[time-nuts] simple, cheap clock for the local LAN

Ralph Smith ralph at ralphsmith.org
Mon Apr 5 12:38:36 EDT 2010

On Apr 5, 2010, at 9:47 AM, Eugen Leitl wrote:

> Hi, 
> I'm thinking about putting a local clock standard (nothing too fancy,
> quartz would probably do) for the local LAN so that I have more or
> less stable clocks when GPS is down for whatever reason.
> I have zero clue about time standards for the low end. Can anyone
> recommend anything affordable? Thanks.

Like Bob Camp and Kasper Pederson have already said, a lot depends on what "low end" and "affordable" mean. That being said a Soekris net4501 fed by a Thunderbolt would be hard to beat. When GPS is down the Thunderbolt will go into holdover and your accuracy is then controlled by its OCXO. A new net4501 is US$173, and Thunderbolts are available for US$120 right now on eBay, and possibly less if you look around. Add a pulse stretcher, either build your own, or get something like the TAPR FatPPS (US$49). That gets you to the neighborhood of US$350. If you want this capable of sub-microsecond accuracy add a clock synthesizer, along with some system board surgery. The TAPR Clock-Block works nicely, US$69.

In 2009, Mark Sims posted information about the Thunderbolt performance in holdover mode. <http://www.febo.com/pipermail/time-nuts/2009-March/036973.html> For 8 hours his unit held the PPS within 150 ns, 11 hours was i us, and 24 hours was 4.5 us.


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