Re: [gpsd-users] Strange loss of 3d fix

[Gary E. Miller]

Yo Svenn!

On Fri, 16 Aug 2019 22:07:56 +0200
Svenn Are Bjerkem <address@hidden> wrote:

> On Thu, 15 Aug 2019 at 21:36, Gary E. Miller <address@hidden> wrote:
> 
> > Yo Svenn!
> >
> > On Thu, 15 Aug 2019 21:28:33 +0200
> > Svenn Are Bjerkem via gpsd-users <address@hidden> wrote:
> >  
> > > when I mount zed-f9P (with ublox antenna) in the best place I have
> > > available regarding clear sky, I loose 3d-fix after about one
> > > minute.  
> >
> > Not good.  I have not had that problem.
> >
> > Did you try a ground plane, or choke ring?  Any nearby metal or
> > other multipath possibilities?
> >
> >  
> I have a metal ground plane underneath the gps antenna of about 20cm
> in diameter

That should help, but a bit small:

https://www.u-blox.com/sites/default/files/products/documents/GPS-Antenna_AppNote_%28GPS-X-08014%29.pdf

Maybe 40mm?

What does "gpsprof" and "gpsprof -t polar" show?

> > What is your lat/lon?  GPS sats do not go above 56 degree latitude.
> >  
> 
> "lat":63.979753900,"lon":11.643938800

Pretty high.  All the GPS are south of you.  Thus the advantage of the
south window that you see.

> > Loosing fix means all the calculated  
> > > parameters are lost as if I just plugged in the gps.  
> >
> > Lost me?  If you GPS did not move the data is still valid.
> >
> > This is an ardusimple with external antenna and 5m cable (the ublox
> >  
> antenna sold by ardusimple)

The GLONASS one, not the GPS only one?  Does cgps confirm you see, and
use GLONASS?  GLONASS helps at high latitude.

5m is fine, I use 20m with not problem.

> > > linux, gitlab:master:LATEST zed f9p ver 1.11  
> >
> > What does that mean?  
> 
> 
> An attempt to tell that I am running the git pull version of gpsd on
> linux, and that the f9p chip has firmware 1.11

Ah, got it.

> I run a test again and this time I recorded a log from gpsd. I have
> been skimming the contents of the log, and at a certain place the
> reported fix is suddenly shorter than it was at the previous time to
> report a fix. I attach the file in case you would take a look at it
> and tell me if it is sane or not.

Odd.  How did you capture that?

I see NMEA, but no u-blox binary.  Did you try to configure u-blox
binary?  What does "ubxtool -p GNSS" say?

> I run it this way : ./gpsd -G -nND5 /dev/ttyACM3 |& tee gpsd.log

Oh, you made a mistake there.  5 is a prameter, not an option.  So your
"-nND5" whould be "-nND 5".  You were not really running at debug level
5.

I prefer:
        gpspipe -w
and
        gpspipe -R

You also need to check your configuration with ubxtool.

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

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

pgpKSUmO1nPBk.pgp
Description: OpenPGP digital signature