[ntp:questions] Installing more stable oscillator?

Richard B. Gilbert rgilbert88 at comcast.net
Sat Jul 14 14:54:39 UTC 2007

Pete Stephenson wrote:
> In article <1184319747.579985.256640 at k79g2000hse.googlegroups.com>,
>  Paul.Croome at softwareag.com 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?

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.

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