Hi Joe, One way to prevent this issue is to make sure you have a good battery in the unit to keep an almanac copy in SRAM..
Try putting the unit outside with a clear sky view. Btw: the error usually depends on when the gps firmware was compiled, as the manufacturer hard-codes the number of leap seconds at that time, and any additional leap seconds will cause the error you are seeing. So a "good" gps may go "bad" when the next leap second happens.. Units with good backup battery usually shouldn't have this problem. Said Sent from my iPad On Mar 3, 2011, at 1:57, Joseph Gray <[email protected]> wrote: > Said, > > I suspected it might have something to do with the almanac. The > Tripmate has been on now for 100 minutes, but has not been able to > track four satellites during that entire time. Does the GPS need to > track at least four satellites continuously during the 12.5 minutes > it takes to download the almanac? If so, then I'll probably need to > place this thing outside tomorrow. > > It's well past my bedtime, so I'll say goodnight. > > Joe Gray > W5JG > > On Thu, Mar 3, 2011 at 2:24 AM, Said Jackson <[email protected]> wrote: >> Hello Joe, >> >> The gps probably has not finished receiving the entire almanac, and is >> "guessing" the number of leapseconds. The offset may go away after the >> almanac has been received. >> >> This can take up to 12.5 minutes. >> >> It is a design flaw in the gps spec in my opinion, they could have >> transmitted the number of leapseconds alongside the gps-time/date. >> >> Bye, Said >> >> Sent From iPhone >> >> On Mar 3, 2011, at 1:06, Joseph Gray <[email protected]> wrote: >> >>> 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 >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
