[aprssig] NMEA Sentence problems into SCS Tracker....from Garmin Etrex

Stephen H. Smith wa8lmf2 at aol.com
Fri Nov 23 13:30:34 EST 2007

Jack Chomley wrote:
> Hi all,
> Yesterday, my trusty Magellan 315 died, it was used on my mobile HF 
> setup, using a SCS DSP Tracker, which all worked fine. So....I hooked 
> my Garmin MAP76S up and away it went.
> I decided to get a Garmin Etrex (basic model) for the job, as all I 
> wanted was NMEA V3 @4800 baud, which is what my other GPS units were 
> working OK with, into the tracker.
> I set the Etrex up and no comms, check the interface settings. all 
> OK....same as the MAP76S, which works.
> Despite resetting everything, still no go :-(
> Next, fire up my RS232 terminal....yep NMEA data is coming out of the 
> Etrex fine, so I log the data sentences, THEN do a "read" on the 
> MAP76S and find differences?
> Etrex  Sentences
> MAP76S Sentences
> Looking at the logged sentence types, there are differences?  I just 
> bought the Etrex new, so I would say the firmware is reasonably up to 
> date, maybe I need to try and load an older version, IF that is at all 
> possible?
> My MAP76S is about 4 years or so old, and its firmware has never been 
> upgraded.
> I would have thought that the $GPRMC sentence would have been 
> sufficient, for the tracker to work off.
> So....I look to the collective wisdom of the group for a solution ;-)

Could it be that your tracker is choking on the longer (more resolution) 
lat/long strings in new GPS hardware?  I recall some discussions 
problems with some hardware being caused by newer longer NMEA strings 
mentioned on this list a year or two ago.  I think the early TH-D7s 
suffered from this problem when the NMEA-0182 Ver 3 format lengthened 
the lat/long strings.

Have you looked at the actual number of digits in the lat / long values 
output by the two devices.    Some GPS devices have menu options to 
"dumb down" the values sent out the port  to NMEA 2.0 lower-res strings 
for the benefit of older programs that choke on the improved longer ones.


Stephen H. Smith    wa8lmf (at) aol.com
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