Comtech EF Data DMDVR20 LBST Rev 1.1 - Manual (Page 31)

Theory of Operation DMDVR20 LBST Satellite Modem
3-10 TM136 – Rev. 1.1
3.5 Clocking Options
The modem supports a number of different clocking options that can be recovered from the
satellite or the terrestrial links. The various clocking options allow users to determine which clock
will best fit their applications. Figure 3-6 gives an overview on how the modem processes the
various clocks for the Tx Clock source and the Rx Buffer Clock source. Tx and Rx Clocks may be
independently locked.
Figure 3-6. Clocking and Polarity Diagram
3.5.1 TX Clock Options
TX clock options can be recovered from the terrestrial interface, satellite interface or internally
generated. The allows users to select SCTE Clock (Terrestrial) or the SCT internal clock. The
modem also allows user to recover the SCT Clock from the satellite (SCR) or from the modem
internally. The modem allows users to select clock polarity. The Tx clock selections available
are: