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

Kasper Pedersen time-nuts at kasperkp.dk
Mon Apr 5 11:20:30 EDT 2010


On 04/05/2010 03:47 PM, 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.

You need to give a ballpark figure for what you want.

A beyond-awful homecooked OCXO like this one
http://n1.taur.dk/timenuts/img_1017_crop.jpg
http://n1.taur.dk/timenuts/img_1020_crop.jpg

http://n1.taur.dk/clock/rate.png is the trace for something of similar 
build quality, and as can be seen, it is on the order of 3ppb/day. Noise 
is due to this being a cheap DCF77 clock driven server.
Combined with something like a D945GSEJT board with the crystal removed 
does give sub-ms 24 hour holdover with plain ntpd.

Now, what is the requirement?

/Kasper




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