Comtech EF Data CRS-170A - Manual (Page 25)

CRS-170A L-Band 1:1 Redundancy Switch MN/CRS170A.IOM
Introduction Revision 13
1–5
1.3 Functional Description
The CRS-170A performs the Tx and Rx coaxial switching required for redundant modem
operation with an outdoor BUC and LNB.
The Tx (transmit) side switches four modem output signals that are multiplexed onto the transmit
coaxial cable:
• 950-2250 MHz L-band transmit RF;
• 10 MHz BUC frequency reference;
• 600 KHz BUC FSK control and status communication;
• BUC DC power supply.
The Rx (receive) side of the switch uses both power dividers and relays to provide the redundant
modem interface for three signals multiplexed onto the LNB coaxial cable:
• 950-2250 MHz L-band receive RF from LNB;
• 10 MHz frequency reference to LNB;
• DC power supply to LNB.
1.3.1 Switch / Modem Operation
The CRS-170A is configured with two modems to form a complete 1:1 redundant modem
system. Within the CRS-170A, a redundancy controller continually monitors the status of faults
for both modems to determine which modem should be Online and Offline. The control cables
between the modems and the CRS-170A include four signal groups:
• First, serial full-duplex communication lines are routed from one modem to the other
modem via the CRS-170A. Using these lines, this Online unit can interrogate the Offline unit
at regular intervals to determine its configuration. If a difference in configuration is
detected, the Online unit will reconfigure the Offline unit so that the configurations are
always synchronized. This process is entirely automatic – if the Offline unit is replaced, it
does not have to be manually reprogrammed to match the Online unit.
• Second, the Modem’s Unit, Tx and Rx faults signals from both modems are routed to the
CRS-170A. This allows the redundancy controller to always know the health status of both
modems.
• Third, the online/offline signals are routed from the CRS-170A to each modem. Based on the
modem faults, the CRS-170A will determine which modem should be Online and Offline. In
the event that both modems indicate faults through some malfunction, the CRS-170A switch
will select, by default, Modem ‘A’.