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Chapter 3 High Accuracy Timing
Basic timing principles
T-BERD/MTS/SC Timing Expansion Module User Manual
Page 22 22112315, Rev. 004 July 2017
Basic timing principles
The TEM Module is designed to provide a stable, highly accurate timing reference
when performing tests that require:
• The precise synchronization of multiple test instruments;
• High accuracy wander analysis,
• Stable and precise external timing references.
Before configuring the TEM to support testing (by placing the module into Tuning
mode), it is useful to review some basic timing principles as they apply to the TEM.
GNSS timing
The TEM Module supports GNSS systems for satellite constellations that are available
worldwide (GPS and GLOSNASS), and in specific areas of the world (for example,
BeiDou). If they are available, satellites supporting different GNSS systems can be
selected together to be used as a synchronization source and derive timing.
Satellite Based Augmentation Systems
A satellite-based augmentation system (SBAS) is a system that provides additional
satellite-broadcast messages to enhance the availability of GNSS satellites during
surveys conducted in areas with poor satellite visibility. The systems are typically
comprised of multiple ground stations that are precisely positioned to support measure-
ments of the GNSS satellites, signals, and environmental factors that may impact the
quality of the signal received.This information is then sent in messages to the supported
satellites so that the messages can be broadcast to GPS receivers.
When using the TEM Module, SBAS should only be selected with a synchronization
source to optimize the availability satellites during surveys. After completing a survey,
the synchronization source should be reset without SBAS to ensure optimal timing
performance. For details, see
“Survey settings” on page 31 .
GNSS antennas
The TEM Module ships with a GNSS antenna that supports all TEM supported GNSS
systems. You can also use your own antenna; however, you should verify that the
antenna supports the GNSS system(s) that you intend to use as synchronization
sources when tuning the oscillator. For example, if you intend to use BeiDou or
GLONASS as a synchronization source, you cannot use a GPS-only antenna.
Position
The position of supporting GNSS antennas is important when using the TEM Module
to conduct surveys (to generate accurate coordinates) and when maintaining precise
timing from a fixed position.