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SLM-3650 Satellite Modem
Maintenance
5.2.3.6
Backward Alarms Faults
Fault/Alarm
BW ALARM RX4
BW ALARM RX3
BW ALARM RX2
BW ALARM RX1
BW ALARM TX4
BW ALARM TX3
BW ALARM TX2
BW ALARM TX1
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Possible Problem and Action
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. Refer to Chapter 2 for the backward alarm theory of operation. If
the user does not wish to monitor the backward alarm faults, the backward
alarm inputs must be grounded at the breakout panel. Refer to Chapter 2 for
breakout panel pinouts.
Receive backward alarm #3. Refer to BW Alarm RX4 for details.
Receive backward alarm #2. Refer to BW Alarm RX4 for details.
Receive backward alarm #1. Refer to BW Alarm RX4 for details.
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 (see Chapter 3 for
clarification). 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.
Transmit backward alarm #3. Refer to BW Alarm TX4 for details.
Transmit backward alarm #2. Refer to BW Alarm TX4 for details.
Transmit backward alarm #1. Refer to BW Alarm TX4 for details.
5–19
Revision 3
MN/SLM3650.IOM
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