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Warning: Installation of antennas and tower climbing can be hazardous to your
health. This information is provided on a as-is basis and naturally, I assume
no responsibility for your safety or how you interpret of implement the
techniques described here. Obtain professional help before installing any tower
or antenna.
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The dual tram/trolley requires a lower support, a upper support along with and
two tram wires and two runners. The idea is to captivate the antenna in
two dimensions so it can only go up or down hill along the plane of the tram
wires. Antennas can be suspended above the support cables, trolley
mode or suspended below the support cables, tram mode. This picture shows the
1990 version of the lower support.
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Current version of the lower support. Note the support cables are of equal
length and are terminated to the lower support using turnbuckles. The
turnbuckles allow for individual adjustment of the support lines. This
have proven to be very useful and allows for the individual tension of each
line. Unequal tension means that one end of the boom will tilt, a technique
useful for clearing beam elements over guy wires. More on this feature later. |
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The upper support is bolted to the tower and the two support lines are
attached. The upper support is made of thick wall aluminum conduit. The spacing
of the two support lines should match the spacing used on the lower
support, in my case, the spacing is 44.5 inches. The dual support lines
should be parallel.
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Between the upper and lower support, two parallel wires are suspended. Two
runners made of thick walled aluminum tubing slide against the parallel wires.
Various adapter plates are attached to the runners allowing support for popular
boom sizes. Shown is the attachment for a two inch boom suspended trolley mode.
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In 2005, new runners were constructed for raising heaver antennas like the
MonstIR.
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Here is a M2 6M7 part way up. The antenna was orientated 180 perpendicular to
the tram lines and the coax is attached allowing for antenna testing. |
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Here is a Force12 EF-240X almost up using the tram mode. The top set of tram
cables used pre-formed guy grips. When pulling up a beam, the runner will
generally stop on the guy grip. Do not force it further or you will deform the
guy grip. You can use a large flat bladed screwdriver to adjust the runner
where it will slip up over the perform guy grips allowing the assembly to be
pulled the final foot or so into the tower. Once the beam is in place, you can
remove the runners assemblies from the beam. Its a good idea to tie the runners
off to the hoist cable and lower them to the ground. The ground crew may get a
little nervous if you allow a lose runner to slide down a tram. |
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Here's one of the Force 12 CX31's headed up using the tram mode. This antenna
was left 1/3 of the way up the dual tram for a week, waiting on the winds to
die down.
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Here's a more detailed view of the CX31 using the tram mode. The CX31 has
a lot of elements close to the tower so it gets a little crowded. Pay close
attention when raising elements that are mounted close to the tower so they
fall into the correct space. I had one element try to place itself inside the
tower. If you think you may have issues with elements close to the tower,
you can always add them once the antenna is mounted on the tower. This is
a good option to consider if you think you may have issues with a close in
element clearing a guy.
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Now for the big one. The antenna is a 3 element full size 40 meter Telerex
40M346 antenna on a 46 foot boom. The weight of the antenna is 177 lbs. The
longest element is 64 feet and the wind surface is 14 square feet. The turning
radius is 40 feet. This is a shot of the antenna going up using the tram
mode in Colorado in 1990. This is a big antenna folks. Slide it up only
when the winds are clam. Even the slightest wind can make this a handful at the
top to the tower.
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This is a shot of the Telerex 40M346 at the top of the tower. Another technique
that I have used is, when the antenna gets to the top of the tower, slack off
the tram lines and just let the antenna fall into the tower. This works very
well on the larger antennas. Also, I use two come-alongs at the top of the
tower to fine tune the antenna into position. One of the come-alongs is
modified with rope which makes it a nice light-weight tool for moving antennas
into their final position. You are not going to move a antenna of this size
very far, from my experience where it lands is where it gets mounted. At the
top of the tower is a Hygain 205, a KLM 15M6 and a KLM 10M6 (not shown) also
erected with the dual tram. |
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This shot shows the main rope used to pull the antenna up the tower. The main
pull rope runs to a pulley located at the upper support and then down to the
base of the tower to a second pulley. Light beams are generally pulled up by
hand and the heavier beams pulled up using a small riding lawnmower. A second
rope is attached feeding off a lawn hose reel, allowing the assembly to be
pulled back to the ground. This is generally not needed as gravity works well
but its there just in case. You can see the dual tram wires running to the
lower support in the background.
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Antenna assembly can be done on saw horses or in my case I use a trampoline.
The antenna is assembled on the trampoline and the dual trams are connected
along with the hoisting rope. You slowly back up the lower support, i.e
tractor, and the dual trams lines tension and raise the antenna off the
trampoline. Watch the longer beam elements so they do not deform if they hit
the ground. Caution: Watch the tension as you can pull the tower over if
the tension gets too tight. Depending on your installation, you might want to
run a back-guy off the top support to help counted tension from the lower
support. |
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One of the big issues with any antenna installation is clearing the guys. If
you use two turnbuckles on the lower support, you can vary the tension and
actually rotate the boom. For this picture, the tension was intentionally
adjusted to show how much a Force12 EF-240X boom could be moved. This technique
is very useful for getting long 40 meter elements over guys. Its also useful to
have ropes tied of each side of the boom allowing further boom adjustment from
the ground. Another technique that has been used is rather than send the
antenna elements up parallel to the tram cable, increase the angle of the
elements. This is easily controlled when you attach the runners to the boom.
Also keep in mind that you can slack off the tram cables and increase the
angle. |
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The dual tram rolled up and ready for its next project. In the summer of
2003 it was used to take down a pair of stacked Force12 CX31's, 3 M2
6M7's, a Force12 EF-240X. Since that time, its been used to put up a pair
of KLM 15M6's and a pair of KLM 10M6's as well as a pair of SteppIR's. In 2005,
the dual tram was used to raise a MonstIR antenna at W5SL's QTH. Details
at: http://www.ab5k.net/W5SL_MonstIR.aspx
Its currently scheduled to raise another MonstIR in September.
More to come...
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John, WE2F, has built a slight variation of the dual tram.
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The WE2F tram variation is action.
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