Comtech EF Data SDM-300A - Manual (Page 48)

SDM-300A Satellite Modem Revision 6
Functional Description MN/SDM300A.IOM
2–8
2.3 Description of the Demodulator
A block diagram of the demodulator is shown in Figure 2-3.
The demodulator converts PSK modulated carriers within the 50 to 180 MHz range to a
demodulated baseband data stream. The converted modulation types are BPSK, Offset QPSK,
QPSK, and 8-PSK (refer to Section 2.2.2 for a description of modulation types). The
demodulator then performs FEC on the data stream using Viterbi or Sequential decoding
algorithms.
DIGITAL
SIGNAL
PROCESSING
DIGITAL
CLOCK
RECOVERY-
LOOP
SWITCH
REF
VCXO
REF
PLL
OC XO
OPT
HIGH
STABILITY
AGC LPF BPF
LO #2
LOOPBACK
RF INPUT
RF INPUT
50 TO 180 MHz
BPF
A TO D
CONVERTER
LO #1
REFERENCE
VITERBI
DECODER
SEQUENTIAL
DECODER
OPTIONAL
REED-SOLOMON
CODEC
DOPPLER/
PLESIOCHRONOUS
BUFFER
MUX
INTERFACE
OPTIONAL
OVERHEAD DEFRAMING
IBS/IDR, ASYNC/AUPC
DROP & INSERT
EXT REFERENCE
OPTIONAL
TURBO
CODEC
Figure 2-3. Demodulator Block Diagram