✘UBX-MON-SPAN and antennas

[Gary E. Miller]

Yo All!

While was playing with a sample u-blox M10 kindly provided by
Uputronics.  I noticed the UBX-MON-SPAN message was not implemented in
ubxtool, and could provide a nice way to compare antennas.  Thus the new
ubxtool command: ubxtool -p MON-SPAN.

When used with "-v3" the output can be cut/pasted into a gnuplot scipt.

UBX-MON-SPAN is also supported on the F9P.

The UBX-MON-SPAN message is a 256 bucket power spectrum around the
frequencies supported by the GNSS receiver.  The M10S is L1 only, and
the F9P is L1 and L2.

So I tested three different antennas:

u-blox ANN-MB-0 L1/L2 antenna
generic GPS only antenna
generic GPS+GLONASS antenna

All sitting side by side on a southern facing window sill.  For each of
them I ran MON-SPAN, extracted the resulting data into dat files, and
plotted them with this script:

$ cat ant.plt
------------
set terminal qt size 600,600

set style line 12 lc rgb'#808080' lt 0 lw 1
set grid back ls 12

set xtics nomirror rotate by -45
set format x "%9.0f"
set yrange [20:180]
plot 'ann-mb0-f9p-L1.dat' using 1:2, 'gps-f9p-L1.dat' using 1:2, \
 'gpsglo-f9p-L1.dat' using 1:2
plot 'ann-mb0-f9p-L2.dat' using 1:2, 'gps-f9p-L2.dat' using 1:2,  \
'gpsglo-f9p-L2.dat' using 1:2
------------

Plotting this way:

$ gnuplot -persist < ant.plt

See the attached plots.  L1.png plots all three in the L1 band, L2.png
the same for L2 band.

Not as big a difference as I would have expected.

L1.png:

The ANN-MB has a noticeable peak for GLONASSS, the GPS antenna peaks
between the GPS and GLONASS frequencies, and the GPS+GLONASS has the
flatest passbandi with a small peak around the GPS center.  Otherwise
they are similar, with the ANN-MB having the best out of band rejection.

L2.png:

All three antennas are similar in the L2 band.  The ANN-MB had the
least gain, and the laast lat pass band.  The GPS antenna had the best
rejection outside the passband.

Summary:

Surprising to me that all three antennas performed so similarly, with no
clear winner.  No need to wonder which of your antennas is best, just
use UBX-MON-SPAN to test them.

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

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

L2.png
Description: PNG image

L1.png
Description: PNG image

pgpUhjwhqYrz7.pgp
Description: OpenPGP digital signature