[time-nuts] Next step up from basic GPS/PPS timekeeping

[Martin Burnicki]

Pete Stephenson wrote:
> On Wed, Feb 24, 2016 at 3:22 PM, Neil Green <ncguk at hotmail.co.uk> wrote:
>> I currently operate a stratum 1 NTP server in the NTP pool using a U-Blox Max-7Q GPS module with PPS attached to, variously, a Raspberry Pi via GPIO or a Celeron mini PC via serial DB-9. The machine does nothing but serve time to the pool. Operating systems of choice are Debian or FreeBSD.
>>
>>
>> What would be my next step up be, hardware-wise, in terms of improving precision, stability, etc? A GPSDO? Budget is limited as far as these things go - about £150 UK/$210 US.
> 
> For what purpose?
> 
> In my experience, NTP is able to sync other systems to within 10-100
> microseconds of an NTP server on a LAN. The vagaries of the internet
> mean that it's unlikely for NTP clients to sync any closer than a few
> tens of milliseconds.

It can be better, but that's not guaranteed. I'm located in Germany and
have a setup measuring the offset of some NTP servers in the U.S.
against a built-in GPS card, and the offset is below 2 ms most of the time.

Martin