Radyne OM20 Specifications download pdf (Page 41)

DMD1050 Satellite Modem Board Theory of Operation

3.10.2 RX Buffer Clock Options

The DMD1050 supports a number of RX Buffer clock options that can be recovered from the

satellite, terrestrial links or internally. The various clocking options allow users to determine

which clock will best fit their applications. Figure 3-9 gives an overview on how the modem

processes the various clocks for the Tx Clock and the Rx Buffer Clock. Tx and Rx Clocks may

be independently locked. The following Buffer clock selections are available on the DMD1050:

� SCTE (External Tx Terrestrial Clock)

� SCT (Internal Oscillator)

� Rx Satellite Clock

The DMD1050 handles RX Buffer clock selections based on source priority levels. Refer to

Appendix D “Web Browser Setup”. The user assigns priorities to the clock sources based on

source selections. Source 1 has the highest priority and Source 3 has the 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 3

SCTE 2 of 3

SCT 3 of 3

3.10.3 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.

3.10.4 SCTE: Serial Clock Transmit External

When SCTE is selected as the Rx Buffer clock, the modem receives the clock from the Transmit

Terrestrial interface.

3.10.5 SCT: Serial Clock Transmit

If SCT clock is selected as the RX Buffer clock source, then it should be configured for internal.

SCT is sometimes referred to as Internal Timing or Send Timing (ST).

3.10.5.1 External Reference: J8 SMA Female

This is not actually a clock, but does have some clocking implications. When the external

reference is used, the master oscillator within the DMD1050 is locked to the external reference,

and the internal accuracy and stability of the DMD1050 assumes that of the External Reference.

Therefore, not only are the transmit frequencies of the DMD1050 locked to the external

reference, but the modem’s internal SCT Oscillator is locked to the external reference as well.

MN-DMD1050 3–19

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Radyne OM20 Specifications Page 41