[ntp:questions] using both a PPS source and a HBG (dcf-77-like) timesource?

Unruh unruh-spam at physics.ubc.ca
Mon Jan 14 23:35:16 UTC 2008

folkert at vanheusden.com (Folkert van Heusden) writes:

>> > Well if I remember correctly someone said to me once that the
>> > time-string returned by cheap gps device (like my garmin 18 lvc)
>> > sometimes is a bit off while its PPS signal is fine.
>> > 

>> > Currently I'm syncing against NMEA/PPS and seeing quiet a big offset:
>> > 

>> >      remote           refid      st t when poll reach   delay   offset 
> jitter
>> > =======================
>> > xGPS_NMEA(0)     .GPS.            0 l    7   16  377    0.000  -185.08 
>  1.001  <---
>> <snip>
>> You can even out that delay in the GPS time by using the 'fudge' option. 

>> Example:
>> server minpoll 4
>> fudge time1 0.185
>> I do the same thing with my GPS 18 LVC, only I use gpsd with the SHM driv

>Ok but the odd thing is: a friend of mine has the exact same garmin 18
>lvc but not this big offset?

He may be running at 9600bd or even higher. But what do you care? You have
the pps. Why would you be even thinking of using the nmea for accuracy. It
may be good for setting the second, but is so so so much worst than the
pps, that it makes no sense to use it for anything but the second. and .18s
is good accuracy for 1 second setting. 

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