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Re: Tripod



My portable AO40 antenna kit has been successfully used in many places with
an ordinary camera tripod.  I started with a square wood crossboom that was
hinged in the middle (to fit in my shipping box).  But the hinge broke
several times.  So now I have converted to square fiberglass tubing for the
crossboom.  The fiberglass crossboom is made of two sizes that nest
together, so I can fit it inside my box.

The best kind of camera tripod to use is a tripod that has a "quick release"
mount.  Then you can permanently attach the removable portion of the quick
release to your crossboom with 2 or more bolts.  That prevents any
accidental rotation of the quick release relative to the crossboom.  There
are many models of camera tripods with quick releases.  I use a Velbon DF-60
tripod which is made in Japan and widely sold.

I recommend using a heavy duty camera tripod because of the wind loading of
a dish.  The wind loading forces you to add weight to the tripod to prevent
the tripod from blowing over in moderate (30-40 km/h) winds.  My Velbon
DF-60 is rated to support 15 pounds (6.8 kg).  Many lightweight tripods are
rated for less than half this much weight.  I added a hook to the bottom of
the tripod center column.  That allows me to hang the weight directly from
the center of the tripod.  It has been very effective to prevent the tripod
from falling over in strong winds.  When traveling, my weight is a cloth bag
filled with locally sourced rocks.  I use only a 60cm dish.  With your 80cm
dish, you will have a more urgent need for a rugged tripod that can handle a
lot of weight to avoid blowing over in strong winds.

The square crossboom also makes it very easy to attach a dish and a yagi.
It is easier to make the connections and maintain correct alignment with
flat surfaces than with the curved surface of a round crossboom.  There are
several methods to use to attach the antennas.  The easiest method is to
drill holes all the way through the crossboom and attach the antennas with
nuts and bolts.  I chose to attach Rivnuts to the crossboom, so I only need
to use bolts (fewer loose parts to keep track of).

I don't have any close-up photos of the mounting system of my AO40 antenna
system.  I can't take photos now because it is loaned out for a DXpedition.
But I'm working on a second antenna system, and I can take closeup photos of
the crossboom and tripod mount for that.  It doesn't have the antenna
mounts, but it has an identical tripod mount.

If you are using a circular-polarized yagi, I recommend that you mount the
yagi in a "X" configuration instead of a "+" configuration.  That way
neither plane is significantly affected by proximity to the ground. More
than half of my yagi extends to the rear of the crossboom.  This yagi
position combined with the heavy yagi feedline results in a good front/rear
balance (all the weight of the dish is in front of the crossboom).  This
position also allows the dish to shield the direct path between the dish
feed and the driven elements of the yagi.  Perhaps that reduces desense a
little bit?

Do not raise the center column of the tripod when used with your portable
AO40 antennas.  The tripod is much more flexible when the center column is
raised.  The result is that the antenas sway more in the wind.  And of
course raising the center column raises the center of gravity, which makes
the tripod more prone to fall over in a strong wind.  You can avoid
interference between the tilt/pan adjustment handle and the tripod legs by
mounting the antennas so that the adjustment handle points UP when the
antennas are pointed at the horizon.

I can email close up digital photos of my tripod/crossboom mount.  The
construction is actually VERY simple.

Wayne Estes W9AE
Mundelein, IL, USA


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