■ FIGURE 11. Measure and
mark the Syntra boom at these
dimensions. The Syntra is bent
at these lines.
bolt them into place. If you find the coax and elements
are still a little wobbly, then wrap each with a strip of
electrician’s tape and reclamp. Finish the antenna by
measuring the length of the elements and cutting them
19-1/2 inches long.
A dipole antenna built this way is more durable than
the older designs I used to use. So now, it was time to see
if I could build a durable boom to hold the antenna a small
distance away from the near spacecraft. I used to laminate
styrofoam with thin plywood to create a composite structure
that was lightweight and resistant to bending. The process
was a little messy and quite time-consuming since it used
epoxy followed with lots of sanding. Eventually, using
plywood began to bother me because I felt high tech
equipment should be made from metal and plastics, and
wood should be used to make nice furniture. Therefore, I
decided to use plastic in a new boom design. Here’s a list
of parts you’ll need to make an antenna boom:
• 1/8” thick Syntra plastic strip (at least 3” by 26”)
■ FIGURE 12. Keep the hot air gun moving to evenly heat
the Syntra, both on top and on the bottom. It's safer it you
do this heating where there is adequate ventilation.
All my near space
experiments and antennas are
mounted to the sides of my
near space modules. Since the
modules are four sided, I refer
to the sides as quads. Each quad is a square opening in
the side of the module where I can bolt panels (quad
panels) holding the experiments for the mission — like
camera boxes and booms.
As I said, in the past I used a lot of thin plywood in
my near space projects, but now I’m replacing the plywood
with plastic. Since the material used to make the airframes
is 3/4 inch thick styrofoam, I start with a square of the
stuff cut to fit the opening of the quad (in my case, that’s
5-1/4 in square). A larger square of Syntra plastic ( 6” by 6”
for my modules) is then glued, centered to the styrofoam
with the Gorilla glue. Gorilla glue requires 24 hours to set,
so do this step before going to bed and let the glue set up
over night. Gorilla glue will hold the styrofoam to the
Syntra, but not strongly enough for the Syntra to be bent.
Therefore, after adding the antenna boom we’ll clamp
another strip of Syntra to the quad panel to strengthen the
bond. Speaking of the antenna boom, it’s a triangularly
shaped plastic strip as you can see in Figure 10.
There is some flexibility in the following design, so
feel free to adapt the directions to your particular needs. I
cut a strip of 1/8 inch thick Syntra sheet to 2-1/2 inches
wide and 15 inches long. Syntra is foamed PVC plastic
and easy to cut and bend. After cutting the strip, I marked
it in the dimensions shown in Figure 11.
The way to shape Syntra is to warm it until it gets soft
and then bend it over a flat surface. I prefer to use a hot air
gun to do the heating and to use a wooden board to bend
the plastic. You’ll need to warm one bend at a time, as Syntra
won’t stay warm enough for you to make more bends. Wave
the hot air gun across one line and be sure to warm both the
top and bottom faces of the Syntra. You’ll know the plastic is
hot enough when it wants to bend under the influence of
gravity. If it gets too hot, the plastic will start to curl and shrink.
Once the hot air gun has warmed the Syntra sufficiently,
shut off the gun and lay the Syntra against a flat surface like a
counter top. Then, bend the Syntra with a board to the desired
angle. Hold the Syntra in place for a few seconds until it has
had enough time to cool. The Syntra will hold its new shape
at that point. Follow up by heating and bending the Syntra
at each line. Afterwards, you might want to reheat one or
two bends and tweak the boom into the perfect shape.
The one inch ears are where the Syntra boom bolts to
the quad panel. I don’t recommend drilling the holes into
the Syntra before heating it since the bending process can
warp the holes. Now, drill two holes into each ear of the
boom that are large enough for the 6-32 bolts. Then, lay
the boom on the Syntra face of the quad panel and mark
the location of the holes. Remove the boom and drill
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November 2011
