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Re: [gpsd-users] Garmin 18X-5Hz

From: Gary E. Miller
Subject: Re: [gpsd-users] Garmin 18X-5Hz
Date: Sat, 13 Aug 2016 12:50:50 -0700

Yo Robin!

On Sat, 13 Aug 2016 21:05:47 +0200
Robin Schwab <address@hidden> wrote:

> You convinced me that the uputronics is the better choice over the 
> adafruit. I read the specs. The Adafruit is limited to 112 kbaud. The 
> uputronics is four times as fast.

I agree, but either are fine, the diffferences are small.

> To my experience once you have established decent satellite signal 
> latency and jitter on the UART are the biggest driver of inaccuracy
> in a GPS/computer setting. Latency is related to baud rate and number
> of nema sentences transmitted. Jitter happens because some nema
> sentences have a different length.

I really don't care.  The PPS is orders of magnitude more precise
than the NMEA stream.  NMEA is mostly just for sanity checking the PPS.

> I tried to make a standalone time server with GPS, gpsd and NTPd.

Works for me.  Look at: gpsd-time-service-howto.txt. And at the
new NTPsec RasPi/NTP howto:

> The 
> approach of David Taylor (who uses a network connected system) of
> giving the gpsd coarse clock a high stratum and the pps stratum 0 did
> not work because you cannot get a lock this way.

ntpd by design needs at least 3 good clocks.  So you need PPS and
at least two other network chimers.

Set the PPS to 'prefer' and the NMEA to 'noselect'.

> So I hope very much that I can improve my results with the already 
> ordered uputronics GPS.

How about these results:



I keep working to make them better.

> The Garmin GPS we are talking about in this thread will probably not 
> even reach the results of the adafruit. It's only advantage is the 
> ready-made housing.

Actaully, no so bad.  Its main drawback is that it needs a very strong
GPS signal and a good skyview.  Plus fiddling with the LVC is a PITA.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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