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DMD50 Universal Satellite Modem
3.7
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 3-7 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.
J19
SD
TT
ST
High Stability
Oscillator
J10
EXT REF
TRANSMIT
RECEIVE
J16
EXT CLK
J8
IDI
CLOCK
RECOVERY
J19
RT
BUFFER CLK POL
RD
DATA POLARITY
3.7.1 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 following paragraphs define the types of clocking options available to the user at the Front
Panel.
SCT (Internal Oscillator)
SCTE (External Tx Terrestrial Clock)
Rx Satellite Clock
MN-DMD50 Revision 4
HIGH STABILITY
INTERNAL
REF FREQ
SRC
EXTERNAL
SCT CLK
SRC
SCR
NORMAL
INVERTED
EXT IDI
EXT BNC
SCT
BUFFER CLK
SRC
SCTE
RX SAT
INVERT NONE
INV. TERR&BASE
INV. BASEBAND
INV. TERR DATA
Figure 3-7. Clocking and Polarity Diagram
INVERT NONE
INV. TERR&BASE
INV. BASEBAND
INV. TERR DATA
DATA POLARITY
SCTE
Tx CLK
CLK POL
SRC
SCT
NORMAL
INVERTED
AUTO
Theory of Operation
CLOCK &
MODULATION
DATA
CLOCK & DATA
DEMODULATION
RECOVERY
3–11
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