On 07/12/2020 17:06, Martin Gregorie wrote:
...
>
> Don't forget that an old GPS unit, provided it has serial NMEA0183 output
> which many of them had, can be used by ntpd as a primary time reference.
> These can be connected to an RPI via a USB-serial adapter. There is a
> reference driver for ntpd that allows it to accept an NMEA0183 primary
> time stream.
>
>
(OP)
I use that on my existing server - a cheapy £5 wonder gps dongle. No PPS
output, just jittery nmea :-{

I did some tests a while ago checking the offsets between my local
ntp/gps and  network servers over many days. There was a systematic,
IIRC diurnal, drift cycle. 10's of msec, no more, but unexplained.

There's also an unexplained step change after booting where the relative
offsets of local gps and net servers shift by maybe 10 or so msec.



--
Mike Scott
Harlow, England

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