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[aprssig] Com port SHARING vs Com Port JOINING

Scott Miller scott at opentrac.org
Tue Jan 15 23:08:27 UTC 2008


For Garmin receivers, at least, my experience is that in NMEA mode they 
output UTC.  In Garmin mode they give GPS time and an offset (about 14 
seconds, last I checked.)

Scott
N1VG

Claude Head III wrote:
> The utility I found for setting the PC's clock is NMEATime. I had known 
> that the GPS system does not correct for leap seconds, but was not 
> actually thinking about that when I first tried NMEATime. Just now went 
> out to the car to check that point.
> 
> I deliberately set the computer's time to several hours, minutes, and 
> seconds in error, then used NMEATime to set the clock. I had a WWV 
> receiver with me , and thus was able to compare the GPS/computer time 
> with WWV @ 10.000 MHz. NMEATime got the time right to within less than 
> about 0.5 seconds. Certainly not the 13 or 14 seconds offset that was 
> mentioned. NMEATime has its own time display, and natively it shows the 
> time as UTC. I guess it is using the computer's internal settings to put 
> the local time in the correct time zone, which is displayed by the 
> computer.
> 
> Come to think of it, I'm not sure whether the correction from "GPS" time 
> to UTC is done inside the Garmin receiver, or by NMEATime. Guess it 
> doesn't really matter. When it gets to the computer display, it is correct!
> 
> Which brings me back to my original request for a utility that will 
> allow both DeLorme Street Atlas and NMEATIME to share the single COM 
> port which the computer has. Thanks to all for the numerous suggestions 
> and hints about such programs, I'm evaluating them now, but have not yet 
> settled on one. I'll publish this information back to the SIG when I 
> have decided.
> 
> Incidentally, I do use Socket Watch to keep the computers in the house 
> and connected to the internet on time. That is a great program - highly 
> recommended.
> 
> This SIG is a treasure house of information!
> 
> 73,
> 
> Claude - K5DTN
>  
> */Robert Bruninga <bruninga at usna.edu>/* wrote:
> 
>      > Also, most folks don't realize that "GPS Time"
>      > is NOT Earth time! The GPS constellation does
>      > not follow leap seconds. This has happened
>      > something like 13 times, so GPS time is off by
>      > About that much from official "Earth Time".
> 
>     True about internal GPS time, but I thought they included those
>     offsets into the Display and serial output when they output time
>     so that it is displayed and produced externally to be UTC time?
> 
>     Bob
> 
> 
>     Merely using a GPS
>      > To update your computer's CMOS clock will not make your
>     computer's
>      > Time "correct". A GPS is generally a fantastic tool for a
>     time
>      > "reference", like a 1ppm time base standard, but it's not an
>     earth
>      > clock. You probably will be much better off simply using a
>     NTP
>      > utility to update the computer time from the Internet, such as
>      > "SocketWatch 32" (www.locutuscodeware.com).
>      >
>      >
>      >
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