Product specifications

CRS-170A L-Band 1:1 Redundancy Switch Revision 3
Introduction MN/CRS170A.IOM
1.2.1 Operation with CDM-625, CDM-570L, CDM-700 and CDM-710
The CRS-170A is configured with two modems to form a complete 1:1 redundant modem.
Software built into the modem M&C and cross connected status and communication between the
modems allows the M&Cs to jointly function for 1:1 switch control. The control cables between
the modems and the CRS-170A include three signal groups that are routed from one modem to
the other through the CRS-170A:
• First, a serial communication line is routed from each modem to the other. The online
unit interrogates the standby unit at regular intervals to determine its configuration. If a
difference in configuration is detected, the online unit automatically reconfigures the
standby unit so that the configurations are always synchronized. If the standby unit is
replaced, it does not have to be manually reprogrammed to match the online unit; the
process is entirely automatic.
• Second, the online status output signal from each modem is routed to the other in
addition to the switch logic within the CRS-170A. Online control from Modem A
overrides online control from Modem B inside the CRS-170A. In the event that both
modems indicate true online status through some malfunction, the CRS-170A switch will
select Modem A.
• Third, the fault status from each modem is routed to the other. The configuration, online
status, and fault communication between the modems allows the offline modem to take
over when the online unit indicates a fault.
Manual switchover is enabled from the front panel or remote control of the online modem.
Automatic switching is inhibited by the User from the online unit. The User can select Unit
Faults only, Unit Faults or Receive Traffic Faults, Unit Faults or Transmit Traffic Faults, or
all three for the switchover criteria. This selection provides a great deal of flexibility in the
operation of the switch. Green LEDs on the antenna side of the CRS-170A indicate which modem
is online.
The control cable from each modem to the CRS-170A also includes +12V power to operate the
CRS-170A. Power from both modems is diode OR’d so that the switch remains active if power is
lost from one of the modems.
The CRS-170A provides L-Band redundancy, but when switching occurs, it accommodates more
than just the L-Band signals. On the Tx side, it switches the Tx L-Band signal, the 10 MHz
reference to the BUC, DC power to the BUC, and FSK signaling to the BUC (on CDM-570L
modems). On the Rx side, it switches the 10 MHz reference to the LNB, and DC power to the
LNB. The Rx L-Band signal from the LNB is split in a power divider to continuously drive both
the online and offline demodulator. The offline demodulator can then maintain lock so that it is
ready to quickly assume online status for receive traffic when a switchover is required.
Data switching is accomplished inside each modem, in the data interface itself. A ‘Y’ cable
connects both the online modem and the offline modem to the terrestrial data source. Transmit
data drives both modems in parallel so that the standby modulator is always ready to come online.
Termination impedance for the modem line receivers is active in the online modem. On the Rx
side of the interface, TRI-STATE
®
control of the offline modem line drivers keeps the offline
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