User's Manual

ISO 9001:2000 Cert. N°4500/1
Version 1.1 SDT_ARK6_User_Manual_ENG_vATSC Page 94 of 206
5.12.1 Holdover Management
The ARK6 includes a holdover function provided by a higher grade Oven-Controlled Crystal Oscillator.
Figure 40. Holdover Management
The ARK6 is equipped with an internal OCXO for improved phase noise and stability. The system is
provided with internal 10MHz and 1PPS signals which are disciplined to the GPS time signal or to the
10MHz and 1PPS external references. The stability of internal frequency and phase is assured by the
highly stable OCXO. If the satellites signal, from the GPS receiver, or the external reference sources are
completely lost, the Holdover mode enables the unit to keep working with internal 10MHz and 1PPS for
the duration of the Holdover Timeout, with very low drift over time. If the timeout period elapses prior
to regain the lock of the selected clock reference source and the Holdover function is enabled, the alarm
“Holdover” is raised.
Depending on the conditions, the Holdover function can work in one of the following state:
1. Holdover OFF
 Condition 1: the clock reference is changed and the OCXO is not locked yet.
 Condition 2: the input clock reference is not present.
 Associated event: “Holdover OFF”-
2. SFN Ready
 Condition: the OCXO is locked to the selected frequency reference and the
system is waiting for the OCXO stabilization.
 Associated event: “Holdover SFN Ready”.
3. Holdover Ready
 Condition 1: the OCXO is stable and the Holdover function is now available.
 Condition 2: the system quit the Holdover mode because the OCXO regain the
lock to the selected clock reference.
 Associated event: “Holdover Ready”.