Comtech EF Data SDM-300A - Manual (Page 354)

SDM-300A Satellite Modem Revision 6
Troubleshooting MN/SDM300A.IOM
18–18
18.3.3.6 Backward Alarms Faults
Fault/Alarm Possible Problem and Action
BW ALARM RX4 Receive backward alarm #4. The distant end of the link is sending backward alarm #4. This indicates
trouble at the distant end, which may be a result of improper transmission at the near end of the link.
The modem will signal this event by setting the deferred maintenance alarm (open collector). This
alarm is a monitor function. The modem reports and records the event, but takes no other action.. If
the user does not wish to monitor the backward alarm faults, the backward alarm inputs must be
grounded at the breakout panel.
BW ALARM RX3 Receive backward alarm #3. Refer to BW Alarm RX4 for details.
BW ALARM RX2 Receive backward alarm #2. Refer to BW Alarm RX4 for details.
BW ALARM RX1 Receive backward alarm #1. Refer to BW Alarm RX4 for details.
BW ALARM TX4 Transmit backward alarm #4. The modem is being instructed to send backward alarm #4 to the distant
end of the link. This alarm is controlled by wiring the backward alarm inputs of the modem to the
demod fault relay and/or other fault outputs in the receive system (see IESS-308 for clarification). The
simplest implementation for single destination service is to wire the demod fault relay between ground
and the four backward alarm inputs This sends all four backward alarms in the event of any major
(prompt) receive fault. This particular alarm is transmitted, reported, and recorded, but the modem
takes no other action. In most cases, this will be sent due to some receive problem with the modem,
so a real fault will probably be occurring if backward alarms are being sent. The transmit backward
alarms are a symptom of trouble, not a cause.
BW ALARM TX3 Transmit backward alarm #3. Refer to BW Alarm TX4 for details.
BW ALARM TX2 Transmit backward alarm #2. Refer to BW Alarm TX4 for details.
BW ALARM TX1 Transmit backward alarm #1. Refer to BW Alarm TX4 for details.