Comtech EF Data DMD-2050E - Manual (Page 58)

DMD2050E Universal Satellite Modem Theory of Operation
MN-DMD2050E Revision 2 3–16
3.5.3 RX Buffer Clock Options
The modem supports a number of RX Buffer clock options that can be recovered from the
satellite, terrestrial links, internally or externally. The various clocking options allow users to
determine which clock will best fit their applications. Figure 3-7 gives an overview on how the
modem processes the various clocks for the Tx Clock and the Rx Buffer Clock. The modem
allows users to select clock polarity Tx and Rx Clocks may be independently locked. The
following RX Buffer clock selections are available:
• Rx Satellite Clock (Recovered from Satellite)
• SCTE (External Tx Terrestrial Clock)
• SCT (Internal Oscillator)
• EXC Clock/EXT BNC (External Clock Source)
• EXT IDI (Drop and Insert)
The modem handles RX Buffer clock selections based on source priority levels. The user
assigns priorities to the clock sources based on source selections. Source 1 has the highest
priority and Source 5 being the last resort or lowest priority. If a fallback clock is selected and
activity is lost at the highest priority source, the modem will fall back to the next highest priority
clock with activity. When activity resumes on a higher priority source, the modem resumes using
the higher priority source
Clock Source Priority
RX SAT 1 (of 5)
SCTE 2 (of 5)
SCT 3 (of 5)
EXC BNC 4 (of 5)
EXT IDI 5 (of 5)
Refer to Front panel setup menus or Web Browser manual MN-DMDREMOTEOP.
3.5.3.1 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 lock to the RX sat clock.
3.5.3.2 SCTE: Serial Clock Transmit External
When SCTE is selected as the Rx Buffer clock, the modem receives the clock from the Transmit
Terrestrial interface.