Comtech EF Data SNM-1001 - Manual (Page 36)

SNM-1001 Network Control Modem Theory of Operation
Rev. 1 4–5
4.2 Demodulator
The modem demodulator converts a QPSK modulated signal of 50 to 180 MHz to a
demodulated baseband data stream. The demodulator then performs error correction on
the data stream, using a Viterbi decoding algorithm.
A block diagram of the demodulator is shown in Figure 4-2.
Demodulator jumper settings for selecting ROM size are listed in Table 4-1.
I
A/D ALIAS
FILTER
AGC
IF FILTER
ALIAS
FILTER
A/D
DIGITAL
DIGITAL
NYQUIST
NYQUIST
Q
90 0
RF
SYNTH
MPC
IF
LOOPBACK
VCO
MPC
DDS
RX DATA SYNCHRONOUS
DESCRAMBLER
MPC
VITERBI
SOFT DECISION
MAPPING
UNIQUE WORD
DETECTOR
DDS
MPC
RX CLOCK
RR
DELAY
RF
BB
IF INPUT
50 TO 180 MHz
-55 TO -30 dBm
DIGITAL
COSTAS
LOOP
DIGITAL
CLOCK
LOOP
MICRO-
PROCESSOR
Figure 4-2. Demodulator Block Diagram Burst Mode