Scte: Serial Clock Transmit External; Sct: Serial Clock Transmit; Ext Clk: External Clock; Bnc Exc: Bnc External Clock - Radyne DMD20 Installation And Operation Manual

DMD20/DMD20 LBST Universal Satellite Modem

3.6.2 SCTE: Serial Clock Transmit External

This clock is the Transmit Terrestrial Clock associated with the interface. With the G.703
Interface selected, SCTE is the clock that is recovered from the G.703 data stream. SCTE is
sometimes referred to as Tx Terrestrial Timing and for Synchronous Interfaces such as RS-422,
SCTE is sometimes referred to as TT (Terminal Timing).

3.6.3 SCT: Serial Clock Transmit

This clock is an internally generated clock that is output from the modem. The clock is generally
used by the Terrestrial Terminal equipment for clocking the transmit data. The frequency of the
clock is set the same as the Transmit Terrestrial Clock rate if internal is selected, or is the receive
clock from the Demodulator if SCR is selected. SCT is sometimes referred to as Internal Timing
or ST (Send Timing).
3.6.4 EXT CLK: External Clock, J16
This is an independent clock source. This clock is most often used if there is a station master
clock. The EXT EXC can be selected, in the Interface/General Menu, to be None, BNC EXC, or
IDI. IDI is used ONLY for D&I cases where external framing is selected. In this case, the EXT
EXC must be set to IDI where the Receive Buffer Clock is derived from the external Receive T1
or E1 Trunk.
3.6.5 BNC EXC: BNC External Clock, J16
Unbalanced external clock input into a BNC connector. This clock can be used to source the
EXT CLK.
Clock specification:
Frequency:
Level:

3.6.6 IDI: Insert Data In

This clock source is only used as an external frame source selected in D&I Mode. If External
Frame Source is selected, then IDI must be selected for the buffer clock. For this case, a
Receive T1/E1 Trunk is input and a buffer clock is derived.

3.6.7 SCR: Serial Clock Receive

This Receive Clock is recovered from the satellite's receive signal from the satellite. SCR is
sometimes referred to as Receive Clock, Satellite Clock, or as RT (Receive Timing).
3.6.8 EXT REF: External Reference, Top BNC Port, J10
This is not actually a clock, but does have some clocking implications. When the external
reference is used, the master oscillator within the DMD20 is locked to the external reference, and
the internal accuracy and stability of the DMD20 assumes that of the External Reference.
Therefore, not only are the transmit frequencies of the DMD20 locked to the external reference,
but the modem's internal SCT Oscillator is locked to the external reference as well.
TM103 – Rev. 2.5
1 MHz to 20 MHz
0.5 Vp-p to 5 Vp-p
Theory of Operation
3-11