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

[Kevin Rosenberg]

I agree, very helpful, thanks Joseph!

I recently got two 18x that I upgraded to 3.50. (I'm starting to work on
integrating some M12+T modules to supplement/replace the 18x's).

Has anyone had trouble with reverting firmware upgrades on Garmin products? 
Of course, feedback on going back from 3.50 to 3.20 on an 18x would be most 
specific to my situation.

Thanks in advance!

Kevin Rosenberg
KR5F

On Jan 4, 2011, at 9:29 PM, Joseph Gray wrote:

> Geoff,
> 
> Thanks a lot for comparing firmwares. That hard information helps tremendously.
> 
> Joe Gray
> W5JG
> 
> On Tue, Jan 4, 2011 at 8:46 PM, Kiwi Geoff <geoff36 at gmail.com> wrote:
>> Joseph Gray wrote:
>>> If I am using the NMEA data (as in the Garmin is the only time
>>> source), what firmware is recommended by all those using a GPS18x-LVC?
>> 
>> I thought I would run some tests for you Joe, using Version 3.0 and 3.2
>> 
>> Although I myself have run version 3.0 for a number of months (when it
>> first came out in 2009) without issues, I take note of what Kasper
>> Pedersen wrote about his experience  - so I have now loaded version
>> 3.2 into my 18x, rather than any newer version (until Garmin fix the
>> NMEA latency issue).
>> 
>> I ran my tests for 2 hours each (7,200 one second samples) with GPS
>> sitting on an inside window sill with a very limited view of the sky,
>> so my readings should be taken as perhaps worse case rather than from
>> a perfect view of the sky. The GPS was using 9 - 10 satellites for the
>> fix solution during the test.
>> 
>> The RF sensitivity of the 18x is much better than the Garmin 18.
>> 
>> I measured the time of the "START" character ($) of the $GPRMC
>> sentence and  the "LAST" 0x10 (Linefeed) character, GPS 18x set to
>> 4800 Baud.
>> 
>> Following times are in milliseconds from the leading edge of the 1PPS marker.
>> 
>> Version 3.00 firmware for Garmin 18x
>> START Min =  365
>> START Avg =  427 (N = 7200)
>> START Max =  499
>> LAST Min =   513
>> LAST Avg =   576 (N = 7200)
>> LAST Max =   648
>> 
>> Version 3.20 firmware for Garmin 18x
>> START Min =  370
>> START Avg =  433  (N = 7200)
>> START Max =  518
>> LAST Min =  519
>> LAST Avg =  582  (N = 7200)
>> LAST Max=  667
>> 
>> So if you use Version 3.20 firmware for the 18x, at 4800 baud the NMEA
>> RMC sentence will give the time of the current UTC second and will be
>> received by an average of 582 ms after the leading edge of the 1PPS
>> transition (with a maximum jitter of plus 85 ms / minus 63 ms).
>> 
>> From what I have said earlier in the thread, and from tests that
>> Kasper Pedersen has done, I think we can say that currently version
>> 3.2 is the "best" version if you want to use the 18x NMEA timestamps
>> to be given early in the second (rather than much later as per version
>> 3.3 and 3.5).
>> 
>> Joe, you can download    GPS18xPC_LVC_320.exe     from here:
>> 
>> http://www.gawisp.com/perry/oem_sensor/
>> 
>> The above file is identical to the one I downloaded in 2009 from Garmin.
>> 
>> Hope that helps.
>> 
>> Regards, Geoff (Christchurch, New Zealand).
>> 
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> 
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