Spectracom VelaSync 1225, User Manual

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duration than a TCXO oscillator (TCXOs are considerably less stable than a Rb oscil-
lator).
Oscillator Phase Drift
The chart below provides typical stability performance for the oscillator types that can
be found in VelaSync 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 temperature 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 tolerated by VelaSync clients, based on the oscillator installed, the larger the Hol-
dover 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 VelaSync, 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
3.3 Managing References
CHAPTER
3
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