[ntp:questions] Questions about joining pool.ntp.org
unruh at wormhole.physics.ubc.ca
Wed Aug 31 16:08:03 UTC 2011
On 2011-08-31, Uwe Klein <uwe at klein-habertwedt.de> wrote:
> David J Taylor wrote:
>> How does this square with those who claim 4ns from their GPS devices?
> The defining document is rather old I guess. A lot happened in between.
> ( I looked into GPS in my diploma thesis ~1987 and not much after that )
The GPS sattelites with their onboard clocks, etc are also rather old.
And I do not see how you can get timing accuracies of 2ns when your
positional accuracy is 5m. I Think that that 2ns is someone's
advertising bunf that totally misunderstood the technical arguments and
simply looked through the documents for the smallest time figure they
could find without caring what it referred to. That document I mentioned
talked about a gps receiver in 2003 which claimed 2ns accuracy. And was
hundereds of ns different from a survey grade instrument.
> GPS over time is not a static thing. Space and Ground Segment have
> changed quite a bit. And most everybody today is working from
> the Coarse Aquisition signal only with precission attributed
> initially to the P/Y-Code.
> And notice that most modern receivers have channels galore.
> What happens if you resolve time from a massively overdetermined
> setup? ( today you see and work on 10..16 sats at any time )
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