Glossary
other corrections which are periodically added to UTC. GPS time was set to match Coordin-
ated Universal Time (UTC) in 1980, but has since diverged. [...]
The GPS navigation message includes the difference between GPS time and UTC, which
as of 2006 is 14 seconds. Receivers subtract this offset from GPS time to calculate UTC and
'local' time. New GPS units may not show the correct UTC time until after receiving the GPS-
UTC Offset message. The GPS-UTC offset field can accommodate 255 leap seconds (eight
bits) which, at the current rate of change of the Earth's rotation, is sufficient to last until the
year 2330.
As opposed to the year, month, and day format of the Julian calendar, the GPS date is
expressed as a week number and a day-of-week number. The week number is transmitted
as a ten-bit field in the C/A and P(Y) navigation messages, and so it becomes zero again
every 1,024 weeks (19.6 years). GPS week zero started at 00:00:00 UTC [...] on January 6,
1980 and the week number became zero again for the first time at 23:59:47 UTC on August
21, 1999 [...]. To determine the current Gregorian date, a GPS receiver must be provided
with the approximate date (to within 3,584 days) to correctly translate the GPS date signal.
To address this concern the modernized GPS navigation messages use a 13-bit field, which
only repeats every 8,192 weeks (157 years), and will not return to zero until near the year
2137."
1
The SyncServer S350i does not include a GPS receiver.
Hardware Clock
The Hardware Clock manages the Input References:
n
Gets the time from the highest priority reference that is available.
n
Applies the UTC offset if the reference is GPS
1
.
n
Passes the time to the NTP daemon.
The NTP daemon includes a preferred server association for the Hardware Clock that can-
not be edited or removed.
Also see TIMING - HW Clock,
NTP - Config
(on page 43), and
Input References
(on page
196).
1
The SyncServer S350i does not include a GPS receiver.
Input References
The SyncServer S350i does not include a GPS receiver,or LF radio.
Input References are timing inputs with connectors on the rear panel of the SyncServer.
These vary by model and include:
n
GPS
n
Timecode (IRIG In)
n
1PPS
n
10MHz
n
LF Radio (Optional)
Page 196
..........................................................................
997-01520-02 Rev. F1
