Comtech EF Data OM20 User Manual
Page 52
OM20 Universal Outdoor Modem
OM20 Theory of Operation
MN-OM20– Revision 5
4–14
SCT (Internal Oscillator)
EXC Clock/EXT BNC (External Clock Source)
EXT IDI (Drop and Insert)
The modem handles RX Buffer clock selections based on source priority levels. The user assigns
priorities to the clock sources based on source selections. Source 1 has the highest priority and
Source 5 being the last resort or lowest priority. If a fallback clock is selected and activity is lost
at the highest priority source, the modem will fall back to the next highest priority clock with
activity. When activity resumes on a higher priority source, the modem resumes using the higher
priority source
Clock Source
Priority
SCT
3
of
5
RX SAT
1
of
5
SCTE
2
of
5
EXC BNC
4
of
5
Not Supported in the OM20
EXT IDI
5
of
5
Refer to the Remote Protocol Manual TM117 for Web Browser manual TM117.
4.7.2.1 RX SAT Clock
The RX Sat clock is recovered from the satellite that is received from the distant end. If selected the Buffer
Clock is lock to the RX sat clock.
4.7.2.2 SCTE: Serial Clock Transmit External
When SCTE is selected as the Rx Buffer clock, the modem receives the clock from the Transmit
Terrestrial interface.
4.7.2.3 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).
4.7.2.4 EXT CLK/EXT BNC:
The External Clock connector is not supported in the OM20.
4.7.2.5 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)