[ntp:questions] UTC Time from NMEA receiver one second behind DCF?

Harald Brinkmann hb7267 at gmx.de
Fri Aug 15 18:33:17 UTC 2008


Unruh wrote:

> hal-usenet at ip-64-139-1-69.sjc.megapath.net (Hal Murray) writes:
> 
> 
>>>> It looks like a weekly pattern.  It will be interesting to see what
>>>> happens during the next week.
>>>
>>>Yes, that fits my observations well, including the weekly pattern...so
>>>far. I suppose you don't know of any workaround for ntp purposes?
> 
>>If it really is a weekly pattern, then it should be possible to
>>hack the NMEA driver to "fix" the problem.  I doubt if anybody is
>>likely to do it.
> 
> A much better fix is to throw away that receiver and get a non-broken one.
> for timing purposes a gps receiver that decides on its own to report the
> wrong time is not worth fixing. Your time is worth more than that.

Just in case anyone is interested: The bug is active again right now
(2008-08-15T18:27 UTC).

Here is a sample ntpq -p

     remote           refid      st t when poll reach   delay   offset 
jitter
==============================================================================
 LOCAL(0)        .LOCL.          10 l   53   64    3    0.000    0.000  
3.906
 GPS_NMEA(0)     .GPS.            3 l   51   64    3    0.000  -987.23
224.958
 ptbtime2.ptb.de .PTB.            1 u   51   64    3   70.359   21.022 
58.591

Here are a couple of NMEA messages off my Navilock:

$GPRMC,182711.000,A,5212.1284,N,00833.4496,E,0.51,173.76,150808,,*07
$GPVTG,173.76,T,,M,0.51,N,0.9,K*69
$GPGGA,182712.000,5212.1283,N,00833.4497,E,1,06,1.1,83.1,M,47.1,M,,0000*67
$GPGSA,A,3,24,21,30,29,13,31,,,,,,,2.1,1.1,1.7*3A
$GPRMC,182712.000,A,5212.1283,N,00833.4497,E,0.78,163.32,150808,,*08
$GPVTG,163.32,T,,M,0.78,N,1.5,K*6E
$GPGGA,182713.000,5212.1282,N,00833.4497,E,1,06,1.1,83.0,M,47.1,M,,0000*66
$GPGSA,A,3,24,21,30,29,13,31,,,,,,,2.1,1.1,1.7*3A
$GPRMC,182713.000,A,5212.1282,N,00833.4497,E,0.43,182.94,150808,,*03
$GPVTG,182.94,T,,M,0.43,N,0.8,K*69
$GPGGA,182714.000,5212.1282,N,00833.4497,E,1,05,1.2,82.9,M,47.1,M,,0000*69

When talking about a workaround I was thinking about a combination of
statuses that are found in these messages that only occurs when the bug is
active. Trying to guess the times at which it will strike is clearly
pointless.

Nevertheless the Garmin unit is on order.

BTW: I didn't know that ordering GPS units from the U.S. would be *that*
difficult. :-(

Cheers

Harald





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