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Operation
3.3.3.1
Demodulator Faults Menu
Refer to Figure 3-9.
Fault/Alarm
CARRIER DETECT
IF SYNTHESIZER
I CHANNEL
Q CHANNEL
BER THRESHOLD
E
/N
THRESHOLD
B
0
MODULE
3–24
Possible Problem and Action
Carried Detect fault. 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.
Indicates the demodulator IF synthesizer is faulted. This is considered a
major fault. Return the demodulator for repair.
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.
Activity fault for the Q channel digital filter. Follow the same procedure
as for the I channel..
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
/N
threshold has been exceeded. This is an alarm based on
b
0
the corrected E
/N
reading on the front panel. Change E
b
0
troubleshoot why corrected E
Demodulator module fault. Typically indicates that the demodulator
module will not program. Return the demodulator for repair.
SDM-2020 Satellite Demodulator
/N
b
/N
is low.
b
0
setting, or
0
Rev. 3
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