[time-nuts] My Garmin 18x, Ver 3.50, currently 1 second slow to UTC

Hal Murray hmurray at megapathdsl.net
Wed Dec 29 04:16:07 EST 2010


> It is possible that this has been reported as I do not see 3.50  available
> on garmin.com. 3.10 is the latest. Could not find anything in  faq's or
> alerts though.

This page has comments for 3.20 and 3.50:
  http://www8.garmin.com/support/download_details.jsp?id=4055
(But it's all in a Windows unpacker and I don't do windows.)


> It would certainly be useful to have a sentence  transmission offset from
> UTC in the NMEA messages (or at least a new message heading/tailing the
> list with that in). 

The problem isn't really the offset, it's the jitter.  If the offset was a 
constant, we could measure it.

I think it also depends upon the firmware version.


> You could scope it, (I am checking a MG1613S at the  moment) but that is not
> that easy if you are selecting just one of the  many messages being output.

You will have to watch it for a while to capture the range.  There is roughly 
150 ms of jitter, at least on an older unit.


> An easier method might be to just have NTP  tell you what it thinks the
> offset is when measured against other  references, then use that as your
> fudge factor.(use noselect directive  for the NMEA server or set its stratum
> high so it doesn't get selected).

That's the way I would do it.



-- 
These are my opinions, not necessarily my employer's.  I hate spam.







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