Microwave Radio Communications SCM4000, Техническое справочное руководство

Страница: 239 / 274

Theory of Operation 8-3 SCM4000 Technical Reference Manual
8.3.4 SCM4000 Modulator/Demodulator Modem
Configuration
The SCM4000 Modulator/Demodulator modem configuration
consists of Modulator and Demodulator modules in a single
assembly. The SCM4000 Modulator/Demodulator provides
modem features configured for your individual requirements.
This modem configuration provides four “line through”
connections, i.e., data in and data out. This payload data is not
changed by the modem itself (ideally) and the modem does not
care about the content of the data, i.e., framing. Therefore, the
modem has to recover the original clock(s) used to input the data
at the Modulator and at the Demodulator. Because of the
inherent transfer function in the modem, the output clock is rate-
locked to the Modulator clock.
The transmitted data can be presented in different combinations
of any of the four data channels. The modem is programmed by
the factory and sets up which channels are used and at what
rates prior to connection.
The Modulator will produce a 70 MHz IF signal, which is
designed to go directly to the radio system for transmission. The
Demodulator will be presented with the same 70 MHz IF signal
after it has been sent over the radio link via the radio system.
A simplified SCM4000 Modulator/Demodulator block diagram is
shown in
Figure 8-1 .
Figure 8-1: SCM4000 Modulator/Demodulator Block
Diagram
8.3.5 SCM4000 Modulator Description
The SCM4000 Modulator configuration receives up to four
independent asynchronous data signals (channels) and
combines the data signals and M-order of Quadrature Amplitude
Modulation (M-QAM) modulates them onto a single 70 MHz
carrier.
The Modulator will allow any symbol rate to be entered over the
specified range for any given modulation mode. The four data
channel interfaces are also completely variable, so different
combinations can be assigned, providing the total is within the
bandwidth assigned by the modulation mode and symbol rate
and applicable to the radio architecture and system design.
POWER SUPPLY
AC/DC
POWER
DISTRIBUTION COMMAND AND
CONTROL AND FRONT PANEL
SCM
MODULATOR
STATUS
DISPLAY KEYPAD
CONTROL
(RS232)
E1/T1
10/100
E1/T1
10/100
RS232/
485
SUM
ALARM
ASI
DS3/
E3
MODULATOR
CORE BOARD
IMB
IF IN
IF
OUT
SCM
DEMODULATOR
STATUS
ASI
SMPTE
ASI
DS3/
E3
RS232/
485
SUM
ALARM
E1/T1
10/100
E1/T1
10/100
DEMODULATOR
CORE BOARD
ASI
DS3/
E3
ASI
SMPTE
ASI
DS3/
E3
POWER
POWER IMB
IF OUT IF IN
1 2
3
1
2
3
INTERFACE BOARD INTERFACE BOARD
MICROPROCESSOR