Comtech EF Data CDM-425, Installation And Operation Manual

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CDM-425 Advanced Satellite Modem
Revision 0
Front Panel Operation 6–31 MN-CDM-425
6.2.1.5 CONFIG: Clocks
Clocking: TxClock Rx-Buffer/Clock
Clock-Ext Freq-Ref Int-Ref-Adjust (

)
Use the
◄ ►
arrow keys to select a parameter. Press ENTER .
6.2.1.5.1 CONFIG: Clocks

Tx Clock
Transmit Clock = Internal(SCT)
(Int(SCT),TxTerr(TT),RxLoop, ETTSTRxS) (

)
Use the
▲▼ arrow keys to select from the options shown in parentheses. Press
ENTER .
Note that:
Setting Function
Internal (SCT) This is the required setting when the Tx interface type is Audio. Indicates that the unit
will supply a clock to the DTE, which is derived from its internal high-stability source.
Tx-Terrestrial (TT) This is the required setting when the modem’s interface type is G.703. Indicates that
the unit expects to receive a clock from the DTE, to which the unit can phase-lock its
internal circuits. If no clock is detected the modem will substitute its internal clock and
generate an alarm.
Rx-Loop-timed Allows the modem’s internal clock to be phase locked to the Rx buffer clock source.
This output clock is Send Timing. Choosing Rx-Loop does not automatically select Rx-
Sat as the buffer clock source. This allows for increased flexibility for modem clock
selection. While you typically should select Rx-Sat, other selections are also available.
Example: You have an available high stability 10 MHz clock source, but the end
equipment only accepts a clock at the information data rate. Selecting Tx Clock = Rx-
Loop and Rx Buffer Clock = EXT-REF provides receive timing and send timing to the
end equipment that is sourced from the 10 MHz reference.
Ext-TT (ST = Rx Sat) Only valid if: RS422 or V.35, Tx and Rx data rates are equal, and no framing. This
mode is available to permit a particular variation of Loop Timing. In this mode, transmit
timing is taken from the TT pins, but ST is active and gives out a copy of the Rx
Satellite Clock.
Appendix E. CLOCK MODES
AND
DROP & INSERT (D&I).