SATELLINE-EASy / SATELLINE-EASy 869
User Guide, Version 3.0
82
Antennas must be installed well away from metallic objects. In the case of small antennas this
distance should be at least ½ m. With large antennas the distance should be >5 m and in case
of repeater antenna combinations >10 m.
If the system contains a large number of radio modems, the best location for an antenna is the
highest point of a building and possibly an additional antenna mast. If a separate antenna mast
is used, the antenna can, if necessary, be installed sideways about 2…3 m from the mast itself.
When installing an antenna possible interference sources must be considered. Such interference
sources are, for example:
•
mobile telephone network base station antennas
•
public telephone network base station antennas
•
television broadcast antennas
•
radio relay antennas
•
other radio modem systems
•
PC-related devices (approximately 5 m radius from antenna)
Please note that antennas are always tuned to a specific frequency range when ordering them.
Simple antennas and antennas, which have been constructed of stacked yagi-antennas, are
typically rather broadband. As the number of yagi-elements increases the frequency range
becomes narrower.
When designing and installing a system it is advisable to prepare to test the system, and also to
consider serviceability of the system. In particular cabling should be planned to allow easy
access and to allow for maintenance. It is often practical to use long antenna cables, so that the
radio modem can be installed far enough from the antenna itself to a location that is easily
accessible.
The type of the antenna cable is dependent on the length of the antenna cable, and the
following table can be used to select a suitable type:
Length
Type
Attenuation 10m/450MHz
<5m
RG58
3.0dB
0…20m
RG213
1.6dB
>20m
ECOFLEX10
0.9dB
>20m
0.8dB*
>20m
ECOFLEX15
0.6dB
*) cable is partially air insulated, so the use of this cable requires
that the connection between the cable and the connectors are fully airtight.
If there is a line-of-sight path between the antennas a 6 dB power marginal is usually adequate.
However, if the connection is built on the reflection and/or the knife-edge diffraction the path
loss can vary even 20 dB depending on the weather conditions. In this case a short test can give
a too positive result of the quality of the connection. Thus the height of the antennas and
topographical obstacles must be surveyed with great care. From time to time a marginal
connection can be used if the data transmission protocol is well prepared for this and the data
transmission that occasionally slows down does not cause any problems to the system.
