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On Thu, 8 Jan 2004 10:49:09 -0800, Chuck Taylor wrote:

>--- Rodney Myrvaagnes wrote:
>
>> A GPS that couldn't tell leap seconds couldn't
>> function at all.
>
>I beg to differ.  So long as the satellite and the
>receiver agree on the presence or absence of leap
>seconds, the system works fine.
>
>Each satellite has its own atomic clock, which starts
>running before it is launched.  Any time adjustments
>due to leap seconds that occur after the launch date
>are taken care of in software.

The only information the receiver has is in the low-bandwidth data
stream, including ephemeris, which it gets from the locked in
satellites. Where else will it get the leap second if not from the sat?

The issue I was
>referring to is that the software in some older GPS
>receivers does not handle those adjustments correctly
>when it displays the time.  There is no problem (due
>to leap seconds) in determining position, only in
>displaying the correct time.
>

If I understand you correctly, the internal time is correct, but the
display is permanently off by as many leap seconds as have passed since
the receiver was manufactured?  When a receiver is so disabled, what
does it do when it has been turned off for months, or carried a long
distance, so it has to reacquire the ephemeris from scratch? Has anyone
ever seen a GPS showing that problem?

I can see this getting OT, but I am really curious about this.

I suppose if the user were aware of such a condition, he could still
use it as a chronometer, with separate knowledge of leap seconds. In
that sense only, it wouldn't be as bad as the problem I raised, where
the screen-writing delay may not even be consistent.



Rodney Myrvaagnes             NYC                                J36 Gjo/a

"Religious wisdom is to wisdom as military music is to music."

   

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