NIST NTP servers

Mel Beckman mel at beckman.org
Fri May 13 14:38:58 UTC 2016


Lamar,

You make it sound like TXCOs are rare, but they're actually quite common in most single board computers. True, you're probably not gonna find them in the $35 cellular-based SBCs, but since these temperature compensated oscillators cost less than a dollar each in quantity, they're quite common in most industrial species for well under $100.

An Ovenized XCO is absolutely not required for IT-grade NTP servers. If you need sub-microsecond  low-jitter leading-edge clocks, for BITS timing of SONET or radio networks for example, then an OXCO is helpful. But NTP itself is not that accurate. NTP can usually maintain time to only within tens of milliseconds over the public Internet, and can only achieve better than one millisecond accuracy in local area networks under ideal conditions. 

 -mel 

> On May 13, 2016, at 7:13 AM, Lamar Owen <lowen at pari.edu> wrote:
> 
>> On 05/11/2016 09:46 PM, Josh Reynolds wrote:
>> maybe try [setting up an NTP server] with an odroid?
>> 
> ...
> 
> I have several ODroid C2's, and the first thing to note about them is that there is no RTC at all.  Also, the oscillator is just a garden-variety non-temperature-compensated quartz crystal, and not necessarily a very precise one, either (precise quartz oscillators can cost more than the whole ODroid board costs).  The XU4 and other ODroid devices make nice single-board ARM computers, but have pretty ratty oscillator precision.
> 
> You really have to have at least a temperature compensated quartz crystal oscillator (TCXO) to even begin to think about an NTP server, for anything but the most rudimentary of timing.  Ovenized quartz oscillators (OCXO) and rubidium standards are the next step up, and most reasonably good GPS-disciplined clocks have at least an ovenized quartz oscillator module (the Agilent Z3816 and kin are of this type).
> 


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