Figure 3-1. Cdm-600 Modem Block Diagram - Comtech EF Data CDM-600 Operating Instructions Manual

CDM-600 Satellite Modem
Functional Description
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.
•
•
These functions are shown in Figure 3-1.
TX G703 T1/E1
DEFRAMER AND
INTERFACE
(U46)
TX AUDIO INTERFACE
(U43 & U50)
RS-422, V.35 OR
RS-232
INTERFACE
(U63 & U67)
LVDS
INTERFACE
(U62 & U64)
G703 T2/E2
INTERFACE
(U74)
OVERHEAD
INTERFACES
(U55, 57, 59, 68, & 75)
RX AUDIO INTERFACE
(U60 & U61)
RX G703 T1/E1
DEFRAMER AND
INTERFACE
(U51)
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.
INT CLK
DDS (U33)
MUX (U22)
TX FRAMING
(IBS, IDR, D&I
OR EDMAC)
IBS OR
EDMAC
SCRAM-
BLER
TX LINE
DECODING
MICROPROCESSOR (U44)
& PROCESSOR FPGA (U49)
RX DE-FRAMING
RX LINE (IBS, IDR, D&I OR
ENCODING EDMAC)
BUFFER IBS OR EDMAC
DESCRAMBLER
INSERT
DEMUX (U19)
INS CLK BUFFER CLK
DDS (U42) DDS (U41)

Figure 3-1. CDM-600 Modem Block Diagram

AS/0423
AS/0424
BASEBAND
MODEM
FRAMING
CARD
CARD
TX REED-
SOLOMON
WITH
SCRAMB-
LER
(U12)
ENC CLK
DDS (U24)
INS CLK
DDS (U42)
RX REED-
SOLOMON
WITH DE-
SCRAMB-
VIT/SEQ/OM73
LER
DESCRAMBLERS
(U20)
DLF/NCO (U47)
3–2
Revision 7
MN/CDM600.IOM
TXFIR (U61)
SEQ VIT/SEQ/OM73
ENCODER SCRAMBLERS
I & Q FILTERS
TX IF
VITERBI
& TCM
CODEC
(U48)
RX IF
TURBO CODEC FIR/PD & I/Q
W/ SCRAMBLER RECOVERY (U45)
& DESCRAMBLER
LDPC CARD
(OPTIONAL CARD)
CARRIER
DACS
(U52)
SEQ
DEC-
ODER
SYM & BIT
TIMING
RECOVERY
BIT/SYM
DACS (U49)