Martyn Smith wrote:
Hello,
I have been asked a question from a friend and would like to hear what
the
time-nuts have to say about the M12+ and M12M GPS receivers.
His questions were:
1) It would be great if you could outline the broad algorithm and bits of
information that go into keeping the 1 pps aligned to UTC. I want to be
able to can ensure that we're at least aware of all the subtle effects
(such
as illustrated in the next question).
2) along with the gps time signal, information is broadcast to relate gps
time to utc. whenever there's a step change in these corrections (such
as on
midnight 31/12/2008), how does the unit react?
2.1) in particular, how quickly does the time code reflect the change,
and is the 1pps affected in any way?
Time-Nuts. Any help on these two questions would be appreciated
Steve Jones
Your friend should download the manual from the Synergy-GPS website.
http://www.synergy-gps.com/
Page 114 of the M12+ Timing receiver manual says:
LEAP SECOND STATUS MESSAGE (@@Bj)
Applicability: M12+ Timing and Positioning Receivers
This message polls the receiver for current leap second status
information that has
been decoded from the Navigation Data message received from the GPS
satellites.
The data sent back by the receiver provides specific date and time
information
pertaining to any future leap second addition or subtraction.
Leap seconds are occasionally inserted in UTC and generally occur on
midnight
UTC June 30th or midnight UTC December 31st. The GPS control segment
typically
notifies GPS users of pending leap second insertions to UTC several
weeks before
the event.
When a leap second is inserted, the time of day will show a value of
'60' in the
seconds field. When a leap second is removed, the date will roll over at
58 seconds.
The 'current UTC offset' will be zero if the receiver is set up to run
in GPS time mode
instead of UTC.
Default mode: Polled
Legacy Compatibility: The @@Bj message was used in an identical manner
in virtually
all Motorola receivers.
--- Graham
==
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