[time-nuts] GPS module recommendation for Pi timing

[Hal Murray]

brian at lloyd.aero said:
> Some of the units may have access to the Internet and I could run NTP on them
> but the majority will be using GPS as the single stand-alone source of UTC.
> The goal is for all the units to be sync'd to UTC as they need to perform
> repetitive functions concurrently. 

If you run NTP without a network connection but with GPS, it will discipline 
the local clock by tweaking the seconds per tick parameter deep inside the 
kernel.

It's a GPSDO implemented in software.  No DAC.  Actually, GPSDC - Clock rather 
than Oscillator.


kb8tq at n1k.org said:
> With a bare crystal, you could easily have a 10’s of ppm sort of error. If
> you do, then any outage over about 100 seconds will hit your limit.  

Unless ntpd has tweaked your clock.  It's good enough to make a rough 
thermometer.


brian at lloyd.aero said:
> I just don't know how clean that output from the Ublox is.

If the output frequency is programmable, it will be derived via a DDS, good 
for long term timing but lots of jitter.

I suggest you get a Ublox development board and/or one or more Pi GPS HATs and 
start experimenting.


-- 
These are my opinions.  I hate spam.