[ntp:questions] Sure Electronics GPS board: Amazing performance. :-)

Chris Albertson albertson.chris at gmail.com
Fri Apr 1 16:57:42 UTC 2011

On Thu, Mar 31, 2011 at 11:03 PM, Terje Mathisen <"terje.mathisen at
tmsw.no"@ntp.org> wrote:

> I don't think any GPS comes even close to 2 ns, given that the entire GPS
> constellation is only required to be within 14 ns or so of UTC.

First off this is a "timing gps".  That means the receiver "knows" the
antenna is not moving and is fixed to a surveyed location..
I think if the receiver does not meet their specs you could ask for a
refund.  They do place that 2ns spec near the top of their data sheet.

I think they do two things
1) The error is predictable, one of the outputs from the device is an
error prediction that looks like a sawtooth function if you plot it.
The 2ns only applies if yo use the error prediction.
2) One can get much better than even 2ns if you average many seconds of signal.

OK, I think I may have confused two email lists.  This one is for NTP
where most people don't need even microsecond accuracy.  But other do
use GPS for calibrating lab instruments and are needing oscillators
with error at the 10E-10 or even better level.

Chris Albertson
Redondo Beach, California

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