Chapter 3
High Accuracy Timing
Basic timing principles
T-BERD/MTS/SC Timing Expansion Module User Manual
July 2017
22112315, Rev. 004
Page 25
) and perform a short survey to generate accurate coordinates (see
GNSS constellations” on page 34
).
External 1 PPS and 10 MHz timing
The TEM Module allows you to synchronize timing to an external 1 PPS reference
signal (provided via the SMB connector labeled 1 PPS IN 1) or a 10 MHz reference
signal (provided via the SMB connector labeled 10 MHz REF IN). After tuning the TEM
Module’s rubidium oscillator to the external signal’s frequency, you can use your test
instrument to:
•
Perform tests using 1 PPS or 10 MHz timing (provided by the oscillator on the
TEM Module).
•
Provide an external 1 PPS or 10 MHz reference to another instrument using the
corresponding 1 PPS OUT or 10 MHz OUT connector on the TEM.
•
Verify the accuracy of the TEM Module in holdover mode in a lab by connecting
either the 1 PPS OUT or the 10 MHz OUT connector to a more accurate clock (for
example, a clock in the laboratory that is directly connected to a GNSS system, or
a clock that has a Cesium oscillator).
External BITS/SETS timing
The TEM Module allows you to synchronize timing to an external BITS/SETS reference
signal (for example, a BITS/SETS signal from another device in a central office) via the
EXT CLK connector on the 5800v2 test instrument. After tuning the TEM Module’s
rubidium oscillator to the external signal’s frequency, you can use your test instrument
to perform tests.
Holdover mode
After the TEM Module’s rubidium oscillator warms up and is tuned to the frequency of
the synchronization source, you can force it into holdover mode, allowing the TEM to
use the oscillator as a stable timing reference for a period of time during testing. After
you force the oscillator into holdover mode, the signal from which synchronization was
obtained can be disconnected without adversely impacting tuning.
The TEM’s oscillator is also automatically placed into holdover mode whenever you
place the TEM into 1PPS Analysis mode. For details, refer to
NOTE:
The TEM Module provides the highest degree of accuracy and stability when
it is operated with a connected GNSS antenna and with an accurate
Antenna Time Bias setting and in fixed timing mode; this is especially import-
ant for absolute time or phase based measurements.
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