Comtech EF Data SNM-1002 - Manual (Page 104)

SNM-1002 LinkSync
 Modem
Revision 2
Theory of Operation MN/SNM1002.OM
4–10
4.3.3.1 BPSK Encoding
The modulator converts transmitted baseband data into a modulated BPSK carrier at
2.4 kbit/s to 1.25 Mbit/s (1/2 rate). Using vector analysis of the constellation pattern,
BPSK represents one symbol with the carrier phase either at 0
° or 180°. The 1/2 rate
encoding at the convolutional encoder provides two symbols output for every bit input.
Code Rate Symbols/Bit Bits/Hz
1/2 2 0.5
4.3.3.2 QPSK Encoding
The modulator converts transmitted baseband data into a modulated QPSK carrier at the
following parameters:
• 4.8 kbit/s to 2.5 Mbit/s (1/2 rate)
• 7.2 kbit/s to 3.75 Mbit/s (3/4 rate)
• 8.4 kbit/s to 4.375 Mbit/s (7/8 rate)
Using vector analysis of the constellation pattern, QPSK represents a symbol with the
carrier phase angle at 45
°, 135°, 225°, or 315°. The 1/2, 3/4, and 7/8 rates encoded at the
convolutional encoder provide the desired input/output bit rates.
Code Rate Symbols/Bit Bits/Hz
1/2 2 1
3/4 1.5
1.33
7/8 1.143 1.75