My microwave antenna installation had some very challenging obstacles that
needed to be overcome. The entire array consisted of a 2 foot dish and 8 small Loop
Yagi's. The array needed to be mounted 5 feet offset from the tower legs on it's own
rotator so the 8 foot long Loop Yagi's could freely swing past the tower legs when
rotated. I also needed to rotate the antennas from the East, through North, West,
and South, but the tower could be an obstruction to the South East since I am only a few
miles from the Atlantic Ocean, and there are no other microwave operators in that
direction. If there ever are in the future, I can still easily work them off the
side, or back of my antenna array. The antennas needed to be mounted on a side arm
because I did not physically have enough space at the top of the tower, nor did I have a
safe amount of wind loading available. I chose to mount the new array several feet
down from the top of the tower (between 85 & 95 feet). The side mount also
needed to have a strange geometry to meet the requirements of pointing in the right
directions.
Since the new array was going to be physically large,
somewhat heavy (appx. 200 pounds), and hanging so far off the side of the tower, I could
not safely construct all the pieces while climbing on the tower. I then decided to
assemble the complete array inside my garage, and then pull it aloft with a custom built
cantilever hoist that bolts to the top plate of the tower, and is lifted by a hand-crank
boat winch with a rather large spool drum that can hold enough rope to do the job.
Once this array was installed on the tower, there was no way I would be able to aim the
antennas, or do any other adjustments. This turned out to be a head-scratching
exercise in mechanical engineering. I'm glad to report that the day we installed the
antennas, everything went perfectly! Boy was I proud!
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In this
photo, we are starting to lift the array off the ground and ready it for the ride up the
tower. You will notice the black pipe frame the array is bolted to. This pipe
frame is actually a dimensional mock up of the tower face at the point the array bolts to
the tower. This was needed to simulate the tower to keep everything aligned during
the assembly of the side bracket. The pipe frame was removed as soon as the array
was hanging freely by the hoisting rope. I kept it on until this point to keep
everything from twisting while it was transitioning from the ground to hanging by the
rope. |
Here
you can see the pipe frame was removed, and the array is ready to be lifted
up along the tower face. You can also see the boat winch bolted to the
tower leg. The gray box near the dish is where the 5 & 10 GHz
transverters are located. They feed the 2 foot dish with short runs of 1/2"
Superflex Heliax. This allowed me to keep the electronics where I can remove them
for repair and still keep them close to the dish to minimize feed line losses. |
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With 2
guys doing the climbing, and a nice warm, windless January day, lifting the array into
position was extremely simple. Here I am guiding the top of the array at the 60 foot
level. Paul (KE1LI) is the guy climbing near the bottom of the array. |
Here is
another shot of us a little higher up the tower. We're getting close
to the final position now. You also have a glimpse of the cantilever hoist looming
above. |
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Here you can
really see the strange geometry of the side bracket as we are bolting it to the tower
face. Everything aligned perfectly. You can also see just how far away from
the tower the rotating mast of the new array is. You sure won't find me climbing out
there! |
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This is the cantilever hoist that carried the load for us. The two
pulleys are sailboat grade rated for 1,650 pounds of safe lifting
load. Having 2 pulleys allowed the ropes to stay clear of the array as it was being
lifted. The hoist is bolted to the top plate of the tower with two 1/2" grade 8
bolts, which are tremendously strong. The 200 pounds of hardware hanging on this rig
was far below it's potential lifting capacity. I custom built the top plate on the
tower out of 1/4" 304 stainless steel, and it has stiffening ribs welded for even
more strength. It is extremely strong!
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Here is
Gary (N1UOM) operating the winch. The duties were divided between Gary and Bill
(WA1RI). |
Here is an image that was compiled
together from 7 individual frame grabs off a DV video tape taken by Paul (N1RHS). It
really gives you a perspective of just how big things really are. Sorry about the
PanaVue messages on the picture - the software was a demo copy. |
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