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CDM-Qx Satellite Modem Revision 5
External Connections MN/CDMQx.IOM
4–8
4.4.4 Alarms Connector
All modules contain an alarm connector. The Alarms connector is a 15-pin 'D' type male
(DB15 M). This provides the user with access to the Form-C relay contacts, which
indicate the fault status of the unit. These are typically connected to an external fault
monitoring system, often found in satellite earth stations.
For a Modulator, TX fault and Unit Fault are supported. The transmit I and Q modulator
samples are available on this connector. Connecting these signals to an oscilloscope in
X,Y mode will provide the modulator signal constellation diagram, which is a useful
diagnostic aid. A pin also is provided which can mute the transmit carrier. This requires
that the pin be shorted to ground, or a TTL ‘low’.
For a Demodulator, RX fault and Unit Fault are supported. If a Modulator and
Demodulator are vertically grouped together as a modem, TX fault and the External
carrier off pin will also be supported. The receive I and Q demodulator samples are
provided on this connector. Connecting these signals to an oscilloscope in X,Y mode will
provide the receive signal constellation diagram, which is a useful diagnostic aid. As an
aid to antenna pointing, or for driving step-track equipment, an analog AGC signal is
provided on Pin 2 of this connector.
Table 4-3. Alarm Interface Connector Pin Assignments
Pin # Signal Function Name
8
15
7
RX Traffic (De-energized, Faulted)
RX Traffic (Energized, No Fault)
RX Traffic
RX-NC
RX-NO
RX-COM
14
6
13
TX Traffic (De-energized, Faulted)
TX Traffic (Energized, No Fault)
TX Traffic
TX-NC
TX-NO
TX-COM
5
12
4
Unit Fault (De-energized, Faulted)
Unit Fault (Energized, No Fault)
Unit Fault
UNIT-NC
UNIT-NO
UNIT-COM
11
3
I Channel (Constellation monitor)
Q Channel (Constellation monitor)
TX or RX-I
TX or RX-Q
10 No Connection N/C
2
AGC Voltage (Rx signal level, 0 to 2.5 volts,
demodulator only)
AGC
9
EXT Carrier OFF (modulator or modulator and
demodulator grouped together)
EXT-OFF
1 Ground GND