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Maintenance
5.2.3.2
Demodulator Faults
Fault/Alarm
CARRIER DETECT
IF SYNTHESIZER
I CHANNEL
Q CHANNEL
BER THRESHOLD
MODULE
5–14
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 EFData 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 EFData Customer Support Department.
SDM-300A Satellite Modem
Rev. 4
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