Specifications

M&C and Interfaces SDM-309B Satellite Modem
4-4–46 MN/U-SDM309B Rev. #
Modem Settings (Slave)
TX_CLOCK TX_TERR
BUF_CLK SATELITE
RX_CLOCK NORMAL
4.3.1.2 Master/Slave G.703
* There is no loop timing selection on board for G.703. It is assumed that any G.703
termination equipment will extract the clock from the satellite signal and turn it around
for retransmitting. The settings for the Master and Slave modems are the same as listed
above.
4.3.1.3 Master/Slave X.21
* Clock must be looped externally at slave end.
Modem Settings (Master)
TX_CLOCK INT
BUF_CLK INT
RX_CLOCK NORMAL
Modem Settings (Slave)
TX_CLOCK TX_TERR
BUFF_CLK SATELITE
RX_CLOCK NORMAL
4.3.1.4 Master/Slave External Station Clock
* Clock must be looped externally at slave end (For RS422 and V.35 see notes in
previous example).
Modem Settings (Master)
RX_CLOCK NORMAL
TX_CLOCK EXT_REF
BUFF_CLOCK EXT_REF
EXT_REF SET TO FREQUENCY OF STATION CLOCK
Modem Settings (Slave)
TX_CLOCK TX_TERR
BUFF_CLK SATELITE
RX_CLK NORMAL
EXT_REF N/A
4.3.2 Master/Master
This application is used where both earth stations have high stability clocks available and
the received data is to be clocked onto the local network.
The disadvantage of the master/master application is that the receive data will slip as the
clock will not be synchronized. The buffer if properly set up will ensure that the slips are