> Olin Lathrop wrote:
>> A more modern approach would be to make a frequency counter gated by the
>> 1Hz signal from a GPS. GPS satellites have their own atomic clocks, so
>> GPS time is also highly accurate. I don't know about short term accuracy
>> though as exported by common GPS receivers.  You'd probably want to
>> observe the target frequency over some time period with the GPS-gated
>> frequency counter.
>
> Generic GPS receiver modules can easily put out a 1 PPS signal that's
> accurate to +/- 500 ns relative to absolute time, and +/- 50 ns is readily
> available with special operating modes. This means that the short-term
> accuracy is better than 1 PPM, and the long-term averaged result can be
> much better than this. With care, you can begin to approach the 1e-14
> accuracy of the Cesium standards themselves, using a good quartz or
> rubidium local oscillator for short-term stability -- and the ability to
> ride through any GPS outages.
>
> I once used GPS-disciplined oscillators as a reference for aligning FM
> broadcast simulcast systems (connected by T1 telephone lines with variable
> latencies) to +/- 1 us overall, and it worked just fine.
>
> As it happens, I'm right now in the middle of building a demonstration
> network time server (SNTP, TIME and DAYTIME protocols) based on a Motorola
> Oncore UT GPS receiver module and the new W7100 Ethernet chip from WIZnet.
> It's a sweet little setup.

For me the definitive GPS disciplined oscillator project is at 
http://www.rt66.com/~shera/ which seems to be simple to make. One of my long 
term projects.

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