[ntp:questions] SIRF time output wobble, GPS or NTP fault?

Chris Albertson albertson.chris at gmail.com
Tue Mar 6 18:57:47 UTC 2012

On Tue, Mar 6, 2012 at 8:07 AM, Ron Frazier (NTP)
<timekeepingntplist at c3energy.com> wrote:
> Hi all,
> I've been seeing some very strange behavior from my USB BU-353 GPS based on
> readings from the Meinberg Server Monitor.  The unit is based on the SIRF
> Star III e/LP chipset.  At first, I thought it was the GPS at fault.  But,

This is perfectly understandable.  Your guess that GPS was "wrong" is
correct if you are using only NEMA and no PPS.    Without  the PPS the
GPS can easy be a full second "off".

The NMEA data only has one second resolution and the GPS's spec says
they only have to be output "sometime within" the second to which they
apply.    It seems that your GPS is following the letter of the spec.

So I think you are correct to blame the GPS.

Chris Albertson
Redondo Beach, California

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