Siemens BS-240 Technical Description page 46

Technical Description (TED:BSS)
BS-240/241
46
The receive path consists of a LNA (Low Noise Amplifier) and a power splitter. The LNA
takes care of a low system noise figure and consists of two branches. In case of
malfunction of one amplifier, the RX gain of the DUAMCO decreases by about 6 dB. The
power splitter distributes the received band to the CUs (Carrier Units). A splitting factor
of 4 (or 8 in case of DUAMCO 8:2) is implemented in order to feed 4 (8) CUs.
The DUAMCO amplifier has two different operation modes which can be selected by
e.g. DIP switches. In the following, Mode 1 is called AMCO mode and the second mode
is called MUCO mode. In the AMCO mode where no TMA (Tower mounted Amplifier) is
used, the DUAMCO gain is around 19 dB. In case a TMA is used, the DUAMCO is
configured in the MUCO mode. In the MUCO mode, the gain is reduced to about 0 dB.
The exact gain of the DUAMCO to compensate the cable losses can be adjusted for this
mode with a e.g., DIP switch. This adjustment is only done once during the installation
of the BTSE by the service personal. The selected mode can be read by O&M SW via
CAN bus interface.
The transmit path consists of isolators, a hybrid coupler with load (for some modules)
and an ASU (Antenna Supervision Unit). The isolators have to protect the PAs (Power
Amplifiers) inside the CUs from each other in order to assure the required intermodula-
tion suppression. Two different hybrid couplers (2:1, 4:1) combine up to 4 carriers to one
antenna. The corresponding not transmitted power is terminated in a load including
cooler. The ASU is responsible for detecting certain reflection factors at the antenna
connector and is connected to the O&M interface.
The O&M interface of the DUAMCO transmits error messages to the BTS core via a
slow O&M bus (CAN bus).
The DUAMCOs x:y are named depending on the number x of transmit connectors fed
by the CUs and the number y of antenna connectors. The following figures show the
different DUAMCOs implemented by a set of equal sub-modules.
The DUAMCOs are implemented for seven different frequency bands: GSM 850,
P-GSM 900, GSM 1800 (DUAMCO 2:2 , DUAMCO 4:2 and DUAMCO 8:2); E-GSM 900,
R-GSM 900, GSM-RE 900, GSM 1900 ( DUAMCO 2:2 and DUAMCO 4:2). The division
of the GSM 900 band (39 MHz) in two interleaved sub-bands (25 MHz each, P-GSM and
GSM-RE) results from the required filter volume for the whole band.(see
Information
Base Station System
Tab. 1.2)
A30808-X3247-L14-2-7618