Transmit Timing; Ext Clk As Tx Clock Source (Rs-422 Or V.35 Interface); Sct Or Scte; Interface - Radyne DMD20 Installation And Operation Manual

Theory of Operation DMD20/DMD20 LBST Universal Satellite Modem
External reference port input is specified at 0 to +6 dBm.

3.7 Transmit Timing

As shown in Figure 3-7, Transmit Terrestrial Data enters the modem and is clocked into a dejitter
FIFO. Data is clocked out of the FIFO by the Modulator Clock. The Modulator Clock and Phase-
Locked Loop (PLL), in conjunction with the Dejitter FIFO, reduces the input jitter. Jitter reduction
exceeds the jitter transfer specified in CCITT G.821.

3.7.1 EXT CLK as TX Clock Source (RS-422 or V.35 Interface)

Data must be clocked into the modem by either the SCTE or SCT Source. If SCTE is selected as
the Tx Clock Source, then SCTE must be supplied to the modem on the EIA-530 port. The output
of the dejitter buffer will be clocked with this source. SCT should be used if SCTE has excessive
jitter.

3.7.2 SCT or SCTE

If SCT is selected, then only data that is synchronous to the SCT Clock is required to be supplied
to the modem. It is intended for the terminal equipment to use the SCT as its clock source. The
Autophase Circuit will automatically ensure that the data is clocked correctly into the modem.
Therefore, a return clock is not necessary. The Clock Polarity should be set to Auto.
If SCTE is selected, then SCTE must be supplied to the modem. The Clock Polarity should be
set to AUTO.
3.7.3 G.703 Interface
If the G.703 Interface is selected, then the Tx Clock Source will default to SCTE and the Clock
Polarity will default to Auto.

3.7.4 Ethernet Data Interface (Optional)

If the Ethernet Data Interface is selected, then the Tx Clock Source will default to SCTE and the
Clock Polarity will default to Normal.

3.8 Receive Timing

Any of the clocking selections, SCTE, SCT, EXT CLK, Ext IDI, or RxSat (SCR) may be selected
as the Buffer Clock. Data will be clocked out of the buffer at the data rate synchronous to the
selected clock source.
3-12 TM103 - Rev. 2.5