Comtech EF Data SNM-1000 - Manual (Page 127)

SNM-1000 Node Control Modem Revision 3
Theory of Operation MN/SNM1000.IOM
4–9
4.2.2 Theory of Modulation Types
The modulation type for the modem is QPSK.
The PSK data transmission encoding method uses the phase modulation technique. This
method varies the phase angle of the carrier wave to represent a different bit value for the
receiver.
• QPSK represents: 4 discrete phase angles represent the 4 possible states of a
symbol.
4.2.2.1 QPSK Encoding
The modulator converts transmitted baseband data into a modulated QPSK carrier at the
following parameters:
• 19.2 kbit/s (1/2 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 rate encoded at the convolutional
encoder provide the desired input/output bit rates.
Code Rate Symbols/Bit Bits/Hz
1/2 2 1
4.2.3 Modulator Specifications
Refer to Chapter 1 for specifications.