Ericsson RBS 2106 Reference Manual page 132

Product Data RBS 2206
Function
The TMA compensates for signal loss in the receiver antenna cables,
reduces system noise and improves uplink sensitivity. The TMA can
consist of a duplex filter. Duplex is the function that allows
communication in two directions (sending and receiving) on the same
communication channel.
The TMA used for 12 TRX products is Dual Duplex TMA (ddTMA).
Requirements
The TMA is mounted as close to the antennas as possible in the
GSM 900, 1800 and 1900 systems, preferably on the same support.
Cable length is approximately 1 m.
Feeder Loss
The GSM 1800 and 1900 receivers are optimized to have a maximum
sensitivity with a feeder loss of 4 dB. Feeder loss of less than 4 dB will
cause a deterioration of receiver sensitivity if strong interfering signals
are present. Feeders with 4 dB loss or more must be selected at sites
where strong interfering signals are expected.
It may be necessary to select a feeder with higher loss and calculate the
length to obtain a total loss of 4 dB.
Dual Duplex TMA (ddTMA)
Figure 61
The ddTMA is to be used for GSM 900, for all macro base stations and
1800 or 1900 systems for RBS 2206 and RBS 2106.
A Dual Duplex TMA contains two duplex filters and a low noise
amplifier. The first duplex filter splits up the signal path from the
antenna into one transmitter and one receiver path. The received signal
is amplified in the low noise amplifier. After amplification, the receiver
and transmitter paths are combined in the second duplex filter.
130 (485)
Antenna
TX/RX
RBS
Dual Duplex TMA (ddTMA)
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ddTMA
P007931A
EN/LZT 720 0008 P2A
2001-11-28