User's Manual

044-05156 Rev C 33
operational band of the amplifiers and must be set during commissioning of the base station, and anytime the
MCR21929-1-2 subrack is replaced.
Setting the pilot tone frequency of the amplifiers requires a laptop interface program. The laptop can be connected
to the MCR21929-1-2’s RS-232 port. The MCR21929-1-2 provides the interface to the amplifiers to set their pilot
frequency and stores this setting in memory. If an amplifier fails, the MCR21929-1-2 programs the pilot frequency of
the replacement amplifier to that of the other installed amplifiers.
4.7 DLNA
4.7.1 Duplexer Overview
The Duplexer Low Noise Amplifier (DLNA) module provides Bandpass filtering for both the uplink (receive) and
downlink (transmit) paths, as well as gain for the receive path and alarm monitoring for receive gain and VSWR.
The DLNA presents excellent return loss on all ports with 18 dB or better. The coupled ports are accurate to +
1.0
dB; the –55 dB sample port is accurate to +
2.5 dB
TX
RX
LNA1:2
FWD
-40 dB
REF
-40 dB
1:2
A:D A:D
micro-C
Alarm
Vcc
Gain
Adjust
Regulator
Vcc
Vcc
RS-485 RX
RS-485 TX
RS-485 RX
Vcc
Temp Sensor
1
2
3
4
VSWR
S1
Gain
Adjust
Antenna
N-F
TX In
N-F
RX Div
SMA-F
RX Main
SMA-F
TX
Sample
-55 dB
+27 VDC
VSWR Alarm
LNA Alarm
04-0066B-A
45 dB
Gain
DLNA Block Diagram
4.7.2 Receive Path Overview
The receive path provides for a variable gain Low Noise Amplifier (LNA) from 43 to 45 dB. The LNA gain is
controlled from a front panel 10-turn potentiometer. The LNA is set to 45 db of gain from the factory. The output of
the LNA is further split into two paths, reducing the receive gain by approximately 3.3 dB, for input to the base
station. The noise figure of the DLNA is typically better than 2 dB at room temperature including all DLNA
components. The main receive path is used for the 8x8 configuration. The diversity receive path is used for the
16x16 configuration.
A microprocessor in the DLNA monitors the current draw of the LNA. If the LNA current draw drops below a
predetermined threshold, an LNA alarm is generated back to the SIM. In addition, a front panel LED is illuminated
when the LNA fails.