[ntp:questions] site with lots of GPS's and accessories

unruh unruh at invalid.ca
Mon Mar 19 16:12:56 UTC 2012


On 2012-03-19, Alby VA <albyva at empire.org> wrote:
> On Mar 19, 2:45?am, unruh <un... at invalid.ca> wrote:
>> On 2012-03-19, David J Taylor <david-tay... at blueyonder.co.uk.invalid> wrote:
>>
>>
>>
>>
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>> >> Hi all,
>>
>> >> I was doing some GPS research and found this site with lots of GPS's and
>> >> accessories. ?Just thought I'd pass it along.
>>
>> >>http://www.gpssensors.com/
>>
>> >> I don't know which ones are timing GPS's.
>>
>> >> Sincerely,
>>
>> >> Ron
>>
>> > Ron,
>>
>> > The one I recognise as being a timing GPS with PPS and suitable for NTP is
>> > one which isn't one that page, but here:
>>
>> > ?https://www.starlite-intl.com/Detail.asp?pid=2320
>>
>> > Same company. ?US $61
>>
>> Certainly the 18xLVC has a PPS pulse, as does the 18x-5 OEM which is a
>> 5PPS. It give about 1us accuracy, not 10ns which is what some might call
>> timeing GPS. But that 1ns is pretty useless for computer timing, since a
>> computer really cannot use better than about 1us accuracy.
>
>
>
>  I'm getting 1us accuracy from my Sure GPS once I did the proper Mods
> per David Taylor's notes.

As per my comment. The interrupt processing/clock reading  time on a PC is of the order
of 1us.
Note that on the Sure, the process of converting to an RS232 signal
means that the PPS signal is of the order of 1us accuracy ( the signal
processors are not the worlds fastests chips)
The actual PPS signal at the PPS pin has a rise time of about 10ns, and
the Sure has a normal sawtooth timing signal, so that would indicate a
few 10s of ns accuracy from the Sure, but the conversion to RS232 washes
that out (and the interrupt processing time on your computer washes that
out as well).


>
> URL: http://godzilla.empire.org
>
>
> assID=0 status=0415 leap_none, sync_uhf_clock, 1 event,
> event_clock_reset,
> version="ntpd 4.2.6p5 at 1.2349-o Mon Feb 20 22:00:33 UTC 2012 (1)",
> processor="amd64", system="FreeBSD/9.0-RELEASE", leap=00, stratum=1,
> precision=-19, rootdelay=0.000, rootdisp=0.401, refid=PPS,
> reftime=d311cdf2.ee1ec49a  Mon, Mar 19 2012 11:23:30.930,
> clock=d311cdfe.0179ea2d  Mon, Mar 19 2012 11:23:42.005, peer=21829,
> tc=4, mintc=3, offset=0.000, frequency=-24.622, sys_jitter=0.002,
> clk_jitter=0.002, clk_wander=0.001
>
>
>



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