Comtech EF Data SMS-758 - Manual (Page 71)

SMS-758 Modem Protection Switch Theory of Operation
MN/SMS758 Rev. 3 4–11
4.4.3 Demodulator Signal Fault
A demodulator signal fault is the failure of all active demodulators on the indicated
downlink to acquire and lock to their signals. The fault alarm indicates a possible down
converter system failure, causing loss of IF to the demodulators.
During normal operation or power-down, the relay is de-energized (COM to NC). When
all demodulators indicate loss of carrier, the relay energizes (COM to NO). The relay
remains energized until the failure is eliminated.
4.5 Online Status Specification
This section defines the protocol and format for reporting the online status of the switch.
The M&C commands the online telemetry module to report online status for all active
prime modulators and demodulators. The status is reported as form-C relay contacts to
the online status connectors (J4 and J5) on the rear panel. (See Section 2.4.4 for
connector locations and pinouts.)
4.5.1 Modulator Online Status
The active modulator’s online status is indicated by form-C relay contacts. When the
prime is online or power is OFF, the relay is de-energized (COM to NC). When a backup
modulator goes online for that prime, the relay energizes (COM to NO).
4.5.2 Demodulator Online Status
The active demodulator’s online status is indicated by form-C relay contacts. When the
prime is online or power is OFF, the relay is de-energized (COM to NC). When a backup
demodulator is online for that prime, the relay is energized (COM to NO).