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Author Topic: Has anyone tried a kite-lofted antenna from a sailboat?  (Read 625 times)
N8QH
Member

Posts: 19




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« on: November 19, 2012, 05:21:35 PM »

I have a 26 foot sloop that I operate on the northern Pacific coast. Both the fore and back stays are about 35 feet in length. I currently am using a delta V loop (using the entire rig of standing rigging), which tunes well all the way down to 160 meters, but the radiation efficiency is low below 30 meters, and the takeoff angle isn't optimal. The stays are too short to use an insulated backstay arrangement.

So I'm starting to experiment with a kite-lofted antenna. In my area, there's plenty of wind, and I should have no trouble getting it to 200 feet. The kite anchor line is copper wire, instead of string, and for a ground plane I can trail another copper line behind the boat. My goal is to get a 5/8 wave antenna lofted for 80 meters (about 170 feet). I can "tune" the antenna by changing its length.

Has anyone else tried this? And suggestions? Naturally, I'll avoid repeating Ben Franklin's experiment during thunderstorms.
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WB6BYU
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Posts: 12979




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« Reply #1 on: November 19, 2012, 07:44:27 PM »

The old "Gibson Girl" lifeboat emergency transmitter from WWII came with
a box kite as well as a hydrogen generator for using a balloon when there
was no wind.  (The nickname came from the shape of the housing, which
was designed to be held between the legs while cranking the generator
by hand.)

I've hoisted a 5/8 wave wire for 80m using a reasonably sized Coyne
kite (triangular box kite with delta wings) in very light winds - it stayed
almost overhead.  But depending on the kit design it may slope off at
a an angle as lot as 30 degrees to the horizon, in which case you may
need to consider using different lengths of wire to optimize radiation
in different directions:  at that low to the horizon a shorter wire may
work better (or a longer one, depending on how much of an arc the
line makes running up to the kite.)


A couple practical comments:  first, make sure you have a DC path to
ground from your wire.  They can develop significant static charges
to ground in the wind - I've had the variable capacitors in my tuner
arc over every few seconds until I added a ground.

Copper wire is not very strong for its weight.  (The Gibson Girl
used braided phosphor bronze wire.)  I recommend using a standard
kite string to actually fly the kit, then a separate wire tied to the
line (possibly some distance down from the kit) that serves as the
antenna.  This can then be relatively light weight because it
doesn't have to take the strain on the line (which can exceed 50
pounds in a gust.)

A practical installation might include a choice of two or three kites
for varying wind speeds.

And you WILL need an antenna tuner if you want to use a 5/8 wave
vertical, because it is NOT self-resonant.  You might be able to get
by without one if you always use 1/4 or 3/4 wavelength wires, but
in practice the wire length may have to vary as you work the kite,
so being able to use whatever length wire you have out is a great
advantage.  (A simple L-network is usually sufficient as long as the
wire is longer than 1/4 wavelength, and if you have the ability to
use just the coil you probably can match shorter lengths as well.)
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K6AER
Member

Posts: 3468




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« Reply #2 on: November 20, 2012, 09:25:40 PM »

In the lsate 70's I lived on a 35 foot sail boat. The radio was a Tempo One with an antenna tuner for the back stay and while out in the open ocean I used a kite with 150 feet of soft strand wire for 40 and 80 meters. Worked damn good.
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