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

[Robin Schwab]

Am 13.08.2016 um 00:35 schrieb Gary E. Miller:
> Yup.  Adafruit Ultimate GPS HAT
>
> https://www.adafruit.com/products/2324
>
> Versus the Uputronics:
>
> https://store.uputronics.com/index.php?route=product/product&product_id=81

Dear Gary, dear Frank
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.

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.

So either if you use GPSD for positioning or time it's important to 
disable unneeded nema sentences in the gps device and set baud rate to 
highest possible.

I tried to make a standalone time server with GPS, gpsd and NTPd. 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. But when you have two stratum 0 
clocks and there is jitter on the "coarse" one you don't get best 
results either.

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

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.

Regards

Robin