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Transmit antennas I use vary by the season and the local weather. At
the previous
QTH there were the combined problems of
neighbours, planning permission, and limited space. To solve the problems, I
opted for 'aerial' aerials. The heart of the fair
weather system was and still is the Helikite in various forms, made here in the UK
by
Allsopp Helikites.
It is a combination kite and helium
balloon (Mylar). Here is a Lightweight Helikite close up. Without wind, it can lift a
few ounces.
But with a fair breeze, it will lift about a
quarter pound of line and antenna. The Sky Hook Helikite is much larger, and will lift more than a pound of payload. As an added bonus, the Sky Hook will fly in rain and snow.
More on the Helikite and its specifications later.
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The mast in the back yard (garden in the UK) is a 12 metre pump
up from
the British Army called a
SCAM12
. It will
nest at just over 2 metres, but a small pump will take it to 12
metres, and
a 40mm coupling at the top allows it to go to 22
metres with a fibreglass fishing pole used as the rest of the vertical.
The 10 metre fishing pole is fitted
to a bit of fibreglass tube mounted
on top of the SCAM12. That gives a 'bad weather' vertical configuration of 22+
metres. This is for nights when the weather goddess makes airborne antennas a hazard.
The 'foul weather' vertical is working against about a kilometre of
wire under
the ground. Radials, about 60 of them, vary in length from 45 to 120 feet. The radials are used in all configurations of Top Band antennas,
from the aerial aerials to the inverted L or vertical which are used in weather that
won't allow an aerostat or kites to fly.
The centre of gravity of the earth
system is offset a few metres from the kite or balloon antenna's feed point in
some anchor configurations, but that doesn't seem to make a big difference.
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One of the easiest to deploy transmit antennas that coincidentally I have become fond of consists of the mast
at 12
metres, a small 4 metre fibreglass stub on the top,
and about a quarter wave (40 metres) of wire on the top of that. I call it the
"Protracted L". The wire is
supported by one or two Helikites depending
on the wind speed. This one is a single Light Weight Helikite as the wind was about 10 miles per hour. If the wind is from about three to eight m.p.h., I use two
of the Light Weights for the added lift.
Again, it uses the station counterpoise/ground screen at the base of the
SCAM12. The Sky Hook Helikite is a bigger lifter, and will allow a heavier
gauge wire for the antenna. It is quite a bit more expensive, but more versatile.
The specifications of the Helikites and what they will lift can be found
elsewhere on this site.
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Here is the 'Protracted L' design using the Sky Hook
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The Sky Hook Helikite will not fly well in winds above about 25 miles per hour, or in
other than light rain.
For high
winds (above about 20 m.p.h. or so), I use a kite lifted antenna. It is a
modified Box Delta or the Delta Conyne. Up to 60 metres (200 feet) of wire can be used
with this
support. The angle of flight is near vertical at most wind speeds, and the kite is very stable even in gusts. It has flown all night in a drizzle many times, and even a moderate snow fall. |
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The Box Delta/Conyne kite will fly in up to 40 miles per hour winds, has a near
vertical angle of flight, and takes the
antenna to more
than 3/8 wave straight up...another killer transmit
antenna! It will fly in the rain and snow because of the rip-stop nylon material and the Krylon plastic coating I have applied
with an aerosol in a fine mist. This is to help shed moisture. The kite is
circled in this picture, as
it is a
LONG way up! In this photo it was a full 60 metres up and the signal
reports in the USA were very, very good.
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If the wind will be gusty, and very strong over night, I use the Cody
War Kite.
Designed in the early 1900's to carry men
aloft, the scaled down version is stable in most wind above 8 mph and has stayed
up in 50+ miles per hour gusts! I use 200 pound breaking strength braided line for
most of the big kites, and for the
Lightweight Helikite about 90 pound. For the Helikite Sky Hook I use 150 pound line.
If you are interested in
kites as the main method of lifting an antenna, HERE
is a good link to what are
called 'cell' kites. Most of the kites I use in my airborne antenna farm
are cells.
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To
the right is a small illustration of how the kite antenna is rigged, and I will have more pictures and hints on how to fly the wind lifted aerials later. The bungee cord is quarter inch, about six feet long to take the stress of the jerking on the kite line. I use
150 pound fishing swivels at both ends of the bungee cord, and a two foot heavy nylon fishing line then goes from the bungee swivel to the antenna wire.
Remember to leave a little bit of wire (12 inches or more) hanging from the swivel attach point to keep high voltage away from the line. Heavy electrical tape or small round plastic curtain rings can hold the wire to the kite line, but I prefer several layers of tape every six feet or so. Details of the static discharge will be shown
later
on this site, but direct or indirect methods can be used.
The vertical is usually 60 metres (200 feet) tall and works a treat on 160 metres.
This kite illustration is the Rock, shown
later, but
the Delta Box, Cody or any kite can be used to hang the aerial in the sky. To allow the kite to fly in more stable or laminar
winds, sometimes about 50 to 80 feet of line is used above the antenna.
More stable air makes a big difference.
For the actual antenna wire, I use 14 AWG insulated flexiweave, or insulated multi-conductor 16
gauge depending on the lifting power of the kite.
Next
Page: More on Balloon
and Kite Lifted Antennas
(Page 3)
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