Welcome to PE1RAH
Portable 2m/70cm
OSCAR antenna
After the Indian HAMSAT
has been launched many hams around the globe asked me for information to get
active on the HAMSAT.
One of the main questions
is for an easy to use antenna. Some 4 years ago I have made a portable antenna
for my trip through Europe. On my webpage you will find information about this
thip I have done together with my radio friend Dirk ON1DLL (now ON5GS).
We made satellite qso’s
from all the countries we visited, and the antenna we use I will describe
below.
The complete antenna can
be seen below:
For the antenna sizes I
have used the excellent program of DL6WU. It is a simple BASIC program running
under DOS, but it gives very good help with constructing an antenna.
The 2m section by DL6WU
antenna program:
The best is to use only
the Progressive Spacing list.
This list uses the
beginning of the boom as reference, this avoids the addition of small errors
when measuring from element to element. The last element will then have the
addition of all errors (e.g 4x 2mm error = 8mm error for the final element !!!)
The 2m section in hardware
looks like this:
For the driver elements
the DL6WU program says “folded dipole”. Because a folded dipole in not easy to
divide in two parts I have used the simpler open dipole with a gamma match.
In practice it doesn’t
really matter if the driver is an open or folded dipole. As far as it radiates
well its okay J
The 2m gamma match:
The gamma match is done
with 2,5mm thick (thinned) copper wire, screwed in the aluminium element.
The gamma match is made
with a small Thompson trimmer, inside the square aluminium pipe.
This is to protect the
fragile trimmer and keep it from de-tuning because of outer forces
(transportation, people who by accident walk over it etc…)
The elements:
The element are made from
6mm aluminium rods, that can be screwed in the boom.
The walls of the boom is
only 2mm thin and to have more “flesh” to make the screw-thread I locally
placed 3mm plates at the inside of the boom. The plates are holded by two small
screws like shown below.
At the places where the
elements will come the boom is 5mm thick (2mm boom + 3mm small plate) and
enough to make the screw-thread.
The 70cm section with the
DL6WU antenna program:
The 70cm section in
hardware:
The elements are mounted
with the same screw principle as the 2m elements.
The spacing between the 2m
and 70cm section can be seen below:
The whole antenna can be
disassembled to parts less than 50cm length.
The boom is 1 meter long,
and cut in half to keep the maximum length around 50cm.
This can be seen below:
The right-side part of the
boom has two ‘L’ –shaped aluminium profiles mount on the boom.
They are slightly bend
inside to fit tightly. The both parts can easily be push together and be
separated in a fraction of a second. J
73 de PE1RAH, William Leijenaar…