Chapter 3
High Accuracy Timing
Forcing the oscillator into holdover mode
T-BERD/MTS/SC Timing Expansion Module User Manual
July 2017
22112315, Rev. 004
Page 35
Tuning to an external reference clock or signal
If you are using an external 1 PPS or 10 MHz reference signal as the synchronization
source, you must provide the signal to the TEM Module via the appropriate input
connector on the module’s connector panel (see
“Exploring the TEM Module connector
).
•
An external 1 PPS reference signal must be provided via the SMB connector
labeled “1 PPS IN 1.”
•
An external 10 MHz reference signal must be provided via the SMB connector
labeled “10 MHz REF IN.”
If you are using an external BITS/SETS reference clock as the synchronization source,
the signal must be provided via EXT CLK connector on the 5800v2 connector panel.
After connecting the cable with the input reference clock or signal, the oscillator will
begin to tune to the synchronization source. You can observe time-stamped events
associated with the tuning process in the Event log (see
of
Chapter 5 “Timing and 1 PPS Analysis Results”
).
Tuning to the internal GNSS receiver
If you are using the internal GNSS receiver as the synchronization source, in addition
to oscillator and timing settings, you must specify:
•
GNSS settings (see
“Specifying GNSS settings” on page 30
)
•
Location settings (
“Specifying location settings” on page 31
If you are conducting a survey to obtain GNSS coordinates, you must then intentionally
start the survey (see
“Surveying GNSS constellations” on page 34
). A survey is not
necessary if the TEM Module already has accurate coordinates and the instrument will
remain in a fixed position.
After the TEM Module’s GNSS receiver receives valid GNSS time information from the
surveyed satellites, the green GNSS Time LED will illuminate, and the oscillator will
begin to tune to the signal(s) provided.
Forcing the oscillator into holdover mode
The rubidium oscillator can be manually forced into holdover mode. Although it can be
forced into holdover mode when it is coarsely tuned, it is strongly recommended that
you wait until the oscillator has reached at least an intermediate tune, which indicates
that it has been tuned for a sufficient period of time to support accuracy in holdover
