Comtech EF Data RCS10 - Manual (Page 210)

Maintenance RCS10 Redundant Communication System
4-2 TM058 - Rev. 2.3
Action: Check that the receive acquisition range is adequate for the possible system
offsets. Setting the value to 30 KHz is a standard value encompassing all normal offsets.
After acquisition, the actual receive frequency can be read from the front panel.
Possible Cause: Transmit carrier incompatible.
Action: Check the receive parameter settings and ensure that they match those on the
modulator.
Possible Cause: Modem is in test mode.
Action: Check the modem front panel for yellow warning LEDs indicating a test mode is
enabled. Self-Test or RF Loopback disconnects the Demodulator from the IF receive input
connector.
4.2.1 DMD10 Fault Philosophy
The DMD10 performs a high degree of self-monitoring and fault isolation. The alarms are separated
into five categories; Major Alarms, Minor Alarms, Common Alarms, Backward Alarms and Latched
Alarms. Also, a feature exists that allows the user to ‘Mask’ out certain Alarms as explained
below.
4.2.2 Alarm Masks
The user has the capability to ‘Mask’ individual alarms on the DMD10. When an Alarm is masked,
the front panel LEDs and the Fault Relays do not get asserted, but the Alarm will still be displayed.
This feature is very helpful during debugging or to lock out a failure that the user is already aware of.
4.2.3 Major Alarms
Major alarms indicate a modem hardware failure. Major alarms may flash briefly during modem
configuration changes and during power up but should not stay illuminated.
Alarms are grouped into Transmit Alarms and Receive Alarms - Transmit and Receive are
completely independent.
4.2.4 Minor Alarms
Minor alarms indicate that a problem may persist outside the modem such as loss of terrestrial
clock, loss of terrestrial data activity, or a detected transmit or receive AIS condition.
Alarms are grouped into Transmit Alarms and Receive Alarms - Transmit and Receive are
completely independent.
4.2.5 Common Alarms
Common alarms may be Major or Minor and are defined as alarms that cannot be classified as
strictly transmit or receive. These alarms are common to both.
4.2.6 Backward Alarms
Backward alarms are alarms that are fed back to or received from the other end of the satellite link.
4.2.7 Latched Alarms
Latched alarms are used to catch intermittent failures. If a fault occurs, the fault indication will be
latched even if the alarm goes away. After the modem is configured and running, it is recommended
that the latched alarms be cleared as a final step.
4.3 DMD10 Fault Tree Matrices
Tables 4-1 through 4-4 represent, in matrix form, the faults that may occur within the DMD10
modem. There are four matrices; Backward alarms, TX Faults, RX Faults and Interface/Common
Equipment Faults.