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

[Pete Stephenson]

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.

The Pi is a decent system, but its ethernet port is connected via USB,
so accuracy isn't as good as it would be on a different, non-USB
system. It's quite satisfactory for serving time to the internet using
NTP.

A GPSDO is handy if you need better precision (but the Pi and the
internet can't deliver that better precision, so this is not a major
advantage for NTP) or holdover in case of issues with GPS. Many also
emit a stable reference frequency: this is useful for providing a
common reference for test equipment like frequency counters, or for
radio/microwave systems that need very high stability. If you don't
have such needs, a GPSDO will be of limited use.

> I appreciate this is basic stuff compared to the usual discussions but this doesn't seem the right question to ask on the NTP lists. Any help appreciated. Thanks.

Welcome, and thanks for providing a server in the NTP pool.

Cheers!
-Pete

-- 
Pete Stephenson