Comtech EF Data SNM-1001L - Manual (Page 35)

SNM-1001L Satellite Modem Revision 1
Introduction MN/SNM1001L.IOM
1–11
The digital clock loop, in conjunction with another DDS, performs the clock recovery
function. The clock loop consists of a phase detector, loop filter, and DDS, all
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 and optional
Sequential decoder. The output is then sent to the optional Reed-Solomon or Overhead
PCB. With the Turbo coding hardware option, the vector rotation circuit output is sent to
the optional Turbo Codec for decoding.
1.8 Description of Monitor & Control
1.8.1 Overview
The Monitor & Control (M&C) monitors the modem and provides configuration updates
to other modems within the modem when necessary. The modem configuration
parameters are maintained in battery-backed RAM, which provides total recovery after
power-down situation. The M&C functions include extensive fault and status reporting.
All modem functions are accessible through a local front panel interface and a remote
communications interface.
A block diagram of the M&C is shown in Figure 1-3.