[time-nuts] Looking for RTC or some combination of MPU/crystal for 0.1ppm accuracy.

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sun Sep 13 00:37:57 UTC 2009

WarrenS wrote:
> It seems like you have given plenty of information for me to give you two possible suggestion.
> Here is an almost no extra cost solution, (just takes care and helps if you have done it before)
> Take a pretty standard xtral osc with EFC,  buffer its output real good, 
> give it good clean power from preferable its own regulator, 
> put a little insulted house around it so that it is not effected by direct air flow and quick temperature changes, 
> Add a processor controlled PLL a driving a Dac to control it freq, 
> Update the PLL loop with the time beacon, (assuming it is good to better than 1us) to correct the Phase offset error, 
> and it is pretty easy to get much better than 0.1 PPM with this.
> I did about the same thing using the 1PPS of my GPS and could get around 1e-8 accuracy. 
> The most important things are if using a cheap $5 osc like I was is to isolate real well it from the effects of PS, 
> load and temperature, and have of low noise reference voltage to provide a settable coarse freq tuning and use the Dac just for fine adj.
> Or of course you could just buy a better osc TCXO and save a lot of development time, but that's not as much fun.
> Depends how may you want to build, Anything below say 50 units the TCXO is going to be the cheaper solution if time is money.
> ws
> **********
That is probably an unnecessarily expensive solution that doesn't
address the fundamental problem of synchronising the RTC associated with
each sensor to a common time base.


More information about the time-nuts mailing list