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SDM-300A Satellite Modem
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
Rev. 4
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.
Maintenance
5–19
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