Service Manual

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6802800U74-AN
Chapter 10: Base Radio
Figure 179: BR-Arch-2 Base Radio – Functional Block Diagram
Upon the power-up, BRC bootloader begins to download application code from SC over the Ethernet
LAN. After successful download, the code is executed. Once the BRC application is started, it gets
configuration parameters from SC. The configured BRC application allows the Base Radio to perform
call processing functions.
Should any alarm conditions arise during BRC application, operation, they are reported to SC over
Ethernet LAN. Alarm conditions may also be verified locally through the Service Access port linked to a
service computer using the get alarms MMI command.
The Base Radio operates in a TDMA (Time Division Multiple Access) mode. This mode, combined with
voice compression techniques, provides an increased channel capacity ratio of as much as 4 to 1. Both
the receive and transmit signals of the Base Radio are divided into four individual timeslots. Each
receive slot has a corresponding transmit slot; this pair of slots comprises a logical RF channel.
The Base Radio uses single, dual, and triple diversity reception for increased talkback coverage area
and improved quality. The Transceiver contains a three-branch receiver section in which all receivers
are used for triple diversity reception.
All receivers within a given Base Radio are programmed to the same receive frequency. The signals
from each receiver are fed to the BRC where a diversity combining algorithm is performed on the
signals. The resultant signal is processed for error correction and then sent to the Site Controller
through the Ethernet LAN with the appropriate control information regarding its destination.
The transmit section of the Base Radio is comprised of the Exciter (EXC) and Power Amplifier (PA).
The EXC processes the information to transmit from the BRC in the proper modulation format. This
RJ45
RJ45
CP2 Circuit
Flash
RAM
BUS
Ethernet
RJ45
RS232+ trig In/Out
Host
P1021NXE2DFB
RF1
RF2
RX front end
RX I&Q
RX I&Q
RX I&Q
Trig In/Out
Interface
DC-
inj.
RX Back end
Abacus III
RF3
SPI
FPGA
DSP
TMS320C6455
RX Metering
and control
CONGO
PLL
16.8MHz
16.8MHz
Osc.
TX I&Q
Interface
Exciter
Metering
and control
SPI
Synthesizer
PLL
7V,12V,28V
Supply
&Ctrl
RODINIA
Baseband
filter
JAVELIN
Driver
Pwr
Detector
Exc.
Out
Transceiver/Controller Board
Exc.
In
PA board
TX
Forward/
reverse
power
meter
Variable
step Att.
PA
feed
back
Circulator
Feedback
Coupler
PA
Driver
28V
7V
Conv.
Pa Metering
and control
Variable
step Att.
PA
in
12V
Conv.
7V+28V
Supply
28V
7V,28V
Supply
&Ctrl