[time-nuts] GLONASS receiver

Chris Albertson albertson.chris at gmail.com
Sun Aug 5 19:05:05 EDT 2012


What specifically are you worried about?  The entire GPS system being
turned off or maybe just a few hours of outage.  Do you think maybe they
will turn SA back on and degrade GPS' performance?   FOr each of these
posabilities there is something different you might do so it helps to know
what exactly you are worried about.

Most (or all?) cell towers have a backup clock in case GPS stops.  What
they are mostly worried about is some local transmitter jamming the GPS
signal because that actually might happen on a radio tower.    What they
all do is keep something like a Rubidium oscillator running or an ovenized
crystal oscillator (OCXO) either of these will "cary" the system through a
24 hour GPS outage.   the Rb unit might take care of your needs (1
millisecond) for weeks of GPS outage

Glassnos is going to hve the same problem.  The Russian government can
change their policy overnight with no warning, just like the US government
might and both might be jammed by the same close by transmitter.  This
applies to Galileo too.

Another good backup system is to simply use Internet pool servers for
absolute time and then also keep a local Rubidium oscillator running.   But
then how to know if the Rb is still running at the "correct" rate.   Better
buy three of them and a spare.

But first you have to ask what happens if you clocks are "off".  How much
money will it cost you if that happens?





On Sun, Aug 5, 2012 at 2:36 PM, Miguel Gonçalves <m at mbg.pt> wrote:

> Hi there!
>
> I currently have 2 embedded machines connected to a Garmin 18 LVC and a
> Sure GPS board.
>
> They are NTP servers for my company's LAN and I, at the moment, I get
> sub-ms accuracy over the LAN.
>
> Everything is fine but I am a bit worried about the GPS reliability
> because GPS is ruled by the USA. Would a GPS disciplined oscillator solve
> any potential problems? A receiver for GLONASS, even though I did not find
> any at a reasonable price, would be better?
>
> An iridium oscillator calibrated, regularly by GPS?
>
> Too many questions... but in the end I would like to know what is the best
> path that I could follow after these GPS receivers.
>
> Many thanks!
>
> Regards,
> Miguel
>
>
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-- 

Chris Albertson
Redondo Beach, California



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