beautypg.com

Comtech EF Data SNM-1002 User Manual

Page 108

background image

SNM-1002 LinkSync

 Modem

Revision 2

Theory of Operation

MN/SNM1002.OM

4–14

implemented digitally. The DDS performs the function of a VCO in an analog
implementation. The recovered data and symbol clocks are then used throughout the
demodulator.

The soft decision mapper converts the digital I and Q data to 3-bit soft decision values.
These values are then fed to the programmable vector rotation circuit, providing
compatibility with spectrum reversal of the I and Q channels.

The output of the vector rotation circuit is then sent to the Viterbi decoder.