[time-nuts] New timing receivers?

Jim Harman j99harman at gmail.com
Mon Apr 28 19:45:15 UTC 2014

On Mon, Apr 28, 2014 at 1:08 AM, Mark Sims <holrum at 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

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


--Jim Harman

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