Comtech EF Data CDM-625 - Manual (Page 129)

CDM-625 Advanced Satellite Modem Revision 15
Front Panel Operation MN-CDM625
5–29
5.2.1.5 CONFIG: Clocks
Clocking: TxClock RxBuffer/Clock
Clock-Ext Freq-Ref Int-Ref-Adjust ()
Use the ◄ ► arrow keys to select TxClock, RxBuffer/Clock, Clock-Ext, Freq-Ref, or Int-Ref-
Adjust, and then press ENTER.
5.2.1.5.1 CONFIG: Clocks  Tx Clock
Transmit Clock = Internal(SCT)
(Int(SCT),TxTerr(TT),RxLoop, ETTSTRxS) ()
Use the ▲▼ arrow keys to select from the choices shown in parentheses, and then press
ENTER. Note the following:
Selection 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 phas e 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 choices are also available.
Example: You have an av ailable hi gh s tability 10 M Hz c lock s ource, but t he 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, V.35, HSSI or LVDS, Tx and Rx data rates are equal, no RS, and
no framing.
This mode is available to permit a par ticular variation of Loop T iming. 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.
Sect. 9.1.1 CLOCK MODES AND DROP & INSERT (D&I).