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

From: Robin Schwab
Subject: Re: [gpsd-users] Garmin 18X-5Hz
Date: Sat, 13 Aug 2016 21:05:47 +0200
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

Am 13.08.2016 um 00:35 schrieb Gary E. Miller:
Yup.  Adafruit Ultimate GPS HAT

Versus the Uputronics:

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.



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