Comtech EF Data CDM-600L, Инструкция по установке и эксплуатации

Страница: 63 / 206

CDM-600L Satellite Modem Revision 0
Front Panel Operation MN/CDM600L.IOM
6–17
CONFIG: CLOCKS: TX CLOCK
Select from the choices shown in the parentheses using the [
↑
] [
↓
] arrow keys, then press
ENTER.
•
INTERNAL (SCT) indicates that the unit will supply a clock to the DTE, which
is derived from its internal high-stability source. This is the required setting when
the TX interface type is Audio.
•
TX-TERRESTRIAL (TT) indicates that the unit expects to receive a clock from
the DTE, to which the unit can phase-lock its internal circuits. If no clock is
detected the modem will substitute its internal clock and generate an alarm. This
is the required setting when the modem’s interface type is G.703.
•
RX-LOOP will allow the modem’s internal clock to be phase locked to the RX
buffer clock source. This output clock is Send Timing. Choosing RX-LOOP will
not automatically select RX-SAT as the buffer clock source. This allows for
increased flexibility for modem clock selection. Normally the user will select
RX-SAT but the other choices also are available.
•
EXTERNAL REFERENCE indicates that an unbalanced high-stability source is
expected at the J9 BNC connector, or a balanced version at the P3A connector.
The frequency must match that programmed in the CONFIG, CLOCKS,
EXTERNAL REFERENCE menu, and
must be equal to the transmit data
rate .
TRANSMIT CLOCK = INTERNAL(SCT)
(INT(SCT),TX-TERR(TT),RX-LOOP,EXT-REF)
Example: The user has an available high stability 10 MHz clock source but the
end equipment will only accept a clock at the information data rate. Selecting TX
Clock = RX-LOOP and RX buffer clock as EXT-REF will provide receive timing
and send timing to the end equipment that is sourced from the 10 MHz
reference.