the longer SecureSync runs in Holdover, the larger the offset to true UTC time will become,
because the undisciplined oscillator will drift over time:
The better the type of oscillator installed, the more stable it is while in Holdover and therefore,
the less its time will drift away from true UTC time. This results in more accurate timing, over
extended durations upon the loss of GPS input. For instance, a Rubidium oscillator will main-
tain significantly better time over a longer Holdover duration than a TCXO oscillator (TCXOs
are considerably less stable than a Rb oscillator).
Oscillator Phase Drift
The chart below provides typical stability performance for the oscillator types that can be found
in SecureSync 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 SecureSync 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 SecureSync, 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
212
CHAPTER 3 • SecureSync User Reference Guide Rev. 26
3.4 Holdover Mode
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