Pete Stephenson wrote: > In article <[EMAIL PROTECTED]>, > [EMAIL PROTECTED] wrote: > > >>NTP's mission in life is to discipline a cheap, unstabilized computer >>system clock (quartz oscillator) to one or more better quality, more >>stable time sources. If your computer has a Grade A system clock, you >>would have to consider carefully whether you would make matters >>better or worse by trying to discipline it from time sources derived >>via the Internet. > > > Indeed. > > I guess my unasked question was, "How can one build a better quality, > more stable time source?" > > I could use NTP to sync my computer's cheap oscillator to an internet > source (what I currently do), or to a radio clock (GPS, CDMA, WWVB, etc. > -- I'd like to do this, but budget and lack of knowledge is currently > preventing this.)...that's not too hard. But how would one build a more > stable source of time? If the external source is interrupted, even with > NTP adjusting for the system's drift, it will still drift further and > further away from the actual time in relatively short order. I'd like to > have a system here that can avoid that, mostly "because I can", not for > any particular reason. > > Surely many of the stratum 1 servers (say, time.nist.gov) that get and > distribute time directly from atomic clocks aren't just off-the-shelf > servers with cheap, unstabilized system clocks, right? I know that many > of the public stratum 1 servers deployed by individuals and > organizations get their time from GPS, and are probably ordinary > computers, but I have this (again, perhaps incorrect) assumption that > the servers that supply the time /to/ the GPS system are not ordinary > computers. > > >>The computer's crystal oscillator (system clock) is an essential part >>of an NTP server; it's the entity that NTP is controlling. Don't >>confuse the external oscillator(s), which NTP uses as its input, and >>the system clock, which is the end result. Using a better-quality, >>e.g. ovenized, quartz oscilllator will give NTP an easier job; but >>NTP has been designed and engineered to cope with the vagaries of >>typical computers with typical system clocks. > > > Perhaps I misunderstand, but are you saying that it's possible to > replace the computer's crystal oscillator with an ovenized quartz > oscillator? Or are you saying that one can use the ovenized quartz > oscillator (or rubidium, cesium, hydrogen maser, etc.) as an external > oscillator, and it would provide PPS input to the computer running NTP? > <snip>
Of course he's saying it's possible! Replacing the oscillator with an OCXO would probably void any warranty you had on the motherboard. You would need a good knowledge of what you were doing or you would need to hire someone who has the necessary know-how. I wouldn't touch it with a ten foot pole! It's also possible, and far less hazardous to your computer, to use a high quality oscillator as an external reference clock for NTP. HP used to make a GPS disciplined crystal oscillator, I think it was a Z3816A, that was used by telephone companies and started appearing on the surplus market three or four years ago. These were much in demand by amateur radio operators as a frequency standard and by time junkies as NTP reference clocks. The cheapest route I know of is to buy a Garmin GPS18LVC GPS timing receiver (< $100 US) add a 5 volt power supply and a DB9 connector and plug it in to a serial port. Install NTPD with the necessary driver, start it up, and wait a few minutes for it to synch up. _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
