Comtech EF Data DMD-2050E - Manual (Page 59)

DMD2050E Universal Satellite Modem Theory of Operation
MN-DMD2050E Revision 2 3–17
3.5.3.3 SCT: Serial Clock Transmit
If SCT clock is selected as the RX Buffer clock source, then it should be configured for internal.
SCT is sometimes referred to as Internal Timing or Send Timing (ST).
3.5.3.4 EXT CLK/EXT BNC: External Clock, J16
The External Clock that can be selected as the RX Buffer clock source. This is a 75ohm
unbalanced BNC connector. This clock source is also identified as EXT BNC. The External
Clock is often used as the station master clock. The RX Clock selection can be accessed in the
INTERFACE/RX SETUP menu. The clock frequency, EXT FREQ can be selected, in the
Interface/General Menu.
Clock specification
Frequency 1 MHz to 20 MHz
Level 0.5 Vp-p to 5 Vp-p (Sine or square wave)
3.5.3.5 EXT IDI: Insert Data In
External IDI is used only for E1/T1 Drop and Insert applications. The available T1/E1 Frame
Source selections are External, Internal, and IDI/DDO Loopback. The T1/E1 Frame Source
selections can be accessed in the INTERFACE/RX SETUP menus. If Ext IDI is selected as the
RX Buffer clock, then user must first specify T1/E1 Frame Source.
• External (RX Buffer Clock recovered from the data)
• Internal (RX Buffer Clock recovered from the internal clock)
• IDI/DDO Loopback (RX Buffer Clock recovered from the data and looped back)
3.5.4 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 modem is locked to the external reference, and
the internal accuracy and stability of the unit assumes that of the External Reference. Therefore,
not only are the transmit frequencies locked to the external reference, but the modem’s internal
SCT Oscillator is locked to the external reference as well.
IMPORTANT
The external reference port input is specified as 0 to +6 dBm.