6
Equipment
6.1
The connection of antennas to radio modems
Recommended antenna types are as follows:
6.1.1 Hand portable equipment
1/4 wave antenna (wave length on 450 MHz is about 70 cm)
Helix antenna
The antennas are mounted directly on to the antenna connector (TNC) at the top of the
radio modem.
6.1.2 Equipment installed in vehicles
1/4-wave antenna
1/2 wave antenna
Ideally the antenna should be installed vertically and it should have at least 0.5 m of open
space surrounding it. In a small system 1/4 wave antenna is adequate. There should be a
ground plane below the antenna (truck bonnet or roof). In weak conditions a 1/2 wave
antenna is the most suitable. It can be mounted at the top of a pipe, as this provides it with
as much open space as possible. In places where the antenna cannot be connected directly
to the TNC a 50 ohm coaxial cable must be used to provide the link between the TNC and
the antenna.
6.1.3 Base station
omnidirectional (1/4, 1/2 or 5/8 wave antenna)
directional (yagi or corner reflecting antenna)
The antenna should be installed in an upright position. The exact location of the antenna
depends on a number of factors from system size to physical ground countours. As a
general rule, the antenna for a base station should be located at the highest point in the
most central location of the system.
Alternatively the base station antenna can be situated inside the building, providing that the
walls of the building do not contain metal.
SATELLINE-1AS and SATELLINE-2AS
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