Re: [ntp:questions] Installing more stable oscillator?
Maarten Wiltink wrote: Keeping a room at a constant temperature might actually be easier than the other thing you could do - not run *any* other services on the computer. No cron at 3am. (Alternatively, make it run at 100% CPU always. Perhaps [EMAIL PROTECTED] would be _good_ for stability.) I used to do something like the following: I did not want setiathome to cause my server (which sits in a badly ventilated closet) to overheat. So I had written a C program that monitored the rate of the CPU fan (which is regulated by the CPU itself) and throttled the setiathome process (by sending it SIGSTOP/SIGCONT signals). The result was that the setiathome process kept the server at a constant temperature (and the CPU fan at around 3000 rpm). This ceased to work when the setiathome project changed their architecture, causing the work to be done by a load of sub-processes rather than the one I knew the pid of. So I dropped setiathome altogether. I haven't kept stats, but the clock now looks less stable (frantic attempt at remaining on-topic). Cheers, Jan ___ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
Re: [ntp:questions] Installing more stable oscillator?
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
Re: [ntp:questions] Installing more stable oscillator?
In article [EMAIL PROTECTED], Richard B. Gilbert [EMAIL PROTECTED] wrote: 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. *nods* I saw one of those on eBay the other day. Very interesting -- it looks like it has an ovenized crystal oscillator and a Motorola Oncore GPS receiver. It's got a variety of outputs, including four PPS outputs. Expensive, but nice. 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. I was looking at that as an option, but I was concerned about GPS signal strength in my area due to buildings and a limited view of the sky[1]. I was told that the GPS 18 LVC is a generally good unit, but that it's antenna reception was not fantastic in areas of marginal reception. The Motorola Oncore receivers look pretty good, as one can attach an active antenna, which should help out a bit with marginal signal strength. That, and you keep all the expensive bits inside the apartment. I'm debating between the GPS 18 and the Oncore, but the GPS 18 does seem quite a bit simpler to setup as one doesn't need to worry about separate boards and whatnot. How good is the GPS 18 LVC as a time source? From what I can read, the leading edge of the PPS pulse is within 1 microsecond of UTC, which is certainly more than adequate for my needs, but it's always nice to do better if possible. :) [1] I live on a first-floor apartment with essentially no usable GPS signal from the window. There are a few locations outside where I can get between 50-70% view of the sky and still have the antenna be within about 20-30 feet of my apartment. -- Pete Stephenson HeyPete.com ___ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
