■ FIGURE 9. An example of a quad. This module is
shorter than most of my other modules, so its quad
isn't square. The opening created by the quad lets me
mount experiments to the outside of the module and
still wire them to the flight computer.
length of the elements. How are we going to turn
them into an antenna?
CONSTRUCTING THE NEARSYS
NEAR SPACE ANTENNA
When I started in this near space business, I
soldered the elements of the dipole to the center
conductor and shield of a coax. I then sealed
everything in hot glue. I found this design worked
well initially, but over time and several landings, the
glue would loosen its grip on the wire elements.
When the elements are too loose, they risk being
broken off the coax. Therefore, I came up with a
design I’ll share with you now. Listed below are the
parts you’ll need for this antenna:
• Perf board (I usually grab the 2” by 3” perf board at my
• Two feet SMA coax cable (I use Jameco part number
• 40 inches of 12 gauge solid wire (household wiring from
a home improvement store)
• Three 1/8” plastic wire clamps (available at Ace
• Three 10-24 nylon bolts 3/8” long (also at Ace)
• Three 10-24 nylon nuts (again at Ace)
Cut the 12 gauge wire in half to make the dipole
elements. Then, strip about 1/8 inch of insulation from
one end of each wire and bend it at a 90 degree angle.
Next, take the RG-174 coax cable and cut one of the
SMA connectors off. That will expose the braid and
Now, strip the outer jacket off the RG-174 to expose
the braided jacket. Then, spread
the woven braid slightly and
push the inner conductor and
the insulation through the
opening in the braid.
Now, strip the inner
conductor to expose the wire
inside, twist the stranded wires,
and also twist the woven braid.
You now have two “wires” that
you can solder to dipole
■ FIGURE 10. A side and top view
of the antenna boom mounted to
a quad. The antenna and its perf
board are bolted to the inside of
the boom where it receives some
protection at landing.
Rather than soldering the coax conductors directly to
the dipole elements, we’ll solder the coax and the
elements to copper traces on the perf board. Those
soldered connections are not nearly strong enough to
keep the antenna together. Therefore, the design uses
nylon wire clamps for strain relief for both elements and
the coax transmission line. You’ll need to enlarge the
openings (pads) in the perf board to fit the elements and
coax braid (the center conductor will fit the pads as they
are currently drilled). Make sure you don’t solder both
dipole elements to the same copper trace. However, the
coax center conductor and braided jacket are soldered to
the same copper trace as each of the elements.
Treat the perf board gingerly for now. Slide one of
each clamp over the coax and both dipole elements.
Then, locate three places on the perf board where the
nylon clamps can be bolted to the perf with the nylon
bolts (without cutting important traces). Drill three large
holes through the perf board for the nylon clamps and
November 2011 57