Re: Fixed-location GPS mode?
- From: Terje Mathisen <terje.mathisen@xxxxxxxxxxxxx>
- Date: Tue, 06 Jun 2006 11:09:01 +0200
Tom Van Baak wrote:
The GPS 18 LVC doesn't have a zero-D mode. However
it is a very nice, compact, easy-to-interface, GPS timing
receiver with a 1 us 1 PPS accuracy spec.
Although this makes it a poor choice for work with atomic
clocks it should be more than enough for NTP, yes?
It is very useful indeed, and at less than $100 for a complete NTP server (assuming you can locate any kind of spare PC at all, a 1995-model Pentium is fine) probably the best value NTP Stratum 1 clock available.
Recent GPS 18 LVC measurements I made showed it
much better than spec; a couple hundred ns peak to
peak and just 80 ns RMS for the 1 PPS output.
Thanks! That's very interesting, and sort of confirms what I've suspected for some years:
Since a working 3 m GPS PVT solution requires ~10 ns time, it really shouldn't be too hard to output the PPS signal within an order of magnitude of this. Giving away two decades (to ~1 us) seems sort of excessive, right?
Yeah, I do know that GPS systems like my Motorola Oncore UT+ has to slave the PPS pulse to an internal 10 MHz (free-running) osc, limiting absolute precision to +/- 50 ns (before the sw sawtooth correction term), but that would still indicate 100 ns as a (cheap) reachable target.
Terje
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- <Terje.Mathisen@xxxxxxxxxxxxx>
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