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Mostrando mensaje 2614
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Asunto: | [dxcolombia] 160m Vertical | Fecha: | Jueves, 8 de Junio, 2006 10:27:36 (-0400) | Autor: | Alexis Deniz M. 4M5DXgroup <yv5ssb @...net>
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This is a 90 foot tall top loaded
vertical for 160 meters.
It is constructed from aluminum irrigation tubing and has four sets of four
guys each. The top guys also serve to support the top load wires. It
has a "temporary" wire stub about 68 feet long hung
off the side to provide operation on 80 meters. More details are pictured below.
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The
most important part of any vertical antenna system is the ground. I like to
put the radials in the ground before putting up the antenna so that the
antenna and guys are not in the way. This is the implement I used to form
shallow trenches for the radial wire to lay in. The local farmers use these
to form corrugations in the field for irrigation water to run through.
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Here
is one of the shallow trenches formed prior to inserting the radial wire. The
orange baling twine is streched out between the vertical base and far end of
the path I want the radial to take. That gives me a guide to follow with the
tractor. I tried to insert the wire in the ground as I pulled the trench but
there were too many rocks. Wound up inserting each wire by hand. I figured
that I walked about 18
miles putting in the radial system.
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Construction
was started by first locating and pouring five concrete piers for the
guy anchors and base. All five are similar except the guy anchors have rings
instead of a threaded stud. After the cement work was done, conduit was
placed in the ground for the coax and control cables. You can see the conduit
in the upper left of the photo. Next the radials were placed in the ground
using the implement shown above, and terminated in a ring around the base. The
green wires are used for connection to the tuner box to be installed last. The
wires are all soldered to a ring formed from copper wire. When all the
soldering is completed the ring was painted with several coats of common PVC
pipe cement and then sprayed with Krylon paint to weatherproof the solder
joints. There are 82 radial
wires, each 100+ feet long.
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The
mast is constructed from 4
inch irrigation tubing. The guy lines are fastened to
the mast with a "wheel line" hub clamp. Using a clamp allows
adjusting the placement of each guy set to minimize mecahnical resonances. When
the mast was first stood up, I watched as the wind caused vibrations. The mast
was then lowered and the position of each clamp was adjusted. The distance
between each guy set is now different and vibration is minimal.
The guys are temporary baling twine. I used it to establish the proper
lengths and when the design was stable, changed to Dacron.
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The
base insulator was made from pieces of PVC pipe. I turned various pipe
fittings on my small lathe and used PVC pipe cement to bond them all
together. The 1/2 inch diameter hole is for the hinge pin. The first
insulator was made from ABS. The ABS got brittle when the temperature dropped
way below freezing and cracked. So
far the PVC has not failed.
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The
mast is fabricated from aluminum irrigation tubing. The bottom 40 foot is 4 inch diameter, 0.075 inch wall
tubing. The next 30 feet
is 4 inch
diameter, 0.05 inch
wall tubing. The top 20
feet is 3
inch diameter, 0.05 wall tubing. I tried a couple
different approaches to splicing the sections together before it became
obvious that more internal support was required to keep the tubing from
collapsing under severe load conditions. This splice was made from PVC
conduit. The pieces were turned on my small lathe and make a snug fit inside
the two pieces of 4 inch
tubing. It didn't need to be made from insulating material but that's what
was handy. A sleeve made from a 1 foot long piece of 0.05 wall tubing to fit
over the outside of the joint. Sheet metal screws through the tubing and into
the PVC keep the whole thing together and provides electrical
continuity.
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A
base was formed from 4 inch
steel "C" channel. The pieces were welded to form hinge points for
the mast and gin pole. The base plate is bolted to the cement footing. 1/2
inch diameter bolts form the hinge pins. In this image, the tubing on the
left is the gin pole in the lowered position and the antenna is on the right
in the raised position. The black base insulator is the old ABS insulator
that failed after this photo was taken.
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The
gin pole is a single 40
foot piece of 0.075 wall tubing. Although difficult to
see in this image, the 90
foot vertical is on the ground to the left with all
guys in place. The top of the gin pole has a guy on each side, a triple line
pulley system to the rear, and four guys to the mast. As the pulley system
pulls the top of the gin pole down, the vertical is raised up. This is a one
man operation. I wanted to get a photo of the thing half raised but couldn't
figure out how to hold the rope and run the camera at the same time!
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In
this image, the gin pole is in the lowered position. The side guys are the
orange baling twine. The four rasing guys on the mast are black dacron. The
yellow rope is part of the two line pulley system. It was later changed to a
three line system to allow raising the mast with less effort on my part. The
rope is tied off to a board. Not shown in the image is the tractor parked on
the board! This was later changed to a pemanent concrete anchor point.
The four raising guys are tied off after the mast is raised. Another set of
full length guys are used to secure the mast from the "forward"
direction
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This
is the tuner box at the base of the vertical. There are four open frame
relays used to switch in different "L" networks. Only two are used
now, for 160 and 80. The relays and network parts are mounted on a
sub-chassis so that it can be easily removed and modified in the
shack/shop.120 VAC is provided for soldering irons and test equipment. In the
lower left the bottom of the mast can be seen in the shadow. You can see part
of the stand off insulator for the bottom end of the 80 meter side mounted
stub.
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