Comtech EF Data DMD1050TS, Installation And Operation Manual

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DMD1050TS Satellite Modem Board
Revision 1
Theory of Operation 3–22 MN-DMD1050TS
3.10.2.1 Rx SAT Clock
The Rx SAT clock is recovered from the satellite that is received from the distant end. If selected,
the Buffer Clock is locked to the Rx SAT clock.
3.10.2.2 SCTE as Rx Buffer Clock
When SCTE is selected as the Rx Buffer clock, the modem receives the clock from the Transmit
Terrestrial interface.
3.10.2.3 SCT as Rx Buffer Clock
If SCT clock is selected as the Rx Buffer clock source, then it must be configured for Internal.
SCT is sometimes referred to as Internal Timing or Send Timing (ST).
3.10.2.4 External Reference: J9 SMA Female
This is not actually a clock, but does have some clocking implications. When the external
reference is used, the master oscillator in the DMD1050TS is locked to the external reference,
and the internal accuracy and stability of the DMD1050TS assumes that of the External
Reference. Therefore, not only are the transmit frequencies of the DMD1050TS locked to the
external reference, but the modem’s internal SCT Oscillator is locked to the external reference as
well.
3.11 Ethernet Data Interface
The modem supports dual port 10/100 Base T Interface. When selected, the Tx Clock Source
defaults to SCTE, and the Clock Polarity defaults to Normal. In addition, the Buffer Clock defaults
to RxSat, and the Buffer Clock Polarity defaults to Normal. See Appendix C for interface set up
and supporting features.