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CDM-600 Satellite Modem Revision 7
Functional Description MN/CDM600.IOM
3–2
removed. Following this, the data passes to the Plesiochronous/Doppler buffer, which has
a programmable size, or may be bypassed. From here, the receive clock and data signals
are routed to the terrestrial interface, and are passed to the externally connected DTE
equipment.
Physically the CDM-600 modem is comprised of two main card assemblies.
• The first of these is the baseband framer card, which includes all of the interface
circuits, the framer/de-framer, plesiochronous/Doppler buffer, Reed Solomon
outer codec, and the main microcontroller.
• The second card is the modem itself, that performs all of signal processing
functions of modulation, demodulation, and Forward Error Correction.
These functions are shown in Figure 3-1.
Figure 3-1. CDM-600 Modem Block Diagram
LVDS
INTERFACE
(U62 & U64)
TX FRAMING
(IBS, IDR, D&I
OR EDMAC)
TX REED-
SOLOMON
WITH
SCRAMB-
LER
(U12)
SEQ
ENCODER
TX G703 T1/E1
DEFRAMER AND
INTERFACE
(U46)
RS-422, V.35 OR
RS-232
INTERFACE
(U63 & U67)
G703 T2/E2
INTERFACE
(U74)
TX LINE
DECODING
RX G703 T1/E1
DEFRAMER AND
INTERFACE
(U51)
IBS OR
EDMAC
SCRAM-
BLER
MUX (U22)
DEMUX (U19)
INT CLK
DDS (U33)
ENC CLK
DDS (U24)
AS/0423
BASEBAND
FRAMING
CARD
AS/0424
MODEM
CARD
I & Q FILTERS
TX IF
RX IF
RX REED-
SOLOMON
WITH DE-
SCRAMB-
LER
(U20)
OVERHEAD
INTERFACES
(U55, 57, 59, 68, & 75)
TX AUDIO INTERFACE
(U43 & U50)
IBS OR EDMAC
DESCRAMBLER
RX DE-FRAMING
(IBS, IDR, D&I OR
EDMAC)
RX AUDIO INTERFACE
(U60 & U61)
BUFFER
INS CLK
DDS (U42)
RX LINE
ENCODING
INSERT
VITERBI
& TCM
CODEC
(U48)
TURBO CODEC
W/ SCRAMBLER
& DESCRAMBLER
(OPTIONAL CARD)
SEQ
DEC-
ODER
VIT/SEQ/OM73
SCRAMBLERS
VIT/SEQ/OM73
DESCRAMBLERS
TXFIR (U61)
FIR/PD & I/Q
RECOVERY (U45)
SYM & BIT
TIMING
RECOVERY
DLF/NCO (U47)
MICROPROCESSOR (U44)
& PROCESSOR FPGA (U49)
BIT/SYM
DACS (U49)
CARRIER
DACS
(U52)
INS CLK
DDS (U42)
BUFFER CLK
DDS (U41)
LDPC CARD