[time-nuts] Time source for indoor standalone PC

Bob Camp lists at rtty.us
Fri May 17 08:02:26 EDT 2013


Rather than getting uber crazy, how about something simple:

Take a cheap telecom Rb from the usual auction sites. Get it running and on frequency. Probably hook a battery into the power supply for backup. Run it's pps into the PC.

At this point you should (with some luck temperature wise) be at < 5x10^-11.  It should stay at this level for quite a while. You should be good to a second for many years.

The only thing you need to do now is a "clock trip" with your wrist watch to set the system each time the PC looses power. I'm guessing that the bunker has pretty good backup power. If not, code up a little PIC to keep time when on battery power. If you go the battery / PIC  route, you probably could set it outside the room and get it a bit closer than you can with your wrist watch. 

If you want to go to the next level with this, do a time check in a couple of years. Correct the Rb for the average error. That should get things *very* close long term. That of course assumes your bunker has better temperature control than mine does ….


On May 17, 2013, at 12:45 AM, Grant Waldram <grant at remobs.com.au> wrote:

> Hi folks. I wouldn't call myself a time nut, so this is really an effort to
> ask for advice from some people who know the field. My first contact with
> time synchronisation was looking at the instrumentation clocks for the
> Woomera rocket test facility when I went out there for a few (large!) hobby
> rocket launches. I can't even remember the system's name but it used a
> series of pulses of various lengths to give a unique time code. But, I
> digress...
> I've not had much need for time synchronisation over the years, but in
> recent years NTP has been able to get me by. Unfortunately I'm now faced
> with a network that needs a moderately correct clock (I'm scared of using
> the word 'acurate' around you folks!) to the order of a few seconds or so,
> but with no possibility of an external internet connection (for a number of
> reasons). At present I'm using one PC running Windows Server as an SNTP
> server to synchronise all of the devices, as it is the only device in a
> physically secure location. This is inside a security-fob protected room. I
> can't get GPS signals in there, and the Australian radio clock network was
> shut down about ten years ago. Our CDMA network was turned off in 2008.
> Right now all I can think of is GSM, and while i know it's not terribly
> accurate it seems like it might be the easiest. It also might be that I've
> got tunnel vision and there's a simpler solution out there.
> I would be quite happy with some sort of dedicated GSM/NTP-server box, and
> there are Arduino/Raspberry Pi/Linux homebuilts for that out there, but I
> have been wondering if one of the fairly common GSM USB sticks could somehow
> be a time source to set the server clock?
> Regards,
> Grant
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