Unruh wrote: > [EMAIL PROTECTED] (Nicola Berndt) writes: > >> Richard B. Gilbert schrieb: >>> David Woolley wrote: >>>> Richard B. Gilbert wrote: >>>> >>>>> To turn your equipment on after months of downtime and expect it to >>>>> lock on to the correct time with millisecond accuracy within seconds >>>>> is asking for a hell of a lot. >>>> Not really. He's starting a GPS receiver at the same time and that has >>>> to lock to 50ns. >>>> >>>> Doing it on a general purpose computer is more difficult, but not >>>> particularly impossible. >>> Even with GPS and a full four satellite fix, ten seconds to synchronize >>> is extremely ambitious!! You can set the time to within whatever >>> precision the hardware and software support but that is only half the >>> problem. You also need to set the correct clock frequency. On a cold >>> start, the clock frequency is a moving target as the hardware warms up. >>> >>> I would expect to wait at least thirty minutes for the system to >>> stabilize with both the correct phase (time) and frequency. > >> To transfer the full almanac of GPS it takes roughly 12 minutes from a >> cold start. Then the receiver knows everything there is for it to know. >> Some receivers (like mine) you can tell it's location, wich gets you in >> the 10 s range for precise time. Then again, who claimed, it has to be >> 10 s? I would be very happy with these 12 mins.. > > For some receivers if they know their position, they can get the time > virutally instantly from "cold start". All you need is one sattelite. If the > receiver has no idea where it is, it can take much longer. > Whether or not the receiver the OP has has that > capability I do not know. > >
There is a subtle difference between *getting* the correct time and *keeping* the correct time! A GPS receiver can generate a Pulse Per Second (PPS) signal accurate to within about 50 nanoseconds. This does not mean that you can get the same accuracy out of your computer! _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
