Figure 4-4. Modem Clocks Internally - Comtech EF Data SLM-7650 Installation And Operation Manual

SLM-7650 Satellite Modem
Theory of Operation
4.4.3.3.2.3 Timing Configuration #3: Modem Clocks Internally
Modem Reference clock is either INT, 1, 5, 10, or 20 MHz
TX Clock source = INT
Buffer clock also is using INT
This user is using the internal modem clock (ST) as the system clock (Figure 4-4).
WARNING: This mode is not recommended for operation at higher data rates. The
modulator will be clocking the send data, for transmission to the satellite, with the same
internal oscillator that is providing the timing to the DTE equipment. Installation variations
WARNING
can cause varying delay between the internal SCT and the incoming send data. There will be
data rate verses cable length combinations that will not operate with the normal transmit
clock phase setting. There are setup options to overcome these situations.
1) If Transmit Element Timing from the DTE (TT) is available, use the TX-TERR
2) If TT is not available, use the TX Clock Phase selection to operate in Normal or
User clocks
TT and SD
from ST
RT clocks
in the RD
User
selection for the TX Clock source.
Invert mode. One of these phases will operate properly.
ST
TT
TRANSMIT
RT
Clock
Master
Modem

Figure 4-4. Modem Clocks Internally

Internal
clock
Reference
To TX IF Output
Receive
Buffer
Modem
4–27
Revision 4
MN/SLM7650.IOM
1, 5, 10,
or 20 MHz
detect
From decoder
User