[time-nuts] Some GPS performance plots
phk at phk.freebsd.dk
Wed Nov 3 10:26:42 EST 2004
In message <4188F835.4010700 at febo.com>, "John R. Ackermann N8UR" writes:
>Poul-Henning Kamp wrote:
>> In message <4188F665.5090502 at febo.com>, "John R. Ackermann N8UR" writes:
>>>Nothing sexy here, but in response to some serious confusion on the NTP
>>>mailing list, I put together some plots of the 1pps output from a
>>>Motorola M12+ Timing Oncore versus an Rb standard. It may be helpful if
>>>you want to point people to info about GPS timing capabilities.
>> You're not being fair to the M12+ here. You should correct the timestamp with the
>> "negative sawtooth correction" field from the serial data stream.
>I know, and I should (and will) note to that on the page. Since I'm
>capturing the 1pps output from the receiver and feeding it into a
>counter, I can't apply the sawtooth correction value the way I could if
>I were processing the data in a PC.
As long as you don't miss out on pulses or serial data it is possible to
correct with post-processing. At least I have been able to make it work
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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