Comtech EF Data SDM-2020 User Manual
Page 94
SDM-2020 Satellite Demodulator
Revision 4
Front Panel Operation
MN/SDM2020D.IOM
6–30
DEMODULATOR
--------
CARRIER DETECT
Indicates the Viterbi/TCM decoder is not locked. This is the most common
fault displayed in the demodulator. Any problem from the input data on the
demodulator end of the circuit at the output of the decoder, can cause this
fault. First, ensure the demodulator has an RF input at the proper frequency
and power level. Ensure the demodulator data rate is properly programmed.
Verify the frequency of the data transmitted from the modulator, is within 100
ppm.
IF SYNTHESIZER
Indicates the demodulator IF synthesizer is faulted. This is considered a
major fault. Return the demodulator for repair.
I CHANNEL
Activity fault for the I channel digital filter. This is considered a major fault. An
fault in this position indicates either a fault in the descrambler, or a loss of
incoming data.
Q CHANNEL
Activity fault for the Q channel digital filter. Follow the same procedure as for
the I channel.
BER THRESHOLD
EB/NO THRESHOLD
The preset BER threshold has been exceeded. This is an alarm based on the
corrected BER reading on the front panel. Change BER setting, or
troubleshoot why corrected BER is high.
The preset E
b
/N
0
threshold has been exceeded. This is an alarm based on
the corrected E
b
/N
0
reading on the front panel. Change E
b
/N
0
setting, or
troubleshoot why corrected E
b
/N
0
is low.
MODULE
Demodulator module fault. Typically indicates that the demodulator module
will not program. Return the demodulator for repair.
CONFIGURATION
Demodulator/decoder configuration fault. Press
for DMD programming faults.
DMD PROGRAMMING