Welcome to PE1RAH
Foldable antenna’s
To improve my portable
back-pack satellite station I have been testing several kinds of idea’s to make
antenna’s more portable. The biggest problem is to get a good antenna during qso’s
and small and light weight to carry.
After Ao-40 got available
for qso and Ao10 was giving less options for portable use I needed to include a
13cm downlink. After many antenna tests the best option was a dish antenna in
combination with a simple patch. I have tested several ideas like an inflatable
antenna that works very well, only the problem is to keep it air-close L As a solution I have made the foldable dish,
that works great, is faster to set up than inflating the inflatable dish, and
its light and small to carry in a back-pack.
Unfortunately I wanted to
have an ever more lighter and bigger version. This decrease the size and weight
of the back-pack station even more. At the moment I am working on a 1,5m dish
that weights only 700grams, and is about half smaller in size to carry.
To have an idea of the
folded dish fabric see the picture below:
The dish reflector side is
a very thin aluminium & plastic foil. The foil is very thin and fragile. To
make it mechanical stronger it is sew within two layers of ripstok. The
aluminium foil is used behind heat-radiators to isolate rooms, and can be
bought at many stores for cheap prices. The ripstok is used for kites, and can
also be bought in any kite store. The ribstok is stretched on an dish-frame
that is made with small and light fibreglass ribs. These can also be bought at
a kite store.
The reflective layer
between the two ribstok layers:
I am still working on the
final finishing touch. Unfortunately I have no time right now and it is
scheduled for a later moment.
A picture of the fibre
glass frame (the outer circle with a
rib to the middle of the dish):
In the middle all the 8
ribs come together at a centre block, see below:
The dish shape is made by
making the diameter of the circle shorter than the rib lengths. (this has to be
calculated very carefully !). Because of this the frame will set itself into
the dish shape. The reflective layer is also made into the dish shape, and are
set together with the glass fibre ribs that have to be put in the sleeves that
are sew in the ribstok fabric.
The foldable yagi:
After I made a bigger,
lighter and smaller to carry dish I also wanted to find some option to decrease
the weight of my 70cm uplink antenna. I have used my 2m/70cm antenna for it,
with only the 70cm elements mounted and put it inside the dish. This had many
advantages. I needed only one tri-pot, I had only one structure to point to the
satellite, and the yagi boom does also function as a carrier for the 13cm patch
antenna. (otherwise I needed 3 more ribs and now only 3 robs to tight the yagi
in the middle of the dish)
Unfortunately the yagi
antenna is a little to heavy and it does deform the parabolic shape of the dish
because of its weight force. To overcome this problem I needed a lighter
version of the 70cm yagi antenna.
My idea was to use
reflective tape that is used to stick the aluminium foil (what I used as dish
reflector). To test the material if it can be used as an uplink antenna I made
a complete 70cm yagi antenna on a piece of paper J The tape that I used can be seen below. It is
not a special kind of tape, it can be bought at many “do it yourself” stores
for little money.
The complete antenna that
I made has 7 elements. I have no digital camera so I can only show small part
of it with my A4-scanner.
Below you can see a
picture of the radiator and first director:
The 50E match is done with
a simple gamma match. It is very simple made because the trimmer capacitor is
also made with the aluminium tape J A more detailed picture can be seen
below:
Because the aluminium tape
does not conduct at the sticking side I have used a small copper strip to make
a reliable contact. The copper strip is taped on the paper with simple plastic
tape, what also is the dielectric of the trimming capacitor !! The copper only
goes till half the gamma match length. After I taped the copper strip, I taped
a small peace of aluminium tape over the plastic tape (what is the dielectric).
By shortening the length of the aluminium tape I was able to tune the
gamma-match very perfectly J
If this antenna works ? I
have made 5 contacts with it via AO40 close to its apogee and with 10W PEP
power !!! To be honest, I was very surprised myself to have such a good contact
with such a simple antenna construction. The test was succeeded and a final
mechanical stronger antenna had to be constructed J This antenna has only one disadvantage what is
the wind. With a strong blow the antenna acts like a kite L
At the moment I am still
working on my final foldable yagi antenna, with less wind load, so it has not
been operational yet, but I like to show some pictures of it:
The antenna can be carried
like a handkerchief in your trouser pocket J
After some de-folding, an
antenna seems to appear J
The elements are made of
litze-wire and are sew inside the thin ribstok strips.
The whole antenna is set
into its shape with a PVC boom (3 parts) and 3 glass fibre ribs. The whole
antenna weights only 270 grams !!
Because the gamma match is
the most fragile part, it is made on a small PCB. (This gamma match is still
not tested, problem is time to do). Finishing the antenna is scheduled for
later.
I hope this will give
amateurs some new idea’s in making antenna’s, and new amateurs an option to do
cheap experiments without needing expensive and difficult aluminium
constructions.
73 de PE1RAH, William Leijenaar…