[time] GPS Time Server Survey

Björn Gabrielsson bg
Thu Apr 24 20:44:41 UTC 2008

Hi Jan,

On Thu, 2008-04-24 at 21:37 +0200, Jan Hoevers wrote:
> Kipton Moravec wrote on 24-4-2008 18:14:
> > 1. A GPS module with the ability to expand the serial port to more than
> > 10 to allow you to use the NTP NEMA driver. The time pulse would be
> > accurate to about 30 nS RMS. Retail cost about $100.
> Quite unlikely, since the GPS system itself does not have 30 ns
> accuracy.  That kind of accuracy is meaningless for pool server
> operators anyhow.  They typically do not own cesium clocks and the
> regular pc oscillator is not stable enough to maintain that kind of
> accuracy.

I agree with your conclusion that 30ns is meaningless for NTP use.

However why do you say the GPS system itself does not have 30ns

The signal in space (SIS) accuracy quoted for the current constellation
is between 1 and 2 meters, which is well below 10ns. 



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