"Richard B. Gilbert" <[EMAIL PROTECTED]> writes: >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! Of course not ( and the GPS18 only gives 1us accuracy anyway) but the OP wanted accuracy to 1ms, which is trivial for both the computer and the gps. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
