Q-Lite Satellite Modem Installation and Operating Handbook
7-3
Modem Tx
Data Interface
FIFO
DDS
PLL
VCXO
TCXO
Tx Data Tx Clock (TT) Internal Tx Clock (ST)
Figure 7-2 External Tx Clock Mode
7.1.1.3 Receive Reference
When
Receive Reference
is selected, it allows the modem to provide an ST clock to the
DTE that is locked to the receive satellite signal. The timing is actually phase locked to
the Rx data rate but at the frequency of the Tx data rate. This is to allow asymmetric
operation. The DTE then synchronises the data going into the modem (SD) to this clock.
If the external clock is missing for any reason then the modem will substitute an internal
clock.
Modem Tx
Data Interface
FIFO
DDS
PLL
VCXO
VCXO
Tx Data Tx Clock (TT) Internal Tx Clock (ST)
PLL
Rx Clk
Figure 7-3 Receive Reference Tx Clock Mode
