[time-nuts] PPS offset between GPS receivers

David J Taylor david-taylor at blueyonder.co.uk
Tue Dec 11 14:22:46 UTC 2012

I'm not sure about the jammer but I'm running a timing receiver in
position hold several floors up, I haven't seen dropouts like this.

ntpd is running with a "noselect" NMEA source since I'm having problems
with ntpd marking the PPS and NMEA as falsetickers. The startup sequence
for the server is this:

* run ntpd -g -q with NMEA enabled
* run chronyd for 3 minutes to set the time and frequency offset
* copy the current frequency to ntpd's drift file, then run ntpd with
NMEA disabled

This hack seems to work everytime with ntpd ready in less than 4 minutes
after turning on. I just hope nothing would happen that changes the

I have seen 0.2 us spikes every hour from some unknown task but the
larger spikes are rare. Another device running the same OpenWrt firmware
but with a timing receiver has only the small periodic spikes.


Sorry, I'm not familiar enough with Linux to be able to help.  On my systems 
there's just the automated start of ntpd, with no 3rd party software, and 
the PPS is a separate kernel-mode driver, not the one integrated into the 
NMEA driver.  It may be best to ask on the Usenet comp.protocols.time.ntp 
group to get NTP working properly.

SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor at blueyonder.co.uk 

More information about the time-nuts mailing list