On Mon, Apr 28, 2014 at 1:08 AM, Mark Sims <hol...@hotmail.com> wrote:
> When I was playing with an Adafruit GPS, it appeared that if it thought > you were not moving it would go into a pseudo-position-hold mode and the > output coords would not change. It took it a while to start outputting new > coords when you started moving again. This test was at walking speeds. I > had to walk maybe 100 feet before it started sending new coords. The 3339 chip has a command PMTK386 to set its "Nav Speed Threshold." This is intended to prevent the position from drifting if the unit is stationary. You can also query the current setting with the PMTK447 command, and it should respond with a PMTK527. For details you can download the document " GlobalTop PMTK command packet." There are several versions available on the web, the newest I was able to find is A11, at http://doxical.free.fr/resources/exstatic/PA6B_Flash/PMTK%20command%20packet-Complete-A11.pdf Note that the document version linked form the Adafruit website is not the newest, and that for some reason the 3318 and 3329 use a different command for this function. I believe the default setting for this option is a firmware option, so units may have different settings at power-up. My unit also seems to wander around, but I have not experimented to see if its location changes correspond to timing changes, or if changing the nav speed threshold affects the timing accuracy. BTW I have not seen the dropped PPS signals some have reported. I am using the Adafruit antenna outdoors, with a view of about half the sky, looking east. -- --Jim Harman _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.