Comtech EF Data SMS-758 User Manual
Page 88
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![background image](/files/778880/content/doc088.png)
Theory of Operation
SMS-758 Modem Protection Switch
4–28
MN/SMS758 Rev. 3
TRANSMIT DATA
RECEIVE DATA
RECEIVE EXTERNAL
REFERENCE CLOCK
TX S/B
TX
PRIME C/U
DATA I/O
RX
TERRESTRIAL
DATA I/O
DATA PATH
SELECTION
RX S/B
RX
NOTE: THE RELAYS ARE SHOWN IN THE NON-ENERGIZED
POSITION CONNECTING THE TERRESTRIAL DATA AND
PRIME MODEM CONNECTORS TOGETHER. STANDBY (S/B)
SIGNALS ARE ROUTED TO THE OFFLINE BACKUP MODEM.
RECEIVE DATA
TRANSMIT DATA
RECEIVE EXTERNAL
REFERENCE CLOCK
MOD AND DEMOD FAULTS
DATA SWITCH
MOTHERBOARD
INSTRUCTION
DECODER
MOD RELAYS
DEMOD RELAYS
FAULTS
TRANSMIT DATA
RECEIVE DATA
RECEIVE EXTERNAL
REFERENCE CLOCK
Figure 4-8. Prime DS-1 and G.703 Interface Switch
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