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Operation
3.3.3
Configuration Interface
Refer to Figure 3-6.
TX CLOCK SOURCE
TX CLOCK PHASE
EXT-CLK FREQ
3–18
Programs the clock source for the modem transmitter clock to the
following configurations:
•
TX TERRESTRIAL: Sets the TX clock to recover timing
from the incoming clock/data.
•
SCT (INTERNAL): Sets the TX clock to operate from the
modem internal clock (this is also the fallback clock).
Note: When loop timing is enabled, SCT (LOOP) is
displayed instead of SCT (INTERNAL).
•
EXT. CLOCK: Sets the TX clock to operate from the
external reference clock. Transmit Clock source must be
phase/frequency locked to the data that is being transmitted.
The correct frequency must be programmed into EXT-CLK
FREQ.
Upon entry, the current transmit clock setting is displayed. Press [↑] or
[↓] to make the selection. Press [ENTER] to execute the change.
Programs the TX clock phase to AUTO, NORMAL, or INVERT.
Upon entry, the current setting of the TX clock phase is displayed.
Press [↑] or [↓] to make the selection. When AUTO is selected, the
modem will automatically select NORMAL or INVERT to properly
phase the TX clock with the TX data. Press [ENTER] to execute the
change.
Programs the external reference clock input frequency between
8.0 kHz and 10.0 MHz.
Note: The clock rate must be equal to the data rate unless the
asymmetrical loop timing option is present.
This clock frequency can be any multiple of 600 Hz from 2.4 to
64 kHz, and can be any multiple of 8 kHz from 64 kHz to 4.376 MHz.
This can be used for the Doppler/plesiochronous buffer reference. It
can be a reference to SCT.
Use the master clock input on J8 for the external master reference. The
external reference on CP3 only allows for 1, 5, 10, and 20 MHz
external reference input.
Upon entry, the current setting for the external reference is displayed.
Press [←] or [→] to increment or decrement the digit at the flashing
cursor. Press [ENTER] to execute the change.
SDM-300A Satellite Modem
Rev. 4
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