J170 Owner Posted December 13, 2011 Share Posted December 13, 2011 I own a Garmin Nuvi GPS that is just fine in off-road mode when flying. I'm curious, is the clock in a GPS updated to GPS time when it receives a signal? Are you aware that GPS time is currently ahead of UTC by some 13 seconds? 1 Link to comment Share on other sites More sharing options...
petetheprinta Posted December 13, 2011 Share Posted December 13, 2011 Hopefully this answers your question :- GPS time is given by its Composite Clock (CC). The CC or "paper" clock consists of all Monitor Station and satellite operational frequency standards. The system was previously referenced to one of the Monitor Station's operational frequency standards and switched from one station to another as needed. The GPS epoch is 0000 UT (midnight) on January 6, 1980. GPS time is not adjusted and therefore is offset from UTC by an integer number of seconds, due to the insertion of leap seconds. The number remains constant until the next leap second occurs. This offset is also given in the navigation (NAV) message and your receiver should apply the correction automatically. As of January 1, 2006, GPS time is ahead of UTC by fourteen (14) seconds. Your Nuvi is prehistoric in GPS terms and is not able to read/understand Nav message and therefore does not self correct. Buy a current aviation GPS if 14 secs is a worry for you. (now it just so happens I have for sale...) Link to comment Share on other sites More sharing options...
J170 Owner Posted December 13, 2011 Author Share Posted December 13, 2011 Hopefully this answers your question :-GPS time is given by its Composite Clock (CC). The CC or "paper" clock consists of all Monitor Station and satellite operational frequency standards. The system was previously referenced to one of the Monitor Station's operational frequency standards and switched from one station to another as needed. The GPS epoch is 0000 UT (midnight) on January 6, 1980. GPS time is not adjusted and therefore is offset from UTC by an integer number of seconds, due to the insertion of leap seconds. The number remains constant until the next leap second occurs. This offset is also given in the navigation (NAV) message and your receiver should apply the correction automatically. As of January 1, 2006, GPS time is ahead of UTC by fourteen (14) seconds. Your Nuvi is prehistoric in GPS terms and is not able to read/understand Nav message and therefore does not self correct. Buy a current aviation GPS if 14 secs is a worry for you. (now it just so happens I have for sale...) Did we do the same GPS course? How come you know these things? I'm the clever techno-babble person here. I have just worked out why some data I have wouldn't line up with some other data collected at the same time. One was referenced to UTC and the other to GPS. (I have that headset in my car) Link to comment Share on other sites More sharing options...
petetheprinta Posted December 13, 2011 Share Posted December 13, 2011 Thanks Kev, I will catch up with you soon and pick up. Link to comment Share on other sites More sharing options...
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