User Manual

AS4000 Wireless Local Loop
System Overview
GSI 002
605-0000-430
Issue 1.2 Date 7/4/99
Page 8 of 8
Modems 1 to15 + Spare
(2 Per Card)
Shelf Interface
Connectors
AIR RAMP
SC TU AU
Cards
Alarm
Panel
FRONT COVER
Figure 17. Modem Shelf with front cover removed
RF Combiner Shelf
The RF Combiner Shelf forms the interface between the Antenna/Feeder Sub-system and
individual Modem Shelves. The RF Combiner Shelf performs the functions necessary to
connect up to four RF signals to the Antenna/Feeder Sub-system.
In the transmit direction, the baseband signals from Modem Shelves one and two are
converted to RF, amplified, combined and filtered before being sent to the first antenna. The
second pair of RF channels (from Modem Shelves three and four) are similarly treated, but
are fed via a duplexer (used in the receive path for extraction of the receive signal) to the
second antenna.
In the receive direction, incoming signals from the antenna are extracted, filtered, amplified
by the LNA and split among the (up to) four RF Cards and their associated Modem
Shelves.
A RF Combiner Shelf (see Figure 18) is equipped with:
• four RF Cards, which converts the baseband signal from each modem shelf into a single
RF channel in the 2 GHz range (and vice versa). This interfaces to the Antenna/Feeder
Sub-system.
• up to two Power Amplifier (PA) modules, each of which caters for 2 RF channels and
amplifies the RF channels received from their associated Modem Shelf equipment.
• a Branching Unit (BU) module, which is essentially a passive unit that performs signal
Combiner, splitting and filtering.