[ntp:questions] GPS-PPS, standalone server. NTP

David Taylor david-taylor at blueyonder.co.uk.invalid
Tue Jun 6 13:28:25 UTC 2017

On 06/06/2017 13:11, girino66 at gmail.com wrote:
> Some GPS will continue to deliver a PPS signal even if the lock is lost. I'm thinking particularly about the Garmin 18xLVC where it is clearly indicated in the documentation (4.4.1): 'After the initial position fix has been calculated, the PPS signal is generated and continues until the unit is powered down.'
> With the use of that 'kind of' GPS, ntpd will continue to provide time service.

As I understand it, NTP will only continue to provide a service if it 
has other "time-of-day" sources available.  Should the NMEA output (as 
the only time-of-day source) become invalid, NTP would reject it, and 
gradually ramp itself up to stratum-16 so as to become invalid as a 
server to its clients.

[1 - I'm unsure off the top of my head what NTP checks to know whether 
NMEA is valid or not.
2 - I wonder what the drift in the GPS 18x LVC is when unlocked?]

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