[ntp:questions] GPS_NEMA, but high offset and jitter?

Kelsey Cummings kgc at sonic.net
Wed Feb 24 19:41:25 UTC 2010


David J Taylor wrote:
> The reach = 0 suggests that the signals from the GPS are not being seen. 

I'm not sure why it lost sync but I went ahead and upgraded to 4.2.7p5 
from the ntp-dev port.

I'm still seeing high offset and variable jitter.

==============================================================================
xGPS_NMEA(1)  .GPS.      0 l   45   64  377    0.000  -311.36  75.859
-time.sr    207.200.81.. 2 u  348  512  377    0.643    0.977   2.984
*clock.sjc.he .CDMA.     1 u  362  512  377    6.348   -2.584   0.289

Or: http://kgc.users.sonic.net/ntp_127_127_20_1-day.png
The initial spike was the last restart.

# Garmin GPS 18 LVC
server  127.127.20.1    mode 0  prefer
fudge   127.127.20.1    flag1 1

Does the GPS_NEMA driver actually make use of the PPS signal (currently 
wired to DCD on serial port) at all or does it just use the GPS sentences?

I'm wired up following http://www.satsignal.eu/ntp/GPS-interface-2.png 
except that I used a NPN transistor to drive the PPS led so it wouldn't 
load the PPS signal.

-K




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