External Gnss Receiver (Gm) - Safran WR-Z16 User Manual

5.2 General Timing Management
Here, Atomic Clocks means that a very stable oscillator based on hyperfine trans-
ition (e.g, Caesium) that provides very low daily uncertainties (e.g., 1 ns/day) is
combined with a GNSS receiver to remove its slow drift using averaging meth-
ods. For telecom, this combination is also known as ePRTC and typically provides
a UTC representation accurate within 10 ns or less. Moreover, in order to guar-
antee the best timing performance (phase noise & determinism) the automatic
alignment of the PPS output onto the PPS input has been disabled.
5.2.1.3

External GNSS Receiver (GM)

Web GUI selection: GM: ext GNSS
It is recommended to use this preset when a third-party GNSS is providing the ref-
erence to the Grand-Master device. This preset will also ensure the automatic
alignment of the PPS input to the PPS output after each time the GNSS locked
itself.
60
Caution:
10 MHz + PPS signal calibration: When using this preset, the
PPS must always keep the same delay in respect to the 10 MHz sig-
nal. The user can use the GM Offset field to compensate this fixed
delay.
The primary timing source is provided using an external GNSS receiver ref-
erence through the front-panel 10 MHz and 1PPS inputs (Grand-Master).
All SFP ports (i.e., wr0-wr1) are configured as WR masters.
Clock accuracy is announced below or equal to 100 nanoseconds.
Alignment of PPS_in VS PPS_out is done automatically (adding ~50ps of
uncertainties).
PPS_in is mandatory to announce a valid time.
Caution:
GNSS PPS output: The GM can lock to the PPS from the
GNSS receiver before GNSS signal locked (before its 10MHz are
locked in phase to its PPS). This causes a jump in the time reference.
To avoid this situation, the user should configure the GNSS to not out-
put any PPS before locking to GNSS signals.
CHAPTER •
5 WR-Z16 User Manual Rev. v5.0