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SLM-3650 Satellite Modem
Maintenance
5.2.3.2
Demodulator Faults
Fault/Alarm
CARRIER DETECT
IF SYNTHESIZER
I CHANNEL
Q CHANNEL
BER THRESHOLD
MODULE
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Possible Problem and Action
Carrier detect fault.
Indicates the decoder is not locked. This is the most common fault displayed
in the modem. Any problem from the input data on the modulator end of the
circuit to the output of the decoder can cause this alarm.
First, ensure the demodulator has an RF input at the proper frequency and
power level. Ensure the demodulator data rate is properly programmed. Refer
to the fault isolation procedure for Data Clock Syn in the modulator section.
Verify the frequency of the data transmitted from the modulator is within 100
PPM.
Demodulator IF synthesizer fault.
Indicates the demodulator IF synthesizer is faulted.
This fault is a hardware failure. Contact the Comtech EF Data Customer
Support Department.
Indicates a loss of activity in the I channel of the quadrature demodulator.
Typically indicates a problem in the modulator side of the circuit. Check for
proper RF input to the demodulator. If the input to the demodulator is correct,
then the problem is in the baseband processing.
Indicates a loss of activity in the Q channel of the quadrature demodulator.
Follow the same procedure for the I channel fault.
Indicates the preset BER threshold has been exceeded.
Setting of this alarm is done in the Utility menu. This is an alarm based on the
corrected BER reading on the front panel.
Demodulator module fault.
Typically indicates that the demodulator module is missing or will not program.
Contact the Comtech EF Data Customer Support Department.
5–14
Revision 3
MN/SLM3650.IOM
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