Comtech EF Data CDM-570A - Manual (Page 583)

CDM-570A/570AL Satellite Modem with Optional Packet Processor MN-CDM570A
Appendix N Revision 2
N–5
The control cable from each CDM/R-570AL-IP 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 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.