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OM20 Universal Outdoor Modem
4.7
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 4-7 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.
J 3
SD
TT
ST
HIGH STABILITY
High Stability
Oscillator
TRANSMIT
RECEIVE
CLOCK
RECOVERY
NORMAL
INVERTED
J 3
RT
BUFFER CLK POL
RD
DATA POLARITY
INVERT NONE
INV . TERR & BASE
INV . BASEBAND
INV . TERR DATA
4.7.1 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:
MN-OM20– Revision 5
SCTE
SCT
INTERNAL
REF FREQ
SRC
SCT CLK
SRC
SCR
IDI
SCT
BUFFER CLK
SRC
SCTE
RX SAT
Figure 4-7. Clocking and Polarity Diagram
INVERT NONE
INV . TERR & BASE
INV . BASEBAND
INV . TERR DATA
DATA POLARITY
CLOCK &
DATA
Tx CLK
CLK POL
SRC
NORMAL
INVERTED
AUTO
CLOCK & DATA
DEMODULATION
RECOVERY
OM20 Theory of Operation
MODULATION
4–12
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