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It is important that the downconverter be positioned very close to the
antenna - long cables should not be used between the antenna and the
down converter because this can degrade system performance.
The downconverter units should be connected directly to the receive
antenna, but where this is not possible a short length of low loss RF
cable such RG213C/U should be used. System performance will be
degraded by the introduction of RF losses at this point.
The down converter should be screwed or strapped to a flat surface or
pole, using the integral mounting holes on the unit. The down converter
is weather proof, and has no special cooling requirements. If the
downconverter is mounted where it is exposed to the weather then the
connector labelled ‘ANT / IN’ should face upwards.
The antenna itself should be separately secured, the TNC connectors should not be
expected to take the strain of the antenna.
Typically antennas and down converters will be positioned outside,
usually on the roof of a building or a vehicle. In a typical installation one
antenna will be mounted to face out from each corner of the building,
giving a 360 degree coverage area. For long range requirements high
gain sector antennas can be employed and the domo ANT12S or
ANT12L are ideal for this purpose. When these 12dBi sector antennas
are deployed on each corner of a building 360 degree performance can
be achieved with 12dBi gain.
The domo Central Receiver uses an advanced diversity technique
called maximum ratio combining to construct a good spectrum from two
potentially damaged received signals. To get the best results from
diversity, the antennas should be physically separated by at least
100cm.
Sometimes better results can be achieved by separating the antennas
further, or by positioning them on different corners of a building. The
optimum antenna placement depends on the environment in which the
equipment is used and the signal path, and is often limited by physical
factors (accessibility for example).
The domo Central Receiver is supplied without antennas since the
optimum choice of antenna will depend on the operational scenario. For
short range or mobile applications, omni directional antennas such as
ANT2L
or
ANT2S
will be most suitable whereas for longer range fixed
links, or where mobile transmit activity is happening in a defined 120
degree arc the higher gain
ANT12L
or
ANT12S
will be more suitable.
Antennas should be screwed directly to the TNC input of the down
converter labelled ‘ANT/RF IN’.
