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Vertical Wire Antenna + Kite
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by LA9GY4 on September 28, 2009
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I am a new ham, so excuse my naive attitude. As a new ham, I am also an avid kite flier.
It has occurred to me that I could easily make a vertical wire antenna in combination with a stable single line lifter kite, using the kite line to lift the vertical.
1.) Anyone tried this already (besides Marconi)?
2.) Do you think I could get away with just using a length of wire, say 1/2 wave?
3.) If I wind the wire separately, I can even imagine tuning the wire using the kite to control the total length...does this make sense?
Thanks for the help!
jay
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RE: Vertical Wire Antenna + Kite
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by W5FYI on September 28, 2009
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Kite-supported antennas are not all that rare; you sometimes see them hoisted during Field Day and other radio events. As a new ham, you should be aware that air/sand/snow and rain will add precipitation static to the wire, but that can be drained to ground through a high-value resistor. You also have to be cognizant of power lines in the area, but as a kite flyer you already knew that.
Actually, some ham publications have published kite designs and kite antennas from time to time. I think that at one time the Air Force survival kit included a box kite to hoist the "Gibson Girl" emergency transmitter's antenna.
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RE: Vertical Wire Antenna + Kite
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by AA4PB on September 28, 2009
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Make SURE that there are no power lines anywhere within reach of the kite! Wind's can change so check all directions.
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RE: Vertical Wire Antenna + Kite
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by WB6BYU on September 28, 2009
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One resource is the LiveWire group, with a website here:
http://www.wireservices.com/livewire.html
Kite lifted antennas are not that uncommon - there have
been a number of designs published over time, especially
for vertical wires on 80 and 160m.
The biggest problem most people have, especially on the
higher bands, is using too long of a wire. Generally
anything over 5/8 or perhaps 3/4 wavelength will have a
higher angle of radiation, so for perhaps 20m and higher
frequencies there generally are easier ways to get the
required height. But kite-supported wires are often sloping
rather that purely vertical, and with proper choice of
wire length can give some low angle gain in the direction
of the slope.
The best bet appears to be to attach a light wire to the
kit string some distance below the kite itself: this
allows you to get it up in the air and relatively stable.
Then you can attach any sort of antenna that the kite
is capable of lifting: a J-pole, for example, doesn't
require a ground plane and can be fed with light coax
(such as RG-174). While coax is relatively heavy compared
to some other feedline options, it can lay on the ground
as the antenna height varies with conditions. The feedline
weight (especially on the higher frequencies where low
loss feedline is recommended) is one of the limiting factors
to what heights are practical with a kite.
Or you can just use the kit as a skyhook to hoist the
top of a loop or one end of a vee beam - they aren't
limited to vertical wires (though you can't put too
much sideways pull on one.) You need to keep the kite
relatively stable, however, and it should be constrained
by the flying line, not the antenna wire.
Safety precautions:
(1) don't fly anywhere near power lines
(2) use a static bleed resistor or RF choke from the
antenna wire to ground.
(3) use a heavy enough line that the kite can't break it
and take off on its own - you don't want 200' of copper
wire flying off across country that may land in power
lines a couple miles away.
(4) observe height limits and regulations. This may
keep you from putting up a 5/8 wave wire on 160m. These
vary by country.
(5) don't try a Ben Franklin and fly in a thunderstorm.
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RE: Vertical Wire Antenna + Kite
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by LA9GY4 on September 28, 2009
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Thanks for the thoughtful responses already posted!
First off, the power line thing is something I had already firmly in mind, but now esp. with regard to line breakage. But that's also something from kiting...now only an 'amplified' danger with the high conductance of the antenna.
For this, I have already designed a quick release so that the antenna (and the radio and tuner) aren't in danger of flying away. This should take care of most immediate safety issues given no power lines in the surrounding area (easy in Norway). I am also trying a kill line to the bridle of the kite to cause it to collapse rather than fly away.
The issue of wire length is indeed the main 'witchcraft' for me. I am still trying to get my head around all the basic principles involved in thinking about wire antenna shapes, and how they work.
Here's where I am at with this: If I have 50m of wire, should I be thinking 40m (for 1/2 on 80m, full on 40m, 2 on 20m, etc.)?
Any more suggestions or insight would be welcomed.
jay
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RE: Vertical Wire Antenna + Kite
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by WB6BYU on September 28, 2009
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The choice of wire length for a particular band will depend
on the distance you want to cover and the angle of the
wire when suspended from the kite.
Let's say you can hang a 40m vertical wire from a kite.
On 160m that is 1/4 wavelength, and it can be fed directly
with coax with a reasonable SWR. It will require some
ground radials for optimum efficiency, but should be a
good antenna for ground wave and low angle DX, though
perhaps with some gaps in the pattern around 100km away.
