[ntp:questions] Re: NMEA and PPS

David Woolley david at djwhome.demon.co.uk
Wed Jul 5 06:19:04 UTC 2006

In article <1152047875.382440.265180 at 75g2000cwc.googlegroups.com>,
"DJ" <drnj at freemail.redherring.co.uk> wrote:

> use of fudge time1 I can get my ntpd to act as a stratum 0 server and

You mean stratum 1.  A value of 0 indicates unsynchronised.  The reference
clock will be stratum zero, but the NTP protocol will report statum

> will track pool ntp servers to within 100ms drift . I wish to improve
> the precision/accuracy and would like to use the PPS kernel/drivers. Is
> this possible with a simple NMEA device i.e. does the PPS kernel patch
> give a better stability or do I need a PPS gps clock ?

You require a time transfer receiver.  Your problems are not fundamental
to NMEA, but navigation receivers will generally not pay attention to
accurate timing of the time messages and even time transfer receivers
may assume that their PPS output is accurate, so the NMEA doesn't need
to be.  I don't know if there are any time transfer receivers without
PPS, although, if there are, they would, presumably have low jitter
NMEA outputs.

The ntpd PPS code is of no benefit unless the receiver generates an
accurate PPS signal.

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