[LinuxPPS] Nmea driver and GPS18LVC

[Paul]

I guess the configuration is in the title. I am using ntp 4.26p5, with 
NMEA compiled in. Hardware is a GPS18LVC, with no buffering.

I`ll ask the questions as they occurred to me rather than at the end.

First, how can I tell if ntp is locking to the NMEA sentences only, 
which I would expect to be rather inaccurate, or to the NMEA and the PPS?

As soon as I powered up the GPS18 ntpq claimed that it was providing a 
stratum 1 time. (Hmm, so much for careful smoothing algorithms). It 
rapidly went to an offset of 0.011 with a jitter of 0.020. More 
significantly offsets to pool servers were of the order of -2 to -5. 
Believable?

Unfortunately next morning things were much worse. While GPS claimed to 
be at an offset of 0.004, with an jitter of 0.013, the offset to the 
pool servers was in the order of 200.

Do you think I am locked to the NMEA only?

Regards

Paul