There is a 30 cm dia wire loop at the
top to prevent corona discharge. The entire spider pole section is
painted with a couple of thick layers of urethane paint. This, I
believe is really important, as it prevents the deterioration of the
fiberglass. The paint is flexible and does not flake off. There are
three kevlar guy ropes attached at 18 meters. The antenna has survived
several storms, including a strom with 82 knot winds (155 km/hour).
Based on the above feedback and the availability of aluminium locally
(6060/6063-T6) I decided to make a 19 meter / 63 feet vertical that I
can also use for 80 meter. Initially it will be an inverted L as my
space is restricted limiting my ability to install hat wires in a
useful sloping angle. I will use the following tapering:
Pipe eimension - Lenght
54mm x 2mm - 6,00
50mm x 2mm - 5,00
45mm x 2mm - 3,00
40mm x 1,5mm - 3,00
37mm x 1,5mm - 3,00
If anyone has a good idea of how to connect/disconnect the horizontal
loading wire for 80 meter operation, or how to load for 80 and 40
meter in addition to 160, I'll be happy to receive feedback on this.
73 de Björn,
SM0MDG
SE0X
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