Chapter 3
High Accuracy Timing
Basic timing principles
T-BERD/MTS/SC Timing Expansion Module User Manual
Page 24
22112315, Rev. 004
July 2017
Fixed position mode
If the values that the TEM Module’s GNSS receiver currently has in memory for position
and altitude are correct and your instrument will remain in the same location, you do not
need to conduct a survey. You can simply verify the fixed position accuracy, latitude,
longitude, and altitude, then select the
Position Fixed
action button provided on the
Location tab. In this mode, precise timing can be maintained using the signal received
from a single satellite.
Receiver modes
When you configure the TEM Module to use GNSS timing as the synchronization
source, the GNSS receiver goes into one of the following receiver modes, which vary
depending on 1) the Survey Mode that you specified, and 2) the information that the
receiver already has. Messages will appear above the LED panel informing you of the
current mode. The receiver may be:
•
Searching for satellites,
•
Collecting or renewing an almanac of information concerning a satellite constella-
tion (which is broadcast by every satellite within the constellation),
•
Receiving detailed ephemeris data from one or more satellites,
•
Calculating the position and timing information using the provided satellite data, or
•
Using position information that it already has, and is providing timing information
without continually recomputing position coordinates.
After the receiver locates satellites that satisfy the criteria that you specified when you
configured the module, an illustration of the satellites and their status (no
signal, signal, ready, or used) is provided in the Satellites Sky Plot results category.
For details, see
of this manual.
Resynchronizing GNSS time
If you are conducting tests indoors and the oscillator was initially tuned using GNSS,
you can periodically resynchronize the oscillator to GNSS by 1) taking the instrument
with a connected GNSS antenna to an outside area with a clear view of open sky, 2)
obtaining an updated position fix, 3) releasing holdover mode, and then 4) letting the
oscillator resynchronize for a short period of time (for example, five to 15 minutes). This
realigns the oscillator with UTC time (as indicated in the Time Results category). After
resynchronization, the oscillator can be placed back into holdover mode, and testing
may resume indoors.
If you are resynchronizing to GNSS time from a new location, for optimal synchroniza-
tion you may need to modify the antenna time bias (see
