User's Manual

Doc. No.
Rev.
Date
1.00
2011-12-08
Damm Cellular Systems A/S, Denmark
TETRAFLEX
®
V7.5 MANUAL - RX Multi coupler for BS41x
TetraFlex® 7.5 Manual 4-15
4.3 RX MULTI COUPLER FOR BS41X
4.3.1 Introduction
The purpose of the RX multi-coupler system is to distribute signals from the RX antennas to
the RX inputs of the TR41x Transceiver.
The Base Station is provided with two completely independent RX signal paths to connect the
two RX antennas.
The use of two RX antennas in a diversity scheme gives a considerably improvement in
sensitivity of the Base Station. The improvement is described in the Diversity Application
Note.
In addition the use of two RX antennas with completely separate signal paths gives
redundancy to the BS RX. If a fault occur in one leg of any of the components (antenna,
feeder, amplifier etc.), the BS will still be able to operate with the other antenna, only loosing
the sensitivity of the diversity gain.
The system includes as standard a Tower Mounted Amplifier to eliminate the sensitivity
degradation normally caused of the RX feeder loss. The TMA can compensate for up to 8dB
feeder loss with no change in RX sensitivity, allowing the use of thin feeders with a
considerably saving in feeder expenses. See the Antenna application note for antenna and
feeder configurations.
The Base Station is provided with an RF Test Loop feature, which allows a transmitter to
generate a test signal for test of the complete RX section, including measurement of RX
sensitivity at the TMA input and measurement of RX antenna return loss.
Dependent of the type of Base Station used, up to 16 TR41x can be connected to a single
Radio Cell, and up to 4 Radio Cells can be configured in a BSC411 Base Station Controller.
4.3.2 RX signal path description
The RX signal normally comes from the RX antenna to the TMA input with a short jumper
cable. The TMA is provided with an N-female connector.
Inside the TMA the signal first passes a dual directional coupler used to insert test signals in
forward and reverse directions. This feature is described in the RFTL section.
The signal then passes a big low-loss pre-selection filter. The input of the filter is DC
grounded to ensure that no DC voltage can be build-up on the antenna feeder. The filter has
the following specifications:
Parameter
400MHz
800MHz
Pass-band width
5MHz
14MHz
Guard-band width
5MHz
25MHz
Out-band rejection
60dB min.
60dB min.
The high 60dB out-band rejection ensures proper duplex operation of the Base Station. With
the required RX-TX antenna isolation of 30dB a total rejection of the TX signal of 90dB is