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✘UBX-MON-SPAN and antennas

From: Gary E. Miller
Subject: ✘UBX-MON-SPAN and antennas
Date: Tue, 22 Feb 2022 15:03:00 -0800

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.


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.


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.


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.

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

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

Attachment: L2.png
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Attachment: L1.png
Description: PNG image

Attachment: pgpUhjwhqYrz7.pgp
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