1.2.1 Operation With Cdm-625 / 840 / 750 / 570L / 700 / 710 / 710G Modems - Comtech EF Data CRS-170A Installation And Operation Manual

CRS-170A L-Band 1:1 Redundancy Switch
Introduction

1.2.1 Operation with CDM-625 / 840 / 750 / 570L / 700 / 710 / 710G Modems

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 modem can interrogate the
Offline modem at regular intervals to determine its configuration. If a difference in
configuration is detected, the Online modem will reconfigure the Offline modem so that
the configurations are always synchronized. This process is entirely automatic – if the
Offline modem is replaced, it does not have to be manually reprogrammed to match the
Online modem.
•
Second, the 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.
•
Fourth, +12V is routed from each modem to the CRS‐170A for operational power. This
power from both modems is diode OR'd so that the switch remains active if power is
lost from one of the modems.
Mode Switches – The Mode DIP switches, located on the antenna side of the CRS‐170A, allow
the switch to operate in two different modes: Normal (Intelligent Controller) Mode and
SDM‐300L/CDM‐600L (Dumb Controller) Mode.
•
Use Normal (Intelligent Controller) Mode for CDM‐625, CDM‐840,
CDM‐750, CDM‐570L, CDM‐700, CDM‐710 and CDM‐710G
modems.
•
Use SDM‐300L/CDM‐600L (Dumb Controller) Mode for SDM‐300L
and CDM‐600L (CLM‐9600L) modems.
IF Switching – 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, on CDM‐570L modems, 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
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Revision 9
MN/CRS170A.IOM