[ntp:questions] Inexpensive OEM GPS units?

Steve Kostecke kostecke at ntp.org
Mon Nov 19 04:58:59 UTC 2007


On 2007-11-19, Chris Adams <cmadams at hiwaay.net> wrote:
> Once upon a time, Steve Kostecke  <kostecke at ntp.org> said:
>>What does ntpq -p show?
>
> $ ntpq -p
>      remote   refid  st t when poll reach   delay   offset  jitter
>===================================================================
<snip>
> xGPS_NMEA(0)  .GPS.   0 l   11   64  377    0.000  143.198  56.164
> *SHM(0)       .SHM.   0 l    2   16  377    0.000   -0.195   0.541

Compare your PPS over USB with PPS on a real serial port:

rackety.udel.edu
remote         refid   st t when poll reach   delay   offset jitter
===================================================================
+SPECTRACOM(1) .GPS1.   0 l   21   64  377    0.000   0.004   0.004
oPPS(0)        .PPS.    0 l    5   16  377    0.000   0.002   0.004

The GPS-18LVC connected to a real serial port on my Soekris would show
jitter of 0.008 and a typical daily peersum (with peer.awk) looked like:

ident          cnt   mean   rms    max   delay   dist   disp
============================================================
127.127.20.0  5235  0.000  0.002  0.014  0.000  0.270  0.248

-- 
Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/




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