On 80m the wire is 1/2 wavelength. You will need a tuner
to match the high input impedance, but efficiency is not
as dependent on a good ground radial system as it is with
a quarter wave wire. As is the case on 160m, this can be
an excellent antenna for DX when used on the beach. The
angle of radiation is low, so it likely will work better
for contacts over 1000km and less well at shorter distances.
On 40m the wire is 1 wavelength long, and at this length
maximum radiation is not perpendicular to the wire but
rather at about 45 degrees to it. Erected vertically
that would optimize communications at a distance around
500km (depending on the height of the ionosphere) as
long as there was sufficient ionization to reflect RF
at that angle and frequency. It would relatively worse
at less than half or more than twice that distance.
But if the antenna is erected at a 45 degree angle (which
is not uncommon, depending on the kite selected) it would
put the major radiation at the horizon in the direction
of the slope (and in reverse), with another radiation
lobe going straight up. Now you have good low angle
radiation for DX and some local high angle work (which,
however, may not be supported by the ionosphere at the
current point in the sunspot cycle), plus lobes in other
directions at other angles - basically a three dimensional
pattern with two cones around the wire.
Longer wires (like using the same wire on 20m where it
would be 2 wavelengths long) will have more lobes in
the pattern, and when tilted will have a more complex
radiation pattern. Generally, maximum radiation will
be more towards the end of the wire as the wire gets
longer, perhaps in the range of 20 to 30 degrees from
the wire axis. These can give good performance at a
low angle, but won't work as well when the wire is
closer to vertical. (The ionosphere is less likely to
reflect RF at high incident angles as the frequency
increases.)
So you need to learn about (1) the radiation patterns
from long wire antennas; (2) what vertical radiation
angles are most effective for communications over
various distances; (3) how the condition of the ionosphere
affects propagation at different vertical angles;
(5) the expected input impedance for different wire
lengths and how to match it; and (6) the effect of a
good ground radial system vs. radiator length.
That's not to say that you can't simply put up a convenient
length of wire and match it with a tuner on all bands:
that is a good way to get started. As you do it you
will begin to notice that different bands give different
results, and these will help you to understand why that
happens and to optimize your installation for your
desired communications path.
Have fun!
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RE: Vertical Wire Antenna + Kite
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by AA4PB on September 28, 2009
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Don't forget that if you are end-feeding a wire antenna you need to lay some counterpoise wires out on the ground to "work against" the antenna. If end-feeding then it would be best to keep the antenna length near (but not exactly on) a multiple of 1/2 wavelength. That keeps the feed impedance high and reduces the amount of current that needs to flow in the counterpoise (improves efficiency). I say "not exactly on" a 1/2 wave because that impedance is too high for many commercial tuners to handle. Changing the length brings the feed impedance down a little. Of course if you custom build a matching network then you can design it to match an exact 1/2 wavelength antenna.
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RE: Vertical Wire Antenna + Kite
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by WX7G on September 29, 2009
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A random length wire such as 20 meters or longer will work on all bands from 80 to 10 meters. Work it against four radial wires 10 meters long and tune it with an antenna tuner and you're on the air.
If you want to avoid radials altogether make the antenna a half wavelength or an integer multiple on the band of interest. It will present a high impedance and needs nothing more than a short ground rod (1/2 meter) to work against.
For direct connection to the radio - no tuner - the wire should be 1/4 wavelength or an odd multiple thereof. Work it against four radial wires 1/8 to 1/4 wavelength long laying on the ground.
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RE: Vertical Wire Antenna + Kite
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by W5FYI on September 29, 2009
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Hi again,
One antenna you might want to try is an end-fed half-wavelength antenna fed with a quarter-wave of transmission line (Zepp antenna). The quarter-wave line will transform the high impedance of the end-fed antenna to a much lower impedance at the transmitter end, for easy matching without a counterpoise.
If the quarter-wave transmission line is too heavy, use a high-impedance tuner to feed the end of a half-wavelength antenna. You shouldn't need a counterpoise--the three to five feet of coax from the rig to the tuner should be more than enough. Do a search for "end fed antenna tuners" and you'll find plenty of designs. A single toroid, variable capacitor, and switch will go together to make a real nice and small multiband QRP Hi-Z tuner.
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RE: Vertical Wire Antenna + Kite
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by LA9GY4 on October 9, 2009
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Still working on getting the materials together, but I thought I'd post two of the better web-based sources for ideas I have found:
http://www.thinlayeranalysis.co.uk/G6LFT_index.html
http://www.qsl.net/g4vgo/more_kites.htm
Thanks again for all the replies.
jay
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