Re: [gpsd-users] Garmin 18X-5Hz

[David J Taylor]

Dear Gary, dear Frank
You convinced me that the uputronics is the better choice over the
adafruit. I read the specs. The Adafruit is limited to 112 kbaud. The
uputronics is four times as fast.
[]
I tried to make a standalone time server with GPS, gpsd and NTPd. The
approach of David Taylor (who uses a network connected system) of giving
the gpsd coarse clock a high stratum and the pps stratum 0 did not work
because you cannot get a lock this way. But when you have two stratum 0
clocks and there is jitter on the "coarse" one you don't get best
results either.
[]
Regards
Robin
=========================================

Robin,

I have tested using /just/ a GPS/PPS Uputronics module to provide an NTP 
server with no Internet connection and it works just as expected.  It's on 
my Web site:

 http://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html#stand-alone

The serial support on the Raspberry Pi changed with model 3, and with the 
Jessie OS, and may still be changing so be prepared to fiddle around a 
little.  You need the "prefer" flag against the serial "time of day" source, 
not against the PPS source (as that had no time-of-day information).  In 
ntp.conf:

# Kernel-mode PPS reference-clock for the precise seconds
server 127.127.22.0 minpoll 4 maxpoll 4
fudge 127.127.22.0 refid kPPS

# Coarse time reference-clock - nearest second
server 127.127.28.0 minpoll 4 maxpoll 4 iburst prefer
fudge 127.127.28.0 time1 +0.105 flag1 1 refid GPSD stratum 1

The older Garmin GPS18 LVC needs to be outdoors as it has a relatively 
insensitive receivers, but the GPS18x LVC works OK for me located indoors on 
the top storey of a building near a south-facing wall.

Cheers,
David
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