[ntp:questions] GPS Time source offset

DJ drnj at freemail.redherring.co.uk
Fri Oct 21 17:29:01 UTC 2005


I have a 4000 GPB ($6000 ?) GPS time source - it works beautifully.
I then took a $200 etrex hand-held GPS, set it to NMEA mode, plugged in
into a serial port on a Linux machine, I then did
ln -fs /dev/ttyS0 /dev/gps0 and configured ntp.conf

server 127.127.1.0
fudge 127.127.1.0 stratum 10

server 127.127.20.0

I started ntpd and then my linux platform appears as a stratum 1
server. However, it seems to have an approx 300mS offset from the 4000
GBP GPS time source. I tried

fudge 127.127.20.0 time1 0.3

or

fudge 127.127.20.0 time1 -0.3

or even

fudge 127.127.20.0 time1 500.0

(+ restarting ntpd each time)

But it seemed to make no difference to the time served from linux
Any idea

1. Why the offset
2. How to adjust for it - so I can make a cheap linux/Etrex GPS stratum
1 server


DJ




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