Comtech EF Data CDM-570 - Manual (Page 454)

CDM-570/570L Satellite Modem with Optional IP Module Revision 12
Appendix H MN/CDM570L.IOM
H–2
The control cable from each modem to the CRS-180 also includes +12V power to operate the
CRS-180. Power from both modems is diode OR’ed so that the switch remains active if power is
lost from one of the modems.
The CRS-180 provides IF redundancy. On the Tx side, it switches the Tx IF signal. The Rx IF
signal from the RF equipment 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.
H.2.2 CRS-170A L-Band 1:1 Redundancy Switch
See the CRS-170A L-Band 1:1 Redundancy Switch Installation and Operation
Manual for more detailed information on the CRS-170A operation.
The CRS-170A L-Band 1:1 Redundancy Switch performs the transmit and receive coaxial
switching required for redundant modem operation with an outdoor BUC and LNB. It switches
all of the BUC and LNB interface signals that are multiplexed onto the transmit and receive
coaxial cables:
• Tx and Rx L-Band signals
• 10 MHz reference to BUC and LNB
• DC Power to BUC and LNB
• FSK signaling to the BUC
Select Unit Faults only, Unit Faults or Receive Traffic Faults, or 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 CDM-570L 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.