Re: [amsat-bb] Time references (UT vs. GPS) Whoa, there!

[Phil Karn <karn@xxxxxxxx>]

Wayne Day wrote:

> So while there IS a 13-second difference between the "GPS time" and 
> UTC, users shouldn't see the difference because the receiver has been 
> told to adjust for the offset.  Which begs the question why Laura is 
> seeing the offset.

Many/most OEM GPS receivers (i.e., those intended for inclusion in some 
larger system, as opposed to direct consumer use) give you a choice 
between GPS and UTC. The receiver can apply the UTC correction or not, 
your choice. Consumer receivers generally apply the correction and 
display UTC.

The GPS timescale is used in some applications where leap seconds would 
cause problems. An example is CDMA digital cellular. Each base station 
has a GPS receiver, and all carrier frequencies, spreading codes, frame 
times, etc are synchronized to it. If a leap second was allowed to 
occur, there would be a "hiccup" in service as all the base stations 
suddenly jumped a second in time and the tracking loops settled down 
again. Using the GPS timescale neatly avoids this problem.

The GPS-UTC difference is broadcast by the base stations to the mobiles 
so the clocks displayed on the phones will be correct.

Phil

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