Oscillator Phase Drift
The chart below provides typical stability performance for the oscillator types that can be found
in VersaSync units. These numbers are based on the oscillator being locked to a reference for
two weeks, but then loses GPS reception for an extended period of time, while the ambient tem-
perature remains stable.
This data can help you determine how long of a Holdover period can be tolerated, based on
how much time drift may occur after GPS input is lost. The larger the time error that can be tol-
erated by VersaSync clients, based on the oscillator installed, the larger the Holdover timeout
period can be set to.
Table 3-3:
Estimated Phase Drifts
1PPS Phase Drift in Holdover
(no reference available)
OCXO
OCXO
(high performance)
CSAC
- 4 hours
3 µs 2.8 µs 1µs
- 24 hours 40 µs 30 µs 7 µs
- 7 days 1.2 ms 0.6 ms 100 µs
To find out which type of oscillator is installed in your VersaSync, navigate to MANAGEMENT
> OTHER: Disciplining, and look for the line item Oscillator Type in the Status panel.
Typical Holdover lengths
The length of the allowed Holdover Timeout period is displayed and configured in seconds.
The table below provides example conversions for typically desired Holdover periods.
Table 3-4:
Typical Holdover lengths in seconds
Desired Holdover Length Holdover Length (in seconds) to be entered
2 hours 7200 seconds (default value)
24 hours 86 400
7 days 604 800
30 days 2 419 200
1 year 29 030 400
Note: Due to Leap Seconds that are periodically inserted into the UTC and Local
timescales, it is not normally recommended to exceed 30 days of Holdover
without an external reference that can supply Leap Second information being
applied (such as GNSS).
Configuring a Holdover value exceeding 30 days could result in a one-second time error in the
UTC or Local timescales until an external reference (GNSS or IRIG input) is restored or a
170
CHAPTER 3 • VersaSync User Manual Rev. 6.0
3.3 Managing References
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