Why symmetrical dipole antenna?
dipole antenna is mostly fitted for the field conditions. Military,
geologist expedition, rescue and emergency communication service-
all of these are used a dipole antenna. The antenna works well
in the near zone (100- 200- 300- km, depends on the Band) that
is needed for communication from a mounting trip. It is important
that the antenna would have some gain because in the mountain
it is used a QRP-equipment. Dipole antenna works well in the forest,
in the deep ravine, among tents in Alpinist Camp.
Figure 1 shows design of the dipole antenna. The antenna
has gain plus 5- dBi.
antenna is a symmetrical dipole (with length a little bit more
the lambdaé4) installed on the top of a plastic fishing
pole. The antenna is fed by a 50- Ohm coaxial cable. The cable
is matching with the antenna with the help of two fixed capacitors.
One is connected to the central core another one is connected
to the braid of the coaxial cable. The value of the capacitors
(50- 200- pF) should be found out for the current antenna system.
Coaxial cable at the feeding terminal is coiled (2- 3 turns) on
to a ferrite ring. Capacitors and the ferrite ring should be protected
from moisture. Those ones may be placed into a plastic box (from
an old 35- mm film) or shrinked.