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

From: Gary E. Miller
Subject: Re: [gpsd-users] Garmin 18X-5Hz
Date: Fri, 12 Aug 2016 13:04:15 -0700

Yo Robin!

On Fri, 12 Aug 2016 21:45:48 +0200
Robin Schwab <address@hidden> wrote:

> Am 12.08.2016 um 20:37 schrieb Gary E. Miller:
> > On thing that is coming to light, ntpd tends to chase quantization
> > errors rather than averge them out.  No solutions yet.
> >
> > For exammple:  
> Hello Gary
> Your graphs are by characteristic very similar to what I got with a 
> raspberrypi 2 and the adafruit GPS.

Here is my Pi2 and adafruit:

> I got much better on an absolute scale but the sawtooth-like waveform
>  remains.

Can you define 'much better'?

I have a daily sawtooth, and a sawtooth every 30 mins.  The daily sawtooth,
and longer term fluctuations, matcch up with the Temp graph at the bottom.

The 30 min sawtooth is when the cron job makes the graphs...

> Strange thing: It can 
> happen that the periodic error disappears but it's unclear to me
> under which circumstances. Without the periodic error I could stretch
> the graph to -+10 us which is imo pretty good for a 100$ hardware
> setup.

Now that I fixed an ntpd thrashing issue I think my PPS will be in
the few microSec range as well.  That last 12 hours data is real good.

> Big advantage of the adafruit: You can set NEMA update rate and UART 
> baud rate separately.

But the Uputronics uses an external antenna.  And has a battery backup.

Side by side I gotta go with the Uputronics.

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

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