EPSILON CLOCK MODEL EC20S Spectracom
29 User’s Manual
The EC20S automatically selects the synchronization source according to the following criteria:
- Whether the EC20S is set in ‘Forced Holdover’ mode or not (see 13.7.3 Force Holdover),
- Whether a synchronization source is forced (see 13.7.3 Force a source as input),
- Whether the synchronization source is enabled or disabled (see 13.7.3 Priority Level),
- The status of the synchronization source (OK/Alarm, see 13.3.2.3 and 13.3.2.5),
- The priority of the synchronization source (see 13.7.3 Priority Level).
10.2 DISCIPLINING ALGORITHM – SFN CONDITIONS
The algorithm is a phase/frequency locked loop-type disciplining algorithm. The phase measures are
filtered by a Kalman filter.
The status of the disciplining process can be:
• Warming up : Step performed after the power-up during which the internal oscillator is
warming up. The oscillator control is not disciplined.
• Tracking search : Fast oscillator disciplining with coarse adjustment of the oscillator command.
The EC20S is searching best disciplining conditions.
• Locked : Accurate oscillator disciplining with long-time constant filtering until the EC20S
meets the ’Locked’ conditions defined as follows: the 10MHz frequency signals are cycle locked
to the 1PPS synchronization source (10 000 000 cycles from the 10 MHz equals 1PPS period)*
and meets a frequency accuracy better than 10
-9
(∆f/f) and a phase accuracy better than 1µs
(microsecond).
The ’Locked’ conditions are reached after a period depending on:
o Whether the oscillator warming up is complete or not,
o Whether the multi-GNSS synchronization source is ‘Locked’ or not (when this source is
used), this point depending on the reception quality of the GNSS receiver, depending
itself on the environmental conditions of the GNSS antenna location. Refer to the
diagrams in the following paragraphs.
*note: By design, the 10MHz frequency signals are always cycle locked to the 1PPS
synchronization source (10 000 000 cycles from the 10 MHz equals 1PPS period) apart from the
Tracking search periods.
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