An article in the March 1981 issue of QST written by John Belrose describes his experiments with Parafoil kites. The
Parafoil is shaped like an airplane wing and tends to hold itself level, so flying it requires little effort if the wind is
steady. Belrose used braided bronze fishing line as his combination antenna wire and kite tether; this wire has a diameter
of about 0.032 inch (0.18 mm). It seems likely that any kind of braided (multi-strand) wire could be used, provided it is
strong enough to endure the whipping and pulling it will be subjected to. The wire is more likely to break if it contains
any kinks, splices, or solder joints. Belrose's article describes antenna matching circuits for 1/2-wavelength antennas for
the 3.8 MHz ham radio frequency.
Balloons
Balloons have also been used by hams, Part 15 experimenters, and low-power broadcasters. Andrew Yoder's book Pirate Radio
briefly mentions Radio Animal's experiments with this technique, and articles in the April 1940 and March 1947 issues of QST
discuss ham radio applications. Any helium-filled balloon or combination of balloons is worth a try. The small balloons sold
in party supply stores don't have much lifting capacity, so you might need a dozen of them to lift a significant length of
antenna, and you would probably want to use the smallest wire that could stand the strain. (Although smaller wire has higher
resistance and makes a less efficient antenna). Larger balloons may be available locally or by mail order from places that
sell novelty items or scientific equipment.
It's true that hydrogen, a gas which is lighter than air, can easily be made by passing an electrical current through
water. However, hydrogen is explosive. Antennas sometimes develop high voltages or have static discharges at their ends, so
you should avoid the temptation to use hydrogen in your balloons unless you want to have a small-scale re-enactment of the
Hindenburg disaster.
If there is very little wind, a weather balloon (of the type used to carry meteorological instruments aloft) can be used.
According to Belrose, these balloons are useless in windy conditions
.
Perhaps the most enjoyable way to use a balloon would be to ride in the gondola of a hot air balloon, with your antenna
dangling underneath you. There are some places where you can pay for a ride in a hot air balloon (if you don't happen to own
one), so maybe this technique could really be used for short transmissions on special occasions. Maybe you could even experiment
with an upside-down vertical grounded antenna, in which the ground radials are located above the vertical radiator!
Antenna system details
You can measure out 1/4, 1/2, or 5/8-wavelength of wire for your frequency, or just spool out whatever amount of wire
your kite or balloon(s) can lift. For best results, rig up some sort of ground system (whether it be radials or a copper ground
rod driven into the earth), and use an antenna tuner to match the transmitter to the load. If you are operating on a beach
or lake-shore, some non-insulated radials placed in the water might turn the entire body of water into a ground plane for
your antenna. Be flexible; experiment with what's available.
Safety tips
Depending on conditions, your antenna can build up a huge charge of static electricity. This charge can hurt you or damage
your equipment. Install a resistor between the bottom of the antenna and a ground rod to bleed off this static charge. Try
a 10,000 ohm power resistor, e.g. if you have a half-watt transmitter, use a resistor rated at 1 watt. Some people prefer
to use a radio-frequency choke instead of a resistor.
Never use a kite- or balloon-supported antenna near power lines, when thunder and lightning are present, or in the flight-path
of airplanes. If you're using a large kite, you might need to rig up some sort of winch to bring the kite down when you are
done. Whatever happens, don't panic and release your antenna into the environment; it might cause an accident when it comes
back down to earth.
