Comtech EF Data SNM-1010L - Manual (Page 250)

SNM-1010L Data/Control Modem Revision 0
Specifications MN/SNM1010L.OM
The modulator converts transmitted baseband data into a modulated QPSK carrier at the
following parameters:
• 4.8 kbps to 2.5 Mbps (1/2 rate)
• 7.2 kbps to 3.75 Mbps (3/4 rate)
• 8.4 kbps to 4.375 Mbps (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
provide the desired input/output bit rates.
Code Rate Symbols/Bit Bits/Hz
1/1 1 2
1/2 2 1
3/4 1.5
1.33
7/8 1.143 1.75
B.3.21.1.3 OQPSK Encoding
The modulator PCB converts the transmitted baseband data into a modulated OQPSK
carrier within the same parameters as QPSK.
The OQPSK modulation is mainly different from QPSK by offsetting the I and Q
channel modulation signals. This offset prevents the RF envelope from going through
zero. Under certain conditions, this may allow less back-off in the High Power
Amplifier (HPA) system. The 1/1, 1/2, 3/4, and 7/8 rates encoded provide the desired
input/output bit rates.
Code Rate Symbols/Bit Bits/Hz
1/1 1 2
1/2 2 1
3/4 1.333
1.5
7/8 1.143 1.75
B.3.21.1.4 8PSK Encoding
B–8