more accurate timing, over extended durations upon the loss of GPS input. For
instance, a Rubidium oscillator will maintain 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 temperature remains stable.
This data can help you determine how long of a Holdover period can be tol-
erated, based on how much time drift may occur after GPS input is lost. The lar-
ger the time error that can be tolerated 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 avail-
able)
TCXO OCXO
Low Phase
Noise OCXO
Rubidium
Low Phase Noise
Rubidium
After 4 hours 12 μs 1μs 0.5 μs 0.2 μs 0.2 μs
After 24 hours 450 μs 25 μs 10 μs 1μs 1μs
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
3.4 Holdover Mode
CHAPTER 3 • SecureSync 2400 User Manual Rev. 5.2
249
To Next Page
Loading...
