[ntp:questions] Offset Average (Normal)?

Chris Albertson albertson.chris at gmail.com
Tue Mar 13 04:35:52 UTC 2012

On Mon, Mar 12, 2012 at 8:21 PM, Alby VA <albyva at empire.org> wrote:

>  The USB is just providing power to the SureGPS. The RS232 is handing
> the
> Rx/Tx/PPS and such. Everything is coming in on /dev/cuau0.

So it is a Sure with PPS and using a real serial port and BSD.

One thing to check is if you are using two drivers, one serial and the
"atom" PPS driver.   This is a common source of error.  You want to be
using a combined s=NMEA/PPS driver.  This will "hide" the jitter on
the NEMA

Also check the polarity on the PPS and make sure it is triggering on
the correct edge.   Remember the in RS232 a binary "1" is negative
volts and a "0" is positive but the control signals are reversed or
"active zero".     One more thing.  Make sure both ends are either TTL
or RS232, Some times you can feed TTL to an RS232 port but that could
be a big source of noise on the PPS line

Are you cable very long.   I once tried to used 100 feet of cat-5
cable for PPS and if never worked well
Finally are you 100% certain the GPS is tracking enough satellites

Chris Albertson
Redondo Beach, California

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