[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?
> 
<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.




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