[time-nuts] NMEA time off

Tom Holmes tholmes at woh.rr.com
Thu Mar 3 18:33:19 UTC 2011


Joe...

Any tips on how you set it up to get those messages?

Tom Holmes, N8ZM
Tipp City, OH
EM79


> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Joseph Gray
> Sent: Thursday, March 03, 2011 4:07 AM
> To: time-nuts at febo.com
> Subject: [time-nuts] NMEA time off
> 
> Months ago a bought an old Delorme Tripmate for $5 (for that price,
> why not?). Tonight I finally got around to fooling with it. After
> finding out that it was designed to talk only to Delorme software
> without some finagling, I got it to spit out NMEA data to Teraterm and
> other programs.
> 
> I discovered two things about the Tripmate. First, the sensitivity
> sucks indoors. It is currently showing 13 satellites visible, but only
> tracking three. Second, the time data from the GPRMC sentence is about
> two seconds behind UTC (using my calibrated eyeball for measuring).
> 
> Is the time delay simply due to a firmware error, a low priority
> processing and outputting the NMEA data, or something else?
> 
> I was going to attach the Tripmate to a modified Linksys WRT54G WiFi
> router and make it an el-cheapo NTP server. No reason, other than just
> for fun. Even without the two second delay, I know that the WRT54G
> will not be a very accurate NTP server. I was assuming that I'd be
> able to at least get better than one second accuracy, though. I guess
> I can just put in a large fudge factor for ntpd to compensate.
> 
> Unrelated to the above, I also have a Timex Ironman runner's watch
> with mating GPS unit (another $5 purchase). The GPS is worn on the arm
> and transmits data to the watch for displaying distance, speed, etc. I
> need to get a battery for the watch, but I believe everything works.
> Taking the GPS unit apart, I find that it is a Garmin. I see some
> interesting test points on the circuit board, so I'm going to see if I
> can get some serial data directly from the GPS, without using the
> watch.
> 
> Joe Gray
> W5JG
> 
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